/*
NAME
  MpegTs.go - provides a data structure intended to encapsulate the properties
  of an MpegTs packet.

DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Nelson-Milton <saxon.milton@gmail.com>

LICENSE
  MpegTs.go is Copyright (C) 2017 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 [GNU licenses](http://www.gnu.org/licenses).
*/

package packets

// Length of some fields in bits
const (
	syncByteLength = 8
	teiLength      = 1
	pusiLength     = 1
	priorityLength = 1
	pidLength      = 13
	tscLength      = 2
	afcLength      = 2
	ccLength       = 4
	packetLength = 188
)

// Index of the fields
const (
	syncByteIndex = 0
	teiIndex      = syncByteIndex + syncByteLength
	pusiIndex     = teiIndex + teiLength
	priorityIndex = pusiIndex + pusiLength
	pidIndex      = priorityIndex + priorityLength
	tscIndex      = pidIndex + pidLength
	afcIndex      = tscIndex + tscLength
	ccIndex       = afcIndex + afcLength
	afIndex       = ccIndex + ccLength
)

type MpegTsPacket struct {
	SyncByte byte
	TEI      bool // Transport Error Indicator
	PUSI     bool // Payload Unit Start Indicator
	Priority bool
	PID      uint16
	TSC      byte   // Transport Scrambling Control
	AFC      byte   // Adaption Field Control
	CC       byte    // Continuity Counter
	AF       []byte // Adaption Field
	Payload  []byte
}

func boolToByte( in bool ) (out uint8){
  if in { out = 1 }
  return
}

func (p *MpegTsPacket) ToByteSlice() (output []byte) {
	output = make([]byte,188)
	output[0] = p.SyncByte
	output[1] = ( boolToByte(p.TEI) << (7-teiIndex%8) ) |
							( boolToByte(p.PUSI) << (7-pusiIndex%8) ) |
							( boolToByte(p.Priority) << (7-priorityIndex%8) ) |
							byte(( p.PID & 0xFF00 ) >> 8)
	output[2] = byte(p.PID & 0x00FF)
	output[3] = ( p.TSC << 6 ) | ( p.AFC << 4 ) | p.CC
	for ii := 4; ii-4 < len(p.AF); ii++ {
		output[ii] = p.AF[ii-4]
	}
	headerSize := packetLength-len(p.Payload)
	for ii := headerSize; ii < packetLength; ii++ {
		output[ii] = p.Payload[ii-headerSize]
	}
	return
}