Refactor implementation to address review comments and API design suggestions from Luke.

pkg/fletchc/lib/compiler.dart

+// Copyright (c) 2015, the Fletch 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.md file.
+
+library fletchc.compiler;
+
+import 'dart:io' show
+    File,
+    Platform;
+
+import 'package:compiler/compiler.dart' show
+    CompilerInputProvider,
+    CompilerOutputProvider,
+    DiagnosticHandler;
+
+import 'package:dart2js_incremental/compiler.dart' show
+    OutputProvider;
+
+import 'package:compiler/src/source_file_provider.dart' show
+    CompilerSourceFileProvider,
+    FormattingDiagnosticHandler,
+    SourceFileProvider;
+
+import 'package:compiler/src/filenames.dart' show
+    appendSlash;
+
+import 'package:compiler/src/apiimpl.dart' as apiimpl;
+
+import 'src/fletch_compiler.dart' as implementation;
+
+class FletchCompiler {
+  final implementation.FletchCompiler _compiler;
+
+  FletchCompiler._(this._compiler);
+
+  factory FletchCompiler(
+      {CompilerInputProvider provider,
+       CompilerOutputProvider outputProvider,
+       DiagnosticHandler handler,
+       /* String or Uri */ libraryRoot,
+       /* String or Uri */ packageRoot,
+       List<String> options,
+       Map<String, dynamic> environment}) {
+    if (options == null) {
+      options = <String>[];
+    }
+
+    final bool isVerbose = apiimpl.Compiler.hasOption(options, '--verbose');
+
+    if (provider == null) {
+      provider = new CompilerSourceFileProvider();
+    }
+
+    if (handler == null) {
+      SourceFileProvider sourceFileProvider = null;
+      if (provider is SourceFileProvider) {
+        sourceFileProvider = provider;
+      }
+      handler = new FormattingDiagnosticHandler(provider)
+          ..throwOnError = false
+          ..verbose = isVerbose;
+    }
+
+    if (outputProvider == null) {
+      outputProvider = new OutputProvider();
+    }
+
+    if (libraryRoot == null) {
+      libraryRoot = _guessLibraryRoot();
+      if (libraryRoot == null) {
+        throw new StateError("Unable to guess libraryRoot.");
+      }
+    }
+
+    if (packageRoot == null) {
+      packageRoot = Uri.base.resolve('packages/');
+    }
+
+
+    if (environment == null) {
+      environment = <String, dynamic>{};
+    }
+
+    implementation.FletchCompiler compiler = new implementation.FletchCompiler(
+        provider,
+        outputProvider,
+        handler,
+        libraryRoot,
+        packageRoot,
+        options,
+        environment);
+
+    compiler.log("Using library root: $libraryRoot");
+    compiler.log("Using package root: $packageRoot");
+
+    return new FletchCompiler._(compiler);
+  }
+
+  void run(Uri script) {
+    _compiler.run(script);
+  }
+
+  static Uri _guessLibraryRoot() {
+    Uri guess = new Uri.file(Platform.executable).resolve('../');
+    if (_looksLikeLibraryRoot(guess)) {
+      return _resolveSymbolicLinks(guess);
+    }
+    guess = guess.resolve('../sdk/');
+    if (_looksLikeLibraryRoot(guess)) {
+      return _resolveSymbolicLinks(guess);
+    }
+    return null;
+  }
+}
+
+/// Resolves any symbolic links in [uri] if its scheme is "file". Otherwise
+/// return the given [uri].
+Uri _resolveSymbolicLinks(Uri uri) {
+  if (uri.scheme != 'file') return uri;
+  File apparentLocation = new File.fromUri(uri);
+  String realLocation = apparentLocation.resolveSymbolicLinksSync();
+  if (uri.path.endsWith("/")) {
+    realLocation = appendSlash(realLocation);
+  }
+  return new Uri.file(realLocation);
+}
+
+bool _looksLikeLibraryRoot(Uri uri) {
+  String expectedFile = 'lib/_internal/libraries.dart';
+  return new File.fromUri(uri.resolve(expectedFile)).existsSync();
+}