// Copyright (c) 2015, 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:analysis_server/src/provisional/completion/dart/completion_dart.dart';
import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart';

/// A completion contributor used to suggest replacing partial identifiers
/// inside a class declaration with templates for inherited members.
class OverrideContributor implements DartCompletionContributor {
  @override
  Future<void> computeSuggestions(
      DartCompletionRequest request, SuggestionBuilder builder) async {
    var targetId = _getTargetId(request.target);
    if (targetId == null) {
      return;
    }
    var classDecl = targetId.thisOrAncestorOfType<ClassOrMixinDeclaration>();
    if (classDecl == null) {
      return;
    }

    var inheritance = InheritanceManager3();

    // Generate a collection of inherited members
    var classElem = classDecl.declaredElement;
    if (classElem == null) {
      return;
    }
    var interface = inheritance.getInterface(classElem);
    var interfaceMap = interface.map;
    var namesToOverride =
        _namesToOverride(classElem.librarySource.uri, interface);

    // Build suggestions
    for (var name in namesToOverride) {
      var element = interfaceMap[name];
      // Gracefully degrade if the overridden element has not been resolved.
      if (element != null) {
        var invokeSuper = interface.isSuperImplemented(name);
        await builder.suggestOverride(targetId, element, invokeSuper);
      }
    }
  }

  /// If the target looks like a partial identifier inside a class declaration
  /// then return that identifier, otherwise return `null`.
  SimpleIdentifier? _getTargetId(CompletionTarget target) {
    var node = target.containingNode;
    if (node is ClassOrMixinDeclaration) {
      var entity = target.entity;
      if (entity is FieldDeclaration) {
        return _getTargetIdFromVarList(entity.fields);
      }
    } else if (node is FieldDeclaration) {
      var entity = target.entity;
      if (entity is VariableDeclarationList) {
        return _getTargetIdFromVarList(entity);
      }
    }
    return null;
  }

  SimpleIdentifier? _getTargetIdFromVarList(VariableDeclarationList fields) {
    var variables = fields.variables;
    if (variables.length == 1) {
      var variable = variables[0];
      var targetId = variable.name;
      if (targetId.name.isEmpty) {
        // analyzer parser
        // Actual: class C { foo^ }
        // Parsed: class C { foo^ _s_ }
        //   where _s_ is a synthetic id inserted by the analyzer parser
        return targetId;
      } else if (fields.keyword == null &&
          fields.type == null &&
          variable.initializer == null) {
        // fasta parser does not insert a synthetic identifier
        return targetId;
      }
    }
    return null;
  }

  /// Return the list of names that belong to the [interface] of a class, but
  /// are not yet declared in the class.
  List<Name> _namesToOverride(Uri libraryUri, Interface interface) {
    var namesToOverride = <Name>[];
    for (var name in interface.map.keys) {
      if (name.isAccessibleFor(libraryUri)) {
        if (!interface.declared.containsKey(name)) {
          namesToOverride.add(name);
        }
      }
    }
    return namesToOverride;
  }
}