package utf16le

import (
	"encoding/binary"
	"unicode/utf16"
)

var (
	le = binary.LittleEndian
)

func EncodedStringLen(s string) int {
	l := 0
	for _, r := range s {
		if 0x10000 <= r && r <= '\U0010FFFF' {
			l += 4
		} else {
			l += 2
		}
	}
	return l
}

func EncodeString(dst []byte, src string) int {
	ws := utf16.Encode([]rune(src))
	for i, w := range ws {
		le.PutUint16(dst[2*i:2*i+2], w)
	}
	return len(ws) * 2
}

func EncodeStringToBytes(s string) []byte {
	if len(s) == 0 {
		return nil
	}
	ws := utf16.Encode([]rune(s))
	bs := make([]byte, len(ws)*2)
	for i, w := range ws {
		le.PutUint16(bs[2*i:2*i+2], w)
	}
	return bs
}

func DecodeToString(bs []byte) string {
	if len(bs) == 0 {
		return ""
	}
	ws := make([]uint16, len(bs)/2)
	for i := range ws {
		ws[i] = le.Uint16(bs[2*i : 2*i+2])
	}
	if len(ws) > 0 && ws[len(ws)-1] == 0 {
		ws = ws[:len(ws)-1]
	}
	return string(utf16.Decode(ws))
}