//go:build wasm && js
// +build wasm,js

package psd

import (
	"io"
)

func decodePackBits(dest []byte, r io.Reader, width int, lines int, large bool) (read int, err error) {
	buf := make([]byte, lines*(get4or8(large)>>1))
	var l int
	if l, err = io.ReadFull(r, buf); err != nil {
		return
	}
	read += l

	total := 0
	lens := make([]int, lines)
	offsets := make([]int, lines)
	ofs := 0
	if large {
		for i := range lens {
			l = int(readUint32(buf, ofs))
			lens[i] = l
			offsets[i] = total
			total += l
			ofs += 4
		}
	} else {
		for i := range lens {
			l = int(readUint16(buf, ofs))
			lens[i] = l
			offsets[i] = total
			total += l
			ofs += 2
		}
	}

	buf = make([]byte, total)
	if l, err = io.ReadFull(r, buf); err != nil {
		return
	}
	read += l

	err = decodePackBitsPerLine(dest, buf, lens)
	return
}

func decodePackBitsPerLine(dest []byte, buf []byte, lens []int) error {
	var l int
	for _, ln := range lens {
		for i := 0; i < ln; {
			if buf[i] <= 0x7f {
				l = int(buf[i]) + 1
				if len(dest) < l || ln-i-1 < l {
					return errBrokenPackBits
				}
				copy(dest[:l], buf[i+1:])
				dest = dest[l:]
				i += l + 1
				continue
			}
			if buf[i] == 0x80 {
				i++
				continue
			}
			l = int(-buf[i]) + 1
			if len(dest) < l || i+1 >= ln {
				return errBrokenPackBits
			}
			for j, c := 0, buf[i+1]; j < l; j++ {
				dest[j] = c
			}
			dest = dest[l:]
			i += 2
		}
		buf = buf[ln:]
	}
	return nil
}