/*
NAME
  psi.go
DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Milton <saxon@ausocean.org>

LICENSE
  psi.go is Copyright (C) 2018 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.
*/

package psi

import (
	"hash/crc32"
)

// Lengths of section definitions
const (
	ESSDDefLen = 5
	DescDefLen = 2
	PMTDefLen  = 4
	PATLen     = 4
	TSSDefLen  = 5
	PSIDefLen  = 3
)

// Table Type IDs
const (
	PATTableID = 0x00
	PMTTableID = 0x02
)

// Consts relating to time description
const (
	timeDescTag  = 234
	timeTagIndx  = 13
	timeDataIndx = 15
	timeDataSize = 8 // bytes, because time is stored in uint64
)

// Consts relating to location description
const (
	locationDescTag  = 235
	locationTagIndx  = 23
	locationDataIndx = 25
	locationDataSize = 32 // bytes
)

// Program specific information
type PSI struct {
	Pf  byte   // Point field
	Pfb []byte // Pointer filler bytes
	Tid byte   // Table ID
	Ssi bool   // Section syntax indicator (1 for PAT, PMT, CAT)
	Pb  bool   // Private bit (0 for PAT, PMT, CAT)
	Sl  uint16 // Section length
	Tss *TSS   // Table syntax section (length defined by SL) if length 0 then nil
	Crc uint32 // crc32 of entire table excluding pointer field, pointer filler bytes and the trailing CRC32
}

// Table syntax section
type TSS struct {
	Tide uint16 // Table ID extension
	V    byte   // Version number
	Cni  bool   // Current/next indicator
	Sn   byte   // Section number
	Lsn  byte   // Last section number
	Sd   SD     // Specific data PAT/PMT
}

// Specific Data, (could be PAT or PMT)
type SD interface {
	Bytes() []byte
}

// Program association table, implements SD
type PAT struct {
	Pn    uint16 // Program Number
	Pmpid uint16 // Program map PID
}

// Program mapping table, implements SD
type PMT struct {
	Pcrpid uint16 // Program clock reference pid
	Pil    uint16 // Program info length
	Pd     []Desc // Program descriptors
	Essd   *ESSD  // Elementary stream specific data
}

// Elementary stream specific data
type ESSD struct {
	St   byte   // Stream type
	Epid uint16 // Elementary pid
	Esil uint16 // Elementary stream
	Esd  []Desc // Elementary stream desriptors
}

// Descriptor
type Desc struct {
	Dt byte   // Descriptor tag
	Dl byte   // Descriptor length
	Dd []byte // Descriptor data
}

// Bytes outputs a byte slice representation of the PSI
func (p *PSI) Bytes() []byte {
	out := make([]byte, 4)
	out[0] = p.Pf
	if p.Pf != 0 {
		panic("No support for pointer filler bytes")
	}
	out[1] = p.Tid
	out[2] = 0x80 | 0x30 | (0x03 & byte(p.Sl>>8))
	out[3] = byte(p.Sl)
	out = append(out, p.Tss.Bytes()...)
	out = addCrc(out)
	return out
}

// Bytes outputs a byte slice representation of the TSS
func (t *TSS) Bytes() []byte {
	out := make([]byte, TSSDefLen)
	out[0] = byte(t.Tide >> 8)
	out[1] = byte(t.Tide)
	out[2] = 0xc0 | (0x3e & (t.V << 1)) | (0x01 & boolToByte(t.Cni))
	out[3] = t.Sn
	out[4] = t.Lsn
	out = append(out, t.Sd.Bytes()...)
	return out
}

// Bytes outputs a byte slice representation of the PAT
func (p *PAT) Bytes() []byte {
	out := make([]byte, PATLen)
	out[0] = byte(p.Pn >> 8)
	out[1] = byte(p.Pn)
	out[2] = 0xe0 | (0x1f & byte(p.Pmpid>>8))
	out[3] = byte(p.Pmpid)
	return out
}

// Bytes outputs a byte slice representation of the PMT
func (p *PMT) Bytes() []byte {
	out := make([]byte, PMTDefLen)
	out[0] = 0xe0 | (0x1f & byte(p.Pcrpid>>8)) // byte 10
	out[1] = byte(p.Pcrpid)
	out[2] = 0xf0 | (0x03 & byte(p.Pil>>8))
	out[3] = byte(p.Pil)
	for _, d := range p.Pd {
		out = append(out, d.Bytes()...)
	}
	out = append(out, p.Essd.Bytes()...)
	return out
}

// Bytes outputs a byte slice representation of the Desc
func (d *Desc) Bytes() []byte {
	out := make([]byte, DescDefLen)
	out[0] = d.Dt
	out[1] = d.Dl
	out = append(out, d.Dd...)
	return out
}

// Bytes outputs a byte slice representation of the ESSD
func (e *ESSD) Bytes() []byte {
	out := make([]byte, ESSDDefLen)
	out[0] = e.St
	out[1] = 0xe0 | (0x1f & byte(e.Epid>>8))
	out[2] = byte(e.Epid)
	out[3] = 0xf0 | (0x03 & byte(e.Esil>>8))
	out[4] = byte(e.Esil)
	for _, d := range e.Esd {
		out = append(out, d.Bytes()...)
	}
	return out
}

func boolToByte(b bool) (o byte) {
	if b {
		o = 0x01
	}
	return
}

func byteToBool(b byte) (o bool) {
	if b != 0 {
		o = true
	}
	return
}

func crc32_MakeTable(poly uint32) *crc32.Table {
	var t crc32.Table
	for i := range t {
		crc := uint32(i) << 24
		for j := 0; j < 8; j++ {
			if crc&0x80000000 != 0 {
				crc = (crc << 1) ^ poly
			} else {
				crc <<= 1
			}
		}
		t[i] = crc
	}
	return &t
}

func crc32_Update(crc uint32, tab *crc32.Table, p []byte) uint32 {
	for _, v := range p {
		crc = tab[byte(crc>>24)^v] ^ (crc << 8)
	}
	return crc
}