Add a simple identifier Scope class and a test. (#9)

* Add a simple identifier Scope class and a test.

* Address comments.

Author: matanlurey

lib/code_builder.dart

@@ -46,6 +46,7 @@ part 'src/builders/statement_builder.dart';
 part 'src/builders/type_builder.dart';
 
 part 'src/pretty_printer.dart';
+part 'src/scope.dart';
 
 /// Base class for building and emitting a Dart language [AstNode].
 abstract class CodeBuilder<A extends AstNode> {

lib/src/scope.dart

@@ -0,0 +1,65 @@
+part of code_builder;
+
+/// Determines an [Identifier] deppending on where it appears.
+///
+/// __Example use__:
+///     void useContext(Scope scope) {
+///       // Prints Identifier "i1.Foo"
+///       print(scope.getIdentifier('Foo', 'package:foo/foo.dart');
+///
+///       // Prints Identifier "i1.Bar"
+///       print(scope.getIdentifier('Bar', 'package:foo/foo.dart');
+///
+///       // Prints Identifier "i2.Baz"
+///       print(scope.getIdentifier('Baz', 'package:bar/bar.dart');
+///     }
+abstract class Scope {
+  /// Create a default scope context.
+  ///
+  /// Actual implementation is _not_ guaranteed, only that all import prefixes
+  /// will be unique in a given scope (actual implementation may be naive).
+  factory Scope() = _IncrementingScope;
+
+  /// Create a context that does _not_ apply any scoping.
+  factory Scope.identity() = _IdentityScope;
+
+  /// Given a [symbol] and its known [importUri], return an [Identifier].
+  Identifier getIdentifier(String symbol, String importUri);
+
+  /// Returns a list of all imports needed to resolve identifiers.
+  Iterable<ImportBuilder> getImports();
+}
+
+class _IdentityScope implements Scope {
+  final Set<String> _imports = new Set<String>();
+
+  @override
+  Identifier getIdentifier(String symbol, String import) {
+    _imports.add(import);
+    return _stringId(symbol);
+  }
+
+  @override
+  Iterable<ImportBuilder> getImports() {
+    return _imports.map/*<ImportBuilder*/((i) => new ImportBuilder(i));
+  }
+}
+
+class _IncrementingScope implements Scope {
+  final Map<String, int> _imports = <String, int>{};
+
+  int _counter = 0;
+
+  @override
+  Identifier getIdentifier(String symbol, String import) {
+    var newId = _imports.putIfAbsent(import, () => ++_counter);
+    return new PrefixedIdentifier(_stringId('_i$newId'),
+        new Token(TokenType.PERIOD, 0), _stringId(symbol));
+  }
+
+  @override
+  Iterable<ImportBuilder> getImports() {
+    return _imports.keys.map/*<ImportBuilder*/(
+        (i) => new ImportBuilder(i, as: '_i${_imports[i]}'));
+  }
+}

test/scope_test.dart

@@ -0,0 +1,55 @@
+import 'package:analyzer/analyzer.dart';
+import 'package:code_builder/code_builder.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Identity scope', () {
+    Scope scope;
+
+    setUp(() => scope = new Scope.identity());
+
+    test('should just output non-prefixed and de-duplicate imports', () {
+      var identifiers = <Identifier> [
+        scope.getIdentifier('Foo', 'package:foo/foo.dart'),
+        scope.getIdentifier('Bar', 'package:foo/foo.dart'),
+        scope.getIdentifier('Baz', 'package:baz/baz.dart'),
+      ].map/*<String>*/((i) => i.toSource());
+
+      expect(identifiers, [
+        'Foo',
+        'Bar',
+        'Baz',
+      ],);
+
+      expect(scope.getImports().map/*<String>*/((i) => i.toAst().toSource()), [
+        r"import 'package:foo/foo.dart';",
+        r"import 'package:baz/baz.dart';",
+      ],);
+    });
+  });
+
+  group('Incrementing scope', () {
+    Scope scope;
+
+    setUp(() => scope = new Scope());
+
+    test('should out prefixed with a counter', () {
+      var identifiers = <Identifier> [
+        scope.getIdentifier('Foo', 'package:foo/foo.dart'),
+        scope.getIdentifier('Bar', 'package:foo/foo.dart'),
+        scope.getIdentifier('Baz', 'package:baz/baz.dart'),
+      ].map/*<String>*/((i) => i.toSource());
+
+      expect(identifiers, [
+        '_i1.Foo',
+        '_i1.Bar',
+        '_i2.Baz',
+      ],);
+
+      expect(scope.getImports().map/*<String>*/((i) => i.toAst().toSource()), [
+        r"import 'package:foo/foo.dart' as _i1;",
+        r"import 'package:baz/baz.dart' as _i2;",
+      ],);
+    });
+  });
+}