// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:analyzer/dart/analysis/results.dart';
import 'package:analyzer/dart/analysis/session.dart';
import 'package:analyzer/dart/element/element2.dart';
import 'package:collection/collection.dart';

/// Represents the location of an [Element2] that exists in a chain of elements
/// from a [LibraryElement2].
///
/// Elements with [Fragment]s or Elements with `null` names anywhere in the
/// chain are not representable.
class ElementLocation2 {
  /// The library that this element belongs to.
  final String _libraryUri;

  /// The [Element2.lookupName] for this element, or the containing element if
  /// this location is a [_MemberElementLocation2].
  final String _topLevelName;

  factory ElementLocation2.decode(String encoded) {
    var components = encoded.split(';');
    return switch (components) {
      [String library, String topName] => ElementLocation2._(library, topName),
      [String library, String topName, String memberName] =>
        _MemberElementLocation2._(library, topName, memberName),
      _ =>
        throw ArgumentError.value(
          encoded,
          'encoded',
          "Encoded string should be in the format 'libraryUri;topLevelName[;memberName]'",
        ),
    };
  }

  ElementLocation2._(this._libraryUri, this._topLevelName);

  String get encoding => '$_libraryUri;$_topLevelName';

  /// Locates the [Element2] represented by this [ElementLocation2] in
  /// [session].
  ///
  /// Returns `null` if the [Element2] cannot be located.
  Future<Element2?> locateIn(AnalysisSession session) async {
    var result = await session.getLibraryByUri(_libraryUri);
    if (result is! LibraryElementResult) return null;

    return result.element2.children2.firstWhereOrNull(
      (child) => child.lookupName == _topLevelName,
    );
  }

  /// Gets an [ElementLocation2] for this element.
  ///
  /// Returns `null` if this element is neither a top level element or a
  /// member of a top level element, or if either do not have a `lookupName`.
  static ElementLocation2? forElement(Element2 element) {
    var library = element.library2;
    if (library == null) return null;
    var libraryUri = library.uri.toString();

    if (element.enclosingElement2 == library) {
      var topName = element.lookupName;

      return topName != null ? ElementLocation2._(libraryUri, topName) : null;
    } else if (element.enclosingElement2?.enclosingElement2 == library) {
      var memberName = element.lookupName;
      var topName = element.enclosingElement2?.lookupName;

      return topName != null && memberName != null
          ? _MemberElementLocation2._(libraryUri, topName, memberName)
          : null;
    } else {
      return null;
    }
  }
}

class _MemberElementLocation2 extends ElementLocation2 {
  /// The [Element2.lookupName] for this member within [_topLevelName].
  final String _memberName;

  _MemberElementLocation2._(
    super.libraryUri,
    super.topLevelName,
    this._memberName,
  ) : super._();

  @override
  String get encoding => '${super.encoding};$_memberName';

  /// Locates the [Element2] represented by this [_MemberElementLocation2] in
  /// [session].
  ///
  /// Returns `null` if the [Element2] cannot be located.
  @override
  Future<Element2?> locateIn(AnalysisSession session) async {
    var topLevel = await super.locateIn(session);

    return topLevel?.children2.firstWhereOrNull(
      (child) => child.lookupName == _memberName,
    );
  }
}