incremental progress aligning code completion api to spec

pkg/analysis_services/lib/completion/completion_computer.dart

 // Copyright (c) 2014, 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.
 
 library services.completion.computer;
 
 import 'dart:async';
 
 import 'package:analysis_services/completion/completion_suggestion.dart';
+import 'package:analysis_services/search/search_engine.dart';
 import 'package:analysis_services/src/completion/top_level_computer.dart';
-import 'package:analysis_services/search/search_engine.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/source.dart';
 
 /**
  * The base class for computing code completion suggestions.
  */
 abstract class CompletionComputer {
 
   /**
-   * Create a collection of code completion computers for the given situation.
-   */
-  static Future<List<CompletionComputer>> create(SearchEngine searchEngine) {
-    List<CompletionComputer> computers = [];
-    computers.add(new TopLevelComputer(searchEngine));
-    return new Future.value(computers);
-  }
-
-  /**
    * Computes [CompletionSuggestion]s for the specified position in the source.
    */
   Future<List<CompletionSuggestion>> compute();
 }
+
+/**
+ * Manages `CompletionComputer`s for a given completion request.
+ */
+abstract class CompletionManager {
+
+  /**
+   * The length of the text to be replaced if the remainder of the identifier
+   * containing the cursor is to be replaced when the suggestion is applied
+   * (that is, the number of characters in the existing identifier).
+   */
+  int get replacementLength;
+
+  /**
+   * The offset of the start of the text to be replaced. This will be different
+   * than the offset used to request the completion suggestions if there was a
+   * portion of an identifier before the original offset. In particular, the
+   * replacementOffset will be the offset of the beginning of said identifier.
+   */
+  int get replacementOffset;
+
+  /**
+   * Generate code completion computers for the given situation.
+   */
+  Future<List<CompletionComputer>> generate();
+
+  /**
+   * Create a manager for the given request.
+   */
+  static CompletionManager create(Source source, int offset,
+      SearchEngine searchEngine) {
+    if (AnalysisEngine.isDartFileName(source.shortName)) {
+      return new DartCompletionManager(source, offset, searchEngine);
+    }
+    return new NoOpCompletionManager(source, offset);
+  }
+}
+
+/**
+ * Manages code completion for a given Dart file completion request.
+ */
+class DartCompletionManager extends CompletionManager {
+  final Source source;
+  final int offset;
+  final SearchEngine searchEngine;
+
+  DartCompletionManager(this.source, this.offset, this.searchEngine);
+
+  @override
+  int get replacementLength => 0;
+
+  @override
+  int get replacementOffset => offset;
+
+  @override
+  Future<List<CompletionComputer>> generate() {
+    List<CompletionComputer> computers = [];
+    computers.add(new TopLevelComputer(searchEngine));
+    return new Future.value(computers);
+  }
+}
+
+class NoOpCompletionComputer extends CompletionComputer {
+  @override
+  Future<List<CompletionSuggestion>> compute() {
+    return new Future.value([]);
+  }
+}
+
+class NoOpCompletionManager extends CompletionManager {
+  final Source source;
+  final int offset;
+
+  NoOpCompletionManager(this.source, this.offset);
+
+  @override
+  int get replacementLength => 0;
+
+  @override
+  int get replacementOffset => offset;
+
+  @override
+  Future<List<CompletionComputer>> generate() {
+    return new Future.value([new NoOpCompletionComputer()]);
+  }
+}