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

  word: $ => $.identifier,

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

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

    statement: $ => prec.right(choice(
      $.expression,
      $.yield,
    )),

    yield: $ => prec.left(
      seq(
        $.expression,
        '->',
        $.expression,
        repeat(prec.left(seq('->', $.expression)))
      )
    ),

    expression: $ => choice(
      $._expression_kind,
      seq('(', $._expression_kind, ')')
    ),

    _expression_kind: $ => prec.right(choice(
      $.value,
      $.identifier,
      $.control_flow,
      $.select,
      $.insert,
      $.function_call,
      $.assignment,
      $.math,
      $.logic,
      $.loop,
      $.match,
    )),

    identifier: $ => /[a-z|_|.]+[0-9]?/,

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

    float: $ => /[-]*[0-9]*[.]{1}[0-9]+/,

    integer: $ => /[-]*[0-9]+[.]{0}/,

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

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

    list: $ => seq(
      '[',
      repeat1(seq(field('item', $.value), optional(','))),
      ']'
    ),

    function: $ => seq(
      'function',
      optional(seq('<', repeat(seq($.identifier, optional(','))), '>')),
      '{',
      repeat1($.statement),
      '}',
    ),

    table: $ => seq(
      'table',
      seq('<', repeat1(seq($.identifier, optional(','))), '>'),
      '{',
      repeat($.list),
      '}',
    ),

    map: $ => seq(
      'map',
      '{',
      repeat(field('key_value_pair', seq($.identifier, "=", $.value))),
      '}',
    ),

    math: $ => prec.right(seq(
      $.expression,
      $.math_operator,
      $.expression,
    )),

    math_operator: $ => choice(
      '+',
      '-',
      '*',
      '/',
      '%',
    ),

    logic: $ => prec.right(seq(
      $.expression,
      $.logic_operator,
      $.expression,
    )),

    logic_operator: $ => choice(
      '==',
      '&&',
      '||',
      'and',
      'or',
    ),

    assignment: $ => prec.right(seq(
      $.identifier,
      choice("=", "+=", "-="),
      $.statement,
    )),

    select: $ => prec.right(seq(
      'select',
      $.identifier,
      'from',
      $.identifier,
      optional(
        seq('where', $.expression)
      ),
    )),

    insert: $ => prec.right(seq(
      'insert',
      repeat1($.list),
      'into',
      $.identifier,
      optional(
        seq('where', $.expression)
      ),
    )),

    control_flow: $ => prec.right(seq(
      'if',
      field('if_expression', $.expression),
      'then',
      field('then_statement', $.statement),
      optional(
        seq('else', 
          field('else_statement', $.statement),
        ),
      ),
    )),

    function_call: $ => prec.right(seq(
      $.identifier,
      '<',
      repeat(seq($.expression, optional(','))),
      '>',
    )),

    loop: $ => choice(
      $.break_loop,
      $.while_loop,
    ),

    while_loop: $ => seq(
      'while',
      $.expression,
      '{',
      $.statement,
      '}',      
    ),

    break_loop: $ => seq(
      'loop',
      '{',
      $.statement,
      '}',      
    ),

    match: $ => seq(
      'match',
      $.expression,
      '{',
      repeat1(seq($.expression, '=>', $.statement)),
      '}',      
    ),
  }
});