// Copyright 2014 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.devtools.build.lib.rules.cpp;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.actions.ActionExecutionContext;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.EnvironmentalExecException;
import com.google.devtools.build.lib.actions.ExecException;
import com.google.devtools.build.lib.actions.UserExecException;
import com.google.devtools.build.lib.profiler.Profiler;
import com.google.devtools.build.lib.profiler.ProfilerTask;
import com.google.devtools.build.lib.vfs.FileSystemUtils;
import com.google.devtools.build.lib.vfs.PathFragment;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * Scans source files to determine the bounding set of transitively referenced include files.
 *
 * <p>Note that include scanning is performance-critical code.
 */
public interface IncludeScanner {
  /**
   * Processes source files and a list of includes extracted from command line flags. Adds all found
   * files to the provided set {@code includes}.
   *
   * <p>The resulting set will include {@code mainSource} and {@code sources}. This has no real
   * impact in the case that we are scanning a single source file, since it is already known to be
   * an input. However, this is necessary when we have more than one source to scan from, for
   * example when building C++ modules. In that case we have one of two possibilities:
   * <ol>
   * <li>We compile a header module - there, the .cppmap file is the main source file (which we do
   *     not include-scan, as that would require an extra parser), and thus already in the input;
   *     all headers in the .cppmap file are our entry points for include scanning, but are not yet
   *     in the inputs - they get added here.</li>
   * <li>We compile an object file that uses a header module; currently using a header module
   *     requires all headers it can reference to be available for the compilation. The header
   *     module can reference headers that are not in the transitive include closure of the current
   *     translation unit. Therefore, {@link CppCompileAction} adds all headers specified
   *     transitively for compiled header modules as include scanning entry points, and we need to
   *     add the entry points to the inputs here.</li></ol>
   * </p>
   * 
   * <p>{@code mainSource} is the source file relative to which the {@code cmdlineIncludes} are
   * interpreted.</p>
   */
  void process(Artifact mainSource, Collection<Artifact> sources,
      Map<Artifact, Artifact> legalOutputPaths, List<PathFragment> includeDirs,
      List<PathFragment> quoteIncludeDirs, List<String> cmdlineIncludes,
      Set<Artifact> includes, ActionExecutionContext actionExecutionContext)
      throws IOException, ExecException, InterruptedException;

  /** Supplies IncludeScanners upon request. */
  interface IncludeScannerSupplier {
    /**
     * Returns the possibly shared scanner to be used for a given pair of include paths. The paths
     * are specified as PathFragments relative to the execution root.
     */
    IncludeScanner scannerFor(List<PathFragment> quoteIncludePaths,
        List<PathFragment> includePaths);
  }

  /**
   * Helper class that exists just to provide a static method that prepares the arguments with which
   * to call an IncludeScanner.
   */
  class IncludeScanningPreparer {
    private IncludeScanningPreparer() {}

    /**
     * Returns the files transitively included by the source files of the given IncludeScannable.
     *
     * @param action IncludeScannable whose sources' transitive includes will be returned.
     * @param includeScannerSupplier supplies IncludeScanners to actually do the transitive
     *                               scanning (and caching results) for a given source file.
     * @param actionExecutionContext the context for {@code action}.
     * @param profilerTaskName what the {@link Profiler} should record this call for.
     */
    public static Collection<Artifact> scanForIncludedInputs(IncludeScannable action,
        IncludeScannerSupplier includeScannerSupplier,
        ActionExecutionContext actionExecutionContext,
        String profilerTaskName)
        throws ExecException, InterruptedException {

      Set<Artifact> includes = Sets.newConcurrentHashSet();

      final List<PathFragment> absoluteBuiltInIncludeDirs = new ArrayList<>();
      includes.addAll(action.getBuiltInIncludeFiles());

      Profiler profiler = Profiler.instance();
      try {
        profiler.startTask(ProfilerTask.SCANNER, profilerTaskName);

        // We need to scan the action itself, but also the auxiliary scannables
        // (for LIPO). There is no need to call getAuxiliaryScannables
        // recursively.
        for (IncludeScannable scannable :
          Iterables.concat(ImmutableList.of(action), action.getAuxiliaryScannables())) {

          Map<Artifact, Artifact> legalOutputPaths = scannable.getLegalGeneratedScannerFileMap();
          // Deduplicate include directories. This can occur especially with "built-in" and "system"
          // include directories because of the way we retrieve them. Duplicate include directories
          // really mess up #include_next directives.
          Set<PathFragment> includeDirs = new LinkedHashSet<>(scannable.getIncludeDirs());
          List<PathFragment> quoteIncludeDirs = scannable.getQuoteIncludeDirs();
          List<String> cmdlineIncludes = scannable.getCmdlineIncludes();

          includeDirs.addAll(scannable.getSystemIncludeDirs());

          // Add the system include paths to the list of include paths.
          for (PathFragment pathFragment : action.getBuiltInIncludeDirectories()) {
            if (pathFragment.isAbsolute()) {
              absoluteBuiltInIncludeDirs.add(pathFragment);
            }
            includeDirs.add(pathFragment);
          }

          List<PathFragment> includeDirList = ImmutableList.copyOf(includeDirs);
          IncludeScanner scanner = includeScannerSupplier.scannerFor(quoteIncludeDirs,
              includeDirList);

          Artifact mainSource =  scannable.getMainIncludeScannerSource();
          Collection<Artifact> sources = scannable.getIncludeScannerSources();
          scanner.process(mainSource, sources, legalOutputPaths, quoteIncludeDirs,
              includeDirList, cmdlineIncludes, includes, actionExecutionContext);
        }
      } catch (IOException e) {
        throw new EnvironmentalExecException(e.getMessage());
      } finally {
        profiler.completeTask(ProfilerTask.SCANNER);
      }

      // Collect inputs and output
      List<Artifact> inputs = new ArrayList<>();
      for (Artifact included : includes) {
        if (FileSystemUtils.startsWithAny(included.getPath().asFragment(),
            absoluteBuiltInIncludeDirs)) {
          // Skip include files found in absolute include directories.
          continue;
        }
        if (included.getRoot().getPath().getParentDirectory() == null) {
          throw new UserExecException(
              "illegal absolute path to include file: " + included.getPath());
        }
        inputs.add(included);
      }
      return inputs;
    }
  }
}