// === TOKENIZER ===
function tokenize(input) {
  const tokens = [];
  let i = 0;

  function match(str) {
    return input.startsWith(str, i);
  }

  function advance(n) {
    i += n;
  }

  function push(type, value = null) {
    tokens.push({ type, value: value ?? type });
  }

  while (i < input.length) {
    if (match('\n*\n')) {
      push('T_CK', '\n*\n');
      advance(3);
    } else if (match('@sel(')) {
      push('T_SEL_OPEN', '@sel(');
      advance(5);
    } else if (match('@ed()')) {
      push('T_EDIT', '@ed()');
      advance(6);
    } else if (match(')')) {
      push('T_PAREN_CLOSE', ')');
      advance(1);
    } else if (match('/')) {
      push('T_SLASH', '/');
      advance(1);
    } else {
      // match text until next special token
      const start = i;
      while (
        i < input.length &&
        !match('\n*\n') &&
        !match('@sel(') &&
        !match('@ed()') &&
        !match(')') &&
        !match('/')
      ) {
        i++;
      }
      const text = input.slice(start, i).trim();
      if (text) {
        push('T_TEXT', text);
      }
    }
  }

  return tokens;
}

// === PARSER ===
function parse(tokens) {
  let pos = 0;

  function peek(type) {
    return tokens[pos]?.type === type;
  }

  function consume(type) {
    const token = tokens[pos];
    if (!token || token.type !== type) {
      throw new Error(`Expected ${type}, got ${token?.type} at position ${pos}`);
    }
    pos++;
    return token;
  }

  function parseText() {
    const token = consume('T_TEXT');
    return { type: 'text', value: token.value };
  }

  function parseEdit() {
    consume('T_EDIT');
    return { type: 'edit' };
  }

  function parseDropdown() {
    consume('T_SEL_OPEN');

    const options = [];
    options.push(consume('T_TEXT').value);

    while (peek('T_SLASH')) {
      consume('T_SLASH');
      options.push(consume('T_TEXT').value);
    }

    consume('T_PAREN_CLOSE');

    return { type: 'dropdown', options };
  }

  function parseE() {
    if (peek('T_SEL_OPEN')) return parseDropdown();
    if (peek('T_EDIT')) return parseEdit();
    if (peek('T_TEXT')) return parseText();
    throw new Error(`Unexpected token at position ${pos}: ${tokens[pos]?.type}`);
  }

  function parseExpr() {
    const elements = [];
    while (
      peek('T_TEXT') ||
      peek('T_EDIT') ||
      peek('T_SEL_OPEN')
    ) {
      elements.push(parseE());
    }
    return elements;
  }

  function parseCl() {
    consume('T_CK');
    return parseExpr(); // Return array of e nodes directly
  }

  function parseProgram() {
    const result = [];
    while (peek('T_CK')) {
      result.push(parseCl());
    }
    return result;
  }

  return parseProgram();
}

const input = `
*
今天我感覺 @sel(開心/普通/沮喪)，也許是因為我終於完成了那個專案 @ed()，雖然還有一些小地方要修正 @ed()。
Today I felt @sel(happy/neutral/down), maybe because I finally finished that project @ed(), although a few things still need fixing @ed().
*

我選擇了一本新書 @sel(小說/歷史/自我成長) 開始閱讀，名字叫 @ed()，它讓我重新思考一些事情 @ed()。
I picked up a new book @sel(fiction/history/self-help) to read, titled @ed(), and it made me reflect on a few things @ed().
*

晚餐我做了 @sel(義大利麵/壽司/沙拉)，因為我最近在嘗試更健康的飲食 @ed()，也開始記錄每天的熱量攝取 @ed()。
For dinner, I made @sel(pasta/sushi/salad), since I’m trying to eat healthier lately @ed(), and started tracking my daily calories @ed().
*

今天我和 @ed() 一起散步，天氣是 @sel(晴天/陰天/下雨)，我們聊了很多最近的煩惱 @ed()。
I went for a walk with @ed() today — the weather was @sel(sunny/cloudy/rainy), and we talked about a lot of recent worries @ed().
*

睡前我花了一點時間做計畫，明天我打算完成 @ed()，而且希望心情是 @sel(積極/平穩/專注)。
Before bed, I spent some time planning — tomorrow I hope to finish @ed(), and be in a @sel(positive/calm/focused) mindset.
`;

const tokens = tokenize(input);
const result = parse(tokens);
console.log(JSON.stringify(result));