// 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.exec;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import com.google.devtools.build.lib.actions.AbstractAction;
import com.google.devtools.build.lib.actions.ActionExecutionContext;
import com.google.devtools.build.lib.actions.BaseSpawn;
import com.google.devtools.build.lib.actions.ExecException;
import com.google.devtools.build.lib.actions.ResourceManager;
import com.google.devtools.build.lib.actions.ResourceManager.ResourceHandle;
import com.google.devtools.build.lib.actions.ResourceSet;
import com.google.devtools.build.lib.analysis.config.BinTools;
import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
import com.google.devtools.build.lib.shell.CommandException;
import com.google.devtools.build.lib.util.CommandBuilder;
import com.google.devtools.build.lib.util.OS;
import com.google.devtools.build.lib.util.OsUtils;
import com.google.devtools.build.lib.vfs.FileSystem;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.UnixFileSystem;
import com.google.devtools.build.lib.vfs.UnixFileSystem.SymlinkStrategy;

import java.util.List;

/**
 * Helper class responsible for the symlink tree creation.
 * Used to generate runfiles and fileset symlink farms.
 */
public final class SymlinkTreeHelper {

  private static final String BUILD_RUNFILES = "build-runfiles" + OsUtils.executableExtension();

  /**
   * These actions run faster overall when serialized, because most of their
   * cost is in the ext2 block allocator, and there's less seeking required if
   * their directory creations get non-interleaved allocations. So we give them
   * a huge resource cost.
   */
  public static final ResourceSet RESOURCE_SET = ResourceSet.createWithRamCpuIo(1000, 0.5, 0.75);

  private final PathFragment inputManifest;
  private final PathFragment symlinkTreeRoot;
  private final boolean filesetTree;

  /**
   * Creates SymlinkTreeHelper instance. Can be used independently of
   * SymlinkTreeAction.
   *
   * @param inputManifest exec path to the input runfiles manifest
   * @param symlinkTreeRoot exec path to the symlink tree location
   * @param filesetTree true if this is fileset symlink tree,
   *                    false if this is a runfiles symlink tree.
   */
  public SymlinkTreeHelper(PathFragment inputManifest, PathFragment symlinkTreeRoot,
      boolean filesetTree) {
    this.inputManifest = inputManifest;
    this.symlinkTreeRoot = symlinkTreeRoot;
    this.filesetTree = filesetTree;
  }

  public PathFragment getSymlinkTreeRoot() { return symlinkTreeRoot; }

  /**
   * Creates a symlink tree using a CommandBuilder. This means that the symlink
   * tree will always be present on the developer's workstation. Useful when
   * running commands locally.
   *
   * Warning: this method REALLY executes the command on the box Blaze was
   * run on, without any kind of synchronization, locking, or anything else.
   *
   * @param config the configuration that is used for creating the symlink tree.
   * @throws CommandException
   */
  public void createSymlinksUsingCommand(Path execRoot,
      BuildConfiguration config, BinTools binTools) throws CommandException {
    List<String> argv = getSpawnArgumentList(execRoot, binTools, config.getShExecutable());

    CommandBuilder builder = new CommandBuilder();
    builder.addArgs(argv);
    builder.setWorkingDir(execRoot);
    builder.build().execute();
  }

  /**
   * Creates symlink tree using appropriate method. At this time tree
   * always created using build-runfiles helper application.
   *
   * Note: method may try to acquire resources - meaning that it would
   * block for undetermined period of time. If it is interrupted during
   * that wait, ExecException will be thrown but interrupted bit will be
   * preserved.
   *  @param action action instance that requested symlink tree creation
   * @param actionExecutionContext Services that are in the scope of the action.
   * @param shExecutable
   */
  public void createSymlinks(
      AbstractAction action,
      ActionExecutionContext actionExecutionContext,
      BinTools binTools,
      PathFragment shExecutable)
      throws ExecException, InterruptedException {
    List<String> args = getSpawnArgumentList(
        actionExecutionContext.getExecutor().getExecRoot(), binTools, shExecutable);
    try (ResourceHandle handle =
        ResourceManager.instance().acquireResources(action, RESOURCE_SET)) {
      actionExecutionContext.getExecutor().getSpawnActionContext(action.getMnemonic()).exec(
          new BaseSpawn.Local(args, ImmutableMap.<String, String>of(), action),
          actionExecutionContext);
    }
  }

  /**
   * Returns the complete argument list build-runfiles has to be called with.
   */
  private List<String> getSpawnArgumentList(
      Path execRoot, BinTools binTools, PathFragment shExecutable) {
    PathFragment path = binTools.getExecPath(BUILD_RUNFILES);
    Preconditions.checkNotNull(path, BUILD_RUNFILES + " not found in embedded tools");

    List<String> args = Lists.newArrayList();
    if (OS.getCurrent() == OS.WINDOWS) {
      // During bootstrapping, build-runfiles is a shell script, that cannot be directly
      // executed on Windows, so we shell out.
      args.add(shExecutable.getPathString());
      args.add("-c");
      args.add("$0 $*");
    }
    args.add(execRoot.getRelative(path).getPathString());

    if (filesetTree) {
      args.add("--allow_relative");
      args.add("--use_metadata");
    }

    FileSystem fs = execRoot.getFileSystem();
    if (fs instanceof UnixFileSystem
        && ((UnixFileSystem) fs).getSymlinkStrategy() == SymlinkStrategy.WINDOWS_COMPATIBLE) {
      args.add("--windows_compatible");
    }

    args.add(inputManifest.getPathString());
    args.add(symlinkTreeRoot.getPathString());

    return args;
  }
}