package launchctx

import "strconv"

// encoding/json replaces unpaired UTF-16 escapes with U+FFFD. Refuse that
// lossy conversion before decoding identities and paths.
func validSurrogates(raw []byte) bool {
	quoted := false
	for i := 0; i < len(raw); i++ {
		if raw[i] == '"' {
			quoted = !quoted
			continue
		}
		if !quoted || raw[i] != '\\' {
			continue
		}
		i++
		if i >= len(raw) {
			return false
		}
		if raw[i] != 'u' {
			continue
		}
		if i+4 >= len(raw) {
			return false
		}
		n, err := strconv.ParseUint(string(raw[i+1:i+5]), 16, 16)
		if err != nil {
			return false
		}
		i += 4
		if n >= 0xdc00 && n <= 0xdfff {
			return false
		}
		if n < 0xd800 || n > 0xdbff {
			continue
		}
		if i+6 >= len(raw) || raw[i+1] != '\\' || raw[i+2] != 'u' {
			return false
		}
		low, err := strconv.ParseUint(string(raw[i+3:i+7]), 16, 16)
		if err != nil || low < 0xdc00 || low > 0xdfff {
			return false
		}
		i += 6
	}
	return true
}