/*
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"

	"bitbucket.org/ausocean/av/rtmp/amf"
)

// 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 represents an RTMP packet.
type packet struct {
	headerType      uint8
	packetType      uint8
	channel         int32
	hasAbsTimestamp bool
	timestamp       uint32
	streamID        uint32
	bodySize        uint32
	buf             []byte
	body            []byte
}

// readFrom reads a packet from the RTMP connection.
func (pkt *packet) readFrom(c *Conn) error {
	var hbuf [fullHeaderSize]byte
	header := hbuf[:]

	_, err := c.read(header[:1])
	if err != nil {
		c.log(DebugLevel, pkg+"failed to read packet header 1st byte", "error", err.Error())
		if err == io.EOF {
			c.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 = c.read(header[:1])
		if err != nil {
			c.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 = c.read(header[:2])
		if err != nil {
			c.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 >= c.channelsAllocatedIn {
		n := pkt.channel + 10
		timestamp := append(c.channelTimestamp, make([]int32, 10)...)

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

		c.channelTimestamp = timestamp
		c.channelsIn = pkts

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

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

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

	if size >= 3 {
		pkt.timestamp = amf.DecodeInt24(header[:3])
		if size >= 6 {
			pkt.bodySize = amf.DecodeInt24(header[3:6])

			if size > 6 {
				pkt.packetType = header[6]
				if size == 11 {
					pkt.streamID = amf.DecodeInt32LE(header[7:11])
				}
			}
		}
	}

	extendedTimestamp := pkt.timestamp == 0xffffff
	if extendedTimestamp {
		_, err = c.read(header[size : size+4])
		if err != nil {
			c.log(DebugLevel, pkg+"failed to read extended timestamp", "error", err.Error())
			return err
		}
		pkt.timestamp = amf.DecodeInt32(header[size : size+4])
		hSize += 4
	}

	pkt.resize(pkt.bodySize, pkt.headerType)

	if pkt.bodySize > c.inChunkSize {
		c.log(WarnLevel, pkg+"reading large packet", "size", int(pkt.bodySize))
	}

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

	// Keep the packet as a reference for other packets on this channel.
	if c.channelsIn[pkt.channel] == nil {
		c.channelsIn[pkt.channel] = &packet{}
	}
	*(c.channelsIn[pkt.channel]) = *pkt

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

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

	c.channelsIn[pkt.channel].body = nil
	c.channelsIn[pkt.channel].hasAbsTimestamp = false
	return nil
}

// resize adjusts the packet's storage (if necessary) to accommodate a body of the given size and header type.
// When headerSizeAuto is specified, the header type is computed based on packet type.
func (pkt *packet) resize(size uint32, ht uint8) {
	if cap(pkt.buf) < fullHeaderSize+int(size) {
		pkt.buf = make([]byte, fullHeaderSize+size)
	}
	pkt.body = pkt.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
	}
}

// writeTo writes a packet to the RTMP connection.
// Packets are written in chunks which are Session.chunkSize in length (128 bytes in length).
// We defer sending small audio packets and combine consecutive small audio packets where possible to reduce I/O.
// When queue is true, we expect a response to this request and cache the method on c.methodCalls.
func (pkt *packet) writeTo(c *Conn, queue bool) error {
	if pkt.body == nil || pkt.bodySize == 0 {
		return errInvalidBody
	}

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

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

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

		c.channelsAllocatedOut = int32(n)
	}

	prevPkt := c.channelsOut[pkt.channel]
	var last int
	if prevPkt != nil && pkt.headerType != headerSizeLarge {
		// Compress header by using the previous 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 {
		c.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.
	buf := pkt.buf
	hSize := headerSizes[pkt.headerType]
	origIdx := fullHeaderSize - hSize

	// Adjust 1 or 2 bytes depending on 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
		c.log(DebugLevel, pkg+"larger timestamp than 24 bits", "timestamp", ts)
	}

	headerIdx := origIdx

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

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

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

	if headerSizes[pkt.headerType] > 1 {
		tmp := ts
		if ts > 0xffffff {
			tmp = 0xffffff
		}
		amf.EncodeInt24(buf[headerIdx:], tmp)
		headerIdx += 3 // 24bits
	}

	if headerSizes[pkt.headerType] > 4 {
		amf.EncodeInt24(buf[headerIdx:], pkt.bodySize)
		headerIdx += 3 // 24bits
		buf[headerIdx] = pkt.packetType
		headerIdx++
	}

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

	if ts >= 0xffffff {
		amf.EncodeInt32(buf[headerIdx:], ts)
		headerIdx += 4 // 32bits
	}

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

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

	// TODO(kortschak): Rewrite this horrific peice of premature optimisation.
	c.log(DebugLevel, pkg+"sending packet", "size", size, "la", c.link.conn.LocalAddr(), "ra", c.link.conn.RemoteAddr())
	for size+hSize != 0 {
		if chunkSize > size {
			chunkSize = size
		}
		bytes := buf[origIdx:][:chunkSize+hSize]
		if c.deferred != nil {
			// Prepend the previously deferred packet and write it with the current one.
			c.log(DebugLevel, pkg+"combining deferred packet", "size", len(c.deferred))
			bytes = append(c.deferred, bytes...)
		}
		_, err := c.write(bytes)
		if err != nil {
			return err
		}
		c.deferred = nil

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

		if size > 0 {
			// We are writing the 2nd or subsequent chunk.
			origIdx -= 1 + cSize
			hSize = 1 + cSize

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

			buf[origIdx] = 0xc0 | ch

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

				if cSize == 2 {
					buf[origIdx+2] = byte(tmp >> 8)
				}
			}
			if ts >= 0xffffff {
				extendedTimestamp := buf[origIdx+1+cSize:]
				amf.EncodeInt32(extendedTimestamp[:4], ts)
			}
		}
	}

	// If we invoked a remote method and queue is true, we queue the method until the result arrives.
	if pkt.packetType == packetTypeInvoke && queue {
		buf := pkt.body[1:]
		meth := amf.DecodeString(buf)
		c.log(DebugLevel, pkg+"queuing method "+meth)
		buf = buf[3+len(meth):]
		txn := int32(amf.DecodeNumber(buf[:8]))
		c.methodCalls = append(c.methodCalls, method{name: meth, num: txn})
	}

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

	return nil
}