// Copyright (c) 2017, 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 'dart:async';

import 'package:front_end/src/base/processed_options.dart';
import 'package:front_end/src/incremental_kernel_generator_impl.dart';
import 'package:kernel/kernel.dart';

import 'compiler_options.dart';

/// Represents the difference between "old" and "new" states of a program.
///
/// Not intended to be implemented or extended by clients.
class DeltaProgram {
  /// The new state of the program.
  ///
  /// It includes full kernels for changed libraries and for libraries that
  /// are affected by the transitive change of API in the changed libraries.
  ///
  /// For VM reload purposes we need to provide also full kernels for the
  /// libraries that are transitively imported by the entry point and
  /// transitively import a changed library.
  ///
  /// Also includes external references to other libraries that were not
  /// modified or affected.
  final Program newProgram;

  DeltaProgram(this.newProgram);

  /// TODO(paulberry): add information about libraries that were removed.
}

/// Interface for generating an initial kernel representation of a program and
/// keeping it up to date as incremental changes are made.
///
/// This class maintains an internal "previous program state"; each
/// time [computeDelta] is called, it updates the previous program state and
/// produces a representation of what has changed.  When there are few changes,
/// a call to [computeDelta] should be much faster than compiling the whole
/// program from scratch.
///
/// This class also maintains a set of "valid sources", which is a (possibly
/// empty) subset of the sources constituting the previous program state.  Files
/// in this set are assumed to be unchanged since the last call to
/// [computeDelta].
///
/// Behavior is undefined if the client does not obey the following concurrency
/// restrictions:
/// - no two invocations of [computeDelta] may be outstanding at any given time.
/// - neither [invalidate] nor [invalidateAll] may be called while an invocation
///   of [computeDelta] is outstanding.
///
/// Not intended to be implemented or extended by clients.
abstract class IncrementalKernelGenerator {
  /// Generates a kernel representation of the changes to the program, assuming
  /// that all valid sources are unchanged since the last call to
  /// [computeDelta].
  ///
  /// Source files in the set of valid sources are guaranteed not to be re-read
  /// from disk; they are assumed to be unchanged regardless of the state of the
  /// filesystem.
  ///
  /// If [watch] is not `null`, then when a source file is first used
  /// by [computeDelta], [watch] is called with the Uri of that source
  /// file and `used` == `true` indicating that the source file is being
  /// used when compiling the program. The content of the file is not read
  /// until the Future returned by [watch] completes. If during a subsequent
  /// call to [computeDelta], a source file that was being used is no longer
  /// used, then [watch] is called with the Uri of that source file and
  /// `used` == `false` indicating that the source file is no longer needed.
  /// Multiple invocations of [watch] may be running concurrently.
  ///
  /// If the future completes successfully, the previous file state is updated
  /// and the set of valid sources is set to the set of all sources in the
  /// program.
  ///
  /// If the future completes with an error (due to errors in the compiled
  /// source code), the caller may consider the previous file state and the set
  /// of valid sources to be unchanged; this means that once the user fixes the
  /// errors, it is safe to call [computeDelta] again.
  Future<DeltaProgram> computeDelta({Future<Null> watch(Uri uri, bool used)});

  /// Remove the file associated with the given file [uri] from the set of
  /// valid files.  This guarantees that those files will be re-read on the
  /// next call to [computeDelta]).
  void invalidate(Uri uri);

  /// Remove all source files from the set of valid sources.  This guarantees
  /// that all files will be re-read on the next call to [computeDelta].
  ///
  /// Note that this does not erase the previous program state; the next time
  /// [computeDelta] is called, if parts of the program are discovered to be
  /// unchanged, parts of the previous program state will still be re-used to
  /// speed up compilation.
  void invalidateAll();

  /// Creates an [IncrementalKernelGenerator] which is prepared to generate
  /// kernel representations of the program whose main library is in the given
  /// [entryPoint].
  ///
  /// The initial "previous program state" is an empty program containing no
  /// code, and the initial set of valid sources is empty.  To obtain a kernel
  /// representation of the program, call [computeDelta].
  static Future<IncrementalKernelGenerator> newInstance(
      CompilerOptions options, Uri entryPoint) async {
    var processedOptions = new ProcessedOptions(options);
    var uriTranslator = await processedOptions.getUriTranslator();
    return new IncrementalKernelGeneratorImpl(
        processedOptions, uriTranslator, entryPoint);
  }
}