dart-sass/lib/src/callable/built_in.dart

// Copyright 2016 Google Inc. Use of this source code is governed by an
// MIT-style license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

import 'package:tuple/tuple.dart';

import '../ast/sass.dart';
import '../callable.dart';
import '../value.dart';
import 'async_built_in.dart';

typedef Value _Callback(List<Value> arguments);

/// A callable defined in Dart code.
///
/// Unlike user-defined callables, built-in callables support overloads. They
/// may declare multiple different callbacks with multiple different sets of
/// arguments. When the callable is invoked, the first callback with matching
/// arguments is invoked.
class BuiltInCallable implements Callable, AsyncBuiltInCallable {
  final String name;

  /// The overloads declared for this callable.
  final _overloads = <Tuple2<ArgumentDeclaration, _Callback>>[];

  /// Creates a callable with a single [arguments] declaration and a single
  /// [callback].
  ///
  /// The argument declaration is parsed from [arguments], which should not
  /// include parentheses. Throws a [SassFormatException] if parsing fails.
  BuiltInCallable(
      this.name, String arguments, Value callback(List<Value> arguments)) {
    _overloads
        .add(new Tuple2(new ArgumentDeclaration.parse(arguments), callback));
  }

  /// Creates a callable with multiple implementations.
  ///
  /// Each key/value pair in [overloads] defines the argument declaration for
  /// the overload (which should not include parentheses), and the callback to
  /// execute if that argument declaration matches. Throws a
  /// [SassFormatException] if parsing fails.
  BuiltInCallable.overloaded(this.name, Map<String, _Callback> overloads) {
    overloads.forEach((arguments, callback) {
      _overloads
          .add(new Tuple2(new ArgumentDeclaration.parse(arguments), callback));
    });
  }

  /// Returns the argument declaration and Dart callback for the given
  /// positional and named arguments.
  ///
  /// Note that this doesn't guarantee that [positional] and [names] are valid
  /// for the returned [ArgumentDeclaration].
  Tuple2<ArgumentDeclaration, _Callback> callbackFor(
          int positional, Set<String> names) =>
      _overloads.take(_overloads.length - 1).firstWhere(
          (overload) => overload.item1.matches(positional, names),
          orElse: () => _overloads.last);
}