// Copyright (c) 2018, 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/protocol/protocol_generated.dart'
    show AnalysisGetSignatureResult;
import 'package:analysis_server/src/computer/computer_hover.dart';
import 'package:analysis_server/src/protocol_server.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/src/dart/ast/element_locator.dart';
import 'package:analyzer/src/dart/ast/utilities.dart';

/**
 * A computer for the signature at the specified offset of a Dart [CompilationUnit].
 */
class DartUnitSignatureComputer {
  final AstNode _node;
  DartUnitSignatureComputer(CompilationUnit _unit, int _offset)
      : _node = new NodeLocator(_offset).searchWithin(_unit);

  bool get offsetIsValid => _node != null;

  /**
   * Returns the computed signature information, maybe `null`.
   */
  AnalysisGetSignatureResult compute() {
    if (_node == null) {
      return null;
    }

    // Find the closest argument list.
    var argsNode = _node;
    while (argsNode != null && !(argsNode is ArgumentList)) {
      // Certain nodes don't make sense to search above for an argument list
      // (for example when inside a function epxression).
      if (argsNode is FunctionExpression) {
        return null;
      }
      argsNode = argsNode.parent;
    }

    if (argsNode == null) {
      return null;
    }

    final args = argsNode;
    String name;
    ExecutableElement execElement;
    if (args.parent is MethodInvocation) {
      MethodInvocation method = args.parent;
      name = method.methodName.name;
      execElement = ElementLocator.locate(method) as ExecutableElement;
    } else if (args.parent is InstanceCreationExpression) {
      InstanceCreationExpression constructor = args.parent;
      name = constructor.constructorName.type.name.name;
      if (constructor.constructorName.name != null) {
        name += ".${constructor.constructorName.name.name}";
      }
      execElement = ElementLocator.locate(constructor) as ExecutableElement;
    }

    if (execElement == null) {
      return null;
    }

    final parameters =
        execElement.parameters.map((p) => _convertParam(p)).toList();

    return new AnalysisGetSignatureResult(name, parameters,
        dartdoc: DartUnitHoverComputer.computeDocumentation(execElement));
  }

  ParameterInfo _convertParam(ParameterElement param) {
    return new ParameterInfo(
        param.isOptionalPositional
            ? ParameterKind.OPTIONAL
            : param.isPositional ? ParameterKind.REQUIRED : ParameterKind.NAMED,
        param.displayName,
        param.type.displayName,
        defaultValue: param.defaultValueCode);
  }
}