// TODO: Research if there is a way to disable languageTool & Grammarly extensions in CKEditor
// TODO: Revise absolute/relative placement of auxiliary <div> we inject into DOM. Absolute is more
//       controllable, but lacks PlacementObserver; relative is tricky to prevent document flow
//       issues, but moves with the DOM element.

/**
 * Collection of all grammar checking services in the document
 *
 * We dispatch relevant window messages to all services registered here.
 */
let besServices = []

// TODO: Window resize may cause host element(s) to move. That needs correction panel and status
//       icon repositioning. Also, should any parent element of our service host element move, we
//       should reposition correction panel and status icon. How to do this? Alas there is no
//       PlacementObserver to monitor host element movements. Switch to relative placement for our
//       auxiliary <div>s?
window.addEventListener('resize', () =>
  besServices.forEach(service => service.onReposition())
)

/**************************************************************************************************
 *
 * Base class for all grammar-checking services
 *
 * This class provides properties and implementations of methods common to all types of HTML
 * controls.
 *
 * This is an intermediate class and may not be used directly in client code.
 *
 *************************************************************************************************/
class BesService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {Element} textElement The element in DOM tree that hosts coordinate-measurable clone of
   *                              the text to proof. Same as hostElement for <div>, separate for
   *                              <textarea> and <input> hosts.
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, textElement, eventSink) {
    this.hostElement = hostElement
    this.textElement = textElement
    this.eventSink = eventSink
    this.results = [] // Results of grammar-checking, one per each block/paragraph of text
    this.createCorrectionPanel()

    // Disable browser built-in spell-checker to prevent collision with our grammar markup.
    this.originalSpellcheck = this.hostElement.spellcheck
    this.hostElement.spellcheck = false

    // This is coppied from https://stackoverflow.com/questions/37444906/how-to-stop-extensions-add-ons-like-grammarly-on-contenteditable-editors
    this.originalDataGramm = this.hostElement.getAttribute('data-gramm')
    this.originalDataGrammEditor =
      this.hostElement.getAttribute('data-gramm_editor')
    this.originalEnableGrammarly = this.hostElement.getAttribute(
      'data-enable-grammarly'
    )
    this.hostElement.setAttribute('data-gramm', 'false')
    this.hostElement.setAttribute('data-gramm_editor', 'false')
    this.hostElement.setAttribute('data-enable-grammarly', 'false')

    this.onScroll = this.onScroll.bind(this)
    this.hostElement.addEventListener('scroll', this.onScroll)

    this.resizeObserver = new ResizeObserver(this.onResize.bind(this))
    this.resizeObserver.observe(this.hostElement)

    this.hostBoundingClientRect = this.hostElement.getBoundingClientRect()
    this.positionObserver = new MutationObserver(this.onBodyMutate.bind(this))
    this.positionObserver.observe(document.body, {
      childList: true,
      subtree: true
    })

    besServices.push(this)
  }

  /**
   * Registers grammar checking service for given DOM element.
   *
   * Note: CKEditor controls are an exception that may not be registered using this method. Use
   * BesCKService.register for that.
   *
   * @param {Element} hostElement Host element
   * @param {*} eventSink Event sink for notifications
   * @returns Grammar checking service registered for given DOM element; unfedined if no service
   *          registered.
   */
  static registerByElement(hostElement, eventSink) {
    if (hostElement.tagName === 'TEXTAREA') {
      return BesTAService.register(hostElement, eventSink)
    } else if (
      hostElement.getAttribute('contenteditable')?.toLowerCase() ===
      'plaintext-only'
    ) {
      return BesDOMPlainTextService.register(hostElement, eventSink)
    } else {
      return BesDOMService.register(hostElement, eventSink)
    }
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    if (this.abortController) this.abortController.abort()
    besServices = besServices.filter(item => item !== this)
    this.positionObserver.disconnect()
    this.resizeObserver.disconnect()
    this.hostElement.removeEventListener('scroll', this.onScroll)
    this.hostElement.setAttribute('spellcheck', this.originalSpellcheck)
    this.hostElement.setAttribute('data-gramm', this.originalDataGramm)
    this.hostElement.setAttribute(
      'data-gramm_editor',
      this.originalDataGrammEditor
    )
    this.hostElement.spellcheck = this.originalSpellcheck
    this.clearCorrectionPanel()
    if (this.eventSink && 'unregister' in this.eventSink)
      this.eventSink.unregister(this)
  }

  /**
   * Returns grammar checking service registered for given DOM element
   *
   * @param {Element} hostElement Host element
   * @returns Grammar checking service registered for given DOM element; unfedined if no service
   *          registered.
   */
  static getServiceByElement(hostElement) {
    return besServices.find(service => service.hostElement === hostElement)
  }

  /**
   * Unregisters grammar checking service
   *
   * @param {Element} hostElement Host element
   */
  static unregisterByElement(hostElement) {
    BesService.getServiceByElement(hostElement)?.unregister()
  }

  /**
   * Called initially when grammar-checking run is started
   */
  onStartProofing() {
    this.proofingCount = 1 // Ref-count how many grammar-checking blocks of text are active
    this.proofingError = null // The first non-fatal error in grammar-checking run
    this.proofingMatches = 0 // Number of grammar mistakes detected in entire grammar-checking run
    this.abortController = new AbortController()
    if (this.eventSink && 'startProofing' in this.eventSink)
      this.eventSink.startProofing(this)
  }

  /**
   * Called when grammar-checking starts proofing each block of text (typically paragraph)
   */
  onProofing() {
    this.proofingCount++
    if (this.eventSink && 'proofing' in this.eventSink)
      this.eventSink.proofing(this)
  }

  /**
   * Called when grammar-checking failed (as 500 Internal server error, timeout, etc.)
   *
   * This error is fatal and proofing will not continue.
   *
   * @param {Response} response HTTP response
   */
  onFailedProofing(response) {
    delete this.abortController
    console.log(`Grammar checking failed: ${response.status} ${response.statusText}`)
    if (this.eventSink && 'failedProofing' in this.eventSink)
      this.eventSink.failedProofing(this, response)
  }

  /**
   * Called when failed to parse result of a grammar-checking of a block of text
   *
   * @param {Error} error Error
   */
  onFailedProofingResult(error) {
    if (error !== 'AbortError') {
      if (!this.proofingError)
        this.proofingError = error
      console.log(`Failed to parse grammar checking results: ${error}`)
    }
    if (this.eventSink && 'failedProofingResult' in this.eventSink)
      this.eventSink.failedProofingResult(this, error)
    if (--this.proofingCount <= 0) this.onEndProofing()
  }

  /**
   * Called when one block of text finished grammar-checking
   *
   * @param {Number} numberOfMatches Number of grammar mistakes discovered
   */
  onProofingProgress(numberOfMatches) {
    this.proofingMatches += numberOfMatches
    if (this.eventSink && 'proofingProgress' in this.eventSink)
      this.eventSink.proofingProgress(this)
    if (--this.proofingCount <= 0) this.onEndProofing()
  }

  /**
   * Called when grammar-checking run is ended
   */
  onEndProofing() {
    delete this.abortController
    if (this.eventSink && 'endProofing' in this.eventSink)
      this.eventSink.endProofing(this)
  }

  /**
   * Called to report scrolling
   */
  onScroll() {
    // Scroll panel is "position: absolute", we need to keep it aligned with the host element.
    this.scrollPanel.style.top = `${-this.hostElement.scrollTop}px`
    this.scrollPanel.style.left = `${-this.hostElement.scrollLeft}px`

    if (this.hostElement !== this.textElement) {
      this.textElement.scrollTop = this.hostElement.scrollTop
      this.textElement.scrollLeft = this.hostElement.scrollLeft
    }
  }

  /**
   * Called to report repositioning
   */
  onReposition() {
    this.setCorrectionPanelSize()
    if (this.eventSink && 'reposition' in this.eventSink)
      this.eventSink.reposition(this)
  }

  /**
   * Called to report resizing
   */
  onResize() {
    this.setCorrectionPanelSize()
    this.repositionAllMarkup()
    if (this.eventSink && 'resize' in this.eventSink)
      this.eventSink.resize(this)
  }

  /**
   * Called to report document body change
   */
  onBodyMutate() {
    const rect = this.hostElement.getBoundingClientRect()
    if (
      rect.top !== this.hostBoundingClientRect.top ||
      rect.left !== this.hostBoundingClientRect.left
    )
      this.onReposition()
    if (
      rect.width !== this.hostBoundingClientRect.width ||
      rect.height !== this.hostBoundingClientRect.height
    )
      this.onResize()
    this.hostBoundingClientRect = rect
  }

  /**
   * Creates grammar mistake markup in DOM.
   *
   * @param {Range} range Grammar mistake range
   * @param {String} ruleId Grammar mistake rule ID as reported by BesStr
   * @returns {Array} Grammar mistake highlight elements
   */
  addMistakeMarkup(range, ruleId) {
    const scrollPanelRect = this.scrollPanel.getBoundingClientRect()
    let highlights = []
    for (let rect of range.getClientRects()) {
      const highlight = document.createElement('div')
      highlight.classList.add(
        ruleId.startsWith('MORFOLOGIK_RULE')
          ? 'bes-spelling-mistake'
          : 'bes-grammar-mistake'
      )
      highlight.style.left = `${rect.left - scrollPanelRect.left}px`
      highlight.style.top = `${rect.top - scrollPanelRect.top}px`
      highlight.style.width = `${rect.width}px`
      highlight.style.height = `${rect.height}px`
      this.scrollPanel.appendChild(highlight)
      highlights.push(highlight)
    }
    return highlights
  }

  /**
   * Tests if given coordinate is inside of a rectangle.
   *
   * @param {Number} x X coordinate
   * @param {Number} y Y coordinate
   * @param {DOMRect} rect Rectangle
   * @returns
   */
  static isPointInRect(x, y, rect) {
    return rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom
  }

  /**
   * Creates auxiliary DOM elements for text adornments.
   */
  createCorrectionPanel() {
    const panelParent = document.createElement('div')
    panelParent.classList.add('bes-correction-panel-parent')

    this.correctionPanel = document.createElement('div')
    this.correctionPanel.classList.add('bes-correction-panel')

    this.scrollPanel = document.createElement('div')
    this.scrollPanel.classList.add('bes-correction-panel-scroll')

    panelParent.appendChild(this.correctionPanel)
    this.correctionPanel.appendChild(this.scrollPanel)
    if (this.isHostElementInline()) {
      this.textElement.parentElement.insertBefore(panelParent, this.textElement)
      this.setCorrectionPanelSize()
    } else {
      document.body.insertBefore(panelParent, document.body.firstChild)
      this.setCorrectionPanelSize()
    }
  }

  /**
   * Clears auxiliary DOM elements for text adornments.
   */
  clearCorrectionPanel() {
    this.correctionPanel.remove()
    this.scrollPanel.remove()
  }

  /**
   * Resizes correction and scroll panels to match host element size.
   */
  setCorrectionPanelSize() {
    // TODO: This woodoo looks so wrong it can't be true. Revise together!
    const styles = window.getComputedStyle(this.textElement)
    this.correctionPanel.style.marginLeft = styles.marginLeft
    this.correctionPanel.style.marginRight = styles.marginRight
    this.correctionPanel.style.paddingLeft = styles.paddingLeft
    this.correctionPanel.style.paddingRight = styles.paddingRight
    this.scrollPanel.style.width = `${this.textElement.scrollWidth}px`
    if (this.isHostElementInline()) {
      const hStyles =
        this.hostElement !== this.textElement
          ? window.getComputedStyle(this.hostElement)
          : styles
      const totalWidth =
        parseFloat(styles.paddingLeft) +
        parseFloat(styles.marginLeft) +
        parseFloat(styles.width) +
        parseFloat(styles.marginRight) +
        parseFloat(styles.paddingRight)
      this.correctionPanel.style.width = `${totalWidth}px`
      this.correctionPanel.style.height = hStyles.height

      this.scrollPanel.style.height = `${this.textElement.scrollHeight}px`
    } else {
      const rect = this.textElement.getBoundingClientRect()
      this.correctionPanel.style.width = styles.width

      const totalHeight =
        parseFloat(styles.paddingTop) +
        parseFloat(styles.marginTop) +
        parseFloat(styles.height) +
        parseFloat(styles.marginBottom) +
        parseFloat(styles.paddingBottom)
      this.correctionPanel.style.height = `${totalHeight}px`
      this.correctionPanel.style.marginTop = `${rect.top + window.scrollY}px`
      this.scrollPanel.style.height = `${this.textElement.scrollHeight}px`
    }
  }

  /**
   * Displays correction panel.
   *
   * @param {*} el Block element/paragraph containing grammar checking rule match
   * @param {*} match Grammar checking rule match
   * @param {PointerEvent} source Click event source
   */
  popupCorrectionPanel(el, match, source) {
    const popup = document.querySelector('bes-popup-el')
    popup.changeMessage(match.match.message)
    popup.appendReplacements(el, match, this, this.isContentEditable())
    popup.show(source.clientX, source.clientY)
  }

  /**
   * Checks if host element content is editable.
   *
   * @returns true if editable; false otherwise
   */
  isContentEditable() {
    switch (this.hostElement.contentEditable) {
      case 'true':
      case 'plaintext-only':
        return true
    }
    return false
  }

  /**
   * Updates all grammar mistake markup positions.
   */
  repositionAllMarkup() {
    this.results.forEach(result => {
      result.matches.forEach(match => {
        if (match.highlights) match.highlights.forEach(h => h.remove())
        match.highlights = this.addMistakeMarkup(
          match.range,
          match.match.rule.id
        )
      })
    })
  }

  /**
   * Replaces grammar checking match with a suggestion provided by grammar checking service.
   *
   * @param {*} el Block element/paragraph containing grammar checking rule match
   * @param {*} match Grammar checking rule match
   * @param {String} replacement Text to replace grammar checking match with
   */
  replaceText(el, match, replacement) {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()
    this.clearProofing(el)
    match.range.deleteContents()
    match.range.insertNode(document.createTextNode(replacement))
    this.proofAll()
  }

  /**
   * Tests if host element is inline
   *
   * @returns true if CSS display property is inline; false otherwise.
   */
  isHostElementInline() {
    switch (
      document.defaultView
        .getComputedStyle(this.hostElement, null)
        .getPropertyValue('display')
        .toLowerCase()
    ) {
      case 'inline':
        return true
      default:
        return false
    }
  }
}

/**************************************************************************************************
 *
 * Grammar-checking service base class for tree-organized editors
 *
 * This class provides common properties and methods for HTML controls where text content is
 * organized as a DOM tree. The grammar is checked recursively and the DOM elements in tree specify
 * which parts of text represent same unit of text: block element => one standalone paragraph
 *
 * This is an intermediate class and may not be used directly in client code.
 *
 *************************************************************************************************/
class BesTreeService extends BesService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {Element} textElement The element in DOM tree that hosts coordinate-measurable clone of
   *                              the text to proof. Same as hostElement for <div>, separate for
   *                              <textarea> and <input> hosts.
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, textElement, eventSink) {
    super(hostElement, textElement, eventSink)
    this.onClick = this.onClick.bind(this)
    this.textElement.addEventListener('click', this.onClick)
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    this.textElement.removeEventListener('click', this.onClick)
    super.unregister()
  }

  /**
   * Recursively grammar-(re)checks our host DOM tree.
   */
  proofAll() {
    this.onStartProofing()
    this.proofNode(this.textElement, this.abortController)
    this.onProofingProgress(0)
  }

  /**
   * Recursively grammar-checks a DOM node.
   *
   * @param {Node} node DOM root node to check
   * @param {AbortController} abortController Abort controller to cancel grammar-checking
   * @returns {Array} Markup of text to check using BesStr
   */
  proofNode(node, abortController) {
    switch (node.nodeType) {
      case Node.TEXT_NODE:
        return [{ text: node.textContent, node: node, markup: false }]

      case Node.ELEMENT_NODE:
        if (this.isBlockElement(node)) {
          // Block elements are grammar-checked independently.
          let result = this.getProofing(node)
          if (result) {
            this.onProofing()
            this.onProofingProgress(result.matches.length)
            return [{ text: `<${node.tagName}/>`, node: node, markup: true }]
          }

          let data = []
          for (const el2 of node.childNodes)
            data = data.concat(this.proofNode(el2, abortController))
          if (data.some(x => !x.markup && !/^\s*$/.test(x.text))) {
            // Block element contains some text.
            this.onProofing()
            const signal = abortController.signal
            fetch(
              new Request(besUrl + '/check', {
                method: 'POST',
                headers: {
                  'Content-Type': 'application/x-www-form-urlencoded'
                },
                body: new URLSearchParams({
                  format: 'plain',
                  data: JSON.stringify({
                    annotation: data.map(x =>
                      x.markup ? { markup: x.text } : { text: x.text }
                    )
                  }),
                  language: node.lang ? node.lang : 'sl',
                  level: 'picky'
                })
              }),
              { signal }
            )
              .then(response => {
                if (!response.ok) {
                  this.onFailedProofing(response)
                  throw new Error('Unexpected BesStr server response')
                }
                return response.json()
              })
              .then(responseData => {
                let matches = []
                responseData.matches.forEach(match => {
                  let range = document.createRange()

                  // Locate start of the grammar mistake.
                  for (
                    let idx = 0, startingOffset = 0;
                    ;
                    startingOffset += data[idx++].text.length
                  ) {
                    if (
                      !data[idx].markup &&
                      /*startingOffset <= match.offset &&*/ match.offset <
                        startingOffset + data[idx].text.length
                    ) {
                      range.setStart(
                        data[idx].node,
                        match.offset - startingOffset
                      )
                      break
                    }
                  }

                  // Locate end of the grammar mistake.
                  let endOffset = match.offset + match.length
                  for (
                    let idx = 0, startingOffset = 0;
                    ;
                    startingOffset += data[idx++].text.length
                  ) {
                    if (
                      !data[idx].markup &&
                      /*startingOffset <= endOffset &&*/ endOffset <=
                        startingOffset + data[idx].text.length
                    ) {
                      range.setEnd(data[idx].node, endOffset - startingOffset)
                      break
                    }
                  }

                  matches.push({
                    highlights: this.addMistakeMarkup(range, match.rule.id),
                    range: range,
                    match: match
                  })
                })
                this.markProofed(node, matches)
                this.onProofingProgress(matches.length)
              })
              .catch(error => this.onFailedProofingResult(error))
          }
          return [{ text: `<${node.tagName}/>`, node: node, markup: true }]
        } else {
          // Inline elements require no markup. Keep plain text only.
          let data = []
          for (const el2 of node.childNodes)
            data = data.concat(this.proofNode(el2, abortController))
          return data
        }

      default:
        return [{ text: `<?${node.nodeType}>`, node: node, markup: true }]
    }
  }

  /**
   * Tests if given block element has already been grammar-checked.
   *
   * @param {Element} el DOM element to check
   * @returns {*} Result of grammar check if the element has already been grammar-checked;
   *              undefined otherwise.
   */
  getProofing(el) {
    return this.results.find(result =>
      BesTreeService.isSameParagraph(result.element, el)
    )
  }

  /**
   * Marks given block element as grammar-checked.
   *
   * @param {Element} el DOM element that was checked
   * @param {Array} matches Grammar mistakes
   */
  markProofed(el, matches) {
    this.results.push({
      element: el,
      matches: matches
    })
  }

  /**
   * Removes given block element from this.results array and clearing its markup.
   *
   * @param {Element} el DOM element for removal
   */
  clearProofing(el) {
    this.clearMarkup(el)
    this.results = this.results.filter(
      result => !BesTreeService.isSameParagraph(result.element, el)
    )
  }

  /**
   * Clears given block element grammar mistake markup.
   *
   * @param {Element} el DOM element we want to clean markup for
   */
  clearMarkup(el) {
    this.results
      .filter(result => BesTreeService.isSameParagraph(result.element, el))
      .forEach(result =>
        result.matches.forEach(match => {
          if (match.highlights) {
            match.highlights.forEach(h => h.remove())
            delete match.highlights
          }
        })
      )
  }

  /**
   * Tests if given block elements represent the same block of text
   *
   * @param {Element} el1 DOM element
   * @param {Element} el2 DOM element
   * @returns {Boolean} true if block elements are the same
   */
  static isSameParagraph(el1, el2) {
    return el1 === el2
  }

  /**
   * Tests if given element is block element.
   *
   * @param {Element} el DOM element
   * @returns false if CSS display property is inline; true otherwise.
   */
  isBlockElement(el) {
    // Always treat our host element as block.
    // Otherwise, should one make it inline, proofing would not start on it misbelieving it's a
    // part of a bigger block of text.
    if (el === this.textElement) return true
    switch (
      document.defaultView
        .getComputedStyle(el, null)
        .getPropertyValue('display')
        .toLowerCase()
    ) {
      case 'inline':
        return false
      default:
        return true
    }
  }

  /**
   * Returns first block parent element of a node.
   *
   * @param {Node} node DOM node
   * @returns {Element} Innermost block element containing given node
   */
  getBlockParent(node) {
    for (; node; node = node.parentNode) {
      if (node.nodeType === Node.ELEMENT_NODE && this.isBlockElement(node))
        return node
    }
    return node
  }

  /**
   * Returns next node in the DOM text flow.
   *
   * @param {Node} node DOM node
   * @returns {Node} Next node
   */
  static getNextNode(node) {
    if (node.firstChild) return node.firstChild
    while (node) {
      if (node.nextSibling) return node.nextSibling
      node = node.parentNode
    }
  }

  /**
   * Returns all ancestors of a node.
   *
   * @param {Node} node DOM node
   * @returns {Array} Array of all ancestors (document...node) describing DOM path
   */
  static getParents(node) {
    let parents = []
    do {
      parents.push(node)
      node = node.parentNode
    } while (node)
    return parents.reverse()
  }

  /**
   * Returns all nodes marked by a range.
   *
   * @param {Range} range DOM range
   * @returns {Array} Array of nodes
   */
  static getNodesInRange(range) {
    let start = range.startContainer
    let end = range.endContainer

    // Common ancestor is the last element common to both elements' DOM path.
    let startAncestors = BesTreeService.getParents(start)
    let endAncestors = BesTreeService.getParents(end)
    let commonAncestor = null
    for (
      let i = 0;
      i < startAncestors.length &&
      i < endAncestors.length &&
      startAncestors[i] === endAncestors[i];
      ++i
    )
      commonAncestor = startAncestors[i]

    let nodes = []
    let node

    // Walk parent nodes from start to common ancestor.
    for (node = start.parentNode; node; node = node.parentNode) {
      nodes.push(node)
      if (node === commonAncestor) break
    }
    nodes.reverse()

    // Walk children and siblings from start until end node is found.
    for (node = start; node; node = BesTreeService.getNextNode(node)) {
      nodes.push(node)
      if (node === end) break
    }

    return nodes
  }

  /**
   * Called to report mouse click
   *
   * Displays or hides grammar mistake popup.
   *
   * @param {PointerEvent} event The event produced by a pointer such as the geometry of the
   *                             contact point, the device type that generated the event, the
   *                             amount of pressure that was applied on the contact surface, etc.
   */
  onClick(event) {
    const source = event?.detail !== 1 ? event?.detail : event
    const el = this.getBlockParent(source.targetElement || source.target)
    if (!el) return

    for (let result of this.results) {
      for (let m of result.matches) {
        for (let h of m.highlights) {
          if (
            BesService.isPointInRect(
              source.clientX,
              source.clientY,
              h.getBoundingClientRect()
            )
          ) {
            this.popupCorrectionPanel(el, m, source)
            return
          }
        }
      }
    }
    BesPopup.hide()
  }
}

/**************************************************************************************************
 *
 * DOM grammar-checking service
 *
 * This class provides grammar-checking functionality to contenteditable="true" HTML controls.
 *
 * May also be used on most of the HTML elements to highlight grammar mistakes. Replacing text with
 * suggestions from the grammar-checker will not be possible when contenteditable is not "true".
 *
 *************************************************************************************************/
class BesDOMService extends BesTreeService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, eventSink) {
    super(hostElement, hostElement, eventSink)
    this.onBeforeInput = this.onBeforeInput.bind(this)
    this.hostElement.addEventListener('beforeinput', this.onBeforeInput)
    this.onInput = this.onInput.bind(this)
    this.hostElement.addEventListener('input', this.onInput)
  }

  /**
   * Registers grammar checking service.
   *
   * @param {Element} hostElement DOM element to register grammar checking service for
   * @param {*} eventSink Event sink for notifications
   * @returns {BesDOMService} Grammar checking service instance
   */
  static register(hostElement, eventSink) {
    let service = BesService.getServiceByElement(hostElement)
    if (service) return service
    service = new BesDOMService(hostElement, eventSink)
    if (service.eventSink && 'register' in service.eventSink)
      service.eventSink.register(service)
    service.proofAll()
    return service
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    this.hostElement.removeEventListener('input', this.onInput)
    this.hostElement.removeEventListener('beforeinput', this.onBeforeInput)
    if (this.timer) clearTimeout(this.timer)
    super.unregister()
  }

  /**
   * Called to report the text is about to change
   *
   * Marks section of the text that is about to change as not-yet-grammar-checked.
   *
   * @param {InputEvent} event The event notifying the user of editable content changes
   */
  onBeforeInput(event) {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()

    // Remove markup of all blocks of text that are about to change.
    let blockElements = new Set()
    event.getTargetRanges().forEach(range => {
      BesDOMService.getNodesInRange(range).forEach(el =>
        blockElements.add(this.getBlockParent(el))
      )
    })
    blockElements.forEach(block => this.clearProofing(block))
  }

  /**
   * Called to report the text has changed
   */
  onInput() {
    // Now that the text is done changing, we can correctly calculate markup position.
    this.repositionAllMarkup()

    // Defer grammar-checking to reduce stress on grammar-checking server.
    this.timer = setTimeout(() => {
      this.proofAll()
      delete this.timer
    }, 1000)
  }
}

/**************************************************************************************************
 *
 * CKEditor grammar-checking service
 *
 * This class provides grammar-checking functionality to CKEditor controls.
 *
 *************************************************************************************************/
class BesCKService extends BesTreeService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {*} ckEditorInstance CKEditor instance
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, ckEditorInstance, eventSink) {
    super(hostElement, hostElement, eventSink)
    this.ckEditorInstance = ckEditorInstance
    this.disableCKEditorSpellcheck()
    this.onChangeData = this.onChangeData.bind(this)
    this.ckEditorInstance.model.document.on('change:data', this.onChangeData)
  }

  /**
   * Registers grammar checking service.
   *
   * @param {Element} hostElement DOM element to register grammar checking service for
   * @param {CKEditorInstance} ckEditorInstance Enable CKEditor tweaks
   * @param {*} eventSink Event sink for notifications
   * @returns {BesCKService} Grammar checking service instance
   */
  static register(hostElement, ckEditorInstance, eventSink) {
    let service = BesService.getServiceByElement(hostElement)
    if (service) return service
    service = new BesCKService(hostElement, ckEditorInstance, eventSink)
    if (service.eventSink && 'register' in service.eventSink)
      service.eventSink.register(service)
    service.proofAll()
    return service
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    this.ckEditorInstance.model.document.off('change:data', this.onChangeData)
    this.restoreCKEditorSpellcheck()
    if (this.timer) clearTimeout(this.timer)
    super.unregister()
  }

  /**
   * Called to report the text has changed
   */
  onChangeData() {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()
    const differ = this.ckEditorInstance.model.document.differ
    for (const entry of Array.from(differ.getChanges())) {
      let element =
        entry.type === 'attribute'
          ? entry.range.start.parent
          : entry._element || entry.position.parent
      const domElement = this.getDomElement(element)
      this.clearProofing(domElement)
    }

    // TODO: Research if input event or any other event that is called *after* the change is
    // completed is possible with CKEditor, and move the code below this line there.
    // SetTimeout is in fact necessary, because if we set specific height to the editable CKeditor
    // element, it will not be updated immediately.
    setTimeout(() => {
      // Now that the text is done changing, we can correctly calculate markup position.
      this.repositionAllMarkup()

      // Defer grammar-checking to reduce stress on grammar-checking server.
      this.timer = setTimeout(() => {
        this.proofAll()
        delete this.timer
      }, 1000)
    }, 0)
  }

  /**
   * This function converts a CKEditor element to a DOM element.
   *
   * @param {CKEditor} element
   * @returns domElement
   */
  getDomElement(element) {
    const viewElement =
      this.ckEditorInstance.editing.mapper.toViewElement(element)
    const domElement =
      this.ckEditorInstance.editing.view.domConverter.mapViewToDom(viewElement)
    return domElement
  }

  /**
   * Disables the CKEditor spellcheck.
   */
  disableCKEditorSpellcheck() {
    this.ckEditorInstance.editing.view.change(writer => {
      const root = this.ckEditorInstance.editing.view.document.getRoot()
      this.originalCKSpellcheck = root.getAttribute('spellcheck')
      writer.setAttribute('spellcheck', false, root)
    })
  }

  /**
   * Restores the CKEditor spellcheck.
   */
  restoreCKEditorSpellcheck() {
    this.ckEditorInstance.editing.view.change(writer => {
      writer.setAttribute(
        'spellcheck',
        this.originalCKSpellcheck,
        this.ckEditorInstance.editing.view.document.getRoot()
      )
    })
  }

  /**
   * Replaces grammar checking match with a suggestion provided by grammar checking service.
   *
   * @param {*} el Block element/paragraph containing grammar checking rule match
   * @param {*} match Grammar checking rule match
   * @param {String} replacement Text to replace grammar checking match with
   */
  replaceText(el, match, replacement) {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()
    this.clearProofing(el)
    const viewRange =
      this.ckEditorInstance.editing.view.domConverter.domRangeToView(
        match.range
      )
    const modelRange =
      this.ckEditorInstance.editing.mapper.toModelRange(viewRange)
    this.ckEditorInstance.model.change(writer => {
      const attributes =
        this.ckEditorInstance.model.document.selection.getAttributes()
      writer.remove(modelRange)
      writer.insertText(replacement, attributes, modelRange.start)
    })
    this.proofAll()
  }

  /**
   * Tests if host element is inline
   *
   * @returns true as CKEditor host elements always behave this way.
   */
  isHostElementInline() {
    return true
  }
}

/**************************************************************************************************
 *
 * Plain-text grammar-checking service
 *
 * This class provides common properties and methods for plain-text-only HTML controls like
 * <input>, <textarea>, <div contenteditable="plaintext-only">...
 *
 *************************************************************************************************/
class BesPlainTextService extends BesService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {Element} textElement The element in DOM tree that hosts coordinate-measurable clone of
   *                              the text to proof. Same as hostElement for <div>, separate for
   *                              <textarea> and <input> hosts.
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, textElement, eventSink) {
    super(hostElement, textElement, eventSink)
    this.reEOP = /(\r?\n){2,}/g
    this.onBeforeInput = this.onBeforeInput.bind(this)
    this.hostElement.addEventListener('beforeinput', this.onBeforeInput)
    this.onInput = this.onInput.bind(this)
    this.hostElement.addEventListener('input', this.onInput)
    this.onClick = this.onClick.bind(this)
    this.hostElement.addEventListener('click', this.onClick)
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    this.hostElement.removeEventListener('click', this.onClick)
    this.hostElement.removeEventListener('input', this.onInput)
    this.hostElement.removeEventListener('beforeinput', this.onBeforeInput)
    if (this.timer) clearTimeout(this.timer)
    super.unregister()
  }

  /**
   * Grammar-(re)checks the host element.
   */
  proofAll() {
    this.onStartProofing()

    let { text, nodes } = this.getTextFromNodes()
    let nextParagraphRange = document.createRange()
    nextParagraphRange.setStartBefore(nodes[0].node)
    for (
      let start = 0, eop, end, nodeIdx = 0;
      start < text.length && nodeIdx < nodes.length;
      start = end
    ) {
      this.reEOP.lastIndex = start
      let match = this.reEOP.exec(text)
      if (match) {
        eop = match.index
        end = this.reEOP.lastIndex
      } else {
        eop = end = text.length
      }

      let paragraphRange = nextParagraphRange
      nextParagraphRange = document.createRange()
      while (nodeIdx < nodes.length && nodes[nodeIdx].end < eop) nodeIdx++
      nextParagraphRange.setStart(
        nodes[nodeIdx].node,
        eop - nodes[nodeIdx].start
      )
      while (nodeIdx < nodes.length && nodes[nodeIdx].end < end) nodeIdx++
      paragraphRange.setEnd(nodes[nodeIdx].node, end - nodes[nodeIdx].start)
      while (nodeIdx < nodes.length && nodes[nodeIdx].end <= end) nodeIdx++

      let result = this.getProofing(paragraphRange)
      if (result) {
        this.onProofing()
        this.onProofingProgress(result.matches.length)
        continue
      }
      let paragraphText = text.substring(start, end)
      if (!/^\s*$/.test(paragraphText)) {
        // Paragraph contains some text.
        this.onProofing()
        const signal = this.abortController.signal
        fetch(
          new Request(besUrl + '/check', {
            method: 'POST',
            headers: {
              'Content-Type': 'application/x-www-form-urlencoded'
            },
            body: new URLSearchParams({
              format: 'plain',
              data: JSON.stringify({
                annotation: [
                  {
                    text: paragraphText
                  }
                ]
              }),
              language: this.hostElement.lang ? this.hostElement.lang : 'sl',
              level: 'picky'
            })
          }),
          { signal }
        )
          .then(response => {
            if (!response.ok) {
              this.onFailedProofing(response)
              throw new Error('Unexpected BesStr server response')
            }
            return response.json()
          })
          .then(responseData => {
            let matches = []
            responseData.matches.forEach(match => {
              let matchRange = document.createRange()
              let nodeIdx = 0,
                matchStart = start + match.offset
              while (nodeIdx < nodes.length && nodes[nodeIdx].end < matchStart)
                nodeIdx++
              matchRange.setStart(
                nodes[nodeIdx].node,
                matchStart - nodes[nodeIdx].start
              )
              let matchEnd = matchStart + match.length
              while (nodeIdx < nodes.length && nodes[nodeIdx].end < matchEnd)
                nodeIdx++
              matchRange.setEnd(
                nodes[nodeIdx].node,
                matchEnd - nodes[nodeIdx].start
              )
              matches.push({
                highlights: this.addMistakeMarkup(matchRange, match.rule.id),
                range: matchRange,
                match: match
              })
            })
            this.markProofed(paragraphRange, matches)
            this.onProofingProgress(matches.length)
          })
          .catch(error => this.onFailedProofingResult(error))
      }
    }

    this.onProofingProgress(0)
  }

  /**
   * Concatenates child text nodes
   *
   * @returns {Object} Concatenated text and array of nodes
   */
  getTextFromNodes() {
    let nodes = []
    let text = ''
    for (
      let node = this.textElement.childNodes[0];
      node;
      node = node.nextSibling
    ) {
      nodes.push({
        node: node,
        start: text.length,
        end: text.length + node.data.length
      })
      text += node.data
    }
    return { text, nodes }
  }

  /**
   * Tests if given paragraph has already been grammar-checked.
   *
   * @param {Range} range Paragraph range
   * @returns {*} Result of grammar check if the element has already been grammar-checked;
   *              undefined otherwise.
   */
  getProofing(range) {
    return this.results.find(result =>
      BesPlainTextService.isSameParagraph(result.range, range)
    )
  }

  /**
   * Marks given paragraph as grammar-checked.
   *
   * @param {Range} range Paragraph range
   * @param {Array} matches Grammar mistakes
   */
  markProofed(range, matches) {
    this.results.push({
      range: range,
      matches: matches
    })
  }

  /**
   * Removes given paragraph from this.results array and clearing its markup.
   *
   * @param {Range} range Paragraph range
   */
  clearProofing(range) {
    this.clearMarkup(range)
    this.results = this.results.filter(
      result => !BesPlainTextService.isSameParagraph(result.range, range)
    )
  }

  /**
   * Clears given paragraph grammar mistake markup.
   *
   * @param {Range} range Paragraph range
   */
  clearMarkup(range) {
    this.results
      .filter(result =>
        BesPlainTextService.isSameParagraph(result.range, range)
      )
      .forEach(result =>
        result.matches.forEach(match => {
          if (match.highlights) {
            match.highlights.forEach(h => h.remove())
            delete match.highlights
          }
        })
      )
  }

  /**
   * Tests if given ranges represent the same paragraph of text
   *
   * @param {Range} range1 Range 1
   * @param {Range} range2 Range 2
   * @returns {Boolean} true if ranges overlap
   */
  static isSameParagraph(range1, range2) {
    return (
      range1.compareBoundaryPoints(Range.START_TO_START, range2) == 0 &&
      range1.compareBoundaryPoints(Range.END_TO_END, range2) == 0
    )
  }

  /**
   * Tests if given ranges overlap or are adjacent to each other
   *
   * @param {Range} range1 Range 1
   * @param {Range} range2 Range 2
   * @returns {Boolean} true if ranges overlap
   */
  static isOverlappingParagraph(range1, range2) {
    const a = range1.compareBoundaryPoints(Range.END_TO_START, range2)
    const b = range1.compareBoundaryPoints(Range.START_TO_END, range2)
    return a == 0 || b == 0 || (a < 0 && b > 0)
  }

  /**
   * Called to report mouse click
   *
   * Displays or hides grammar mistake popup.
   *
   * @param {PointerEvent} event The event produced by a pointer such as the geometry of the
   *                             contact point, the device type that generated the event, the
   *                             amount of pressure that was applied on the contact surface, etc.
   */
  onClick(event) {
    const source = event?.detail !== 1 ? event?.detail : event
    const el = source.targetElement || source.target || this.hostElement
    if (!el) return

    for (let result of this.results) {
      for (let m of result.matches) {
        for (let h of m.highlights) {
          if (
            BesService.isPointInRect(
              source.clientX,
              source.clientY,
              h.getBoundingClientRect()
            )
          ) {
            this.popupCorrectionPanel(result.range, m, source)
            return
          }
        }
      }
    }
    BesPopup.hide()
  }

  /**
   * Simple string compare.
   *
   * For performance reasons, this method compares only string beginnings and endings. Maximum one
   * difference is reported.
   *
   * @param {String} x First string
   * @param {String} y Second string
   * @returns {Array} Array of string differences
   */
  static diffStrings(x, y) {
    let m = x.length,
      n = y.length
    for (let i = 0; ; ++i) {
      if (i >= m && i >= n) return []
      if (i >= m) return [{ type: '+', start: i, length: n - i }]
      if (i >= n) return [{ type: '-', start: i, end: m }]
      if (x.charAt(i) !== y.charAt(i)) {
        for (;;) {
          if (m <= i) return [{ type: '+', start: i, length: n - i }]
          if (n <= i) return [{ type: '-', start: i, end: m }]
          --m, --n
          if (x.charAt(m) !== y.charAt(n))
            return [{ type: '*', start: i, end: m + 1, length: n - i + 1 }]
        }
      }
    }
  }
}

/**************************************************************************************************
 *
 * Plain-text grammar-checking service
 *
 * This class provides grammar-checking functionality to contenteditable="plaintext-only" HTML
 * controls.
 *
 * Note: Chrome and Edge only, as Firefox reverts contenteditable="plaintext-only" to "false". The
 * grammar mistakes will be highlighted nevertheless, but consider using BesDOMService on Firefox
 * instead.
 *
 *************************************************************************************************/
class BesDOMPlainTextService extends BesPlainTextService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, eventSink) {
    super(hostElement, hostElement, eventSink)
  }

  /**
   * Registers grammar checking service.
   *
   * @param {Element} hostElement DOM element to register grammar checking service for
   * @param {*} eventSink Event sink for notifications
   * @returns {BesDOMPlainTextService} Grammar checking service instance
   */
  static register(hostElement, eventSink) {
    let service = BesService.getServiceByElement(hostElement)
    if (service) return service
    service = new BesDOMPlainTextService(hostElement, eventSink)
    if (service.eventSink && 'register' in service.eventSink)
      service.eventSink.register(service)
    service.proofAll()
    return service
  }

  /**
   * Called to report the text is about to change
   *
   * Marks section of the text that is about to change as not-yet-grammar-checked.
   *
   * @param {InputEvent} event The event notifying the user of editable content changes
   */
  onBeforeInput(event) {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()

    // Firefox does not support contenteditable="plaintext-only" at all, Chrome/Edge's InputEvent.
    // getTargetRanges() return a useless empty array for contenteditable="plaintext-only". This
    // makes tracking location of changes a pain. We need to save the text on beforeinput and
    // compare it to the text on input event to do the this.clearProofing().
    let { text } = this.getTextFromNodes()
    this.textBeforeChange = text
    // Continues in onInput...
  }

  /**
   * Called to report the text has changed
   *
   * @param {InputEvent} event The event notifying the user of editable content changes
   */
  onInput(event) {
    // ...Continued from onBeforeInput: Remove markup of all paragraphs that changed.
    // Use the offsets before change, as paragraph changes have not been updated yet.
    let paragraphRanges = new Set()
    this.getTargetRanges().forEach(range => {
      this.results.forEach(result => {
        if (BesPlainTextService.isOverlappingParagraph(result.range, range))
          paragraphRanges.add(result.range)
      })
    })
    paragraphRanges.forEach(range => this.clearProofing(range))
    delete this.textBeforeChange

    // Now that the text is done changing, we can correctly calculate markup position.
    this.repositionAllMarkup()

    // Defer grammar-checking to reduce stress on grammar-checking server.
    this.timer = setTimeout(() => {
      this.proofAll()
      delete this.timer
    }, 1000)
  }

  /**
   * Returns an array of ranges that will be affected by a change to the DOM.
   *
   * This method attempts to fix the Chrome/Edge shortcoming in InputEvent.getTargetRanges()
   * failing to return meaningful range array on beforeinput event.
   */
  getTargetRanges() {
    let textA = this.textBeforeChange
    let { text, nodes } = this.getTextFromNodes()
    let textB = text
    let nodesB = nodes
    let diff = BesPlainTextService.diffStrings(textA, textB)
    let ranges = []
    for (
      let i = 0, j = 0, nodeIdxB = 0, diffIdx = 0;
      diffIdx < diff.length;
      ++diffIdx
    ) {
      let length = diff[diffIdx].start - i
      i = diff[diffIdx].start
      j += length
      while (nodeIdxB < nodesB.length && nodesB[nodeIdxB].end < j) nodeIdxB++
      let range = document.createRange()
      range.setStart(nodesB[nodeIdxB].node, j - nodesB[nodeIdxB].start)
      switch (diff[diffIdx].type) {
        case '-': {
          // Suppose some text was deleted.
          i = diff[diffIdx].end
          range.setEnd(nodesB[nodeIdxB].node, j - nodesB[nodeIdxB].start)
          break
        }
        case '+': {
          // Suppose some text was inserted.
          let b = j + diff[diffIdx].length
          while (nodeIdxB < nodesB.length && nodesB[nodeIdxB].end < b)
            nodeIdxB++
          range.setEnd(nodesB[nodeIdxB].node, (j = b) - nodesB[nodeIdxB].start)
          break
        }
        case 'x': {
          // Suppose some text was replaced.
          i = diff[diffIdx].end
          let b = j + diff[diffIdx].length
          while (nodeIdxB < nodesB.length && nodesB[nodeIdxB].end < b)
            nodeIdxB++
          range.setEnd(nodesB[nodeIdxB].node, (j = b) - nodesB[nodeIdxB].start)
          break
        }
      }
      ranges.push(range)
    }
    return ranges
  }
}

/**************************************************************************************************
 *
 * Plain-text grammar-checking service
 *
 * This class provides grammar-checking functionality to <textarea> HTML controls.
 *
 *************************************************************************************************/
class BesTAService extends BesPlainTextService {
  /**
   * Constructs class.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {*} eventSink Event sink for notifications
   */
  constructor(hostElement, eventSink) {
    super(hostElement, BesTAService.createTextElement(hostElement), eventSink)
    this.textElement.replaceChildren(
      document.createTextNode(this.hostElement.value)
    )
  }

  /**
   * Registers grammar checking service.
   *
   * @param {Element} hostElement DOM element to register grammar checking service for
   * @param {*} eventSink Event sink for notifications
   * @returns {BesTAService} Grammar checking service instance
   */
  static register(hostElement, eventSink) {
    let service = BesService.getServiceByElement(hostElement)
    if (service) return service
    service = new BesTAService(hostElement, eventSink)
    if (service.eventSink && 'register' in service.eventSink)
      service.eventSink.register(service)
    service.proofAll()
    return service
  }

  /**
   * Creates a clone div element for the <textarea> element
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @returns The element in DOM tree that hosts text to proof. Same as hostElement, separate for
   *          <textarea> and <input> hosts.
   */
  static createTextElement(hostElement) {
    const textElement = document.createElement('div')
    textElement.classList.add('bes-text-panel')
    textElement.style.zIndex = hostElement.style.zIndex - 1
    BesTAService.setTextElementSize(hostElement, textElement)
    hostElement.parentNode.insertBefore(textElement, hostElement)
    return textElement
  }

  /**
   * Sets the size of the clone div element to match the <textarea> element
   * TODO: This method should sync text element size only. Add another method for keeping styles in
   *       sync using MutationObserver.
   *
   * @param {Element} hostElement The element in DOM tree we are providing grammar-checking service
   *                              for
   * @param {Element} textElement The element in DOM tree that hosts coordinate-measurable clone of
   *                              the text to proof. Same as hostElement for <div>, separate for
   *                              <textarea> and <input> hosts.
   */
  static setTextElementSize(hostElement, textElement) {
    const rect = hostElement.getBoundingClientRect()
    const scrollTop = window.scrollY || document.documentElement.scrollTop
    const scrollLeft = window.scrollX || document.documentElement.scrollLeft
    const styles = window.getComputedStyle(hostElement)

    textElement.style.fontSize = styles.fontSize
    textElement.style.fontFamily = styles.fontFamily
    textElement.style.lineHeight = styles.lineHeight
    textElement.style.whiteSpace = styles.whiteSpace
    textElement.style.whiteSpaceCollapse = styles.whiteSpaceCollapse
    textElement.style.hyphens = styles.hyphens
    textElement.style.margin = styles.margin
    textElement.style.border = styles.border
    textElement.style.borderRadius = styles.borderRadius
    textElement.style.padding = styles.padding
    textElement.style.height = styles.height
    textElement.style.minHeight = styles.minHeight
    textElement.style.maxHeight = styles.maxHeight
    textElement.style.overflow = styles.overflow
    textElement.style.overflowWrap = styles.overflowWrap
    textElement.style.top = `${rect.top + scrollTop}px`
    textElement.style.left = `${rect.left + scrollLeft}px`
    textElement.style.width = styles.width
    textElement.style.minWidth = styles.minWidth
    textElement.style.maxWidth = styles.maxWidth
  }

  /**
   * Called to report resizing
   */
  onResize() {
    BesTAService.setTextElementSize(this.hostElement, this.textElement)
    super.onResize()
  }

  /**
   * Called to report repositioning
   */
  onReposition() {
    BesTAService.setTextElementSize(this.hostElement, this.textElement)
    super.onReposition()
  }

  /**
   * Called to report the text is about to change
   *
   * @param {InputEvent} event The event notifying the user of editable content changes
   */
  onBeforeInput(event) {
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()
  }

  /**
   * Called to report <textarea> content change
   */
  onInput(event) {
    // Determine ranges of text that will change.
    let { text, nodes } = this.getTextFromNodes()
    let textA = text
    let nodesA = nodes
    let textB = this.hostElement.value
    let diff = BesPlainTextService.diffStrings(textA, textB)
    let changes = []
    for (
      let i = 0, j = 0, nodeIdxA = 0, diffIdx = 0;
      diffIdx < diff.length;
      ++diffIdx
    ) {
      let length = diff[diffIdx].start - i
      i = diff[diffIdx].start
      while (nodeIdxA < nodesA.length && nodesA[nodeIdxA].end < i) nodeIdxA++
      let change = {
        range: document.createRange()
      }
      change.range.setStart(nodesA[nodeIdxA].node, i - nodesA[nodeIdxA].start)
      j += length
      switch (diff[diffIdx].type) {
        case '-': {
          // Suppose some text was deleted.
          while (
            nodeIdxA < nodesA.length &&
            nodesA[nodeIdxA].end < diff[diffIdx].end
          )
            nodeIdxA++
          change.range.setEnd(
            nodesA[nodeIdxA].node,
            (i = diff[diffIdx].end) - nodesA[nodeIdxA].start
          )
          break
        }
        case '+': {
          // Suppose some text was inserted.
          let b = j + diff[diffIdx].length
          change.range.setEnd(nodesA[nodeIdxA].node, i - nodesA[nodeIdxA].start)
          change.replacement = textB.substring(j, b)
          j = b
          break
        }
        case 'x': {
          // Suppose some text was replaced.
          while (
            nodeIdxA < nodesA.length &&
            nodesA[nodeIdxA].end < diff[diffIdx].end
          )
            nodeIdxA++
          change.range.setEnd(
            nodesA[nodeIdxA].node,
            (i = diff[diffIdx].end) - nodesA[nodeIdxA].start
          )
          let b = j + diff[diffIdx].length
          change.replacement = textB.substring(j, b)
          j = b
          break
        }
      }
      changes.push(change)
    }

    // Clear proofing for paragraphs that are about to change.
    let paragraphRanges = new Set()
    changes.forEach(change => {
      this.results.forEach(result => {
        if (
          BesPlainTextService.isOverlappingParagraph(result.range, change.range)
        )
          paragraphRanges.add(result.range)
      })
    })
    paragraphRanges.forEach(range => this.clearProofing(range))

    // Sync changes between hostElement and textElement.
    changes.forEach(change => {
      change.range.deleteContents()
      if (change.replacement)
        change.range.insertNode(document.createTextNode(change.replacement))
    })

    // Now that the text is done changing, we can correctly calculate markup position.
    this.repositionAllMarkup()

    // Defer grammar-checking to reduce stress on grammar-checking server.
    this.timer = setTimeout(() => {
      this.proofAll()
      delete this.timer
    }, 1000)
  }

  /**
   * Checks if host element content is editable.
   *
   * @returns true if editable; false otherwise
   */
  isContentEditable() {
    return !this.hostElement.disabled && !this.hostElement.readOnly
  }

  /**
   * Replaces grammar checking match with a suggestion provided by grammar checking service.
   *
   * @param {*} el Block element/paragraph containing grammar checking rule match
   * @param {*} match Grammar checking rule match
   * @param {String} replacement Text to replace grammar checking match with
   */
  replaceText(el, match, replacement) {
    super.replaceText(el, match, replacement)
    let { text, nodes } = this.getTextFromNodes()
    this.hostElement.value = text
  }
}

/**************************************************************************************************
 *
 * Grammar mistake popup dialog
 *
 * This is internal class implementing the pop-up dialog user may invoke by clicking on a
 * highlighted grammar mistake in text.
 *
 *************************************************************************************************/
class BesPopup extends HTMLElement {
  constructor() {
    super()
    this.attachShadow({ mode: 'open' })
  }

  /**
   * Called each time the element is added to the document
   */
  connectedCallback() {
    this.shadowRoot.innerHTML = `
      <style>
        :host {
          display: none;
        }
        :host(.show){
          z-index: 10;
          display: block;
        }
        .popup-text {
          font-size: 0.93rem;
          max-width: 160px;
          color: black;
          text-align: center;
          padding: 8px 0;
          z-index: 1;
        }
        .bes-popup-container {
          font-family: Arial, sans-serif;
          visibility: hidden;
          min-width: 200px;
          max-width: 350px;
          background-color: rgb(241, 243, 249);
          box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
          border-radius: 5px;
          padding: 8px;
          z-index: 1;
        }
        .bes-toolbar {
          display: flex;
          justify-content: end;
          padding: 5px 2px;
        }
        .bes-toolbar button {
          margin-right: 2px;
        }
        .bes-popup-title {
          flex-grow: 1;
          cursor: grab;
        }
        .bes-text-div{
          background-color: white;
          padding: 10px;
          border-radius: 5px;
        }
        .bes-replacement-btn{
          margin: 4px 1px;
          padding: 4px;
          border: none;
          border-radius: 5px;
          background-color: #239aff;
          color: white;
          cursor: pointer;
        }
        .bes-replacement-btn:hover{
          background-color: #1976f0;
        }
        .bes-replacement-div{
          margin-top: 4px;
        }
        :host(.show) .bes-popup-container {
          visibility: visible;
          animation: fadeIn 1s;
        }
        @keyframes fadeIn {
          from {opacity: 0;}
          to {opacity:1 ;}
        }
      </style>
      <div class="bes-popup-container">
        <div class="bes-toolbar">
          <div class="bes-popup-title">Besana</div>
          <button class="bes-close-btn" onclick="BesPopup.hide()">X</button>
        </div>
        <div class="bes-text-div">
          <span class="popup-text">
          </span>
          <div class="bes-replacement-div">
          </div>
        </div>
      </div>
    `
    this.addEventListener('mousedown', this.onMouseDown)
  }

  /**
   * Shows popup window.
   *
   * @param {Number} x X location hint
   * @param {Number} y Y location hint
   */
  show(x, y) {
    this.style.position = 'fixed'

    // Element needs some initial placement for the browser to provide this.offsetWidth and this.
    // offsetHeight measurements.
    // The fade-in effect on the popup window should prevent flicker.
    this.style.left = `0px`
    this.style.top = `0px`
    this.classList.add('show')

    if (x + this.offsetWidth <= window.innerWidth) {
      this.style.left = `${x}px`
    } else if (this.offsetWidth <= x) {
      this.style.left = `${x - this.offsetWidth}px`
    } else {
      this.style.left = `${(window.innerWidth - this.offsetWidth) / 2}px`
    }

    if (y + 20 + this.offsetHeight <= window.innerHeight) {
      this.style.top = `${y + 20}px`
    } else if (this.offsetHeight <= y) {
      this.style.top = `${y - this.offsetHeight}px`
    } else {
      this.style.top = `${(window.innerHeight - this.offsetHeight) / 2}px`
    }
  }

  /**
   * Clears all grammar mistake suggestions.
   */
  clearReplacements() {
    Array.from(
      this.shadowRoot.querySelector('.bes-replacement-div')?.children
    ).forEach(replacement => replacement.remove())
  }

  /**
   * Adds a grammar mistake suggestion.
   *
   * @param {*} el Block element/paragraph containing the grammar mistake
   * @param {*} match Grammar checking rule match
   * @param {BesService} service Grammar checking service
   * @param {Boolean} allowReplacements Host element is mutable and grammar mistake may be replaced
   *                                    by suggestion
   */
  appendReplacements(el, match, service, allowReplacements) {
    const replacementDiv = this.shadowRoot.querySelector('.bes-replacement-div')
    match.match.replacements.forEach(replacement => {
      const replacementBtn = document.createElement('button')
      replacementBtn.classList.add('bes-replacement-btn')
      replacementBtn.textContent = replacement.value
      replacementBtn.addEventListener('click', () => {
        if (allowReplacements) {
          service.replaceText(el, match, replacement.value)
          BesPopup.hide()
        }
      })
      replacementDiv.appendChild(replacementBtn)
    })
  }

  /**
   * Sets grammar mistake description
   *
   * @param {String} text
   */
  changeMessage(text) {
    this.clearReplacements()
    this.shadowRoot.querySelector('.popup-text').innerText = text
  }

  /**
   * Handles the mousedown event.
   *
   * @param {MouseEvent} e Event
   */
  onMouseDown(e) {
    e.preventDefault()
    this.initialMouseX = e.clientX
    this.initialMouseY = e.clientY
    this.handleMouseMove = this.onMouseMove.bind(this)
    document.addEventListener('mousemove', this.handleMouseMove)
    this.handleMouseUp = this.onMouseUp.bind(this)
    document.addEventListener('mouseup', this.handleMouseUp)
  }

  /**
   * Handles the mousemove event.
   *
   * @param {MouseEvent} e Event
   */
  onMouseMove(e) {
    e.preventDefault()

    let diffX = this.initialMouseX - e.clientX
    this.initialMouseX = e.clientX
    let left = this.offsetLeft - diffX
    left = Math.max(0, Math.min(left, window.innerWidth - this.offsetWidth))
    this.style.left = `${left}px`

    let diffY = this.initialMouseY - e.clientY
    this.initialMouseY = e.clientY
    let top = this.offsetTop - diffY
    top = Math.max(0, Math.min(top, window.innerHeight - this.offsetHeight))
    this.style.top = `${top}px`
  }

  /**
   * Handles the mouseup event.
   *
   * @param {MouseEvent} e Event
   */
  onMouseUp(e) {
    document.removeEventListener('mouseup', this.handleMouseUp)
    document.removeEventListener('mousemove', this.handleMouseMove)
  }

  /**
   * Dismisses all the popups.
   */
  static hide() {
    document
      .querySelectorAll('bes-popup-el')
      .forEach(popup => popup.classList.remove('show'))
  }
}

customElements.define('bes-popup-el', BesPopup)

// /*************************************************************************
//  *
//  * Status pop-up
//  *
//  *************************************************************************/
// class BesStatusPopup extends HTMLElement {
//   constructor() {
//     super()
//     this.attachShadow({ mode: 'open' })
//   }

//   /**
//    * Called each time the element is added to the document
//    */
//   connectedCallback() {
//     this.shadowRoot.innerHTML = `
//       <style>
//         :host {
//           display: none;
//         }
//         :host(.show){
//           z-index: 10;
//         }
//         .popup-text {
//           max-width: 160px;
//           color: black;
//           text-align: center;
//           padding: 8px 0;
//           z-index: 1;
//         }
//         .bes-popup-container {
//           visibility: hidden;
//           max-width: 300px;
//           background-color: rgb(241, 243, 249);
//           box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
//           border-radius: 5px;
//           padding: 8px;
//           z-index: 1;
//         }
//         .bes-toolbar {
//           display: flex;
//           justify-content: end;
//           padding: 5px 2px;
//         }
//         .bes-toolbar button {
//           margin-right: 2px;
//         }
//         .bes-popup-title {
//           flex-grow: 1;
//         }
//         .bes-text-div{
//           background-color: white;
//           padding: 10px;
//           border-radius: 5px;
//         }
//         .bes-service-btn{
//           background-color: none;
//           width: 30px;
//           height: 30px;
//           display: flex;
//           justify-content: center;
//           align-items: center;
//         }
//         .bes-turn-off{
//           width: 20px;
//           height: 20px;
//         }
//         :host(.show) .bes-popup-container {
//           visibility: visible;
//           animation: fadeIn 1s;
//         }
//         @keyframes fadeIn {
//           from {opacity: 0;}
//           to {opacity:1 ;}
//         }
//       </style>
//       <div class="bes-popup-container">
//         <div class="bes-toolbar">
//           <div class="bes-popup-title">Besana</div>
//           <button class="bes-close-btn" onclick="BesStatusPopup.hide()">X</button>
//         </div>
//         <div class="bes-text-div">
//           <span class="popup-text">
//             Če želite izključiti preverjanje pravopisa, kliknite na gumb.
//           </span>
//           <button class="bes-service-btn">
//             <img class="bes-turn-off" src="/images/turn-off-svgrepo-com.svg" alt="Izključi preverjanje pravopisa">
//           </button>
//         </div>
//       </div>
//     `
//   }

//   /**
//    * Shows popup window.
//    *
//    * @param {Number} x X location hint
//    * @param {Number} y Y location hint
//    * @param {BesService} service Grammar checking service
//    */
//   show(x, y, service) {
//     this.style.position = 'fixed'
//     this.style.display = 'block'

//     // Element needs some initial placement for the browser to provide this.offsetWidth and this.offsetHeight measurements.
//     // The fade-in effect on the popup window should prevent flicker.
//     this.style.left = `0px`
//     this.style.top = `0px`
//     this.classList.add('show')

//     if (x + this.offsetWidth <= window.innerWidth) {
//       this.style.left = `${x}px`
//     } else if (this.offsetWidth <= x) {
//       this.style.left = `${x - this.offsetWidth}px`
//     } else {
//       this.style.left = `${x - this.offsetWidth / 2}px`
//     }

//     if (y + 20 + this.offsetHeight <= window.innerHeight) {
//       this.style.top = `${y + 20}px`
//     } else if (this.offsetHeight <= y) {
//       this.style.top = `${y - this.offsetHeight}px`
//     } else {
//       this.style.top = `${y - this.offsetHeight / 2}px`
//     }

//     if (service) {
//       const disableButton = this.shadowRoot.querySelector('.bes-service-btn')
//       disableButton.onclick = () => {
//         service.unregister()
//         BesStatusPopup.hide()
//       }
//     }
//     this.classList.add('show')
//   }

//   /**
//    * Dismisses all the popups.
//    */
//   static hide() {
//     const popup = document.querySelector('bes-popup-status.show')
//     popup?.classList?.remove('show')
//   }
// }

// customElements.define('bes-popup-status', BesStatusPopup)

// Auto-register all elements with bes-service class.
window.addEventListener('load', () => {
  document
    .querySelectorAll('.bes-service')
    .forEach(hostElement => BesService.registerByElement(hostElement))
})