content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.beam.sdk.io;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.nio.channels.ReadableByteChannel;
  import java.nio.channels.WritableByteChannel;
  import java.util.Collection;
  import java.util.List;
  import org.apache.beam.sdk.io.fs.CreateOptions;
  import org.apache.beam.sdk.io.fs.MatchResult;
  import org.apache.beam.sdk.io.fs.MoveOptions;
  import org.apache.beam.sdk.io.fs.ResourceId;
  import org.apache.beam.sdk.metrics.Lineage;
  
  /**
   * File system interface in Beam.
   *
   * <p>It defines APIs for writing file systems agnostic code.
   *
   * <p>All methods are protected, and they are for file system providers to implement. Clients should
   * use the {@link FileSystems} utility.
   */
  public abstract class FileSystem<ResourceIdT extends ResourceId> {
    /**
     * This is the entry point to convert user-provided specs to {@link ResourceIdT ResourceIds}.
     * Callers should use {@link #match} to resolve users specs ambiguities before calling other
     * methods.
     *
     * <p>Implementation should handle the following ambiguities of a user-provided spec:
     *
     * <ol>
     *   <li>{@code spec} could be a glob or a uri. {@link #match} should be able to tell and choose
     *       efficient implementations.
     *   <li>The user-provided {@code spec} might refer to files or directories. It is common that
     *       users that wish to indicate a directory will omit the trailing {@code /}, such as in a
     *       spec of {@code "/tmp/dir"}. The {@link FileSystem} should be able to recognize a
     *       directory with the trailing {@code /} omitted, but should always return a correct {@link
     *       ResourceIdT} (e.g., {@code "/tmp/dir/"} inside the returned {@link MatchResult}.
     * </ol>
     *
     * <p>All {@link FileSystem} implementations should support glob in the final hierarchical path
     * component of {@link ResourceIdT}. This allows SDK libraries to construct file system agnostic
     * spec. {@link FileSystem FileSystems} can support additional patterns for user-provided specs.
     *
     * @return {@code List<MatchResult>} in the same order of the input specs.
     * @throws IllegalArgumentException if specs are invalid.
     * @throws IOException if all specs failed to match due to issues like: network connection,
     *     authorization. Exception for individual spec need to be deferred until callers retrieve
     *     metadata with {@link MatchResult#metadata()}.
     */
    protected abstract List<MatchResult> match(List<String> specs) throws IOException;
  
    /**
     * Returns a write channel for the given {@link ResourceIdT}.
     *
     * <p>The resource is not expanded; it is used verbatim.
     *
     * @param resourceId the reference of the file-like resource to create
     * @param createOptions the configuration of the create operation
     */
    protected abstract WritableByteChannel create(ResourceIdT resourceId, CreateOptions createOptions)
        throws IOException;
  
    /**
     * Returns a read channel for the given {@link ResourceIdT}.
     *
     * <p>The resource is not expanded; it is used verbatim.
     *
     * <p>If seeking is supported, then this returns a {@link java.nio.channels.SeekableByteChannel}.
     *
     * @param resourceId the reference of the file-like resource to open
     */
    protected abstract ReadableByteChannel open(ResourceIdT resourceId) throws IOException;
  
    /**
     * Copies a {@link List} of file-like resources from one location to another.
     *
     * <p>The number of source resources must equal the number of destination resources. Destination
     * resources will be created recursively.
     *
     * @param srcResourceIds the references of the source resources
     * @param destResourceIds the references of the destination resources
     * @throws FileNotFoundException if the source resources are missing. When copy throws, each
     *     resource might or might not be copied. In such scenarios, callers can use {@code match()}
     *     to determine the state of the resources.
     */
    protected abstract void copy(List<ResourceIdT> srcResourceIds, List<ResourceIdT> destResourceIds)
        throws IOException;
  
    /**
     * Renames a {@link List} of file-like resources from one location to another.
     *
     * <p>The number of source resources must equal the number of destination resources. Destination
     * resources will be created recursively.
     *
     * @param srcResourceIds the references of the source resources
     * @param destResourceIds the references of the destination resources
     * @param moveOptions move options specifying handling of error conditions
     * @throws UnsupportedOperationException if move options are specified and not supported by the
     *     FileSystem
     * @throws FileNotFoundException if the source resources are missing. When rename throws, the
     *     state of the resources is unknown but safe: for every (source, destination) pair of
     *     resources, the following are possible: a) source exists, b) destination exists, c) source
     *     and destination both exist. Thus no data is lost, however, duplicated resource are
     *     possible. In such scenarios, callers can use {@code match()} to determine the state of the
     *     resource.
     */
    protected abstract void rename(
        List<ResourceIdT> srcResourceIds,
        List<ResourceIdT> destResourceIds,
        MoveOptions... moveOptions)
        throws IOException;
  
    /**
     * Deletes a collection of resources.
     *
     * @param resourceIds the references of the resources to delete.
     * @throws FileNotFoundException if resources are missing. When delete throws, each resource might
     *     or might not be deleted. In such scenarios, callers can use {@code match()} to determine
     *     the state of the resources.
     */
    protected abstract void delete(Collection<ResourceIdT> resourceIds) throws IOException;
  
    /**
     * Returns a new {@link ResourceId} for this filesystem that represents the named resource. The
     * user supplies both the resource spec and whether it is a directory.
     *
     * <p>The supplied {@code singleResourceSpec} is expected to be in a proper format, including any
     * necessary escaping, for this {@link FileSystem}.
     *
     * <p>This function may throw an {@link IllegalArgumentException} if given an invalid argument,
     * such as when the specified {@code singleResourceSpec} is not a valid resource name.
     */
    protected abstract ResourceIdT matchNewResource(String singleResourceSpec, boolean isDirectory);
  
    /**
     * Get the URI scheme which defines the namespace of the {@link FileSystem}.
     *
     * @see <a href="https://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>
     */
    protected abstract String getScheme();
  
    public enum LineageLevel {
      FILE,
      TOP_LEVEL
    }
  
    /** Report {@link Lineage} metrics for resource id at file level. */
    protected void reportLineage(ResourceIdT resourceId, Lineage lineage) {
      reportLineage(resourceId, lineage, LineageLevel.FILE);
    }
  
    /**
     * Report {@link Lineage} metrics for resource id to a given level.
     *
     * <p>Unless override by FileSystem implementations, default to no-op.
     */
    protected void reportLineage(ResourceIdT unusedId, Lineage unusedLineage, LineageLevel level) {}
  }
  