// TODO: Port popup dialog from service.js
// TODO: Test with contenteditable="plaintext-only"
// TODO: Implement <textarea> class
// TODO: Port CKEditor class from service.js

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

window.addEventListener('resize', () =>
  besServices.forEach(service => service.onResize())
)

window.addEventListener('scroll', () =>
  besServices.forEach(service => service.onScroll())
)

/*************************************************************************
 *
 * Base class for all grammar-checking services
 *
 *************************************************************************/
class BesService {
  constructor(hostElement) {
    this.hostElement = hostElement
    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.handleScroll = () => this.onScroll()
    this.hostElement.addEventListener('scroll', this.handleScroll)

    besServices.push(this)
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    besServices = besServices.filter(item => item !== this)
    this.hostElement.removeEventListener('scroll', this.handleScroll)
    this.hostElement.spellcheck = this.originalSpellcheck
    this.clearCorrectionPanel()
  }

  /**
   * Called initially when grammar-checking run is started
   */
  onStartProofing() {
    this.proofingCount = 0 // 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.updateStatusIcon('bes-status-loading', 'Besana preverja pravopis.')
  }

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

  /**
   * 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) {
    this.updateStatusIcon(
      'bes-status-error',
      `Pri preverjanju pravopisa je prišlo do napake ${response.status} ${response.statusText}.`
    )
  }

  /**
   * Called when failed to parse result of a grammar-checking of a block of text
   *
   * @param {Error} error Error
   */
  onFailedProofingResult(error) {
    if (!this.proofingError) this.proofingError = 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.proofingCount <= 0) this.onEndProofing()
  }

  /**
   * Called when grammar-checking run is ended
   */
  onEndProofing() {
    if (this.proofingError) {
      this.updateStatusIcon(
        'bes-status-error',
        `Pri obdelavi odgovora pravopisnega strežnika je prišlo do napake: ${this.proofingError}`
      )
    } else if (this.proofingMatches > 0)
      this.updateStatusIcon(
        'bes-status-mistakes',
        `Število napak: ${this.proofingMatches}`
      )
    else this.updateStatusIcon('bes-status-success', 'V besedilu ni napak.')
  }

  /**
   * 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`
  }

  /**
   * Called to report resizing
   */
  onResize() {
    this.setCorrectionPanelSize()
    this.setStatusDivPosition()
  }

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

    this.correctionPanel.appendChild(this.scrollPanel)
    panelParent.appendChild(this.correctionPanel)
    this.hostElement.parentElement.insertBefore(panelParent, this.hostElement)

    this.statusDiv = document.createElement('div')
    this.statusDiv.classList.add('bes-status-div')
    this.statusIcon = document.createElement('div')
    this.statusIcon.classList.add('bes-status-icon')
    this.statusDiv.appendChild(this.statusIcon)
    this.setStatusDivPosition()
    this.hostElement.parentNode.insertBefore(
      this.statusDiv,
      this.hostElement.nextSibling
    )
    const statusPopup = document.createElement('bes-popup-status-el')
    document.body.appendChild(statusPopup)
    this.statusDiv.addEventListener('click', e =>
      this.handleStatusClick(e, statusPopup)
    )
  }

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

  /**
   * Resizes correction and scroll panels to match host element size.
   */
  setCorrectionPanelSize() {
    const styles = window.getComputedStyle(this.hostElement)
    const totalWidth = parseFloat(styles.width)
    const totalHeight =
      parseFloat(styles.height) +
      parseFloat(styles.marginTop) +
      parseFloat(styles.marginBottom) +
      parseFloat(styles.paddingTop) +
      parseFloat(styles.paddingBottom)
    this.correctionPanel.style.width = `${totalWidth}px`
    this.correctionPanel.style.height = `${totalHeight}px`
    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.height = `${this.hostElement.scrollHeight}px`
  }

  /**
   * Repositions status DIV element.
   */
  setStatusDivPosition() {
    const rect = this.hostElement.getBoundingClientRect()
    const scrollTop = window.scrollY || document.documentElement.scrollTop
    this.statusDiv.style.left = `${rect.right - 40}px`
    this.statusDiv.style.top = `${rect.top + rect.height - 30 + scrollTop}px`
  }

  /**
   * Sets status icon style and title.
   *
   * @param {String} status CSS class name to set status icon to
   * @param {String} title Title of the status icon
   */
  updateStatusIcon(status, title) {
    const statuses = [
      'bes-status-loading',
      'bes-status-success',
      'bes-status-mistakes',
      'bes-status-error'
    ]
    statuses.forEach(statusClass => {
      this.statusIcon.classList.remove(statusClass)
    })
    this.statusIcon.classList.add(status)
    this.statusDiv.title = title
  }
}

/*************************************************************************
 *
 * DOM grammar-checking service
 *
 *************************************************************************/
class BesDOMService extends BesService {
  constructor(hostElement) {
    super(hostElement)
    this.results = [] // Results of grammar-checking, one per each block of text
    this.handleBeforeInput = event => this.onBeforeInput(event)
    this.hostElement.addEventListener('beforeinput', this.handleBeforeInput)
    this.handleInput = () => this.onInput()
    this.hostElement.addEventListener('input', this.handleInput)
  }

  /**
   * Registers grammar checking service.
   *
   * @param {Element} hostElement DOM element to register grammar checking service for
   * @returns {BesService} Grammar checking service instance
   */
  static register(hostElement) {
    let service = new BesDOMService(hostElement)
    service.proofAll()
    return service
  }

  /**
   * Unregisters grammar checking service.
   */
  unregister() {
    this.hostElement.removeEventListener('input', this.handleInput)
    this.hostElement.removeEventListener('beforeinput', this.handleBeforeInput)
    if (this.timer) clearTimeout(this.timer)
    if (this.abortController) this.abortController.abort()
    super.unregister()
  }

  /**
   * Called initially when grammar-checking run is started
   */
  onStartProofing() {
    super.onStartProofing()
    this.abortController = new AbortController()
  }

  /**
   * 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
    super.onFailedProofing(response)
  }

  /**
   * Called when grammar-checking run is ended
   */
  onEndProofing() {
    delete this.abortController
    super.onEndProofing()
  }

  /**
   * Called to report scrolling
   */
  onScroll() {
    super.onScroll()

    // Markup is in a "position:absolute" <div> element requiring repositioning when scrolling host element or window.
    // It is defered to reduce stress in a flood of scroll events.
    // TODO: We could technically just update scrollTop and scrollLeft of all markup rects for even better performance?
    if (this.scrollTimeout) clearTimeout(this.scrollTimeout)
    this.scrollTimeout = setTimeout(() => {
      this.repositionAllMarkup()
      delete this.scrollTimeout
    }, 500)
  }

  /**
   * Called to report resizing
   */
  onResize() {
    super.onResize()

    // When window is resized, host element might resize too.
    // This may cause text to re-wrap requiring markup re
    this.repositionAllMarkup()
  }

  /**
   * 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 => {
        if (
          el === this.hostElement ||
          Array.from(this.hostElement.childNodes).includes(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)
  }

  /**
   * Recursively grammar-(re)checks our host DOM tree.
   */
  proofAll() {
    this.onStartProofing()
    this.proofNode(this.hostElement, this.abortController)
    if (this.proofingCount == 0) {
      // No text blocks were discovered for proofing. onProofingProgress() will not be called
      // and we need to notify manually.
      this.onEndProofing()
    }
  }

  /**
   * 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.
          if (this.isProofed(node))
            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 ← not needed, kept for reference &&*/ endOffset <=
                        startingOffset + data[idx].text.length
                    ) {
                      range.setEnd(data[idx].node, endOffset - startingOffset)
                      break
                    }
                  }

                  const { clientRects, highlights } =
                    this.addMistakeMarkup(range)
                  matches.push({
                    rects: clientRects,
                    highlights: highlights,
                    range: range,
                    match: match
                  })
                })
                this.markProofed(node, matches)
                this.onProofingProgress(matches.length)
              })
              .catch(error => {
                if (error.name === 'AbortError') return
                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 {Boolean} true if the element has already been grammar-checked; false otherwise.
   */
  isProofed(el) {
    return this.results?.find(result => result.element === el) != null
  }

  /**
   * Marks given block element as grammar-checked.
   *
   * @param {Element} el DOM element that was checked
   * @param {Array} matches Grammar mistakes
   */
  markProofed(el, matches) {
    this.clearProofing(el)
    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 => result.element !== el)
  }

  /**
   * Creates grammar mistake markup in DOM.
   *
   * @param {Range} range Grammar mistake range
   * @returns {Object} Client rectangles and grammar mistake highlight elements
   */
  addMistakeMarkup(range) {
    const clientRects = range.getClientRects()
    const scrollPanelRect = this.scrollPanel.getBoundingClientRect()
    let highlights = []
    for (let i = 0, n = clientRects.length; i < n; ++i) {
      const rect = clientRects[i]
      const highlight = document.createElement('div')
      highlight.classList.add('bes-typo-mistake')
      const topPosition = rect.top - scrollPanelRect.top
      const leftPosition = rect.left - scrollPanelRect.left
      highlight.style.left = `${leftPosition}px`
      highlight.style.top = `${topPosition}px`
      highlight.style.width = `${rect.width}px`
      highlight.style.height = `${rect.height}px`
      this.scrollPanel.appendChild(highlight)
      highlights.push(highlight)
    }
    return { clientRects, highlights }
  }

  /**
   * Updates grammar mistake markup positions.
   *
   * @param {Element} el DOM element we want to update markup for
   *
   * TODO: Unused
   */
  repositionMarkup(el) {
    let result = this.results?.find(result => result.element === el)
    if (!result) return
    result.matches.forEach(match => {
      const { clientRects, highlights } = this.addMistakeMarkup(match.range)
      match.rects = clientRects
      if (match.highlights) match.highlights.forEach(h => h.remove())
      match.highlights = highlights
    })
  }

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

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

  /**
   * Clears all grammar mistake markup.
   *
   * TODO: Unused
   */
  clearAllMarkup() {
    this.results.forEach(result => {
      result.matches.forEach(match => {
        if (match.highlights) {
          match.highlights.forEach(h => h.remove())
          delete match.highlights
        }
      })
    })
  }

  /**
   * 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.hostElement) 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 = BesDOMService.getParents(start)
    let endAncestors = BesDOMService.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 = BesDOMService.getNextNode(node)) {
      nodes.push(node)
      if (node == end) break
    }

    return nodes
  }
}

// Auto-register all elements with bes-service class.
window.addEventListener('load', () => {
  document.querySelectorAll('.bes-service').forEach(hostElement => {
    // TODO: Treat contenteditable="plaintext-only" separately. It requires manual paragraph splitting on \n\n.
    if (hostElement.tagName === 'TEXTAREA') BesTAService.register(hostElement)
    else BesDOMService.register(hostElement)
  })
})