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

  word: $ => $.identifier,

  extras: $ => [
    $._line_comment,
    $._block_comment,
    /\s/
  ],

  rules: {

    // --- sources

    source_file: $ => repeat1($._statement),

    _statement: $ => choice(
      $.import,
      $.type_definition,
      $.function_definition,
      $.typeclass_definition,
    ),

    import: $ => seq(
      choice('::', 'import'),
      field('name', choice($.simple_name_identifier, '_')),
      optional(seq('=', field('module', $.simple_name_identifier))),
      optional(seq(':', repeat(choice(
        $.simple_type_identifier,
        $.simple_name_identifier,
        $.typeclass_identifier,
        seq('(',$.operator, ')'),
      )))),
      ';',
    ),

    constraint: $ => seq('?', $._expression),

    // --- definitions

    type_definition: $ => seq(
      optional($.definition_info),
      repeat($.annotation_info),
      optional('^'),
      field('name', $.simple_type_identifier),
      optional(seq(repeat($.argument_type_identifier), '=', choice($.variant_type, $.tuple_type))),
      choice(seq('{', repeat($.function_definition), '}'), ';')
    ),

    function_definition: $ => seq(
      optional($.definition_info),
      repeat($.annotation_info),
      repeat(seq($.constraint, ';')),
      /*optional(seq(*/optional(choice(choice('%', 'let'), choice('$', 'var')))/*, '.'))*/,
      field('name', $.simple_name_identifier),
      repeat(seq(
        optional($.annotation_identifier),
        $.argument_name_identifier,
        optional('?'),
      )),
      optional(seq(':', repeat1(seq(
        optional($.annotation_identifier),
        optional(choice(choice('->', 'out'), choice('<-', 'in'), choice('<>', 'ref'))),
        $.type,
      )))),
      choice(seq('=', choice(prec(2, $.block), seq($._super_expression, ';'))), ';'),
    ),

    typeclass_definition: $ => seq(
      optional($.definition_info),
      repeat($.annotation_info),
      $.typeclass_identifier,
      optional(seq(':', repeat($.typeclass_identifier))),
      choice(seq('{', repeat($.function_definition), '}'), ';'),
    ),

    // --- flow control

    case: $ => seq(
      choice(':=', '=:'),
      $._expression,
      optional(seq(choice('??', 'if'), $._expression)),
      optional(seq(choice('->', 'do'), $._expression)),
    ),

    match: $ => seq(
      $._expression,
      repeat1($.case),
    ),

    condition: $ => seq(
      choice('??', 'if'),
      $._expression,
      choice('->', 'do'),
      $._expression,
      repeat(seq(
        choice('!!', 'elif'),
        $._expression,
        choice('->', 'do'),
        $._expression,
      )),
      optional(seq(choice('!!->', 'else'), $._expression)),
    ),

    loop: $ => seq(
      choice('@', 'for'),
      optional(choice(
        field('condition', $._expression),
        seq(field('variable', $._expression), ':', field('interval', $._expression)),
      )),
      choice('->', 'do'),
      field('expression', $._expression),
    ),

    // --- operators

    comma_expression: $ => prec.left(seq($._super_expression, ',', $._super_expression)),

    operator_expression: $ => prec.left(choice(
      prec(4, seq($._expression, field('name', $.operator), $._expression)),
      prec(3, seq($._expression, field('name', $.operator_tail1), $._expression)),
      prec(2, seq($._expression, field('name', $.operator_tail2), $._expression)),
      prec(1, seq($._expression, field('name', $.operator_tail3), $._expression)),
    )),

    // --- continers

    block: $ => seq('{', repeat(seq($._super_expression, ';')), '}'),

    array: $ => seq('[[', repeat1($._scoped_expression), ']]'),

    // --- modifiers

    return: $ => seq(choice('return', 'bring'), field('value', $._expression)),

    name_definition: $ => seq(
      choice(choice('%', 'let'), choice('$', 'var')),
      choice($.simple_name_identifier, $.placeholder),
    ),

    array_access: $ => seq($._scoped_expression, '[', $._super_expression, ']'),

    tuple_access: $ => seq($._scoped_expression, '.', $.number_literal),

    loop_control: $ => choice('break', 'continue'),

    reference: $ => prec(-1, seq(choice(choice('<>', 'ref'), choice('<-', 'in')), $._scoped_expression)),

    suffix_expression: $ => seq($._scoped_expression, choice('?', '!')),

    // --- other

    name_expression: $ => seq(
      choice(
        seq($.type, '.', field('name', $.simple_name_identifier)),
        seq($._scoped_expression, '.', field('name', $.simple_name_identifier)),
        field('name', $._name_identifier),
        seq('(', field('name', $.operator), ')'),
      ),
      repeat(seq(optional($.annotation_identifier), $._scoped_expression)),
    ),

    constructor: $ => seq(
      $.type,
      repeat1(seq(optional($.annotation_identifier), $._scoped_expression)),
    ),

    lambda: $ => seq(
      '\\',
      repeat($.argument_name_identifier),
      '->',
      $._expression,
    ),

    // --- expression

    _super_expression: $ => choice(
      $.match,
      $.condition,
      $.loop,
      $.comma_expression,
      $._expression,
    ),

    _expression: $ => choice(
      $.operator_expression,
      $.return,
      $.name_expression,
      $.constructor,
      $.lambda,
      $._not_name_scoped_expression,
    ),

    _scoped_expression: $ => choice(
      $._name_identifier,
      $._not_name_scoped_expression,
    ),

    _not_name_scoped_expression: $ => choice(
      $.block,
      $.array,
      $.placeholder,
      $.name_definition,
      $.array_access,
      $.tuple_access,
      $.loop_control,
      $.reference,
      $.suffix_expression,
      $._literal,
      seq('(', $._super_expression, ')'),
    ),

    // --- type

    variant_type: $ => seq(
      optional('|'),
      $.tuple_type,
      repeat1(seq('|', $.tuple_type)),
    ),

    tuple_type: $ => seq(
      optional('&'),
      $._annotated_type,
      repeat(seq('&', $._annotated_type)),
    ),

    _annotated_type: $ => seq(optional($.annotation_identifier), $.type),

    type: $ => seq(
      optional('^'),
      field('name', $._type_identifier),
      optional('?'),
      optional(seq('[', repeat1($.type), ']'))
    ),

    // --- comments

    definition_info: $ => repeat1(seq(': ', /[^\n]*/)),
    annotation_info: $ => seq($.annotation_identifier, /[^\n]*/),

    _line_comment: $ => token(seq('//', /[^\n]*/)),
    _block_comment: $ => token(seq('/*', /([^*]|(\*[^/]))*/, '*/')),

    // --- tokens

    _name_identifier: $ => choice($.argument_name_identifier, $.simple_name_identifier),
    _type_identifier: $ => choice($.argument_type_identifier, $.simple_type_identifier),

    placeholder: $ => '_',

    simple_name_identifier: $ => token(seq(repeat(seq(/[a-z_][a-z0-9_]*/, '.')), /[a-z_][a-z0-9_]*/)),

    simple_type_identifier: $ => /([a-z_][a-z0-9_]*\.)*[A-Z][a-zA-Z0-9]*/,
    typeclass_identifier: $ => /([a-z_][a-z0-9_]*\.)*#[A-Z][a-zA-Z0-9]*/,
    argument_name_identifier: $ => /'[a-z_][a-z0-9_]*/,
    argument_type_identifier: $ => /'[A-Z][a-zA-Z0-9]*/,
    annotation_identifier: $ => /@[a-z_][a-z0-9_]*/,

    operator: $ => /([+\-*/%^!?|&,<>=]+)|\.+/,
    operator_tail1: $ => /[+\-*/%^!?|&,<>=]+\./,
    operator_tail2: $ => /[+\-*/%^!?|&,<>=]+\.\./,
    operator_tail3: $ => /[+\-*/%^!?|&,<>=]+\.\.\./,

    float_number_literal: $ => /[0-9]+\.[0-9]+/,
    number_literal: $ => /[0-9]+/,
    string_literal: $ => seq('\"', /([^\\\"]|(\\.))*/, '\"'),
    char_literal: $ => seq('\'\'', /[^\\\']|(\\.)/, '\'\''),
    bool_literal: $ => choice('true', 'false'),
    unit_literal: $ => '()',
    null_literal: $ => 'null',

    _literal: $ => choice(
      $.float_number_literal,
      $.number_literal,
      $.string_literal,
      $.char_literal,
      $.bool_literal,
      $.unit_literal,
      $.null_literal,
    ),

    identifier: $ => /([@'#]?[a-zA-Z0-9_]+)|([+\-*/%^!?|&,<>=]+\.?\.?\.?)|\.+/,
  }
});