package zerolog

import "unicode/utf8"

const hex = "0123456789abcdef"

func appendJSONString(dst []byte, s string) []byte {
	dst = append(dst, '"')
	for i := 0; i < len(s); {
		if b := s[i]; b < utf8.RuneSelf {
			switch b {
			case '"', '\\':
				dst = append(dst, '\\', b)
			case '\b':
				dst = append(dst, '\\', 'b')
			case '\f':
				dst = append(dst, '\\', 'f')
			case '\n':
				dst = append(dst, '\\', 'n')
			case '\r':
				dst = append(dst, '\\', 'r')
			case '\t':
				dst = append(dst, '\\', 't')
			default:
				if b >= 0x20 {
					dst = append(dst, b)
				} else {
					dst = append(dst, '\\', 'u', '0', '0', hex[b>>4], hex[b&0xF])
				}
			}
			i++
			continue
		}
		r, size := utf8.DecodeRuneInString(s[i:])
		if r == utf8.RuneError && size == 1 {
			dst = append(dst, `\ufffd`...)
			i++
			continue
		}
		dst = append(dst, s[i:i+size]...)
		i += size
	}
	return append(dst, '"')
}