package util

import (
	"errors"
	"strconv"
	"strings"
)

func InterpretString(in string) (string, error) {
	in = in[1 : len(in)-1]
	sb := strings.Builder{}
	s := []rune(in)
	for i := 0; i < len(s); {
		r := s[i]
		if r == '\\' {
			if i == len(s)-1 {
				return "", errors.New("illegal escape character")
			}
			switch s[i+1] {
			case 'a':
				sb.WriteRune('\a')
				i += 2
				break
			case 'b':
				sb.WriteRune('\b')
				i += 2
				break
			case 'f':
				sb.WriteRune('\f')
				i += 2
				break
			case 'n':
				sb.WriteRune('\n')
				i += 2
				break
			case 'r':
				sb.WriteRune('\r')
				i += 2
				break
			case 't':
				sb.WriteRune('\t')
				i += 2
				break
			case 'v':
				sb.WriteRune('\v')
				i += 2
				break
			case '\\':
				sb.WriteRune('\\')
				i += 2
				break
			case '"':
				sb.WriteRune('"')
				i += 2
				break
			case 'u':
				sub := s[i+2 : i+6]
				n, err := strconv.ParseInt(string(sub), 16, 64)
				if err != nil {
					return "", err
				}
				sb.WriteRune(rune(n))
				i += 6
			case 'U':
				sub := s[i+2 : i+10]
				n, err := strconv.ParseInt(string(sub), 16, 64)
				if err != nil {
					return "", err
				}
				sb.WriteRune(rune(n))
				i += 10
			case '0', '1', '2', '3', '4', '5', '6', '7':
				sub := s[i+1 : i+4]
				n, err := strconv.ParseInt(string(sub), 8, 64)
				if err != nil {
					return "", err
				}
				sb.WriteRune(rune(n))
				i += 4
			case 'x':
				sub := s[i+2 : i+4]
				n, err := strconv.ParseInt(string(sub), 16, 64)
				if err != nil {
					return "", err
				}
				sb.WriteRune(rune(n))
				i += 4
			default:
				return "", errors.New("could not parse escape character")
			}
		} else {
			sb.WriteRune(r)
			i++
		}
	}
	return sb.String(), nil
}