// Copyright 2019 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.remote.merkletree;

import build.bazel.remote.execution.v2.Digest;
import com.google.common.base.Preconditions;
import com.google.devtools.build.lib.actions.ActionInput;
import com.google.devtools.build.lib.actions.ActionInputHelper;
import com.google.devtools.build.lib.actions.FileArtifactValue;
import com.google.devtools.build.lib.actions.MetadataProvider;
import com.google.devtools.build.lib.actions.cache.VirtualActionInput;
import com.google.devtools.build.lib.remote.merkletree.DirectoryTree.DirectoryNode;
import com.google.devtools.build.lib.remote.merkletree.DirectoryTree.FileNode;
import com.google.devtools.build.lib.remote.util.DigestUtil;
import com.google.devtools.build.lib.vfs.Dirent;
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.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

/** Builder for directory trees. */
class DirectoryTreeBuilder {

  private interface FileNodeVisitor<T> {

    /**
     * Visits an {@code input} and adds {@link FileNode}s to {@code currDir}.
     *
     * <p>This method mutates its parameter {@code currDir}.
     *
     * @param input the file or directory to add to {@code currDir}.
     * @param path the path of {@code input} in the merkle tree.
     * @param currDir the directory node representing {@code path} in the merkle tree.
     * @return Returns the number of {@link FileNode}s added to {@code currDir}.
     */
    int visit(T input, PathFragment path, DirectoryNode currDir) throws IOException;
  }

  static DirectoryTree fromActionInputs(
      SortedMap<PathFragment, ActionInput> inputs,
      MetadataProvider metadataProvider,
      Path execRoot,
      DigestUtil digestUtil)
      throws IOException {
    Map<PathFragment, DirectoryNode> tree = new HashMap<>();
    int numFiles = buildFromActionInputs(inputs, metadataProvider, execRoot, digestUtil, tree);
    return new DirectoryTree(tree, numFiles);
  }

  /**
   * Creates a tree of files and directories from a list of files.
   *
   * <p>This method retrieves file metadata from the filesystem. It does not use Bazel's caches.
   * Thus, don't use this method during the execution phase. Use {@link #fromActionInputs} instead.
   *
   * @param inputFiles map of paths to files. The key determines the path at which the file should
   *     be mounted in the tree.
   */
  static DirectoryTree fromPaths(SortedMap<PathFragment, Path> inputFiles, DigestUtil digestUtil)
      throws IOException {
    Map<PathFragment, DirectoryNode> tree = new HashMap<>();
    int numFiles = buildFromPaths(inputFiles, digestUtil, tree);
    return new DirectoryTree(tree, numFiles);
  }

  /**
   * Adds the files in {@code inputs} as nodes to {@code tree}.
   *
   * <p>This method mutates {@code tree}.
   *
   * @param inputs map of paths to files. The key determines the path at which the file should be
   *     mounted in the tree.
   * @return the number of file nodes added to {@code tree}.
   */
  private static int buildFromPaths(
      SortedMap<PathFragment, Path> inputs,
      DigestUtil digestUtil,
      Map<PathFragment, DirectoryNode> tree)
      throws IOException {
    return build(
        inputs,
        tree,
        (input, path, currDir) -> {
          if (!input.isFile(Symlinks.NOFOLLOW)) {
            throw new IOException(String.format("Input '%s' is not a file.", input));
          }
          Digest d = digestUtil.compute(input);
          currDir.addChild(new FileNode(path.getBaseName(), input, d));
          return 1;
        });
  }

  /**
   * Adds the files in {@code inputs} as nodes to {@code tree}.
   *
   * <p>This method mutates {@code tree}.
   *
   * @return the number of file nodes added to {@code tree}.
   */
  private static int buildFromActionInputs(
      SortedMap<PathFragment, ActionInput> inputs,
      MetadataProvider metadataProvider,
      Path execRoot,
      DigestUtil digestUtil,
      Map<PathFragment, DirectoryNode> tree)
      throws IOException {
    return build(
        inputs,
        tree,
        (input, path, currDir) -> {
          if (input instanceof VirtualActionInput) {
            VirtualActionInput virtualActionInput = (VirtualActionInput) input;
            Digest d = digestUtil.compute(virtualActionInput);
            currDir.addChild(new FileNode(path.getBaseName(), virtualActionInput.getBytes(), d));
            return 1;
          }

          FileArtifactValue metadata =
              Preconditions.checkNotNull(
                  metadataProvider.getMetadata(input),
                  "missing metadata for '%s'",
                  input.getExecPathString());
          switch (metadata.getType()) {
            case REGULAR_FILE:
              Digest d = DigestUtil.buildDigest(metadata.getDigest(), metadata.getSize());
              currDir.addChild(
                  new FileNode(
                      path.getBaseName(), ActionInputHelper.toInputPath(input, execRoot), d));
              return 1;

            case DIRECTORY:
              SortedMap<PathFragment, ActionInput> directoryInputs =
                  explodeDirectory(path, execRoot);
              return buildFromActionInputs(
                  directoryInputs, metadataProvider, execRoot, digestUtil, tree);

            case SYMLINK:
              throw new IllegalStateException(
                  String.format(
                      "Encountered symlink input '%s', but all"
                          + " symlinks should have been resolved by SkyFrame. This is a bug.",
                      path));

            case SPECIAL_FILE:
              throw new IOException(
                  String.format(
                      "The '%s' is a special input which is not supported"
                          + " by remote caching and execution.",
                      path));

            case NONEXISTENT:
              throw new IOException(String.format("The file type of '%s' is not supported.", path));
          }

          return 0;
        });
  }

  private static <T> int build(
      SortedMap<PathFragment, T> inputs,
      Map<PathFragment, DirectoryNode> tree,
      FileNodeVisitor<T> fileNodeVisitor)
      throws IOException {
    if (inputs.isEmpty()) {
      return 0;
    }

    PathFragment dirname = null;
    DirectoryNode dir = null;
    int numFiles = 0;
    for (Map.Entry<PathFragment, T> e : inputs.entrySet()) {
      // Path relative to the exec root
      PathFragment path = e.getKey();
      T input = e.getValue();
      if (dirname == null || !path.getParentDirectory().equals(dirname)) {
        dirname = path.getParentDirectory();
        dir = tree.get(dirname);
        if (dir == null) {
          dir = new DirectoryNode(dirname.getBaseName());
          tree.put(dirname, dir);
          createParentDirectoriesIfNotExist(dirname, dir, tree);
        }
      }

      numFiles += fileNodeVisitor.visit(input, path, dir);
    }

    return numFiles;
  }

  private static SortedMap<PathFragment, ActionInput> explodeDirectory(
      PathFragment dirname, Path execRoot) throws IOException {
    SortedMap<PathFragment, ActionInput> inputs = new TreeMap<>();
    explodeDirectory(dirname, inputs, execRoot);
    return inputs;
  }

  private static void explodeDirectory(
      PathFragment dirname, SortedMap<PathFragment, ActionInput> inputs, Path execRoot)
      throws IOException {
    Collection<Dirent> entries = execRoot.getRelative(dirname).readdir(Symlinks.FOLLOW);
    for (Dirent entry : entries) {
      String basename = entry.getName();
      PathFragment path = dirname.getChild(basename);
      switch (entry.getType()) {
        case FILE:
          inputs.put(path, ActionInputHelper.fromPath(path));
          break;

        case DIRECTORY:
          explodeDirectory(path, inputs, execRoot);
          break;

        case SYMLINK:
          throw new IllegalStateException(
              String.format(
                  "Encountered symlink input '%s', but all"
                      + " symlinks should have been resolved by readdir. This is a bug.",
                  path));

        case UNKNOWN:
          throw new IOException(String.format("The file type of '%s' is not supported.", path));
      }
    }
  }

  private static void createParentDirectoriesIfNotExist(
      PathFragment dirname, DirectoryNode dir, Map<PathFragment, DirectoryNode> tree) {
    PathFragment parentDirname = dirname.getParentDirectory();
    DirectoryNode prevDir = dir;
    while (parentDirname != null) {
      DirectoryNode parentDir = tree.get(parentDirname);
      if (parentDir != null) {
        parentDir.addChild(prevDir);
        break;
      }

      parentDir = new DirectoryNode(parentDirname.getBaseName());
      parentDir.addChild(prevDir);
      tree.put(parentDirname, parentDir);

      parentDirname = parentDirname.getParentDirectory();
      prevDir = parentDir;
    }
  }

  private DirectoryTreeBuilder() {}
}