/**
 * @file SCL grammar for tree-sitter
 * @author Jacob Signorovitch <jacob.signorovitch@gmail.com>
 * @license MIT
 */

/// <reference types="tree-sitter-cli/dsl" />
// @ts-check

// grammar.js
const PREC = {
  assign: 0, // right-assoc
  add: 1, // left-assoc
  mul: 2, // left-assoc
  call: 3,
  funcdef: 4,
  lambda: 5,
};

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

  // Whitespace is of no consequence.
  extras: ($) => [/\s/],

  conflicts: ($) => [[$.params, $._exp]],

  rules: {
    // A file is zero or more expressions.
    source_file: ($) => repeat($._exp),

    // Everything is expressions. Makes this a lot easier.
    _exp: ($) =>
      choice(
        $.num,
        $.word,
        $.binexp,
        $.callexp,
        $.funcdef,
        $.lambda,
        $.vardef,
        $.parexp,
      ),

    // Literals / identifiers.
    num: (_) => /\d+/,
    word: (_) => /[a-zA-Z_]\w*/,

    // Binary expressions with precedence and left associativity.
    binexp: ($) =>
      choice(
        prec.left(
          PREC.add,
          seq(
            field("left", $._exp),
            field("op", choice("+", "-")),
            field("right", $._exp),
          ),
        ),
        prec.left(
          PREC.mul,
          seq(
            field("left", $._exp),
            field("op", choice("*", "/")),
            field("right", $._exp),
          ),
        ),
      ),

    // Function call: prefer this over plain `word` via precedence.
    callexp: ($) =>
      prec(
        PREC.call,
        seq(field("fn", $.word), "(", optional(commaSep($._exp)), ")"),
      ),

    // Convenient function definition (sugar): `f(x, y, ...) body`.
    // Give it higher precedence than calls to resolve the shared prefix.
    funcdef: ($) =>
      prec(
        PREC.funcdef,
        seq(
          field("name", $.word),
          field("params", $.params),
          field("body", $._exp),
        ),
      ),

    // Lambda: `\(x, y, ...) body`.
    lambda: ($) =>
      prec(
        PREC.lambda,
        seq("\\", field("params", $.params), field("body", $._exp)),
      ),

    // Variable definition / assignment: `x = expr`.
    // Lowest precedence, right-associative: `a = b = c` → `a = (b = c)`.
    vardef: ($) =>
      prec.right(
        PREC.assign,
        seq(field("name", $.word), "=", field("value", $._exp)),
      ),

    // Parameter list node used by funcdef and lambda.
    params: ($) => seq("(", optional(commaSep($.word)), ")"),

    // Parenthesized expression.
    parexp: ($) => seq("(", $._exp, ")"),
  },
});

function commaSep(rule) {
  return seq(rule, repeat(seq(",", rule)));
}