module.exports = grammar({
  name: 'dust',

  word: $ => $.identifier,

  rules: {
    root: $ => repeat1($.item),
    
    item: $ => choice(
      $.comment,
      $.statement,
    ),

    comment: $ => prec.left(seq(token('#'), /.*/)),

    statement: $ => choice(
      $.closed_statement,
      $.open_statement,
    ),

    closed_statement: $ => seq($.expression, $.close),

    open_statement: $ => prec.left(seq($.expression)),

    expression: $ => choice(
      $.value,
      $.identifier,
      $.operation,
      $.control_flow,
    ),

    close: $ => ";",

    identifier: $ => /[a-zA-Z|_|.]+(_[a-zA-Z]+)*/,

    value: $ => choice(
      $.integer,
      $.float,
      $.string,
      $.list,
      $.empty,
      $.boolean,
      $.function,
    ), 

    float: $ => /\d+\.\d*/,
    
    integer: $ => /\d+/,

    string: $ => /("|'|`)(.*?)("|'|`)/,

    function: $ => /{(.*?)}/,

    empty: $ => '()',

    boolean: $ => choice(
      'true',
      'false',
    ),

    list: $ => seq(
      '(',
      repeat1(seq($.value, optional(','))),
      ')'
    ),

    operator: $ => choice(
      '+',
      '-',
      '=',
      '==',
    ),

    operation: $ => prec.left(seq(
      $.expression,
      $.operator, 
      $.expression,
    )),

    control_flow: $ => prec.right(seq(
      'if',
      $.expression,
      'then',
      $.statement,
      optional(seq('else', $.statement))
    )),
  }
});