const PREC = {
  range: 15,
  call: 14,
  field: 13,
  unary: 12,
  cast: 11,
  multiplicative: 10,
  additive: 9,
  shift: 8,
  bitand: 7,
  bitxor: 6,
  bitor: 5,
  comparative: 4,
  and: 3,
  or: 2,
  assign: 0,
  closure: -1,
};

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

  externals: ($) => [
    $._string_content,
    $.raw_string_literal,
    $.float_literal,
    $.block_comment,
  ],

  extras: (_) => [/\s/],

  word: ($) => $.identifier,

  inline: ($) => [$._declaration_statement],

  supertypes: ($) => [
    $._expression,
    $._literal,
    $._literal_pattern,
    $._declaration_statement,
    $._pattern,
  ],

  rules: {
    source_file: ($) => repeat($._statement),

    // statements

    _statement: ($) => choice($.expression_statement, $._declaration_statement),

    expression_statement: ($) => choice(seq($._expression, ";")),

    _declaration_statement: ($) => choice($.let_declaration),

    let_declaration: ($) =>
      seq(
        "let",
        field("pattern", $._pattern),
        optional(seq("=", field("value", $._expression))),
        ";"
      ),

    // patterns

    _pattern: ($) => choice($._literal_pattern, $.identifier, "_"),

    // expressions

    _expression: ($) =>
      choice($.assignment_expression, $._literal, prec.left($.identifier)),

    assignment_expression: ($) =>
      prec.left(
        PREC.assign,
        seq(field("left", $._expression), "=", field("right", $._expression))
      ),

    // literals
    _literal: ($) =>
      choice($.string_literal, $.raw_string_literal, $.integer_literal),

    _literal_pattern: ($) =>
      choice($.string_literal, $.raw_string_literal, $.integer_literal),

    integer_literal: (_) => token(seq(choice(/[0-9][0-9_]*/))),

    string_literal: ($) => seq(
      alias(/b?"/, '"'),
      repeat(choice($.escape_sequence, $._string_content)),
      token.immediate('"')
    ),

    escape_sequence: (_) =>
      token.immediate(
        seq(
          "\\",
          choice(
            /[^xu]/,
            /u[0-9a-fA-F]{4}/,
            /u{[0-9a-fA-F]+}/,
            /x[0-9a-fA-F]{2}/
          )
        )
      ),

    // identifiers

    identifier: ($) => /(r#)?[_\p{XID_Start}][_\p{XID_Continue}]*/,
  },
});