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

  word: $ => $.identifier,

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

  rules: {
    root: $ =>
      prec(1, repeat1($.statement)),

    _comment: $ => /[#][^#\n]*[#|\n]/,

    block: $ =>
      seq(
        optional("async"),
        "{",
        repeat1($.statement),
        "}",
      ),

    statement: $ =>
      prec.left(
        seq(
          choice(
            $.assignment,
            $.block,
            $.expression,
            $.for,
            $.if_else,
            $.index_assignment,
            $.match,
            $.return,
            $.use,
            $.while,
          ),
          optional(";"),
        ),
      ),

    expression: $ =>
      prec.right(
        choice(
          $._expression_kind,
          seq(
            "(",
            $._expression_kind,
            ")",
          ),
        ),
      ),

    _expression_kind: $ =>
      prec.right(
        choice(
          $.function_call,
          $.identifier,
          $.index,
          $.logic,
          $.math,
          $.value,
          $.yield,
        ),
      ),

    _expression_list: $ =>
      repeat1(
        prec.right(
          seq(
            $.expression,
            optional(","),
          ),
        ),
      ),

    identifier: $ =>
      /[_a-zA-Z]+[_a-zA-Z0-9]?/,

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

    integer: $ =>
      token(
        prec.left(
          seq(
            optional("-"),
            repeat1(
              choice(
                "1",
                "2",
                "3",
                "4",
                "5",
                "6",
                "7",
                "8",
                "9",
                "0",
              ),
            ),
          ),
        ),
      ),

    float: $ =>
      token(
        prec.left(
          seq(
            optional("-"),
            repeat1(
              choice(
                "1",
                "2",
                "3",
                "4",
                "5",
                "6",
                "7",
                "8",
                "9",
                "0",
              ),
            ),
            ".",
            repeat1(
              choice(
                "1",
                "2",
                "3",
                "4",
                "5",
                "6",
                "7",
                "8",
                "9",
                "0",
              ),
            ),
          ),
        ),
      ),

    string: $ =>
      /("[^"]*?")|('[^']*?')|(`[^`]*?`)/,

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

    list: $ =>
      seq(
        "[",
        repeat(
          prec.left(
            seq(
              $.expression,
              optional(","),
            ),
          ),
        ),
        "]",
      ),

    map: $ =>
      seq(
        "{",
        repeat(
          seq(
            $.identifier,
            "=",
            $.statement,
            optional(","),
          ),
        ),
        "}",
      ),

    index: $ =>
      prec.left(
        1,
        seq(
          $.expression,
          ":",
          $.expression,
          optional(
            seq("..", $.expression),
          ),
        ),
      ),

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

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

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

    logic_operator: $ =>
      choice(
        "==",
        "!=",
        "&&",
        "||",
        ">",
        "<",
        ">=",
        "<=",
      ),

    assignment: $ =>
      seq(
        field(
          "identifier",
          $.identifier,
        ),
        optional(
          field(
            "type",
            $.type_definition,
          ),
        ),
        field(
          "assignment_operator",
          $.assignment_operator,
        ),
        field("statement", $.statement),
      ),

    index_assignment: $ =>
      seq(
        $.index,
        $.assignment_operator,
        $.statement,
      ),

    assignment_operator: $ =>
      prec.right(
        choice("=", "+=", "-="),
      ),

    if_else: $ =>
      prec.right(
        seq(
          $.if,
          repeat($.else_if),
          optional($.else),
        ),
      ),

    if: $ =>
      seq("if", $.expression, $.block),

    else_if: $ =>
      seq(
        "else if",
        $.expression,
        $.block,
      ),

    else: $ => seq("else", $.block),

    match: $ =>
      prec.right(
        seq(
          "match",
          $.expression,
          repeat1(
            seq(
              $.expression,
              "=>",
              $.block,
            ),
          ),
        ),
      ),

    while: $ =>
      seq(
        "while",
        $.expression,
        $.block,
      ),

    for: $ =>
      seq(
        choice("for", "async for"),
        $.identifier,
        "in",
        $.expression,
        $.block,
      ),

    identifier_list: $ =>
      prec.right(
        choice(
          seq(
            "|",
            repeat(
              seq(
                $.identifier,
                optional(","),
              ),
            ),
            "|",
          ),
        ),
      ),

    table: $ =>
      prec.right(
        seq(
          "table",
          $.identifier_list,
          $.expression,
        ),
      ),

    return: $ =>
      seq("return", $.expression),

    use: $ => seq("use", $.string),

    type_definition: $ =>
      seq("<", $.type, ">"),

    type: $ =>
      prec.right(
        choice(
          "any",
          "bool",
          seq(
            "fn",
            repeat(
              seq(
                $.type,
                optional(","),
              ),
            ),
            optional(seq("->", $.type)),
          ),
          "int",
          seq("list", $.type),
          "map",
          "num",
          "str",
        ),
      ),

    function: $ =>
      seq(
        "|",
        repeat(
          seq(
            $.identifier,
            optional(","),
          ),
        ),
        "|",
        $.block,
      ),

    function_call: $ =>
      prec.right(
        1,
        seq(
          "(",
          $.expression,
          optional($._expression_list),
          ")",
        ),
      ),

    yield: $ =>
      prec.left(
        seq(
          $.expression,
          "->",
          "(",
          $.expression,
          optional($._expression_list),
          ")",
        ),
      ),
  },
});