import {
  isHexDigit,
  isWhiteSpace,
  isValidEscape,
  consumeEscaped,
  decodeEscaped,
} from '../tokenizer/index.js';

const SPACE = 0x0020; // U+0020 SPACE
const REVERSE_SOLIDUS = 0x005c; // U+005C REVERSE SOLIDUS (\)
const QUOTATION_MARK = 0x0022; // "
const APOSTROPHE = 0x0027; // '
const LEFTPARENTHESIS = 0x0028; // U+0028 LEFT PARENTHESIS (()
const RIGHTPARENTHESIS = 0x0029; // U+0029 RIGHT PARENTHESIS ())

export function decode(str) {
  const len = str.length;
  let start = 4; // length of "url("
  let end = str.charCodeAt(len - 1) === RIGHTPARENTHESIS ? len - 2 : len - 1;
  let decoded = '';

  while (start < end && isWhiteSpace(str.charCodeAt(start))) {
    start++;
  }

  while (start < end && isWhiteSpace(str.charCodeAt(end))) {
    end--;
  }

  for (let i = start; i <= end; i++) {
    let code = str.charCodeAt(i);

    if (code === REVERSE_SOLIDUS) {
      // special case at the ending
      if (i === end) {
        // if the next input code point is EOF, do nothing
        // otherwise include last left parenthesis as escaped
        if (i !== len - 1) {
          decoded = str.substr(i + 1);
        }
        break;
      }

      code = str.charCodeAt(++i);

      // consume escaped
      if (isValidEscape(REVERSE_SOLIDUS, code)) {
        const escapeStart = i - 1;
        const escapeEnd = consumeEscaped(str, escapeStart);

        i = escapeEnd - 1;
        decoded += decodeEscaped(str.substring(escapeStart + 1, escapeEnd));
      } else {
        // \r\n
        if (code === 0x000d && str.charCodeAt(i + 1) === 0x000a) {
          i++;
        }
      }
    } else {
      decoded += str[i];
    }
  }

  return decoded;
}

export function encode(str) {
  let encoded = '';
  let wsBeforeHexIsNeeded = false;

  for (let i = 0; i < str.length; i++) {
    const code = str.charCodeAt(i);

    // If the character is NULL (U+0000), then the REPLACEMENT CHARACTER (U+FFFD).
    if (code === 0x0000) {
      encoded += '\uFFFD';
      continue;
    }

    // If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F,
    // the character escaped as code point.
    // Note: Do not compare with 0x0001 since 0x0000 is precessed before
    if (code <= 0x001f || code === 0x007f) {
      encoded += '\\' + code.toString(16);
      wsBeforeHexIsNeeded = true;
      continue;
    }

    if (
      code === SPACE ||
      code === REVERSE_SOLIDUS ||
      code === QUOTATION_MARK ||
      code === APOSTROPHE ||
      code === LEFTPARENTHESIS ||
      code === RIGHTPARENTHESIS
    ) {
      encoded += '\\' + str.charAt(i);
      wsBeforeHexIsNeeded = false;
    } else {
      if (wsBeforeHexIsNeeded && isHexDigit(code)) {
        encoded += ' ';
      }

      encoded += str.charAt(i);
      wsBeforeHexIsNeeded = false;
    }
  }

  return 'url(' + encoded + ')';
}