/*
 * Copyright 2016 Google LLC
 *
 * 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.cloud.storage.contrib.nio;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.cloud.storage.StorageOptions;
import com.google.common.collect.ImmutableSet;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.file.FileStore;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.PathMatcher;
import java.nio.file.WatchService;
import java.nio.file.attribute.FileTime;
import java.nio.file.attribute.UserPrincipalLookupService;
import java.util.Objects;
import java.util.Set;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;

/**
 * Google Cloud Storage {@link FileSystem} implementation.
 *
 * @see <a href="https://developers.google.com/storage/docs/concepts-techniques#concepts">
 *        Concepts and Terminology</a>
 * @see <a href="https://developers.google.com/storage/docs/bucketnaming">
 *        Bucket and Object Naming Guidelines</a>
 */
@ThreadSafe
public final class CloudStorageFileSystem extends FileSystem {

  public static final String URI_SCHEME = "gs";
  public static final String GCS_VIEW = "gcs";
  public static final String BASIC_VIEW = "basic";
  public static final int BLOCK_SIZE_DEFAULT = 2 * 1024 * 1024;
  public static final FileTime FILE_TIME_UNKNOWN = FileTime.fromMillis(0);
  public static final Set<String> SUPPORTED_VIEWS = ImmutableSet.of(BASIC_VIEW, GCS_VIEW);

  private final CloudStorageFileSystemProvider provider;
  private final String bucket;
  private final CloudStorageConfiguration config;

  // Users can change this: then this affects every filesystem object created
  // later, including via SPI. This is meant to be done only once, at the beginning
  // of some main program, in order to force all libraries to use some settings we like.
  // Libraries should never call this. It'll cause surprise to the writers of the main
  // program and they'll be unhappy. Instead, create your own filesystem object with the
  // right configuration and pass it along.
  private static CloudStorageConfiguration userSpecifiedDefault = CloudStorageConfiguration.DEFAULT;

  // Don't call this one, call the one in CloudStorageFileSystemProvider.
  static void setDefaultCloudStorageConfiguration(CloudStorageConfiguration config) {
    if (null == config) {
      userSpecifiedDefault = CloudStorageConfiguration.DEFAULT;
    } else {
      userSpecifiedDefault = config;
    }
  }

  static CloudStorageConfiguration getDefaultCloudStorageConfiguration() {
    return userSpecifiedDefault;
  }

  /**
   * Returns Google Cloud Storage {@link FileSystem} object for {@code bucket}.
   *
   * <p><b>NOTE:</b> You may prefer to use Java's standard API instead:<pre>   {@code
   *
   *   FileSystem fs = FileSystems.getFileSystem(URI.create("gs://bucket"));}</pre>
   *
   * <p>However some systems and build environments might be flaky when it comes to Java SPI. This
   * is because services are generally runtime dependencies and depend on a META-INF file being
   * present in your jar (generated by Google Auto at compile-time). In such cases, this method
   * provides a simpler alternative.
   *
   * @see #forBucket(String, CloudStorageConfiguration)
   * @see java.nio.file.FileSystems#getFileSystem(java.net.URI)
   */
  @CheckReturnValue
  public static CloudStorageFileSystem forBucket(String bucket) {
    return forBucket(bucket, userSpecifiedDefault);
  }

  /**
   * Creates new file system instance for {@code bucket}, with customizable settings.
   *
   * @see #forBucket(String)
   */
  @CheckReturnValue
  public static CloudStorageFileSystem forBucket(String bucket, CloudStorageConfiguration config) {
    checkArgument(
        !bucket.startsWith(URI_SCHEME + ":"), "Bucket name must not have schema: %s", bucket);
    return new CloudStorageFileSystem(
        new CloudStorageFileSystemProvider(), bucket, checkNotNull(config));
  }

  /**
   * Returns Google Cloud Storage {@link FileSystem} object for {@code bucket}.
   *
   * <p>Google Cloud Storage file system objects are basically free. You can create as many as you
   * want, even if you have multiple instances for the same bucket. There's no actual system
   * resources associated with this object. Therefore calling {@link #close()} on the returned value
   * is optional.
   *
   * <p><b>Note:</b> It is also possible to instantiate this class via Java's
   * {@code FileSystems.getFileSystem(URI.create("gs://bucket"))}. We discourage you
   * from using that if possible, for the reasons documented in
   * {@link CloudStorageFileSystemProvider#newFileSystem(URI, java.util.Map)}
   *
   * @see java.nio.file.FileSystems#getFileSystem(URI)
   */
  @CheckReturnValue
  public static CloudStorageFileSystem forBucket(String bucket, CloudStorageConfiguration config,
      @Nullable StorageOptions storageOptions) {
    checkArgument(!bucket.startsWith(URI_SCHEME + ":"),
        "Bucket name must not have schema: %s", bucket);
    return new CloudStorageFileSystem(new CloudStorageFileSystemProvider(storageOptions),
        bucket, checkNotNull(config));
  }

  CloudStorageFileSystem(
      CloudStorageFileSystemProvider provider, String bucket, CloudStorageConfiguration config) {
    checkArgument(!bucket.isEmpty(), "bucket");
    this.provider = provider;
    this.bucket = bucket;
    this.config = config;
  }

  @Override
  public CloudStorageFileSystemProvider provider() {
    return provider;
  }

  /**
   * Returns Cloud Storage bucket name being served by this file system.
   */
  public String bucket() {
    return bucket;
  }

  /**
   * Returns configuration object for this file system instance.
   */
  public CloudStorageConfiguration config() {
    return config;
  }

  /**
   * Converts Cloud Storage object name to a {@link Path} object.
   */
  @Override
  public CloudStoragePath getPath(String first, String... more) {
    checkArgument(
        !first.startsWith(URI_SCHEME + ":"),
        "Google Cloud Storage FileSystem.getPath() must not have schema and bucket name: %s",
        first);
    return CloudStoragePath.getPath(this, first, more);
  }

  /**
   * Does nothing currently. This method <i>might</i> be updated in the future to close all channels
   * associated with this file system object. However it's unlikely that even then, calling this
   * method will become mandatory.
   */
  @Override
  public void close() throws IOException {
    // TODO(#809): Synchronously close all channels associated with this FileSystem instance.
  }

  /**
   * Returns {@code true}, even if you previously called the {@link #close()} method.
   */
  @Override
  public boolean isOpen() {
    return true;
  }

  /**
   * Returns {@code false}.
   */
  @Override
  public boolean isReadOnly() {
    return false;
  }

  /**
   * Returns {@value UnixPath#SEPARATOR}.
   */
  @Override
  public String getSeparator() {
    return Character.toString(UnixPath.SEPARATOR);
  }

  @Override
  public Iterable<Path> getRootDirectories() {
    return ImmutableSet.<Path>of(CloudStoragePath.getPath(this, UnixPath.ROOT));
  }

  /**
   * Returns nothing because Google Cloud Storage doesn't have disk partitions of limited size, or
   * anything similar.
   */
  @Override
  public Iterable<FileStore> getFileStores() {
    return ImmutableSet.of();
  }

  @Override
  public Set<String> supportedFileAttributeViews() {
    return SUPPORTED_VIEWS;
  }

  @Override
  public PathMatcher getPathMatcher(String syntaxAndPattern) {
    return FileSystems.getDefault().getPathMatcher(syntaxAndPattern);
  }

  /**
   * Throws {@link UnsupportedOperationException} because this feature hasn't been implemented yet.
   */
  @Override
  public UserPrincipalLookupService getUserPrincipalLookupService() {
    // TODO: Implement me.
    throw new UnsupportedOperationException();
  }

  /**
   * Throws {@link UnsupportedOperationException} because this feature hasn't been implemented yet.
   */
  @Override
  public WatchService newWatchService() throws IOException {
    // TODO: Implement me.
    throw new UnsupportedOperationException();
  }

  @Override
  public boolean equals(Object other) {
    return this == other
        || other instanceof CloudStorageFileSystem
            && Objects.equals(config, ((CloudStorageFileSystem) other).config)
            && Objects.equals(bucket, ((CloudStorageFileSystem) other).bucket);
  }

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

  @Override
  public String toString() {
    try {
      return new URI(URI_SCHEME, bucket, null, null).toString();
    } catch (URISyntaxException e) {
      throw new AssertionError(e);
    }
  }
}
