package main

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"os"

	"bitbucket.org/ausocean/av/stream/mts"
	"github.com/Comcast/gots/packet"
)

const (
	PatPid                     = 0
	PmtPid                     = 4096
	VideoPid                   = 256
	HeadSize                   = 4
	DefaultAdaptationSize      = 2
	AdaptationIdx              = 4
	AdaptationControlIdx       = 3
	AdaptationBodyIdx          = AdaptationIdx + 1
	AdaptationControlMask      = 0x30
	DefaultAdaptationBodySize  = 1
	DiscontinuityIndicatorMask = 0x80
	DiscontinuityIndicatorIdx  = AdaptationIdx + 1
)

// Various errors that we can encounter.
const (
	errBadInPath         = "No file path provided, or file does not exist"
	errCantCreateOut     = "Can't create output file"
	errCantGetPid        = "Can't get pid from packet"
	errReadFail          = "Read failed"
	errWriteFail         = "Write to file failed"
	errBadMode           = "Bad fix mode"
	errAdaptationPresent = "Adaptation field is already present in packet"
	errNoAdaptationField = "No adaptation field in this packet"
)

// Consts describing flag usage.
const (
	inUsage   = "The path to the file to be repaired"
	outUsage  = "Output file path"
	modeUsage = "Fix mode: 0 = cc-shift, 1 = di-update"
)

// Repair modes.
const (
	ccShift = iota
	diUpdate
)

var ccMap = map[int]byte{
	PatPid:   16,
	PmtPid:   16,
	VideoPid: 16,
}

// packetNo will keep track of the ts packet number for reference.
var packetNo int

// Option defines a func that performs an action on p in order to change a ts option.
type Option func(p *Packet)

// Packet is a byte array of size PacketSize i.e. 188 bytes. We define this
// to allow us to write receiver funcs for the [PacketSize]byte type.
type Packet [mts.PacketSize]byte

// CC returns the CC of p.
func (p *Packet) CC() byte {
	return (*p)[3] & 0x0f
}

// setCC sets the CC of p.
func (p *Packet) setCC(cc byte) {
	(*p)[3] |= cc & 0xf
}

// setDI sets the discontinuity counter of p.
func (p *Packet) setDI(di bool) {
	if di {
		p[5] |= 0x80
	} else {
		p[5] &= 0x7f
	}
}

// addAdaptationField adds an adaptation field to p, and applys the passed options to this field.
// TODO: this will probably break if we already have adaptation field.
func (p *Packet) addAdaptationField(options ...Option) error {
	if p.hasAdaptation() {
		return errors.New(errAdaptationPresent)
	}
	// Create space for adaptation field.
	copy(p[HeadSize+DefaultAdaptationSize:], p[HeadSize:len(p)-DefaultAdaptationSize])

	// TODO: seperate into own function
	// Update adaptation field control.
	p[AdaptationControlIdx] &= 0xff ^ AdaptationControlMask
	p[AdaptationControlIdx] |= AdaptationControlMask
	// Default the adaptationfield.
	p.resetAdaptation()

	// Apply and options that have bee passed.
	for _, option := range options {
		option(p)
	}
	return nil
}

// resetAdaptation sets fields in ps adaptation field to 0 if the adaptation field
// exists, otherwise an error is returned.
func (p *Packet) resetAdaptation() error {
	if !p.hasAdaptation() {
		return errors.New(errNoAdaptationField)
	}
	p[AdaptationIdx] = DefaultAdaptationBodySize
	p[AdaptationBodyIdx] = 0x00
	return nil
}

// hasAdaptation returns true if p has an adaptation field and false otherwise.
func (p *Packet) hasAdaptation() bool {
	afc := p[AdaptationControlIdx] & AdaptationControlMask
	if afc == 0x20 || afc == 0x30 {
		return true
	} else {
		return false
	}
}

// DiscontinuityIndicator returns and Option that will set p's discontinuity
// indicator according to f.
func DiscontinuityIndicator(f bool) Option {
	return func(p *Packet) {
		set := byte(DiscontinuityIndicatorMask)
		if !f {
			set = 0x00
		}
		p[DiscontinuityIndicatorIdx] &= 0xff ^ DiscontinuityIndicatorMask
		p[DiscontinuityIndicatorIdx] |= DiscontinuityIndicatorMask & set
	}
}

func main() {
	// Deal with input flags
	inPtr := flag.String("in", "", inUsage)
	outPtr := flag.String("out", "out.ts", outUsage)
	modePtr := flag.Int("mode", diUpdate, modeUsage)
	flag.Parse()

	// Try and open the given input file, otherwise panic - we can't do anything
	inFile, err := os.Open(*inPtr)
	defer inFile.Close()
	if err != nil {
		panic(errBadInPath)
	}

	// Try and create output file, otherwise panic - we can't do anything
	outFile, err := os.Create(*outPtr)
	defer outFile.Close()
	if err != nil {
		panic(errCantCreateOut)
	}

	// Read each packet from the input file reader
	var p Packet
	for {
		// If we get an end of file then return, otherwise we panic - can't do anything else
		if _, err := inFile.Read(p[:mts.PacketSize]); err == io.EOF {
			return
		} else if err != nil {
			panic(errReadFail + ": " + err.Error())
		}
		packetNo++

		// Get the pid from the packet
		pid, err := packet.Pid((*packet.Packet)(&p))
		if err != nil {
			panic(errCantGetPid)
		}

		// Get the cc from the packet and also the expected cc (if exists)
		cc := p.CC()
		expect, exists := expectedCC(int(pid))
		if !exists {
			updateCCMap(int(pid), cc)
		} else {
			switch *modePtr {
			// ccShift mode shifts all CC regardless of presence of Discontinuities or not
			case ccShift:
				p.setCC(expect)
				// diUpdate mode finds discontinuities and sets the discontinuity indicator to true.
				// If we have a pat or pmt then we need to add an adaptation field and then set the DI.
			case diUpdate:
				if cc != expect {
					fmt.Printf("***** Discontinuity found (packetNo: %v pid: %v, cc: %v, expect: %v)\n", packetNo, pid, cc, expect)
					if p.hasAdaptation() {
						p.setDI(true)
					} else {
						p.addAdaptationField(DiscontinuityIndicator(true))
					}
					updateCCMap(int(pid), p.CC())
				}
			default:
				panic(errBadMode)
			}
		}

		// Write this packet to the output file.
		if _, err := outFile.Write(p[:]); err != nil {
			panic(errWriteFail + ": " + err.Error())
		}
	}
}

// expectedCC returns the expected cc for the given pid. If the cc hasn't been
// used yet, then 16 and false is returned.
func expectedCC(pid int) (byte, bool) {
	cc := ccMap[pid]
	if cc == 16 {
		return 16, false
	}
	ccMap[pid] = (cc + 1) & 0xf
	return cc, true
}

// updateCCMap updates the cc for the passed pid.
func updateCCMap(pid int, cc byte) {
	ccMap[pid] = (cc + 1) & 0xf
}