// Copyright 2014 Google Inc. 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.util;

import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.vfs.FileSystem;
import com.google.devtools.build.lib.vfs.JavaIoFileSystem;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.UnionFileSystem;
import com.google.devtools.build.lib.vfs.UnixFileSystem;
import com.google.devtools.build.lib.vfs.ZipFileSystem;

import java.io.IOException;
import java.util.Map;

/**
 * This static file system singleton manages access to a single default
 * {@link FileSystem} instance created within the methods of this class.
 */
@ThreadSafe
public final class FileSystems {

  private FileSystems() {}

  private static FileSystem defaultFileSystem;

  /**
   * Initializes the default {@link FileSystem} instance as a platform native
   * (Unix) file system, creating one iff needed, and returns the instance.
   *
   * <p>This method is idempotent as long as the initialization is of the same
   * type (Native/JavaIo/Union).
   */
  public static synchronized FileSystem initDefaultAsNative() {
    if (!(defaultFileSystem instanceof UnixFileSystem)) {
      defaultFileSystem = new UnixFileSystem();
    }
    return defaultFileSystem;
  }

  /**
   * Initializes the default {@link FileSystem} instance as a java.io.File
   * file system, creating one iff needed, and returns the instance.
   *
   * <p>This method is idempotent as long as the initialization is of the same
   * type (Native/JavaIo/Union).
   */
  public static synchronized FileSystem initDefaultAsJavaIo() {
    if (!(defaultFileSystem instanceof JavaIoFileSystem)) {
      defaultFileSystem = new JavaIoFileSystem();
    }
    return defaultFileSystem;
  }

  /**
   * Initializes the default {@link FileSystem} instance as a
   * {@link UnionFileSystem}, creating one iff needed,
   * and returns the instance.
   *
   * <p>This method is idempotent as long as the initialization is of the same
   * type (Native/JavaIo/Union).
   *
   * @param prefixMapping the desired mapping of path prefixes to delegate file systems
   * @param rootFileSystem the default file system for paths that don't match any prefix map
   */
  public static synchronized FileSystem initDefaultAsUnion(
      Map<PathFragment, FileSystem> prefixMapping, FileSystem rootFileSystem) {
    if (!(defaultFileSystem instanceof UnionFileSystem)) {
      defaultFileSystem = new UnionFileSystem(prefixMapping, rootFileSystem);
    }
    return defaultFileSystem;
  }

  /**
   * Returns a new instance of a simple {@link FileSystem} implementation that
   * presents the contents of a zip file as a read-only file system view.
   */
  public static FileSystem newZipFileSystem(Path zipFile) throws IOException {
    return new ZipFileSystem(zipFile);
  }
}