// 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.vfs;

import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.devtools.build.lib.skyframe.serialization.DeserializationContext;
import com.google.devtools.build.lib.skyframe.serialization.ObjectCodec;
import com.google.devtools.build.lib.skyframe.serialization.SerializationContext;
import com.google.devtools.build.lib.skyframe.serialization.SerializationException;
import com.google.protobuf.CodedInputStream;
import com.google.protobuf.CodedOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import javax.annotation.Nullable;

/**
 * A root path used in {@link RootedPath} and in artifact roots.
 *
 * <p>A typical root could be the exec path, a package root, or an output root specific to some
 * configuration. We also support absolute roots for non-hermetic paths outside the user workspace.
 */
public interface Root extends Comparable<Root>, Serializable {

  ObjectCodec<Root> CODEC = new RootCodec();

  /** Constructs a root from a path. */
  static Root fromPath(Path path) {
    return new PathRoot(path);
  }

  /** Returns an absolute root. Can only be used with absolute path fragments. */
  static Root absoluteRoot(FileSystem fileSystem) {
    return fileSystem.getAbsoluteRoot();
  }

  /** Returns a path by concatenating the root and the root-relative path. */
  Path getRelative(PathFragment rootRelativePath);

  /** Returns a path by concatenating the root and the root-relative path. */
  Path getRelative(String rootRelativePath);

  /** Returns the relative path between the root and the given path. */
  PathFragment relativize(Path path);

  /** Returns the relative path between the root and the given absolute path fragment. */
  PathFragment relativize(PathFragment absolutePathFragment);

  /** Returns whether the given path is under this root. */
  boolean contains(Path path);

  /** Returns whether the given absolute path fragment is under this root. */
  boolean contains(PathFragment absolutePathFragment);

  /**
   * Returns the underlying path. Please avoid using this method.
   *
   * <p>Not all roots are backed by paths, so this may return null.
   */
  @Nullable
  Path asPath();

  boolean isAbsolute();

  /** Implementation of Root that is backed by a {@link Path}. */
  final class PathRoot implements Root {
    private final Path path;

    PathRoot(Path path) {
      this.path = path;
    }

    @Override
    public Path getRelative(PathFragment rootRelativePath) {
      return path.getRelative(rootRelativePath);
    }

    @Override
    public Path getRelative(String rootRelativePath) {
      return path.getRelative(rootRelativePath);
    }

    @Override
    public PathFragment relativize(Path path) {
      return path.relativeTo(this.path);
    }

    @Override
    public PathFragment relativize(PathFragment absolutePathFragment) {
      Preconditions.checkArgument(absolutePathFragment.isAbsolute());
      return absolutePathFragment.relativeTo(path.asFragment());
    }

    @Override
    public boolean contains(Path path) {
      return path.startsWith(this.path);
    }

    @Override
    public boolean contains(PathFragment absolutePathFragment) {
      return absolutePathFragment.isAbsolute()
          && absolutePathFragment.startsWith(path.asFragment());
    }

    @Override
    public Path asPath() {
      return path;
    }

    @Override
    public boolean isAbsolute() {
      return false;
    }

    @Override
    public String toString() {
      return path.toString();
    }

    @Override
    public int compareTo(Root o) {
      if (o instanceof AbsoluteRoot) {
        return 1;
      } else if (o instanceof PathRoot) {
        return path.compareTo(((PathRoot) o).path);
      } else {
        throw new AssertionError("Unknown Root subclass: " + o.getClass().getName());
      }
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      PathRoot pathRoot = (PathRoot) o;
      return path.equals(pathRoot.path);
    }

    @Override
    public int hashCode() {
      return path.hashCode();
    }
  }

  /** An absolute root of a file system. Can only resolve absolute path fragments. */
  final class AbsoluteRoot implements Root {
    private FileSystem fileSystem; // Non-final for serialization

    AbsoluteRoot(FileSystem fileSystem) {
      this.fileSystem = fileSystem;
    }

    @Override
    public Path getRelative(PathFragment rootRelativePath) {
      Preconditions.checkArgument(rootRelativePath.isAbsolute());
      return fileSystem.getPath(rootRelativePath);
    }

    @Override
    public Path getRelative(String rootRelativePath) {
      return getRelative(PathFragment.create(rootRelativePath));
    }

    @Override
    public PathFragment relativize(Path path) {
      return path.asFragment();
    }

    @Override
    public PathFragment relativize(PathFragment absolutePathFragment) {
      Preconditions.checkArgument(absolutePathFragment.isAbsolute());
      return absolutePathFragment;
    }

    @Override
    public boolean contains(Path path) {
      return true;
    }

    @Override
    public boolean contains(PathFragment absolutePathFragment) {
      return absolutePathFragment.isAbsolute();
    }

    @Override
    public boolean isAbsolute() {
      return true;
    }

    @Override
    public Path asPath() {
      return null;
    }

    @Override
    public String toString() {
      return "<absolute root>";
    }

    @Override
    public int compareTo(Root o) {
      if (o instanceof AbsoluteRoot) {
        return Integer.compare(fileSystem.hashCode(), ((AbsoluteRoot) o).fileSystem.hashCode());
      } else if (o instanceof PathRoot) {
        return -1;
      } else {
        throw new AssertionError("Unknown Root subclass: " + o.getClass().getName());
      }
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      AbsoluteRoot that = (AbsoluteRoot) o;
      return Objects.equal(fileSystem, that.fileSystem);
    }

    @Override
    public int hashCode() {
      return Objects.hashCode(fileSystem);
    }

    @SuppressWarnings("unused")
    private void readObject(ObjectInputStream in) throws IOException {
      fileSystem = Path.getFileSystemForSerialization();
    }

    @SuppressWarnings("unused")
    private void writeObject(ObjectOutputStream out) throws IOException {
      Preconditions.checkState(
          fileSystem == Path.getFileSystemForSerialization(),
          "%s %s",
          fileSystem,
          Path.getFileSystemForSerialization());
    }
  }

  /** Codec to serialize {@link Root}s. */
  class RootCodec implements ObjectCodec<Root> {
    @Override
    public Class<Root> getEncodedClass() {
      return Root.class;
    }

    @Override
    public void serialize(
        SerializationContext context,
        Root obj,
        CodedOutputStream codedOut)
        throws SerializationException, IOException {
      if (obj instanceof PathRoot) {
        codedOut.writeBoolNoTag(false);
        Path.CODEC.serialize(context, ((PathRoot) obj).path, codedOut);
      } else if (obj instanceof AbsoluteRoot) {
        Preconditions.checkArgument(
            ((AbsoluteRoot) obj).fileSystem == context.getDependency(FileSystem.class));
        codedOut.writeBoolNoTag(true);
      } else {
        throw new AssertionError("Unknown Root subclass: " + obj.getClass().getName());
      }
    }

    @Override
    public Root deserialize(DeserializationContext context, CodedInputStream codedIn)
        throws SerializationException, IOException {
      boolean isAbsolute = codedIn.readBool();
      if (isAbsolute) {
        return context.getDependency(FileSystem.class).getAbsoluteRoot();
      } else {
        Path path = Path.CODEC.deserialize(context, codedIn);
        return new PathRoot(path);
      }
    }
  }
}