//This File includes code from:
//Copyright(c) 2018 Mark Heath, Andrew Ward & Contributors
//Licensed under the MIT License (see LICENSE (Nlayer).txt)
using System;
using System.IO;

namespace NLayer.Decoder
{
    class MpegStreamReader
    {
        ID3Frame _id3Frame, _id3v1Frame;
        RiffHeaderFrame _riffHeaderFrame;

        VBRInfo _vbrInfo;
        MpegFrame _first, _current, _last, _lastFree;

        long _readOffset, _eofOffset;
        Stream _source;
        bool _canSeek, _endFound, _mixedFrameSize;
        object _readLock = new object();
        object _frameLock = new object();

        internal MpegStreamReader(Stream source)
        {
            _source = source;
            _canSeek = source.CanSeek;
            _readOffset = 0L;
            _eofOffset = long.MaxValue;

            // find the first Mpeg frame
            var frame = FindNextFrame();
            while (frame != null && !(frame is MpegFrame))
            {
                frame = FindNextFrame();
            }

            // if we still don't have a frame, we never sync'ed
            if (frame == null) throw new InvalidDataException("Not a valid MPEG file!");

            // the very next frame "should be" an mpeg frame
            frame = FindNextFrame();

            // if not, it's not a valid file
            if (frame == null || !(frame is MpegFrame)) throw new InvalidDataException("Not a valid MPEG file!");

            // seek to the first frame
            _current = _first;
        }

        FrameBase FindNextFrame()
        {
            // if we've found the end, don't bother looking for anything else
            if (_endFound) return null;

            var freeFrame = _lastFree;
            var lastFrameStart = _readOffset;

            lock (_frameLock)
            {
                // read 3 bytes
                var syncBuf = new byte[4];
                try
                {
                    if (Read(_readOffset, syncBuf, 0, 4) == 4)
                    {
                        // now loop until a frame is found
                        do
                        {
                            var sync = (uint)(syncBuf[0] << 24 | syncBuf[1] << 16 | syncBuf[2] << 8 | syncBuf[3]);

                            lastFrameStart = _readOffset;

                            // try ID3 first (for v2 frames)
                            if (_id3Frame == null)
                            {
                                var f = ID3Frame.TrySync(sync);
                                if (f != null)
                                {
                                    if (f.Validate(_readOffset, this))
                                    {
                                        if (!_canSeek) f.SaveBuffer();

                                        _readOffset += f.Length;
                                        DiscardThrough(_readOffset, true);

                                        return _id3Frame = f;
                                    }
                                }
                            }

                            // now look for a RIFF header
                            if (_first == null && _riffHeaderFrame == null)
                            {
                                var f = RiffHeaderFrame.TrySync(sync);
                                if (f != null)
                                {
                                    if (f.Validate(_readOffset, this))
                                    {
                                        _readOffset += f.Length;
                                        DiscardThrough(_readOffset, true);

                                        return _riffHeaderFrame = f;
                                    }
                                }
                            }

                            // finally, just try for an MPEG frame
                            var frame = MpegFrame.TrySync(sync);
                            if (frame != null)
                            {
                                if (frame.Validate(_readOffset, this)
                                   && !(freeFrame != null
                                       && (frame.Layer != freeFrame.Layer
                                          || frame.Version != freeFrame.Version
                                          || frame.SampleRate != freeFrame.SampleRate
                                          || frame.BitRateIndex > 0
                                          )
                                       )
                                   )
                                {
                                    if (!_canSeek)
                                    {
                                        frame.SaveBuffer();
                                        DiscardThrough(_readOffset + frame.FrameLength, true);
                                    }

                                    _readOffset += frame.FrameLength;

                                    if (_first == null)
                                    {
                                        if (_vbrInfo == null && (_vbrInfo = frame.ParseVBR()) != null)
                                        {
                                            return FindNextFrame();
                                        }
                                        else
                                        {
                                            frame.Number = 0;
                                            _first = _last = frame;
                                        }
                                    }
                                    else
                                    {
                                        if (frame.SampleCount != _first.SampleCount)
                                        {
                                            _mixedFrameSize = true;
                                        }

                                        frame.SampleOffset = _last.SampleCount + _last.SampleOffset;
                                        frame.Number = _last.Number + 1;
                                        _last = (_last.Next = frame);
                                    }

                                    if (frame.BitRateIndex == 0)
                                    {
                                        _lastFree = frame;
                                    }

                                    return frame;
                                }
                            }

                            // if we've read MPEG frames and can't figure out what frame type we have, try looking for a new ID3 tag
                            if (_last != null)
                            {
                                var f = ID3Frame.TrySync(sync);
                                if (f != null)
                                {
                                    if (f.Validate(_readOffset, this))
                                    {
                                        if (!_canSeek) f.SaveBuffer();

                                        // if it's a v1 tag, go ahead and parse it
                                        if (f.Version == 1)
                                        {
                                            _id3v1Frame = f;
                                        }
                                        else
                                        {
                                            // grrr...  the ID3 2.4 spec says tags can be anywhere in the file and that later tags can override earlier ones...  boo
                                            _id3Frame.Merge(f);
                                        }

                                        _readOffset += f.Length;
                                        DiscardThrough(_readOffset, true);

                                        return f;
                                    }
                                }
                            }

                            // well, we didn't find anything, so rinse and repeat with the next byte
                            ++_readOffset;
                            if (_first == null || !_canSeek) DiscardThrough(_readOffset, true);
                            Buffer.BlockCopy(syncBuf, 1, syncBuf, 0, 3);
                        } while (Read(_readOffset + 3, syncBuf, 3, 1) == 1);
                    }

                    // move the "end of frame" marker for the last free format frame (in case we have one)
                    // this is because we don't include the last four bytes otherwise
                    lastFrameStart += 4;

                    _endFound = true;
                    return null;
                }
                finally
                {
                    if (freeFrame != null)
                    {
                        freeFrame.Length = (int)(lastFrameStart - freeFrame.Offset);

                        if (!_canSeek)
                        {
                            // gotta finish filling the buffer!!
                            throw new InvalidOperationException("Free frames cannot be read properly from forward-only streams!");
                        }

                        // if _lastFree hasn't changed (we got a non-MPEG frame), clear it out
                        if (_lastFree == freeFrame)
                        {
                            _lastFree = null;
                        }
                    }
                }
            }
        }

        class ReadBuffer
        {
            public byte[] Data;
            public long BaseOffset;
            public int End;
            public int DiscardCount;

            object _localLock = new object();

            public ReadBuffer(int initialSize)
            {
                initialSize = 2 << (int)Math.Log(initialSize, 2);

                Data = new byte[initialSize];
            }

            public int Read(MpegStreamReader reader, long offset, byte[] buffer, int index, int count)
            {
                lock (_localLock)
                {
                    var startIdx = EnsureFilled(reader, offset, ref count);
                    
                    Buffer.BlockCopy(Data, startIdx, buffer, index, count);
                }
                return count;
            }

            public int ReadByte(MpegStreamReader reader, long offset)
            {
                lock (_localLock)
                {
                    var count = 1;
                    var startIdx = EnsureFilled(reader, offset, ref count);
                    if (count == 1)
                    {
                        return Data[startIdx];
                    }
                }
                return -1;
            }

            int EnsureFilled(MpegStreamReader reader, long offset, ref int count)
            {
                // if the offset & count are inside our buffer's range, just return the appropriate index
                var startIdx = (int)(offset - BaseOffset);
                int endIdx = startIdx + count;
                if (startIdx < 0 || endIdx > End)
                {
                    int readStart = 0, readCount = 0, moveCount = 0;
                    long readOffset = 0;

                    #region Decision-Making

                    if (startIdx < 0)
                    {
                        // if we can't seek, there's nothing we can do
                        if (!reader._source.CanSeek) throw new InvalidOperationException("Cannot seek backwards on a forward-only stream!");

                        // if there's data in the buffer, try to keep it (up to doubling the buffer size)
                        if (End > 0)
                        {
                            // if doubling the buffer would push it past the max size, don't check it
                            if ((startIdx + Data.Length > 0) || (Data.Length * 2 <= 16384 && startIdx + Data.Length * 2 > 0))
                            {
                                endIdx = End;
                            }
                        }

                        // we know we'll have to start reading here
                        readOffset = offset;

                        // if the end of the request is before the start of our buffer...
                        if (endIdx < 0)
                        {
                            // ... just truncate and move on
                            Truncate();

                            // set up our read parameters
                            BaseOffset = offset;
                            startIdx = 0;
                            endIdx = count;

                            // how much do we need to read?
                            readCount = count;
                        }
                        else // i.e., endIdx >= 0
                        {
                            // we have overlap with existing data...  save as much as possible
                            moveCount = -endIdx;
                            readCount = -startIdx;
                        }
                    }
                    else // i.e., startIdx >= 0
                    {
                        // we only get to here if at least one byte of the request is past the end of the read data
                        // start with the simplest scenario and work our way up

                        // 1) We just need to fill the buffer a bit more
                        if (endIdx < Data.Length)
                        {
                            readCount = endIdx - End;
                            readStart = End;
                            readOffset = BaseOffset + readStart;
                        }
                        // 2) We need to discard some bytes, then fill the buffer
                        else if (endIdx - DiscardCount < Data.Length)
                        {
                            moveCount = DiscardCount;
                            readStart = End;
                            readCount = endIdx - readStart;
                            readOffset = BaseOffset + readStart;
                        }
                        // 3) We need to expand the buffer to hold all the existing & requested data
                        else if (Data.Length * 2 <= 16384)
                        {
                            // by definition, we discard
                            moveCount = DiscardCount;
                            readStart = End;
                            readCount = endIdx - End;
                            readOffset = BaseOffset + readStart;
                        }
                        // 4) We have to throw away some data that hasn't been discarded
                        else
                        {
                            // just truncate
                            Truncate();

                            // set up our read parameters
                            BaseOffset = offset;
                            readOffset = offset;
                            startIdx = 0;
                            endIdx = count;

                            // how much do we have to read?
                            readCount = count;
                        }
                    }

                    #endregion

                    #region Buffer Resizing & Data Moving

                    if (endIdx - moveCount > Data.Length || readStart + readCount - moveCount > Data.Length)
                    {
                        var newSize = Data.Length * 2;
                        while (newSize < endIdx - moveCount)
                        {
                            newSize *= 2;
                        }

                        var newBuf = new byte[newSize];
                        if (moveCount < 0)
                        {
                            // reverse copy
                            Buffer.BlockCopy(Data, 0, newBuf, -moveCount, End + moveCount);

                            DiscardCount = 0;
                        }
                        else
                        {
                            // forward or neutral copy
                            Buffer.BlockCopy(Data, moveCount, newBuf, 0, End - moveCount);

                            DiscardCount -= moveCount;
                        }
                        Data = newBuf;
                    }
                    else if (moveCount != 0)
                    {
                        if (moveCount > 0)
                        {
                            // forward move
                            Buffer.BlockCopy(Data, moveCount, Data, 0, End - moveCount);

                            DiscardCount -= moveCount;
                        }
                        else
                        {
                            // backward move
                            for (int i = 0, srcIdx = Data.Length - 1, destIdx = Data.Length - 1 - moveCount; i < moveCount; i++, srcIdx--, destIdx--)
                            {
                                Data[destIdx] = Data[srcIdx];
                            }

                            DiscardCount = 0;
                        }
                    }

                    BaseOffset += moveCount;
                    readStart -= moveCount;
                    startIdx -= moveCount;
                    endIdx -= moveCount;
                    End -= moveCount;

                    #endregion

                    #region Buffer Filling

                    lock (reader._readLock)
                    {
                        if (readCount > 0 && reader._source.Position != readOffset && readOffset < reader._eofOffset)
                        {
                            if (reader._canSeek)
                            {
                                try
                                {
                                    reader._source.Position = readOffset;
                                }
                                catch (EndOfStreamException)
                                {
                                    reader._eofOffset = reader._source.Length;
                                    readCount = 0;
                                }
                            }
                            else
                            {
                                // ugh, gotta read bytes until we've reached the desired offset
                                var seekCount = readOffset - reader._source.Position;
                                while (--seekCount >= 0)
                                {
                                    if (reader._source.ReadByte() == -1)
                                    {
                                        reader._eofOffset = reader._source.Position;
                                        readCount = 0;
                                        break;
                                    }
                                }
                            }
                        }

                        while (readCount > 0 && readOffset < reader._eofOffset)
                        {
                            var temp = reader._source.Read(Data, readStart, readCount);
                            if (temp == 0)
                            {
                                break;
                            }
                            readStart += temp;
                            readOffset += temp;
                            readCount -= temp;
                        }

                        if (readStart > End)
                        {
                            End = readStart;
                        }

                        if (End < endIdx)
                        {
                            // we didn't get a full read...
                            count = Math.Max(0, End - startIdx);
                        }
                        // NB: if desired, switch to "minimal reads" by commenting-out this clause
                        else if (End < Data.Length)
                        {
                            // try to finish filling the buffer
                            var temp = reader._source.Read(Data, End, Data.Length - End);
                            End += temp;
                        }
                    }

                    #endregion
                }

                return startIdx;
            }

            public void DiscardThrough(long offset)
            {
                lock (_localLock)
                {
                    var count = (int)(offset - BaseOffset);
                    DiscardCount = Math.Max(count, DiscardCount);

                    if (DiscardCount >= Data.Length) CommitDiscard();
                }
            }

            void Truncate()
            {
                End = 0;
                DiscardCount = 0;
            }

            void CommitDiscard()
            {
                if (DiscardCount >= Data.Length || DiscardCount >= End)
                {
                    // we have been told to discard the entire buffer
                    BaseOffset += DiscardCount;
                    End = 0;
                }
                else
                {
                    // just discard the first part...
                    //Array.Copy(_readBuf, _readBufDiscardCount, _readBuf, 0, _readBufEnd - _readBufDiscardCount);
                    Buffer.BlockCopy(Data, DiscardCount, Data, 0, End - DiscardCount);
                    BaseOffset += DiscardCount;
                    End -= DiscardCount;
                }
                DiscardCount = 0;
            }
        }

        ReadBuffer _readBuf = new ReadBuffer(2048);

        internal int Read(long offset, byte[] buffer, int index, int count)
        {
            // make sure the offset is at least positive
            if (offset < 0L) throw new ArgumentOutOfRangeException("offset");

            // make sure the buffer is valid
            if (index < 0 || index + count > buffer.Length) throw new ArgumentOutOfRangeException("index");

            return _readBuf.Read(this, offset, buffer, index, count);
        }

        internal int ReadByte(long offset)
        {
            if (offset < 0L) throw new ArgumentOutOfRangeException("offset");

            return _readBuf.ReadByte(this, offset);
        }

        internal void DiscardThrough(long offset, bool minimalRead)
        {
            _readBuf.DiscardThrough(offset);
        }


        internal void ReadToEnd()
        {
            try
            {
                var maxAllocation = 40000;
                if (_id3Frame != null)
                {
                    maxAllocation += _id3Frame.Length;
                }

                while (!_endFound)
                {
                    FindNextFrame();

                    while (!_canSeek && FrameBase.TotalAllocation >= maxAllocation)
                    {
#if NET35 
                        System.Threading.Thread.Sleep(500);
#else
                        System.Threading.Tasks.Task.Delay(500).Wait(); //
#endif
                    }
                }
            }
            catch (ObjectDisposedException)
            {
                // in case the stream was disposed before we finished...
            }
        }


        internal bool CanSeek
        {
            get { return _canSeek; }
        }

        internal long SampleCount
        {
            get
            {
                if (_vbrInfo != null) return _vbrInfo.VBRStreamSampleCount;

                if (!_canSeek) return -1;

                ReadToEnd();
                return _last.SampleCount + _last.SampleOffset;
            }
        }

        internal int SampleRate
        {
            get
            {
                if (_vbrInfo != null) return _vbrInfo.SampleRate;
                return _first.SampleRate;
            }
        }

        internal int Channels
        {
            get
            {
                if (_vbrInfo != null) return _vbrInfo.Channels;
                return _first.Channels;
            }
        }

        internal int FirstFrameSampleCount
        {
            get { return (_first != null ? _first.SampleCount : 0); }
        }


        internal long SeekTo(long sampleNumber)
        {
            if (!_canSeek) throw new InvalidOperationException("Cannot seek!");

            // first try to "seek" by calculating the frame number
            var cnt = (int)(sampleNumber / _first.SampleCount);
            var frame = _first;
            if (_current != null && _current.Number <= cnt && _current.SampleOffset <= sampleNumber)
            {
                // if this fires, we can short-circuit things a bit...
                frame = _current;
                cnt -= frame.Number;
            }
            while (!_mixedFrameSize && --cnt >= 0 && frame != null)
            {
                // make sure we have more frames to look at
                if (frame == _last && !_endFound)
                {
                    do
                    {
                        FindNextFrame();
                    } while (frame == _last && !_endFound);
                }

                // if we've found a different frame size, fall through...
                if (_mixedFrameSize)
                {
                    break;
                }

                frame = frame.Next;
            }

            // this should not run unless we found mixed frames...
            while (frame != null && frame.SampleOffset + frame.SampleCount < sampleNumber)
            {
                if (frame == _last && !_endFound)
                {
                    do
                    {
                        FindNextFrame();
                    } while (frame == _last && !_endFound);
                }

                frame = frame.Next;
            }
            if (frame == null) return -1;
            return (_current = frame).SampleOffset;
        }

        internal MpegFrame NextFrame()
        {
            // if _current is null, we've returned the last frame already
            var frame = _current;
            if (frame != null)
            {
                if (_canSeek)
                {
                    frame.SaveBuffer();
                    DiscardThrough(frame.Offset + frame.FrameLength, false);
                }

                if (frame == _last && !_endFound)
                {
                    do
                    {
                        FindNextFrame();
                    } while (frame == _last && !_endFound);
                }

                _current = frame.Next;

                if (!_canSeek)
                {
                    // if we're in a forward-only stream, don't bother keeping the frames that have already been processed
                    lock (_frameLock)
                    {
                        var temp = _first;
                        _first = temp.Next;
                        temp.Next = null;
                    }
                }
            }
            return frame;
        }

        internal MpegFrame GetCurrentFrame()
        {
            return _current;
        }
    }
}
