idrec.h

/*
    SPDX-License-Identifier: MIT
    Copyright © 2016-2022 Amebis
*/
 
#pragma once
 
#include <ios>
#include <istream>
#include <ostream>
 
 
namespace stdex {
    namespace idrec {
        template <class T_ID>
        _Success_(return) bool read_id(_In_ std::istream& stream, _Out_ T_ID &id, _In_opt_ std::streamoff end = (std::streamoff)-1)
        {
            if (end == (std::streamoff)-1 || stream.tellg() < end) {
                stream.read((char*)&id, sizeof(id));
                return stream.good();
            } else
                return false;
        }
 
 
        template <class T_SIZE, unsigned int ALIGN>
        bool ignore(_In_ std::istream& stream)
        {
            // Read record size.
            T_SIZE size;
            stream.read((char*)&size, sizeof(size));
            if (!stream.good()) return false;
 
            // Skip the record data.
            size += (T_SIZE)(ALIGN - size) % ALIGN;
            stream.ignore(size);
            if (!stream.good()) return false;
 
            return true;
        }
 
 
        template <class T_ID, class T_SIZE, unsigned int ALIGN>
        bool find(_In_ std::istream& stream, _In_ T_ID id, _In_opt_ std::streamoff end = (std::streamoff)-1)
        {
            T_ID _id;
 
            while (end == (std::streamoff)-1 || stream.tellg() < end) {
                stream.read((char*)&_id, sizeof(_id));
                if (!stream.good()) return false;
 
                if (_id == id) {
                    // The record was found.
                    return true;
                } else
                    ignore<T_SIZE, ALIGN>(stream);
            }
 
            return false;
        }
 
 
        template <class T_ID, class T_SIZE>
        std::streamoff open(_In_ std::ostream& stream, _In_ T_ID id)
        {
            std::streamoff start = stream.tellp();
 
            // Write ID.
            if (stream.fail()) return (std::streamoff)-1;
            stream.write((const char*)&id, sizeof(id));
 
            // Write 0 as a placeholder for data size.
            if (stream.fail()) return (std::streamoff)-1;
            T_SIZE size = 0;
            stream.write((const char*)&size, sizeof(size));
 
            return start;
        }
 
 
        template <class T_ID, class T_SIZE, unsigned int ALIGN>
        std::streamoff close(_In_ std::ostream& stream, _In_ std::streamoff start)
        {
            std::streamoff end = stream.tellp();
            T_SIZE
                size      = (T_SIZE)(end - start - sizeof(T_ID) - sizeof(T_SIZE)),
                remainder = (T_SIZE)(ALIGN - size) % ALIGN; // Number of bytes we need to add, to keep the data integral number of ALIGN blocks long
 
            if (remainder) {
                // Append padding.
                static const char padding[ALIGN] = {};
                stream.write(padding, remainder);
                end += remainder;
            }
 
            // Update the data size.
            if (stream.fail()) return (std::streamoff)-1;
            stream.seekp(start + sizeof(T_ID));
            stream.write((const char*)&size, sizeof(size));
            stream.seekp(end);
 
            return end;
        }
 
 
        template <class T, class T_ID, class T_SIZE, unsigned int ALIGN>
        class record
        {
        public:
            record(_In_ T &d) : data(d) {}
 
 
            record(_In_ const T &d) : data((T&)d) {}
 
 
            const record<T, T_ID, T_SIZE, ALIGN>& operator =(_In_ const record<T, T_ID, T_SIZE, ALIGN> &r)
            {
                data = r.data;
                return *this;
            }
 
 
            static std::streamoff open(_In_ std::ostream& stream)
            {
                return stdex::idrec::open<T_ID, T_SIZE>(stream, id);
            }
 
 
            static std::streamoff close(_In_ std::ostream& stream, _In_ std::streamoff start)
            {
                return stdex::idrec::close<T_ID, T_SIZE, ALIGN>(stream, start);
            }
 
 
            static bool find(_In_ std::istream& stream, _In_opt_ std::streamoff end = (std::streamoff)-1)
            {
                return stdex::idrec::find<T_ID, T_SIZE, ALIGN>(stream, id, end);
            }
 
 
            static const T_ID id;   
            T &data;                
        };
    };
};
 
 
template <class T, class T_ID, class T_SIZE, unsigned int ALIGN>
std::ostream& operator <<(_In_ std::ostream& stream, _In_ const stdex::idrec::record<T, T_ID, T_SIZE, ALIGN> r)
{
    // Parameter r does not need to be passed by reference. It has only one field (data), which is a reference itself already. The id field is static anyway.
 
    std::streamoff start = r.open(stream);
    if (stream.fail()) return stream;
    stream << r.data;
    r.close(stream, start);
 
    return stream;
}
 
 
template <class T, class T_ID, class T_SIZE, unsigned int ALIGN>
std::istream& operator >>(_In_ std::istream& stream, _In_ stdex::idrec::record<T, T_ID, T_SIZE, ALIGN> r)
{
    // Parameter r does not need to be passed by reference. It has only one field (data), which is a reference itself already. The id field is static anyway.
 
    // Read data size.
    T_SIZE size;
    stream.read((char*)&size, sizeof(size));
    if (!stream.good()) return stream;
 
    // Read data.
    std::streamoff start = stream.tellg();
    stream >> r.data; // TODO: operator >> should not read past the record data! Make a size limited stream and read from it instead.
 
    size += (T_SIZE)(ALIGN - size) % ALIGN;
    stream.seekg(start + size);
 
    return stream;
}