// SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

// Package oggreader implements the Ogg media container reader
package oggreader

import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"strings"
)

const (
	pageHeaderTypeBeginningOfStream = 0x02
	pageHeaderSignature             = "OggS"

	idPageBasePayloadLength = 19
	pageHeaderLen           = 27
)

var (
	errNilStream                       = errors.New("stream is nil")
	errBadIDPageSignature              = errors.New("bad header signature")
	errBadOpusTagsSignature            = errors.New("bad opus tags signature")
	errBadIDPageType                   = errors.New("wrong header, expected beginning of stream")
	errBadIDPageLength                 = errors.New("payload for id page must be 19 bytes")
	errBadIDPagePayloadSignature       = errors.New("bad payload signature")
	errShortPageHeader                 = errors.New("not enough data for payload header")
	errChecksumMismatch                = errors.New("expected and actual checksum do not match")
	errUnsupportedChannelMappingFamily = errors.New("unsupported channel mapping family")
)

// OggReader is used to read Ogg files and return page payloads.
type OggReader struct {
	stream               io.Reader
	bytesReadSuccesfully int64
	checksumTable        *[256]uint32
	doChecksum           bool
}

// OggHeader contains Opus codec metadata parsed from an Opus ID page.
// This header is extracted from an Ogg page payload that starts with the OpusHead
// signature (the first page of an Opus stream in an Ogg container).
//
// Use OggPageHeader.OpusPacketType() to classify a page payload as OpusHead,
// and OggPageHeader.ParseOpusHeader() to parse the OpusHead payload.
//
// https://tools.ietf.org/html/rfc7845.html#section-3
type OggHeader struct {
	ChannelMap   uint8
	Channels     uint8
	OutputGain   uint16
	PreSkip      uint16
	SampleRate   uint32
	Version      uint8
	StreamCount  uint8
	CoupledCount uint8
	// ChannelMapping we store it as a string to be comparable (maps/struct equality)
	// while still holding raw bytes.
	ChannelMapping string
}

// ParseOpusHead parses an Opus head from the page payload.
func ParseOpusHead(payload []byte) (*OggHeader, error) {
	if len(payload) < idPageBasePayloadLength {
		return nil, errBadIDPageLength
	}

	header := parseBasicHeaderFields(payload)
	if err := parseChannelMapping(header, payload); err != nil {
		return nil, err
	}

	return header, nil
}

// OggPageHeader is the metadata for a Page
// Pages are the fundamental unit of multiplexing in an Ogg stream
//
// https://tools.ietf.org/html/rfc7845.html#section-1
type OggPageHeader struct {
	GranulePosition uint64

	sig           [4]byte
	version       uint8
	headerType    uint8
	Serial        uint32
	index         uint32
	segmentsCount uint8
}

type HeaderType string

const (
	headerUnknown  HeaderType = ""
	HeaderOpusID   HeaderType = "OpusHead"
	HeaderOpusTags HeaderType = "OpusTags"
)

func opusPayloadSignature(payload []byte) (HeaderType, bool) {
	if len(payload) < 8 {
		return headerUnknown, false
	}

	sig := HeaderType(payload[:8])
	if sig == HeaderOpusID || sig == HeaderOpusTags {
		return sig, true
	}

	return headerUnknown, false
}

// HeaderType classifies the page.
func (p *OggPageHeader) HeaderType(payload []byte) (HeaderType, bool) {
	sig, ok := opusPayloadSignature(payload)

	if !ok || (sig == HeaderOpusID && p.headerType != pageHeaderTypeBeginningOfStream) {
		return headerUnknown, false
	}

	return sig, true
}

type Option func(*OggReader) error

// NewWith returns a new Ogg reader and Ogg header
// with an io.Reader input.
//
// Warning: NewWith only parses the first OpusHead (a single logical bitstream/track)
// and returns a single OggHeader. If you need to handle Ogg containers with multiple
// Opus headers/tracks, use NewWithOptions and scan pages (e.g. via ParseNextPage)
// to find and parse each OpusHead.
func NewWith(in io.Reader) (*OggReader, *OggHeader, error) {
	return newWith(in /* doChecksum */, true)
}

// NewWithOptions returns a new Ogg reader.
func NewWithOptions(in io.Reader, options ...Option) (*OggReader, error) {
	reader := &OggReader{
		stream:        in,
		checksumTable: generateChecksumTable(),
		doChecksum:    true,
	}

	for _, option := range options {
		if err := option(reader); err != nil {
			return nil, err
		}
	}

	return reader, nil
}

// WithDoChecksum is an option to set the doChecksum flag
// Default is true.
func WithDoChecksum(doChecksum bool) Option {
	return func(o *OggReader) error {
		o.doChecksum = doChecksum

		return nil
	}
}

func newWith(in io.Reader, doChecksum bool) (*OggReader, *OggHeader, error) {
	if in == nil {
		return nil, nil, errNilStream
	}

	reader := &OggReader{
		stream:        in,
		checksumTable: generateChecksumTable(),
		doChecksum:    doChecksum,
	}

	header, err := reader.readOpusHeader()
	if err != nil {
		return nil, nil, err
	}

	return reader, header, nil
}

func (o *OggReader) readOpusHeader() (*OggHeader, error) {
	payload, pageHeader, err := o.ParseNextPage()
	if err != nil {
		return nil, err
	}

	if err := validateOpusPageHeader(pageHeader, payload); err != nil {
		return nil, err
	}

	header := parseBasicHeaderFields(payload)
	if err := parseChannelMapping(header, payload); err != nil {
		return nil, err
	}

	return header, nil
}

func validateOpusPageHeader(pageHeader *OggPageHeader, payload []byte) error {
	if string(pageHeader.sig[:]) != pageHeaderSignature {
		return errBadIDPageSignature
	}

	if pageHeader.headerType != pageHeaderTypeBeginningOfStream {
		return errBadIDPageType
	}

	if len(payload) < idPageBasePayloadLength {
		return errBadIDPageLength
	}

	if sig, ok := opusPayloadSignature(payload); !ok || sig != HeaderOpusID {
		return fmt.Errorf("%w: expected OpusHead, got %s", errBadIDPagePayloadSignature, sig)
	}

	return nil
}

func parseBasicHeaderFields(payload []byte) *OggHeader {
	header := &OggHeader{}
	header.Version = payload[8]
	header.Channels = payload[9]
	header.PreSkip = binary.LittleEndian.Uint16(payload[10:12])
	header.SampleRate = binary.LittleEndian.Uint32(payload[12:16])
	header.OutputGain = binary.LittleEndian.Uint16(payload[16:18])
	header.ChannelMap = payload[18]

	return header
}

// parseChannelMapping parses channel mapping data based on the channel map family.
// https://datatracker.ietf.org/doc/html/rfc7845#section-5.1.1
// family mapping of 2 and 3 are defined in https://datatracker.ietf.org/doc/html/rfc8486
func parseChannelMapping(header *OggHeader, payload []byte) error {
	switch header.ChannelMap {
	case 0:
		return validatePayloadLength(payload, idPageBasePayloadLength)
	case 1, 2, 255:
		return parseExtendedChannelMapping(header, payload)
	case 3:
		return fmt.Errorf("%w: ambisonics family type 3 is not supported", errUnsupportedChannelMappingFamily)
	default:
		return errUnsupportedChannelMappingFamily
	}
}

func validatePayloadLength(payload []byte, expectedLen int) error {
	if len(payload) != expectedLen {
		return errBadIDPageLength
	}

	return nil
}

func parseExtendedChannelMapping(header *OggHeader, payload []byte) error {
	expectedPayloadLen := 21 + int(header.Channels)
	if err := validatePayloadLength(payload, expectedPayloadLen); err != nil {
		return err
	}

	header.StreamCount = payload[19]
	header.CoupledCount = payload[20]
	header.ChannelMapping = string(payload[21:expectedPayloadLen])

	return nil
}

// ParseNextPage reads from stream and returns Ogg page payload, header,
// and an error if there is incomplete page data.
func (o *OggReader) ParseNextPage() ([]byte, *OggPageHeader, error) { //nolint:cyclop
	header := make([]byte, pageHeaderLen)

	n, err := io.ReadFull(o.stream, header)
	if err != nil {
		return nil, nil, err
	} else if n < len(header) {
		return nil, nil, errShortPageHeader
	}

	pageHeader := &OggPageHeader{
		sig: [4]byte{header[0], header[1], header[2], header[3]},
	}

	pageHeader.version = header[4]
	pageHeader.headerType = header[5]
	pageHeader.GranulePosition = binary.LittleEndian.Uint64(header[6 : 6+8])
	pageHeader.Serial = binary.LittleEndian.Uint32(header[14 : 14+4])
	pageHeader.index = binary.LittleEndian.Uint32(header[18 : 18+4])
	pageHeader.segmentsCount = header[26]

	sizeBuffer := make([]byte, pageHeader.segmentsCount)
	if _, err = io.ReadFull(o.stream, sizeBuffer); err != nil {
		return nil, nil, err
	}

	payloadSize := 0
	for _, s := range sizeBuffer {
		payloadSize += int(s)
	}

	payload := make([]byte, payloadSize)
	if _, err = io.ReadFull(o.stream, payload); err != nil {
		return nil, nil, err
	}

	if o.doChecksum {
		var checksum uint32
		updateChecksum := func(v byte) {
			checksum = (checksum << 8) ^ o.checksumTable[byte(checksum>>24)^v]
		}

		for index := range header {
			// Don't include expected checksum in our generation
			if index > 21 && index < 26 {
				updateChecksum(0)

				continue
			}

			updateChecksum(header[index])
		}
		for _, s := range sizeBuffer {
			updateChecksum(s)
		}
		for index := range payload {
			updateChecksum(payload[index])
		}

		if binary.LittleEndian.Uint32(header[22:22+4]) != checksum {
			return nil, nil, errChecksumMismatch
		}
	}

	o.bytesReadSuccesfully += int64(len(header) + len(sizeBuffer) + len(payload))

	return payload, pageHeader, nil
}

// ResetReader resets the internal stream of OggReader. This is useful
// for live streams, where the end of the file might be read without the
// data being finished.
func (o *OggReader) ResetReader(reset func(bytesRead int64) io.Reader) {
	o.stream = reset(o.bytesReadSuccesfully)
}

func generateChecksumTable() *[256]uint32 {
	var table [256]uint32
	const poly = 0x04c11db7

	for i := range table {
		r := uint32(i) << 24 //nolint:gosec // G115
		for range 8 {
			if (r & 0x80000000) != 0 {
				r = (r << 1) ^ poly
			} else {
				r <<= 1
			}
		}
		table[i] = (r & 0xffffffff) //nolint:gosec // no out of bounds access here.
	}

	return &table
}

// OpusTags is the metadata for an OpusTags page.
// https://www.xiph.org/vorbis/doc/v-comment.html
type OpusTags struct {
	Vendor       string
	UserComments []UserComment
}

// UserComment is a key-value pair of a vorbis comment.
type UserComment struct {
	Comment string
	Value   string
}

// ParseOpusTags parses an OpusTags from the page payload.
// https://datatracker.ietf.org/doc/html/rfc7845#section-5.2
func ParseOpusTags(payload []byte) (*OpusTags, error) {
	const (
		headerMagicLen = 8
		u32Size        = 4
		minHeaderLen   = headerMagicLen + u32Size + u32Size
	)

	if err := validateOpusTagsHeader(payload, minHeaderLen); err != nil {
		return nil, err
	}

	vendor, vendorEnd, err := parseVendorString(payload, headerMagicLen, u32Size, minHeaderLen)
	if err != nil {
		return nil, err
	}

	userComments, err := parseUserComments(payload, vendorEnd, u32Size)
	if err != nil {
		return nil, err
	}

	return &OpusTags{
		Vendor:       vendor,
		UserComments: userComments,
	}, nil
}

func validateOpusTagsHeader(payload []byte, minHeaderLen int) error {
	if len(payload) < minHeaderLen {
		return fmt.Errorf("%w: payload too short", errBadOpusTagsSignature)
	}

	got := HeaderType(payload[:8])
	if got != HeaderOpusTags {
		return fmt.Errorf("%w: expected %q, got %q", errBadOpusTagsSignature, HeaderOpusTags, got)
	}

	return nil
}

func parseVendorString(payload []byte, headerMagicLen, u32Size, minHeaderLen int) (string, int, error) {
	vendorLen32 := binary.LittleEndian.Uint32(payload[headerMagicLen : headerMagicLen+u32Size])
	if int(vendorLen32) > len(payload)-minHeaderLen {
		return "", 0, fmt.Errorf("%w: payload too short for vendor string", errBadOpusTagsSignature)
	}
	vendorLen := int(vendorLen32)

	vendorStart := headerMagicLen + u32Size
	vendorEnd := vendorStart + vendorLen
	if vendorEnd+u32Size > len(payload) {
		return "", 0, fmt.Errorf("%w: payload too short for vendor+comment count", errBadOpusTagsSignature)
	}

	vendor := string(payload[vendorStart:vendorEnd])

	return vendor, vendorEnd, nil
}

func parseUserComments(payload []byte, vendorEnd, u32Size int) ([]UserComment, error) {
	userCommentCount32 := binary.LittleEndian.Uint32(payload[vendorEnd : vendorEnd+u32Size])
	if int(userCommentCount32) > (len(payload)-vendorEnd)/u32Size {
		return nil, fmt.Errorf("%w: unreasonable comment count", errBadOpusTagsSignature)
	}
	userCommentCount := int(userCommentCount32)

	pos := vendorEnd + u32Size
	userComments := make([]UserComment, userCommentCount)

	for i := range userComments {
		comment, nextPos, err := parseSingleUserComment(payload, pos, u32Size, i)
		if err != nil {
			return nil, err
		}
		userComments[i] = comment
		pos = nextPos
	}

	return userComments, nil
}

func parseSingleUserComment(payload []byte, pos, u32Size, index int) (UserComment, int, error) {
	if pos+u32Size > len(payload) {
		return UserComment{}, 0, fmt.Errorf("%w: payload too short for comment len %d", errBadOpusTagsSignature, index)
	}

	commentLen32 := binary.LittleEndian.Uint32(payload[pos : pos+u32Size])
	pos += u32Size

	commentLen := int(commentLen32)
	if commentLen < 0 || pos+commentLen > len(payload) {
		return UserComment{}, 0, fmt.Errorf("%w: payload too short for comment %d", errBadOpusTagsSignature, index)
	}

	comment := string(payload[pos : pos+commentLen])
	pos += commentLen

	parts := strings.SplitN(comment, "=", 2)
	if len(parts) != 2 {
		return UserComment{}, 0, fmt.Errorf("%w: invalid comment %d", errBadOpusTagsSignature, index)
	}

	return UserComment{
		Comment: parts[0],
		Value:   parts[1],
	}, pos, nil
}