package astisub

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"math/bits"
	"sort"
	"strings"
	"time"

	"github.com/asticode/go-astikit"
	"github.com/asticode/go-astits"
)

// Errors
var (
	ErrNoValidTeletextPID = errors.New("astisub: no valid teletext PID")
)

type teletextCharset [96][]byte

type teletextNationalSubset [13][]byte

// Teletext PES data types
const (
	teletextPESDataTypeEBU     = "EBU"
	teletextPESDataTypeUnknown = "unknown"
)

func teletextPESDataType(dataIdentifier uint8) string {
	switch {
	case dataIdentifier >= 0x10 && dataIdentifier <= 0x1f:
		return teletextPESDataTypeEBU
	}
	return teletextPESDataTypeUnknown
}

// Teletext PES data unit ids
const (
	teletextPESDataUnitIDEBUNonSubtitleData = 0x2
	teletextPESDataUnitIDEBUSubtitleData    = 0x3
	teletextPESDataUnitIDStuffing           = 0xff
)

// TeletextOptions represents teletext options
type TeletextOptions struct {
	Page int
	PID  int
}

// ReadFromTeletext parses a teletext content
// http://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.03.01_60/en_300472v010301p.pdf
// http://www.etsi.org/deliver/etsi_i_ets/300700_300799/300706/01_60/ets_300706e01p.pdf
// TODO Update README
// TODO Add tests
func ReadFromTeletext(r io.Reader, o TeletextOptions) (s *Subtitles, err error) {
	// Init
	s = &Subtitles{}
	var dmx = astits.NewDemuxer(context.Background(), r)

	// Get the teletext PID
	var pid uint16
	if pid, err = teletextPID(dmx, o); err != nil {
		if err != ErrNoValidTeletextPID {
			err = fmt.Errorf("astisub: getting teletext PID failed: %w", err)
		}
		return
	}

	// Create character decoder
	cd := newTeletextCharacterDecoder()

	// Create page buffer
	b := newTeletextPageBuffer(o.Page, cd)

	// Loop in data
	var firstTime, lastTime time.Time
	var d *astits.DemuxerData
	var ps []*teletextPage
	for {
		// Fetch next data
		if d, err = dmx.NextData(); err != nil {
			if err == astits.ErrNoMorePackets {
				err = nil
				break
			}
			err = fmt.Errorf("astisub: fetching next data failed: %w", err)
			return
		}

		// We only parse PES data
		if d.PES == nil {
			continue
		}

		// This data is not of interest to us
		if d.PID != pid || d.PES.Header.StreamID != astits.StreamIDPrivateStream1 {
			continue
		}

		// Get time
		t := teletextDataTime(d)
		if t.IsZero() {
			continue
		}

		// First and last time
		if firstTime.IsZero() || firstTime.After(t) {
			firstTime = t
		}
		if lastTime.IsZero() || lastTime.Before(t) {
			lastTime = t
		}

		// Append pages
		ps = append(ps, b.process(d.PES, t)...)
	}

	// Dump buffer
	ps = append(ps, b.dump(lastTime)...)

	// Parse pages
	for _, p := range ps {
		p.parse(s, cd, firstTime)
	}
	return
}

// TODO Add tests
func teletextDataTime(d *astits.DemuxerData) time.Time {
	if d.PES.Header != nil && d.PES.Header.OptionalHeader != nil && d.PES.Header.OptionalHeader.PTS != nil {
		return d.PES.Header.OptionalHeader.PTS.Time()
	} else if d.FirstPacket != nil && d.FirstPacket.AdaptationField != nil && d.FirstPacket.AdaptationField.PCR != nil {
		return d.FirstPacket.AdaptationField.PCR.Time()
	}
	return time.Time{}
}

// If the PID teletext option is not indicated, it will walk through the ts data until it reaches a PMT packet to
// detect the first valid teletext PID
// TODO Add tests
func teletextPID(dmx *astits.Demuxer, o TeletextOptions) (pid uint16, err error) {
	// PID is in the options
	if o.PID > 0 {
		pid = uint16(o.PID)
		return
	}

	// Loop in data
	var d *astits.DemuxerData
	for {
		// Fetch next data
		if d, err = dmx.NextData(); err != nil {
			if err == astits.ErrNoMorePackets {
				err = ErrNoValidTeletextPID
				return
			}
			err = fmt.Errorf("astisub: fetching next data failed: %w", err)
			return
		}

		// PMT data
		if d.PMT != nil {
			// Retrieve valid teletext PIDs
			var pids []uint16
			for _, s := range d.PMT.ElementaryStreams {
				for _, dsc := range s.ElementaryStreamDescriptors {
					if dsc.Tag == astits.DescriptorTagTeletext || dsc.Tag == astits.DescriptorTagVBITeletext {
						pids = append(pids, s.ElementaryPID)
					}
				}
			}

			// No valid teletext PIDs
			if len(pids) == 0 {
				err = ErrNoValidTeletextPID
				return
			}

			// Set pid
			pid = pids[0]
			log.Printf("astisub: no teletext pid specified, using pid %d", pid)

			// Rewind
			if _, err = dmx.Rewind(); err != nil {
				err = fmt.Errorf("astisub: rewinding failed: %w", err)
				return
			}
			return
		}
	}
}

type teletextPageBuffer struct {
	cd             *teletextCharacterDecoder
	currentPage    *teletextPage
	donePages      []*teletextPage
	magazineNumber uint8
	pageNumber     int
	receiving      bool
}

func newTeletextPageBuffer(page int, cd *teletextCharacterDecoder) *teletextPageBuffer {
	return &teletextPageBuffer{
		cd:             cd,
		magazineNumber: uint8(page / 100),
		pageNumber:     page % 100,
	}
}

// TODO Add tests
func (b *teletextPageBuffer) dump(lastTime time.Time) (ps []*teletextPage) {
	if b.currentPage != nil {
		b.currentPage.end = lastTime
		ps = []*teletextPage{b.currentPage}
	}
	return
}

// TODO Add tests
func (b *teletextPageBuffer) process(d *astits.PESData, t time.Time) (ps []*teletextPage) {
	// Data identifier
	var offset int
	dataIdentifier := uint8(d.Data[offset])
	offset += 1

	// Check data type
	if teletextPESDataType(dataIdentifier) != teletextPESDataTypeEBU {
		return
	}

	// Loop through data units
	for offset < len(d.Data) {
		// ID
		id := uint8(d.Data[offset])
		offset += 1

		// Length
		length := uint8(d.Data[offset])
		offset += 1

		// Offset end
		offsetEnd := offset + int(length)
		if offsetEnd > len(d.Data) {
			break
		}

		// Parse data unit
		b.parseDataUnit(d.Data[offset:offsetEnd], id, t)

		// Seek to end of data unit
		offset = offsetEnd
	}

	// Dump buffer
	ps = b.donePages
	b.donePages = []*teletextPage(nil)
	return ps
}

// TODO Add tests
func (b *teletextPageBuffer) parseDataUnit(i []byte, id uint8, t time.Time) {
	// Check id
	if id != teletextPESDataUnitIDEBUSubtitleData {
		return
	}

	// Field parity: i[0]&0x20 > 0
	// Line offset: uint8(i[0] & 0x1f)
	// Framing code
	framingCode := uint8(i[1])

	// Check framing code
	if framingCode != 0xe4 {
		return
	}

	// Magazine number and packet number
	h1, ok := astikit.ByteHamming84Decode(i[2])
	if !ok {
		return
	}
	h2, ok := astikit.ByteHamming84Decode(i[3])
	if !ok {
		return
	}
	h := h2<<4 | h1
	magazineNumber := h & 0x7
	if magazineNumber == 0 {
		magazineNumber = 8
	}
	packetNumber := h >> 3

	// Parse packet
	b.parsePacket(i[4:], magazineNumber, packetNumber, t)
}

// TODO Add tests
func (b *teletextPageBuffer) parsePacket(i []byte, magazineNumber, packetNumber uint8, t time.Time) {
	if packetNumber == 0 {
		b.parsePacketHeader(i, magazineNumber, t)
	} else if b.receiving && magazineNumber == b.magazineNumber && (packetNumber >= 1 && packetNumber <= 25) {
		b.parsePacketData(i, packetNumber)
	} else {
		// Designation code
		designationCode, ok := astikit.ByteHamming84Decode(i[0])
		if !ok {
			return
		}

		// Parse packet
		if b.receiving && magazineNumber == b.magazineNumber && packetNumber == 26 {
			// TODO Implement
		} else if b.receiving && magazineNumber == b.magazineNumber && packetNumber == 28 {
			b.parsePacket28And29(i[1:], packetNumber, designationCode)
		} else if magazineNumber == b.magazineNumber && packetNumber == 29 {
			b.parsePacket28And29(i[1:], packetNumber, designationCode)
		} else if magazineNumber == 8 && packetNumber == 30 {
			b.parsePacket30(i, designationCode)
		}
	}
}

// TODO Add tests
func (b *teletextPageBuffer) parsePacketHeader(i []byte, magazineNumber uint8, t time.Time) (transmissionDone bool) {
	// Page number units
	pageNumberUnits, ok := astikit.ByteHamming84Decode(i[0])
	if !ok {
		return
	}

	// Page number tens
	pageNumberTens, ok := astikit.ByteHamming84Decode(i[1])
	if !ok {
		return
	}
	pageNumber := int(pageNumberTens)*10 + int(pageNumberUnits)

	// 0xff is a reserved page number value
	if pageNumberTens == 0xf && pageNumberUnits == 0xf {
		return
	}

	// Update magazine and page number
	if b.magazineNumber == 0 && b.pageNumber == 0 {
		// C6
		controlBits, ok := astikit.ByteHamming84Decode(i[5])
		if !ok {
			return
		}
		subtitleFlag := controlBits&0x8 > 0

		// This is a subtitle page
		if subtitleFlag {
			b.magazineNumber = magazineNumber
			b.pageNumber = pageNumber
			log.Printf("astisub: no teletext page specified, using page %d%.2d", b.magazineNumber, b.pageNumber)
		}
	}

	// C11 --> C14
	controlBits, ok := astikit.ByteHamming84Decode(i[7])
	if !ok {
		return
	}
	magazineSerial := controlBits&0x1 > 0
	charsetCode := controlBits >> 1

	// Page transmission is done
	if b.receiving && ((magazineSerial && pageNumber != b.pageNumber) ||
		(!magazineSerial && pageNumber != b.pageNumber && magazineNumber == b.magazineNumber)) {
		b.receiving = false
		return
	}

	// Invalid magazine or page number
	if pageNumber != b.pageNumber || magazineNumber != b.magazineNumber {
		return
	}

	// Now that we know when the previous page ends we can add it to the done slice
	if b.currentPage != nil {
		b.currentPage.end = t
		b.donePages = append(b.donePages, b.currentPage)
	}

	// Reset
	b.receiving = true
	b.currentPage = newTeletextPage(charsetCode, t)
	return
}

// TODO Add tests
func (b *teletextPageBuffer) parsePacketData(i []byte, packetNumber uint8) {
	// Make sure the map is initialized
	if _, ok := b.currentPage.data[packetNumber]; !ok {
		b.currentPage.data[packetNumber] = make([]byte, 40)
	}

	// Loop through input
	b.currentPage.rows = append(b.currentPage.rows, int(packetNumber))
	for idx := uint8(0); idx < 40; idx++ {
		v, ok := astikit.ByteParity(bits.Reverse8(i[idx]))
		if !ok {
			v = 0
		}
		b.currentPage.data[packetNumber][idx] = v
	}
}

// TODO Add tests
func (b *teletextPageBuffer) parsePacket28And29(i []byte, packetNumber, designationCode uint8) {
	// Invalid designation code
	if designationCode != 0 && designationCode != 4 {
		return
	}

	// Triplet 1
	// TODO triplet1 should be the results of hamming 24/18 decoding
	triplet1 := uint32(i[2])<<16 | uint32(i[1])<<8 | uint32(i[0])

	// We only process x/28 format 1
	if packetNumber == 28 && triplet1&0xf > 0 {
		return
	}

	// Update character decoder
	if packetNumber == 28 {
		b.cd.setTripletX28(triplet1)
	} else {
		b.cd.setTripletM29(triplet1)
	}
}

// TODO Add tests
func (b *teletextPageBuffer) parsePacket30(i []byte, designationCode uint8) {
	// Switch on designation code to determine format
	switch designationCode {
	case 0, 1:
		b.parsePacket30Format1(i)
	case 2, 3:
		b.parsePacket30Format2(i)
	}
}

func (b *teletextPageBuffer) parsePacket30Format1(i []byte) {
	// TODO Implement

}

func (b *teletextPageBuffer) parsePacket30Format2(i []byte) {
	// TODO Implement
}

type teletextCharacterDecoder struct {
	c                   teletextCharset
	lastPageCharsetCode *uint8
	tripletM29          *uint32
	tripletX28          *uint32
}

func newTeletextCharacterDecoder() *teletextCharacterDecoder {
	return &teletextCharacterDecoder{}
}

// TODO Add tests
func (d *teletextCharacterDecoder) setTripletM29(i uint32) {
	if *d.tripletM29 != i {
		d.tripletM29 = astikit.UInt32Ptr(i)
		d.updateCharset(d.lastPageCharsetCode, true)
	}
}

// TODO Add tests
func (d *teletextCharacterDecoder) setTripletX28(i uint32) {
	if *d.tripletX28 != i {
		d.tripletX28 = astikit.UInt32Ptr(i)
		d.updateCharset(d.lastPageCharsetCode, true)
	}
}

// TODO Add tests
func (d *teletextCharacterDecoder) decode(i byte) []byte {
	if i < 0x20 {
		return []byte{}
	}
	return d.c[i-0x20]
}

// TODO Add tests
func (d *teletextCharacterDecoder) updateCharset(pageCharsetCode *uint8, force bool) {
	// Charset is up to date
	if d.lastPageCharsetCode != nil && *pageCharsetCode == *d.lastPageCharsetCode && !force {
		return
	}
	d.lastPageCharsetCode = pageCharsetCode

	// Get triplet
	var triplet uint32
	if d.tripletX28 != nil {
		triplet = *d.tripletX28
	} else if d.tripletM29 != nil {
		triplet = *d.tripletM29
	}

	// Get charsets
	d.c = *teletextCharsetG0Latin
	var nationalOptionSubset *teletextNationalSubset
	if v1, ok := teletextCharsets[uint8((triplet&0x3f80)>>10)]; ok {
		if v2, ok := v1[*pageCharsetCode]; ok {
			d.c = *v2.g0
			nationalOptionSubset = v2.national
		}
	}

	// Update g0 with national option subset
	if nationalOptionSubset != nil {
		for k, v := range nationalOptionSubset {
			d.c[teletextNationalSubsetCharactersPositionInG0[k]] = v
		}
	}
}

type teletextPage struct {
	charsetCode uint8
	data        map[uint8][]byte
	end         time.Time
	rows        []int
	start       time.Time
}

func newTeletextPage(charsetCode uint8, start time.Time) *teletextPage {
	return &teletextPage{
		charsetCode: charsetCode,
		data:        make(map[uint8][]byte),
		start:       start,
	}
}

func (p *teletextPage) parse(s *Subtitles, d *teletextCharacterDecoder, firstTime time.Time) {
	// Update charset
	d.updateCharset(astikit.UInt8Ptr(p.charsetCode), false)

	// No data
	if len(p.data) == 0 {
		return
	}

	// Order rows
	sort.Ints(p.rows)

	// Create item
	i := &Item{
		EndAt:   p.end.Sub(firstTime),
		StartAt: p.start.Sub(firstTime),
	}

	// Loop through rows
	for _, idxRow := range p.rows {
		parseTeletextRow(i, d, nil, p.data[uint8(idxRow)])
	}

	// Append item
	s.Items = append(s.Items, i)
}

type decoder interface {
	decode(i byte) []byte
}

type styler interface {
	hasBeenSet() bool
	hasChanged(s *StyleAttributes) bool
	parseSpacingAttribute(i byte)
	propagateStyleAttributes(s *StyleAttributes)
	update(sa *StyleAttributes)
}

func parseTeletextRow(i *Item, d decoder, fs func() styler, row []byte) {
	// Loop through columns
	var l = Line{}
	var li = LineItem{InlineStyle: &StyleAttributes{}}
	var started bool
	var s styler
	for _, v := range row {
		// Create specific styler
		if fs != nil {
			s = fs()
		}

		// Get spacing attributes
		var color *Color
		var doubleHeight, doubleSize, doubleWidth *bool
		switch v {
		case 0x0:
			color = ColorBlack
		case 0x1:
			color = ColorRed
		case 0x2:
			color = ColorGreen
		case 0x3:
			color = ColorYellow
		case 0x4:
			color = ColorBlue
		case 0x5:
			color = ColorMagenta
		case 0x6:
			color = ColorCyan
		case 0x7:
			color = ColorWhite
		case 0xa:
			started = false
		case 0xb:
			started = true
		case 0xc:
			doubleHeight = astikit.BoolPtr(false)
			doubleSize = astikit.BoolPtr(false)
			doubleWidth = astikit.BoolPtr(false)
		case 0xd:
			doubleHeight = astikit.BoolPtr(true)
		case 0xe:
			doubleWidth = astikit.BoolPtr(true)
		case 0xf:
			doubleSize = astikit.BoolPtr(true)
		default:
			if s != nil {
				s.parseSpacingAttribute(v)
			}
		}

		// Style has been set
		if color != nil || doubleHeight != nil || doubleSize != nil || doubleWidth != nil || (s != nil && s.hasBeenSet()) {
			// Style has changed
			if color != li.InlineStyle.TeletextColor || doubleHeight != li.InlineStyle.TeletextDoubleHeight ||
				doubleSize != li.InlineStyle.TeletextDoubleSize || doubleWidth != li.InlineStyle.TeletextDoubleWidth ||
				(s != nil && s.hasChanged(li.InlineStyle)) {
				// Line has started
				if started {
					// Append line item
					appendTeletextLineItem(&l, li, s)

					// Create new line item
					sa := &StyleAttributes{}
					*sa = *li.InlineStyle
					li = LineItem{InlineStyle: sa}
				}

				// Update style attributes
				if color != nil && color != li.InlineStyle.TeletextColor {
					li.InlineStyle.TeletextColor = color
				}
				if doubleHeight != nil && doubleHeight != li.InlineStyle.TeletextDoubleHeight {
					li.InlineStyle.TeletextDoubleHeight = doubleHeight
				}
				if doubleSize != nil && doubleSize != li.InlineStyle.TeletextDoubleSize {
					li.InlineStyle.TeletextDoubleSize = doubleSize
				}
				if doubleWidth != nil && doubleWidth != li.InlineStyle.TeletextDoubleWidth {
					li.InlineStyle.TeletextDoubleWidth = doubleWidth
				}
				if s != nil {
					s.update(li.InlineStyle)
				}
			}
		} else if started {
			// Append text
			li.Text += string(d.decode(v))
		}
	}

	// Append line item
	appendTeletextLineItem(&l, li, s)

	// Append line
	if len(l.Items) > 0 {
		i.Lines = append(i.Lines, l)
	}
}

func appendTeletextLineItem(l *Line, li LineItem, s styler) {
	// There's some text
	if len(strings.TrimSpace(li.Text)) > 0 {
		// Make sure inline style exists
		if li.InlineStyle == nil {
			li.InlineStyle = &StyleAttributes{}
		}

		// Get number of spaces before
		li.InlineStyle.TeletextSpacesBefore = astikit.IntPtr(0)
		for _, c := range li.Text {
			if c == ' ' {
				*li.InlineStyle.TeletextSpacesBefore++
			} else {
				break
			}
		}

		// Get number of spaces after
		li.InlineStyle.TeletextSpacesAfter = astikit.IntPtr(0)
		for idx := len(li.Text) - 1; idx >= 0; idx-- {
			if li.Text[idx] == ' ' {
				*li.InlineStyle.TeletextSpacesAfter++
			} else {
				break
			}
		}

		// Propagate style attributes
		li.InlineStyle.propagateTeletextAttributes()
		if s != nil {
			s.propagateStyleAttributes(li.InlineStyle)
		}

		// Append line item
		li.Text = strings.TrimSpace(li.Text)
		l.Items = append(l.Items, li)
	}
}