/**
 * 简单 json5 解析 (支持 // 单行注释, /* 多行注释 *\/, 字符串, 转义)
 * 不支持: 数字下划线, 十六进制等扩展
 */
'use strict';

function parseJson5(text) {
  let i = 0;
  const len = text.length;

  function peek() { return text[i]; }
  function next() { return text[i++]; }

  function skipWsAndComments() {
    while (i < len) {
      const c = text[i];
      if (c === ' ' || c === '\t' || c === '\n' || c === '\r') {
        i++;
        continue;
      }
      if (c === '/' && text[i + 1] === '/') {
        while (i < len && text[i] !== '\n') i++;
        continue;
      }
      if (c === '/' && text[i + 1] === '*') {
        i += 2;
        while (i < len && !(text[i] === '*' && text[i + 1] === '/')) i++;
        i += 2;
        continue;
      }
      break;
    }
  }

  function readString() {
    const quote = next(); // " or '
    let out = '';
    while (i < len) {
      const c = next();
      if (c === '\\') {
        const esc = next();
        switch (esc) {
          case 'n': out += '\n'; break;
          case 't': out += '\t'; break;
          case 'r': out += '\r'; break;
          case '\\': out += '\\'; break;
          case '"': out += '"'; break;
          case "'": out += "'"; break;
          case '/': out += '/'; break;
          case 'b': out += '\b'; break;
          case 'f': out += '\f'; break;
          case 'u': {
            const hex = text.substr(i, 4);
            i += 4;
            out += String.fromCharCode(parseInt(hex, 16));
            break;
          }
          default: out += esc;
        }
        continue;
      }
      if (c === quote) return out;
      out += c;
    }
    throw new Error('unterminated string');
  }

  function readValue() {
    skipWsAndComments();
    const c = peek();
    if (c === '"' || c === "'") return readString();
    if (c === '{') return readObject();
    if (c === '[') return readArray();
    if (c === 't' || c === 'f') return readBoolOrNull();
    if (c === 'n') return readBoolOrNull();
    if (c === '-' || (c >= '0' && c <= '9')) return readNumber();
    throw new Error(`unexpected char '${c}' at ${i}`);
  }

  function readObject() {
    next(); // {
    const obj = {};
    while (true) {
      skipWsAndComments();
      if (peek() === '}') { next(); return obj; }
      // key
      let key;
      if (peek() === '"' || peek() === "'") key = readString();
      else {
        // bareword (json5 allows unquoted keys)
        let s = '';
        while (i < len && /[A-Za-z0-9_$-]/.test(text[i])) s += text[i++];
        key = s;
      }
      skipWsAndComments();
      if (next() !== ':') throw new Error(`expected ':' at ${i}`);
      obj[key] = readValue();
      skipWsAndComments();
      const nc = next();
      if (nc === ',') continue;
      if (nc === '}') return obj;
      throw new Error(`expected , or } at ${i}`);
    }
  }

  function readArray() {
    next(); // [
    const arr = [];
    while (true) {
      skipWsAndComments();
      if (peek() === ']') { next(); return arr; }
      arr.push(readValue());
      skipWsAndComments();
      const nc = next();
      if (nc === ',') continue;
      if (nc === ']') return arr;
      throw new Error(`expected , or ] at ${i}`);
    }
  }

  function readBoolOrNull() {
    if (text.substr(i, 4) === 'true') { i += 4; return true; }
    if (text.substr(i, 5) === 'false') { i += 5; return false; }
    if (text.substr(i, 4) === 'null') { i += 4; return null; }
    throw new Error(`bad literal at ${i}`);
  }

  function readNumber() {
    let s = '';
    if (peek() === '-') s += next();
    while (i < len && /[0-9.eE+-]/.test(text[i])) s += next();
    const n = parseFloat(s);
    if (isNaN(n)) throw new Error(`bad number '${s}'`);
    return n;
  }

  skipWsAndComments();
  const result = readValue();
  skipWsAndComments();
  if (i < len) throw new Error(`trailing chars at ${i}: ${text.substr(i, 30)}`);
  return result;
}

module.exports = parseJson5;