/**
 * @since 2019-12-29 09:04
 * @author vivaxy
 * @see https://gist.github.com/pascaldekloe/62546103a1576803dade9269ccf76330
 */
export function encode(string: string) {
  let i = 0;
  let bytes = new Uint8Array(string.length * 4);
  for (let ci = 0; ci != string.length; ci++) {
    let c = string.charCodeAt(ci);
    if (c < 128) {
      bytes[i++] = c;
      continue;
    }
    if (c < 2048) {
      bytes[i++] = (c >> 6) | 192;
    } else {
      if (c > 0xd7ff && c < 0xdc00) {
        if (++ci >= string.length) {
          throw new Error('UTF-8 encode: incomplete surrogate pair');
        }
        const c2 = string.charCodeAt(ci);
        if (c2 < 0xdc00 || c2 > 0xdfff) {
          throw new Error(
            'UTF-8 encode: second surrogate character 0x' +
              c2.toString(16) +
              ' at index ' +
              ci +
              ' out of range',
          );
        }
        c = 0x10000 + ((c & 0x03ff) << 10) + (c2 & 0x03ff);
        bytes[i++] = (c >> 18) | 240;
        bytes[i++] = ((c >> 12) & 63) | 128;
      } else {
        bytes[i++] = (c >> 12) | 224;
      }
      bytes[i++] = ((c >> 6) & 63) | 128;
    }
    bytes[i++] = (c & 63) | 128;
  }
  return bytes.subarray(0, i);
}

export function decode(bytes: Uint8Array) {
  let i = 0;
  let s = '';
  while (i < bytes.length) {
    let c = bytes[i++];
    if (c > 127) {
      if (c > 191 && c < 224) {
        if (i >= bytes.length) {
          throw new Error('UTF-8 decode: incomplete 2-byte sequence');
        }
        c = ((c & 31) << 6) | (bytes[i++] & 63);
      } else if (c > 223 && c < 240) {
        if (i + 1 >= bytes.length) {
          throw new Error('UTF-8 decode: incomplete 3-byte sequence');
        }
        c = ((c & 15) << 12) | ((bytes[i++] & 63) << 6) | (bytes[i++] & 63);
      } else if (c > 239 && c < 248) {
        if (i + 2 >= bytes.length) {
          throw new Error('UTF-8 decode: incomplete 4-byte sequence');
        }
        c =
          ((c & 7) << 18) |
          ((bytes[i++] & 63) << 12) |
          ((bytes[i++] & 63) << 6) |
          (bytes[i++] & 63);
      } else {
        throw new Error(
          'UTF-8 decode: unknown multibyte start 0x' +
            c.toString(16) +
            ' at index ' +
            (i - 1),
        );
      }
    }
    if (c <= 0xffff) {
      s += String.fromCharCode(c);
    } else if (c <= 0x10ffff) {
      c -= 0x10000;
      s += String.fromCharCode((c >> 10) | 0xd800);
      s += String.fromCharCode((c & 0x3ff) | 0xdc00);
    } else {
      throw new Error(
        'UTF-8 decode: code point 0x' +
          c.toString(16) +
          ' exceeds UTF-16 reach',
      );
    }
  }
  return s;
}