const TokenizerFSA = (() => {
  // Define the states
  const states = {
    START: 'START',
    IN_WORD: 'IN_WORD',
    IN_NUMBER: 'IN_NUMBER',
    IN_SYMBOL: 'IN_SYMBOL'
  };

  // Utility functions to check character types
  const isLetter = char => /[a-zA-Z]/.test(char);
  const isDigit = char => /\d/.test(char);
  const isSymbol = char => /\W/.test(char) && !/\s/.test(char);

  // Add a token to the list if it's not empty
  const addToken = (token, tokens) => {
    if (token) tokens.push(token);
  };

  // Process a single character and update the state and token accordingly
  const processChar = (state, char, token, tokens) => {
    switch (state) {
      case states.START:
        if (isLetter(char)) return { state: states.IN_WORD, token: char };
        if (isDigit(char)) return { state: states.IN_NUMBER, token: char };
        if (isSymbol(char)) return { state: states.IN_SYMBOL, token: char };
        return { state: states.START, token: '' }; // Remain in START state for spaces or other characters

      case states.IN_WORD:
        if (isLetter(char)) return { state, token: token + char };
        addToken(token, tokens);
        return { state: states.START, token: '' };

      case states.IN_NUMBER:
        if (isDigit(char)) return { state, token: token + char };
        addToken(token, tokens);
        return { state: states.START, token: '' };

      case states.IN_SYMBOL: // FIXME: symbols aren't being well handled
        if (isSymbol(char)) return { state, token: token + char };
        addToken(token, tokens);
        return { state: states.START, token: '' };

      default:
        return { state: states.START, token: '' };
    }
  };

  // Tokenize the entire input text
  const tokenize = text => {
    let state = states.START;
    let token = '';
    const tokens = [];

    for (const char of text) {
      const result = processChar(state, char, token, tokens);
      state = result.state;
      token = result.token;
    }

    // Add the last token if any
    addToken(token, tokens);

    return tokens;
  };

  return { tokenize };
})();

// FIXME: symbols aren't being well handled, and consecutive, identical numbers are being ignored
const text = "Hello, world! 123";
const tokens = TokenizerFSA.tokenize(text);
console.log(tokens);  // Output: ['Hello', ',', 'world', '!', '123']

const text2 = "Oh no, it's 3.14159! Is it delicious? Is it mysterious? Who knows!";
const tokens2 = TokenizerFSA.tokenize(text2);
console.log(tokens2);

const text3 = "über l337 hard test";
const tokens3 = TokenizerFSA.tokenize(text3);
console.log(tokens3);