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

  word: $ => $.identifier,

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

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

    statement: $ => prec.right(choice(
      $.open_statement,
      $.yield_statement,
    )),

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

    yield_statement: $ => seq($.open_statement, '->', $.open_statement),

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

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

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

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

    integer: $ => /\d+/,

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

    empty: $ => '()',

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

    list: $ => seq(
      '[',
      repeat1(seq($.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(seq($.identifier, "=", $.value)),
      '}',
    ),

    operator: $ => choice(
      '=',
      '+',
      '-',
      '*',
      '/',
      '%',
      '==',
      '+=',
      '-=',
      '&&',
      '||',
      'and',
      'or',
      'insert',
      'into',
      'select',
      'from',
      'where',
    ),

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

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

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

    tool: $ => choice(
      "output",
    ),
  }
});