// Copyright 2018 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.worker;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.sandbox.SandboxHelpers.SandboxInputs;
import com.google.devtools.build.lib.sandbox.SandboxHelpers.SandboxOutputs;
import com.google.devtools.build.lib.sandbox.SymlinkedSandboxedSpawn;
import com.google.devtools.build.lib.sandbox.SynchronousTreeDeleter;
import com.google.devtools.build.lib.vfs.FileStatus;
import com.google.devtools.build.lib.vfs.FileSystemUtils;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.Symlinks;
import java.io.IOException;
import java.util.LinkedHashSet;
import java.util.Optional;
import java.util.Set;

/** Creates and manages the contents of a working directory of a persistent worker. */
final class WorkerExecRoot extends SymlinkedSandboxedSpawn {
  private final Path workDir;
  private final SandboxInputs inputs;
  private final SandboxOutputs outputs;
  private final Set<PathFragment> workerFiles;

  public WorkerExecRoot(
      Path workDir, SandboxInputs inputs, SandboxOutputs outputs, Set<PathFragment> workerFiles) {
    super(
        workDir,
        workDir,
        ImmutableList.of(),
        ImmutableMap.of(),
        inputs,
        outputs,
        ImmutableSet.of(),
        new SynchronousTreeDeleter(),
        /*statisticsPath=*/ null);
    this.workDir = workDir;
    this.inputs = inputs;
    this.outputs = outputs;
    this.workerFiles = workerFiles;
  }

  @Override
  public void createFileSystem() throws IOException {
    workDir.createDirectoryAndParents();

    // First compute all the inputs and directories that we need. This is based only on
    // `workerFiles`, `inputs` and `outputs` and won't do any I/O.
    Set<PathFragment> inputsToCreate = new LinkedHashSet<>();
    Set<PathFragment> dirsToCreate = new LinkedHashSet<>();
    populateInputsAndDirsToCreate(inputsToCreate, dirsToCreate);

    // Then do a full traversal of the `workDir`. This will use what we computed above, delete
    // anything unnecessary and update `inputsToCreate`/`dirsToCreate` if something is can be left
    // without changes (e.g., a symlink that already points to the right destination).
    cleanExisting(workDir, inputsToCreate, dirsToCreate);

    // Finally, create anything that is still missing.
    createDirectories(dirsToCreate);
    createInputs(inputsToCreate);
  }

  /** Populates the provided sets with the inputs and directories than need to be created. */
  private void populateInputsAndDirsToCreate(
      Set<PathFragment> inputsToCreate, Set<PathFragment> dirsToCreate) {
    // Add all worker files and the ancestor directories.
    for (PathFragment path : workerFiles) {
      inputsToCreate.add(path);
      for (int i = 0; i < path.segmentCount(); i++) {
        dirsToCreate.add(path.subFragment(0, i));
      }
    }

    // Add all inputs files and the ancestor directories.
    Iterable<PathFragment> allInputs =
        Iterables.concat(inputs.getFiles().keySet(), inputs.getSymlinks().keySet());
    for (PathFragment path : allInputs) {
      inputsToCreate.add(path);
      for (int i = 0; i < path.segmentCount(); i++) {
        dirsToCreate.add(path.subFragment(0, i));
      }
    }

    // Add all ouput directories.
    dirsToCreate.addAll(outputs.dirs());

    // And all ancestor directories of outputs. Note that we don't add the files themselves -- any
    // pre-existing files that have the same path as an output should get deleted.
    for (PathFragment path : Iterables.concat(outputs.files(), outputs.dirs())) {
      for (int i = 0; i < path.segmentCount(); i++) {
        dirsToCreate.add(path.subFragment(0, i));
      }
    }
  }

  /**
   * Deletes unnecessary files/directories and updates the sets if something on disk is already
   * correct and doesn't need any changes.
   */
  private void cleanExisting(
      Path root, Set<PathFragment> inputsToCreate, Set<PathFragment> dirsToCreate)
      throws IOException {
    for (Path path : root.getDirectoryEntries()) {
      FileStatus stat = path.stat(Symlinks.NOFOLLOW);
      PathFragment pathRelativeToWorkDir = path.relativeTo(workDir);
      Optional<PathFragment> destination = getExpectedSymlinkDestination(pathRelativeToWorkDir);
      if (destination.isPresent()) {
        if (stat.isSymbolicLink() && path.readSymbolicLink().equals(destination.get())) {
          inputsToCreate.remove(pathRelativeToWorkDir);
        } else {
          path.delete();
        }
      } else if (stat.isDirectory()) {
        if (dirsToCreate.contains(pathRelativeToWorkDir)) {
          cleanExisting(path, inputsToCreate, dirsToCreate);
          dirsToCreate.remove(pathRelativeToWorkDir);
        } else {
          path.deleteTree();
        }
      } else if (!inputsToCreate.contains(pathRelativeToWorkDir)) {
        path.delete();
      }
    }
  }

  private Optional<PathFragment> getExpectedSymlinkDestination(PathFragment fragment) {
    Path file = inputs.getFiles().get(fragment);
    if (file != null) {
      return Optional.of(file.asFragment());
    }
    return Optional.ofNullable(inputs.getSymlinks().get(fragment));
  }

  private void createDirectories(Iterable<PathFragment> dirsToCreate) throws IOException {
    for (PathFragment fragment : dirsToCreate) {
      workDir.getRelative(fragment).createDirectory();
    }
  }

  private void createInputs(Iterable<PathFragment> inputsToCreate) throws IOException {
    for (PathFragment fragment : inputsToCreate) {
      Path key = workDir.getRelative(fragment);
      if (inputs.getFiles().containsKey(fragment)) {
        Path fileDest = inputs.getFiles().get(fragment);
        if (fileDest != null) {
          key.createSymbolicLink(fileDest);
        } else {
          FileSystemUtils.createEmptyFile(key);
        }
      } else if (inputs.getSymlinks().containsKey(fragment)) {
        PathFragment symlinkDest = inputs.getSymlinks().get(fragment);
        if (symlinkDest != null) {
          key.createSymbolicLink(symlinkDest);
        }
      }
    }
  }
}