/*
NAME
  packet.go

DESCRIPTION
  RTMP packet functionality.

AUTHORS
  Saxon Nelson-Milton <saxon@ausocean.org>
  Dan Kortschak <dan@ausocean.org>
  Alan Noble <alan@ausocean.org>

LICENSE
  packet.go is Copyright (C) 2017-2019 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt.  If not, see http://www.gnu.org/licenses.

	Derived from librtmp under the GNU Lesser General Public License 2.1
	Copyright (C) 2005-2008 Team XBMC http://www.xbmc.org
	Copyright (C) 2008-2009 Andrej Stepanchuk
	Copyright (C) 2009-2010 Howard Chu
*/

package rtmp

import (
	"encoding/binary"
	"io"
)

// Packet types.
const (
	packetTypeChunkSize        = 0x01
	packetTypeBytesReadReport  = 0x03
	packetTypeControl          = 0x04
	packetTypeServerBW         = 0x05
	packetTypeClientBW         = 0x06
	packetTypeAudio            = 0x08
	packetTypeVideo            = 0x09
	packetTypeFlexStreamSend   = 0x0F // not implemented
	packetTypeFlexSharedObject = 0x10 // not implemented
	packetTypeFlexMessage      = 0x11 // not implemented
	packetTypeInfo             = 0x12
	packetTypeInvoke           = 0x14
	packetTypeFlashVideo       = 0x16 // not implemented
)

// Header sizes.
const (
	headerSizeLarge   = 0
	headerSizeMedium  = 1
	headerSizeSmall   = 2
	headerSizeMinimum = 3
	headerSizeAuto    = 4
)

// Special channels.
const (
	chanBytesRead = 0x02
	chanControl   = 0x03
	chanSource    = 0x04
)

// headerSizes defines header sizes for header types 0, 1, 2 and 3 respectively:
//   0: full header (12 bytes)
//   1: header without message ID (8 bytes)
//   2: basic header + timestamp (4 byes)
//   3: basic header (chunk type and stream ID) (1 byte)
var headerSizes = [...]int{12, 8, 4, 1}

// packet defines an RTMP packet.
type packet struct {
	headerType      uint8
	packetType      uint8
	channel         int32
	hasAbsTimestamp bool
	timestamp       uint32
	info            int32
	bodySize        uint32
	bytesRead       uint32
	chunk           *chunk
	header          []byte
	body            []byte
}

// chunk defines an RTMP packet chunk.
type chunk struct {
	headerSize int32
	data       []byte
	header     [fullHeaderSize]byte
}

// read reads a packet.
func (pkt *packet) read(s *Session) error {
	var hbuf [fullHeaderSize]byte
	header := hbuf[:]

	_, err := s.read(header[:1])
	if err != nil {
		s.log(DebugLevel, pkg+"failed to read packet header 1st byte", "error", err.Error())
		if err == io.EOF {
			s.log(WarnLevel, pkg+"EOF error; connection likely terminated")
		}
		return err
	}
	pkt.headerType = (header[0] & 0xc0) >> 6
	pkt.channel = int32(header[0] & 0x3f)
	header = header[1:]

	switch {
	case pkt.channel == 0:
		_, err = s.read(header[:1])
		if err != nil {
			s.log(DebugLevel, pkg+"failed to read packet header 2nd byte", "error", err.Error())
			return err
		}
		header = header[1:]
		pkt.channel = int32(header[0]) + 64

	case pkt.channel == 1:
		_, err = s.read(header[:2])
		if err != nil {
			s.log(DebugLevel, pkg+"failed to read packet header 3rd byte", "error", err.Error())
			return err
		}
		header = header[2:]
		pkt.channel = int32(binary.BigEndian.Uint16(header[:2])) + 64
	}

	if pkt.channel >= s.channelsAllocatedIn {
		n := pkt.channel + 10
		timestamp := append(s.channelTimestamp, make([]int32, 10)...)

		var pkts []*packet
		if s.channelsIn == nil {
			pkts = make([]*packet, n)
		} else {
			pkts = append(s.channelsIn[:pkt.channel:pkt.channel], make([]*packet, 10)...)
		}

		s.channelTimestamp = timestamp
		s.channelsIn = pkts

		for i := int(s.channelsAllocatedIn); i < len(s.channelTimestamp); i++ {
			s.channelTimestamp[i] = 0
		}
		for i := int(s.channelsAllocatedIn); i < int(n); i++ {
			s.channelsIn[i] = nil
		}
		s.channelsAllocatedIn = n
	}

	size := headerSizes[pkt.headerType]
	switch {
	case size == fullHeaderSize:
		pkt.hasAbsTimestamp = true
	case size < fullHeaderSize:
		if s.channelsIn[pkt.channel] != nil {
			*pkt = *(s.channelsIn[pkt.channel])
		}
	}
	size--

	if size > 0 {
		_, err = s.read(header[:size])
		if err != nil {
			s.log(DebugLevel, pkg+"failed to read packet header", "error", err.Error())
			return err
		}
	}
	hSize := len(hbuf) - len(header) + size

	if size >= 3 {
		pkt.timestamp = amfDecodeInt24(header[:3])
		if size >= 6 {
			pkt.bodySize = amfDecodeInt24(header[3:6])
			pkt.bytesRead = 0

			if size > 6 {
				pkt.packetType = header[6]

				if size == 11 {
					pkt.info = decodeInt32LE(header[7:11])
				}
			}
		}
	}

	extendedTimestamp := pkt.timestamp == 0xffffff
	if extendedTimestamp {
		_, err = s.read(header[size : size+4])
		if err != nil {
			s.log(DebugLevel, pkg+"failed to read extended timestamp", "error", err.Error())
			return err
		}
		// TODO: port this
		pkt.timestamp = amfDecodeInt32(header[size : size+4])
		hSize += 4
	}

	if pkt.bodySize > 0 && pkt.body == nil {
		pkt.resize(pkt.bodySize, (hbuf[0]&0xc0)>>6)
	}

	toRead := int32(pkt.bodySize - pkt.bytesRead)
	chunkSize := s.inChunkSize

	if toRead < chunkSize {
		chunkSize = toRead
	}

	if pkt.chunk != nil {
		panic("non-nil chunk")
		pkt.chunk.headerSize = int32(hSize)
		copy(pkt.chunk.header[:], hbuf[:hSize])
		pkt.chunk.data = pkt.body[pkt.bytesRead : pkt.bytesRead+uint32(chunkSize)]
	}

	_, err = s.read(pkt.body[pkt.bytesRead:][:chunkSize])
	if err != nil {
		s.log(DebugLevel, pkg+"failed to read packet body", "error", err.Error())
		return err
	}

	pkt.bytesRead += uint32(chunkSize)

	// keep the packet as ref for other packets on this channel
	if s.channelsIn[pkt.channel] == nil {
		s.channelsIn[pkt.channel] = &packet{}
	}
	*(s.channelsIn[pkt.channel]) = *pkt

	if extendedTimestamp {
		s.channelsIn[pkt.channel].timestamp = 0xffffff
	}

	if pkt.bytesRead != pkt.bodySize {
		panic("readPacket: bytesRead != bodySize")
	}

	if !pkt.hasAbsTimestamp {
		// timestamps seem to always be relative
		pkt.timestamp += uint32(s.channelTimestamp[pkt.channel])
	}
	s.channelTimestamp[pkt.channel] = int32(pkt.timestamp)

	s.channelsIn[pkt.channel].body = nil
	s.channelsIn[pkt.channel].bytesRead = 0
	s.channelsIn[pkt.channel].hasAbsTimestamp = false
	return nil
}

// resize adjusts the packet's storage to accommodate a body of the given size and header type.
func (pkt *packet) resize(size uint32, ht uint8) {
	buf := make([]byte, fullHeaderSize+size)
	pkt.header = buf
	pkt.body = buf[fullHeaderSize:]
	if ht != headerSizeAuto {
		pkt.headerType = ht
		return
	}
	switch pkt.packetType {
	case packetTypeVideo, packetTypeAudio:
		if pkt.timestamp == 0 {
			pkt.headerType = headerSizeLarge
		} else {
			pkt.headerType = headerSizeMedium
		}
	case packetTypeInfo:
		pkt.headerType = headerSizeLarge
		pkt.bodySize += 16
	default:
		pkt.headerType = headerSizeMedium
	}
}

// write sends a packet.
// When queue is true, we expect a response to this request and cache the method on s.methodCalls.
func (pkt *packet) write(s *Session, queue bool) error {
	if pkt.body == nil {
		return errInvalidBody
	}

	if pkt.channel >= s.channelsAllocatedOut {
		s.log(DebugLevel, pkg+"growing channelsOut", "channel", pkt.channel)
		n := int(pkt.channel + 10)

		var pkts []*packet
		if s.channelsOut == nil {
			pkts = make([]*packet, n)
		} else {
			pkts = append(s.channelsOut[:pkt.channel:pkt.channel], make([]*packet, 10)...)
		}
		s.channelsOut = pkts

		for i := int(s.channelsAllocatedOut); i < n; i++ {
			s.channelsOut[i] = nil
		}

		s.channelsAllocatedOut = int32(n)
	}

	prevPkt := s.channelsOut[pkt.channel]
	var last int
	if prevPkt != nil && pkt.headerType != headerSizeLarge {
		// compress a bit by using the prev packet's attributes
		if prevPkt.bodySize == pkt.bodySize && prevPkt.packetType == pkt.packetType && pkt.headerType == headerSizeMedium {
			pkt.headerType = headerSizeSmall
		}

		if prevPkt.timestamp == pkt.timestamp && pkt.headerType == headerSizeSmall {
			pkt.headerType = headerSizeMinimum
		}

		last = int(prevPkt.timestamp)
	}

	if pkt.headerType > 3 {
		s.log(WarnLevel, pkg+"unexpected header type", "type", pkt.headerType)
		return errInvalidHeader
	}

	// The complete packet starts from headerSize _before_ the start the body.
	// origIdx is the original offset, which will be 0 for a full (12-byte) header or 11 for a minimum (1-byte) header.
	headBytes := pkt.header
	hSize := headerSizes[pkt.headerType]
	origIdx := fullHeaderSize - hSize

	// adjust 1 or 2 bytes for the channel
	cSize := 0
	switch {
	case pkt.channel > 319:
		cSize = 2
	case pkt.channel > 63:
		cSize = 1
	}

	if cSize != 0 {
		origIdx -= cSize
		hSize += cSize
	}

	// adjust 4 bytes for the timestamp
	var ts uint32
	if prevPkt != nil {
		ts = uint32(int(pkt.timestamp) - last)
	}
	if ts >= 0xffffff {
		origIdx -= 4
		hSize += 4
		s.log(DebugLevel, pkg+"larger timestamp than 24 bits", "timestamp", ts)
	}

	headerIdx := origIdx

	c := pkt.headerType << 6
	switch cSize {
	case 0:
		c |= byte(pkt.channel)
	case 1:
		// Do nothing.
	case 2:
		c |= 1
	}
	headBytes[headerIdx] = c
	headerIdx++

	if cSize != 0 {
		tmp := pkt.channel - 64
		headBytes[headerIdx] = byte(tmp & 0xff)
		headerIdx++

		if cSize == 2 {
			headBytes[headerIdx] = byte(tmp >> 8)
			headerIdx++
		}
	}

	if headerSizes[pkt.headerType] > 1 {
		res := ts
		if ts > 0xffffff {
			res = 0xffffff
		}
		amfEncodeInt24(headBytes[headerIdx:], int32(res))
		headerIdx += 3 // 24bits
	}

	if headerSizes[pkt.headerType] > 4 {
		amfEncodeInt24(headBytes[headerIdx:], int32(pkt.bodySize))
		headerIdx += 3 // 24bits
		headBytes[headerIdx] = pkt.packetType
		headerIdx++
	}

	if headerSizes[pkt.headerType] > 8 {
		binary.LittleEndian.PutUint32(headBytes[headerIdx:headerIdx+4], uint32(pkt.info))
		headerIdx += 4 // 32bits
	}

	if ts >= 0xffffff {
		amfEncodeInt32(headBytes[headerIdx:], int32(ts))
		headerIdx += 4 // 32bits
	}

	size := int(pkt.bodySize)
	chunkSize := int(s.outChunkSize)

	if s.deferred == nil {
		// Defer sending small audio packets (at most once).
		if pkt.packetType == packetTypeAudio && size < chunkSize {
			s.deferred = headBytes[origIdx:][:size+hSize]
			s.log(DebugLevel, pkg+"deferred sending packet", "size", size, "la", s.link.conn.LocalAddr(), "ra", s.link.conn.RemoteAddr())
			return nil
		}
	} else {
		// Send previously deferrd packet if combining it with the next one would exceed the chunk size.
		if len(s.deferred)+size+hSize > chunkSize {
			s.log(DebugLevel, pkg+"sending deferred packet separately", "size", len(s.deferred))
			_, err := s.write(s.deferred)
			if err != nil {
				return err
			}
			s.deferred = nil
		}
	}

	// TODO(kortschak): Rewrite this horrific peice of premature optimisation.
	// NB: RTMP wants packets in chunks which are 128 bytes by default, but the server may request a different size.
	s.log(DebugLevel, pkg+"sending packet", "la", s.link.conn.LocalAddr(), "ra", s.link.conn.RemoteAddr(), "size", size)
	for size+hSize != 0 {
		if chunkSize > size {
			chunkSize = size
		}
		bytes := headBytes[origIdx:][:chunkSize+hSize]
		if s.deferred != nil {
			// Prepend the previously deferred packet and write it with the current one.
			s.log(DebugLevel, pkg+"combining deferred packet", "size", len(s.deferred))
			bytes = append(s.deferred, bytes...)
		}
		_, err := s.write(bytes)
		if err != nil {
			return err
		}
		s.deferred = nil

		size -= chunkSize
		origIdx += chunkSize + hSize
		hSize = 0

		if size > 0 {
			origIdx -= 1 + cSize
			hSize = 1 + cSize

			if ts >= 0xffffff {
				origIdx -= 4
				hSize += 4
			}

			headBytes[origIdx] = 0xc0 | c

			if cSize != 0 {
				tmp := int(pkt.channel) - 64
				headBytes[origIdx+1] = byte(tmp)

				if cSize == 2 {
					headBytes[origIdx+2] = byte(tmp >> 8)
				}
			}
			if ts >= 0xffffff {
				extendedTimestamp := headBytes[origIdx+1+cSize:]
				amfEncodeInt32(extendedTimestamp[:4], int32(ts))
			}
		}
	}

	// We invoked a remote method
	if pkt.packetType == packetTypeInvoke {
		buf := pkt.body[1:]
		meth := amfDecodeString(buf)
		s.log(DebugLevel, pkg+"invoking method "+meth)
		// keep it in call queue till result arrives
		if queue {
			buf = buf[3+len(meth):]
			txn := int32(amfDecodeNumber(buf[:8]))
			s.methodCalls = append(s.methodCalls, method{name: meth, num: txn})
		}
	}

	if s.channelsOut[pkt.channel] == nil {
		s.channelsOut[pkt.channel] = &packet{}
	}
	*(s.channelsOut[pkt.channel]) = *pkt

	return nil
}

func decodeInt32LE(data []byte) int32 {
	return int32(data[3])<<24 | int32(data[2])<<16 | int32(data[1])<<8 | int32(data[0])
}

func encodeInt32LE(dst []byte, v int32) int32 {
	binary.LittleEndian.PutUint32(dst, uint32(v))
	return 4
}