package qmc

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

type musicExTagV1 struct {
	songID        uint32
	unknown1      uint32
	unknown2      uint32
	mediaID       string
	mediaFileName string
	unknown3      uint32
	tagSize       uint32
	tagVersion    uint32
	tagMagic      []byte
}

func newMusicExTag(f io.ReadSeeker) (*musicExTagV1, error) {
	_, err := f.Seek(-16, io.SeekEnd)
	if err != nil {
		return nil, fmt.Errorf("musicex seek error: %w", err)
	}

	buffer := make([]byte, 16)
	bytesRead, err := f.Read(buffer)
	if err != nil {
		return nil, fmt.Errorf("get musicex error: %w", err)
	}
	if bytesRead != 16 {
		return nil, fmt.Errorf("MusicExV1: read %d bytes (expected %d)", bytesRead, 16)
	}

	tag := &musicExTagV1{
		tagSize:    binary.LittleEndian.Uint32(buffer[0x00:0x04]),
		tagVersion: binary.LittleEndian.Uint32(buffer[0x04:0x08]),
		tagMagic:   buffer[0x08:0x10],
	}

	if !bytes.Equal(tag.tagMagic, []byte("musicex\x00")) {
		return nil, errors.New("MusicEx magic mismatch")
	}
	if tag.tagVersion != 1 {
		return nil, fmt.Errorf("unsupported musicex tag version: %d", tag.tagVersion)
	}

	if tag.tagSize < 0xC0 {
		return nil, fmt.Errorf("unsupported musicex tag size: 0x%x", tag.tagSize)
	}

	buffer = make([]byte, tag.tagSize)
	bytesRead, err = f.Read(buffer)
	if err != nil {
		return nil, err
	}
	if uint32(bytesRead) != tag.tagSize {
		return nil, fmt.Errorf("MusicExV1: read %d bytes (expected %d)", bytesRead, tag.tagSize)
	}

	tag.songID = binary.LittleEndian.Uint32(buffer[0x00:0x04])
	tag.unknown1 = binary.LittleEndian.Uint32(buffer[0x04:0x08])
	tag.unknown2 = binary.LittleEndian.Uint32(buffer[0x08:0x0C])
	tag.mediaID = readUnicodeTagName(buffer[0x0C:], 30*2)
	tag.mediaFileName = readUnicodeTagName(buffer[0x48:], 50*2)
	tag.unknown3 = binary.LittleEndian.Uint32(buffer[0xAC:0xB0])
	return tag, nil
}

// readUnicodeTagName reads a buffer to maxLen.
// reconstruct text by skipping alternate char (ascii chars encoded in UTF-16-LE),
// until finding a zero or reaching maxLen.
func readUnicodeTagName(buffer []byte, maxLen int) string {
	builder := strings.Builder{}

	for i := 0; i < maxLen; i += 2 {
		chr := buffer[i]
		if chr != 0 {
			builder.WriteByte(chr)
		} else {
			break
		}
	}

	return builder.String()
}