/*
 * 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.util.gcsfs;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Strings.isNullOrEmpty;

import com.google.api.services.storage.model.StorageObject;
import java.io.File;
import java.io.IOException;
import java.io.Serializable;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.file.FileSystem;
import java.nio.file.LinkOption;
import java.nio.file.Path;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.Iterator;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Implements the Java NIO {@link Path} API for Google Cloud Storage paths.
 *
 * <p>GcsPath uses a slash ('/') as a directory separator.  Below is
 * a summary of how slashes are treated:
 * <ul>
 *   <li> A GCS bucket may not contain a slash.  An object may contain zero or
 *        more slashes.
 *   <li> A trailing slash always indicates a directory, which is compliant
 *        with POSIX.1-2008.
 *   <li> Slashes separate components of a path.  Empty components are allowed,
 *        these are represented as repeated slashes.  An empty component always
 *        refers to a directory, and always ends in a slash.
 *   <li> {@link #getParent()}} always returns a path ending in a slash, as the
 *        parent of a GcsPath is always a directory.
 *   <li> Use {@link #resolve(String)} to append elements to a GcsPath -- this
 *        applies the rules consistently and is highly recommended over any
 *        custom string concatenation.
 * </ul>
 *
 * <p>GcsPath treats all GCS objects and buckets as belonging to the same
 * filesystem, so the root of a GcsPath is the GcsPath bucket="", object="".
 *
 * <p>Relative paths are not associated with any bucket.  This matches common
 * treatment of Path in which relative paths can be constructed from one
 * filesystem and appended to another filesystem.
 *
 * @see <a href=
 * "http://docs.oracle.com/javase/tutorial/essential/io/pathOps.html"
 * >Java Tutorials: Path Operations</a>
 */
public class GcsPath implements Path, Serializable {

  public static final String SCHEME = "gs";

  /**
   * Creates a GcsPath from a URI.
   *
   * <p>The URI must be in the form {@code gs://[bucket]/[path]}, and may not
   * contain a port, user info, a query, or a fragment.
   */
  public static GcsPath fromUri(URI uri) {
    checkArgument(uri.getScheme().equalsIgnoreCase(SCHEME), "URI: %s is not a GCS URI", uri);
    checkArgument(uri.getPort() == -1,
        "GCS URI may not specify port: %s (%i)", uri, uri.getPort());
    checkArgument(
        isNullOrEmpty(uri.getUserInfo()),
        "GCS URI may not specify userInfo: %s (%s)", uri, uri.getUserInfo());
    checkArgument(
        isNullOrEmpty(uri.getQuery()),
        "GCS URI may not specify query: %s (%s)", uri, uri.getQuery());
    checkArgument(
        isNullOrEmpty(uri.getFragment()),
        "GCS URI may not specify fragment: %s (%s)", uri, uri.getFragment());

    return fromUri(uri.toString());
  }

  /**
   * Pattern that is used to parse a GCS URL.
   *
   * <p>This is used to separate the components.  Verification is handled
   * separately.
   */
  public static final Pattern GCS_URI =
      Pattern.compile("(?<SCHEME>[^:]+)://(?<BUCKET>[^/]+)(/(?<OBJECT>.*))?");

  /**
   * Creates a GcsPath from a URI in string form.
   *
   * <p>This does not use URI parsing, which means it may accept patterns that
   * the URI parser would not accept.
   */
  public static GcsPath fromUri(String uri) {
    Matcher m = GCS_URI.matcher(uri);
    checkArgument(m.matches(), "Invalid GCS URI: %s", uri);

    checkArgument(m.group("SCHEME").equalsIgnoreCase(SCHEME),
        "URI: %s is not a GCS URI", uri);
    return new GcsPath(null, m.group("BUCKET"), m.group("OBJECT"));
  }

  /**
   * Pattern that is used to parse a GCS resource name.
   */
  private static final Pattern GCS_RESOURCE_NAME =
      Pattern.compile("storage.googleapis.com/(?<BUCKET>[^/]+)(/(?<OBJECT>.*))?");

  /**
   * Creates a GcsPath from a OnePlatform resource name in string form.
   */
  public static GcsPath fromResourceName(String name) {
    Matcher m = GCS_RESOURCE_NAME.matcher(name);
    checkArgument(m.matches(), "Invalid GCS resource name: %s", name);

    return new GcsPath(null, m.group("BUCKET"), m.group("OBJECT"));
  }

  /**
   * Creates a GcsPath from a {@linkplain StorageObject}.
   */
  public static GcsPath fromObject(StorageObject object) {
    return new GcsPath(null, object.getBucket(), object.getName());
  }

  /**
   * Creates a GcsPath from bucket and object components.
   *
   * <p>A GcsPath without a bucket name is treated as a relative path, which
   * is a path component with no linkage to the root element.  This is similar
   * to a Unix path that does not begin with the root marker (a slash).
   * GCS has different naming constraints and APIs for working with buckets and
   * objects, so these two concepts are kept separate to avoid accidental
   * attempts to treat objects as buckets, or vice versa, as much as possible.
   *
   * <p>A GcsPath without an object name is a bucket reference.
   * A bucket is always a directory, which could be used to lookup or add
   * files to a bucket, but could not be opened as a file.
   *
   * <p>A GcsPath containing neither bucket or object names is treated as
   * the root of the GCS filesystem.  A listing on the root element would return
   * the buckets available to the user.
   *
   * <p>If {@code null} is passed as either parameter, it is converted to an
   * empty string internally for consistency.  There is no distinction between
   * an empty string and a {@code null}, as neither are allowed by GCS.
   *
   * @param bucket a GCS bucket name, or none ({@code null} or an empty string)
   *               if the object is not associated with a bucket
   *               (e.g. relative paths or the root node).
   * @param object a GCS object path, or none ({@code null} or an empty string)
   *               for no object.
   */
  public static GcsPath fromComponents(@Nullable String bucket,
                                       @Nullable String object) {
    return new GcsPath(null, bucket, object);
  }

  @Nullable
  private transient FileSystem fs;
  @Nonnull
  private final String bucket;
  @Nonnull
  private final String object;

  /**
   * Constructs a GcsPath.
   *
   * @param fs the associated FileSystem, if any
   * @param bucket the associated bucket, or none ({@code null} or an empty
   *               string) for a relative path component
   * @param object the object, which is a fully-qualified object name if bucket
   *               was also provided, or none ({@code null} or an empty string)
   *               for no object
   * @throws java.lang.IllegalArgumentException if the bucket of object names
   *         are invalid.
   */
  public GcsPath(@Nullable FileSystem fs,
                 @Nullable String bucket,
                 @Nullable String object) {
    if (bucket == null) {
      bucket = "";
    }
    checkArgument(!bucket.contains("/"),
        "GCS bucket may not contain a slash");
    checkArgument(bucket.isEmpty()
                || bucket.matches("[a-z0-9][-_a-z0-9.]+[a-z0-9]"),
            "GCS bucket names must contain only lowercase letters, numbers, "
                + "dashes (-), underscores (_), and dots (.). Bucket names "
                + "must start and end with a number or letter. "
                + "See https://developers.google.com/storage/docs/bucketnaming "
                + "for more details.  Bucket name: " + bucket);

    if (object == null) {
      object = "";
    }
    checkArgument(
        object.indexOf('\n') < 0 && object.indexOf('\r') < 0,
        "GCS object names must not contain Carriage Return or "
            + "Line Feed characters.");

    this.fs = fs;
    this.bucket = bucket;
    this.object = object;
  }

  /**
   * Returns the bucket name associated with this GCS path, or an empty string
   * if this is a relative path component.
   */
  public String getBucket() {
    return bucket;
  }

  /**
   * Returns the object name associated with this GCS path, or an empty string
   * if no object is specified.
   */
  public String getObject() {
    return object;
  }

  public void setFileSystem(FileSystem fs) {
    this.fs = fs;
  }

  @Override
  public FileSystem getFileSystem() {
    return fs;
  }

  // Absolute paths are those that have a bucket and the root path.
  @Override
  public boolean isAbsolute() {
    return !bucket.isEmpty() || object.isEmpty();
  }

  @Override
  public GcsPath getRoot() {
    return new GcsPath(fs, "", "");
  }

  @Override
  public GcsPath getFileName() {
    int nameCount = getNameCount();
    if (nameCount < 2) {
      throw new UnsupportedOperationException(
          "Can't get filename from root path in the bucket: " + this);
    }
    return getName(nameCount - 1);
  }

  /**
   * Returns the <em>parent path</em>, or {@code null} if this path does not
   * have a parent.
   *
   * <p>Returns a path that ends in '/', as the parent path always refers to
   * a directory.
   */
  @Override
  public GcsPath getParent() {
    if (bucket.isEmpty() && object.isEmpty()) {
      // The root path has no parent, by definition.
      return null;
    }

    if (object.isEmpty()) {
      // A GCS bucket. All buckets come from a common root.
      return getRoot();
    }

    // Skip last character, in case it is a trailing slash.
    int i = object.lastIndexOf('/', object.length() - 2);
    if (i <= 0) {
      if (bucket.isEmpty()) {
        // Relative paths are not attached to the root node.
        return null;
      }
      return new GcsPath(fs, bucket, "");
    }

    // Retain trailing slash.
    return new GcsPath(fs, bucket, object.substring(0, i + 1));
  }

  @Override
  public int getNameCount() {
    int count = bucket.isEmpty() ? 0 : 1;
    if (object.isEmpty()) {
      return count;
    }

    // Add another for each separator found.
    int index = -1;
    while ((index = object.indexOf('/', index + 1)) != -1) {
      count++;
    }

    return object.endsWith("/") ? count : count + 1;
  }

  @Override
  public GcsPath getName(int count) {
    checkArgument(count >= 0);

    Iterator<Path> iterator = iterator();
    for (int i = 0; i < count; ++i) {
      checkArgument(iterator.hasNext());
      iterator.next();
    }

    checkArgument(iterator.hasNext());
    return (GcsPath) iterator.next();
  }

  @Override
  public GcsPath subpath(int beginIndex, int endIndex) {
    checkArgument(beginIndex >= 0);
    checkArgument(endIndex > beginIndex);

    Iterator<Path> iterator = iterator();
    for (int i = 0; i < beginIndex; ++i) {
      checkArgument(iterator.hasNext());
      iterator.next();
    }

    GcsPath path = null;
    while (beginIndex < endIndex) {
      checkArgument(iterator.hasNext());
      if (path == null) {
        path = (GcsPath) iterator.next();
      } else {
        path = path.resolve(iterator.next());
      }
      ++beginIndex;
    }

    return path;
  }

  @Override
  public boolean startsWith(Path other) {
    if (other instanceof GcsPath) {
      GcsPath gcsPath = (GcsPath) other;
      return startsWith(gcsPath.bucketAndObject());
    } else {
      return startsWith(other.toString());
    }
  }

  @Override
  public boolean startsWith(String prefix) {
    return bucketAndObject().startsWith(prefix);
  }

  @Override
  public boolean endsWith(Path other) {
    if (other instanceof GcsPath) {
      GcsPath gcsPath = (GcsPath) other;
      return endsWith(gcsPath.bucketAndObject());
    } else {
      return endsWith(other.toString());
    }
  }

  @Override
  public boolean endsWith(String suffix) {
    return bucketAndObject().endsWith(suffix);
  }

  // TODO: support "." and ".." path components?
  @Override
  public GcsPath normalize() {
    return this;
  }

  @Override
  public GcsPath resolve(Path other) {
    if (other instanceof GcsPath) {
      GcsPath path = (GcsPath) other;
      if (path.isAbsolute()) {
        return path;
      } else {
        return resolve(path.getObject());
      }
    } else {
      return resolve(other.toString());
    }
  }

  @Override
  public GcsPath resolve(String other) {
    if (bucket.isEmpty() && object.isEmpty()) {
      // Resolve on a root path is equivalent to looking up a bucket and object.
      other = SCHEME + "://" + other;
    }

    if (other.startsWith(SCHEME + "://")) {
      GcsPath path = GcsPath.fromUri(other);
      path.setFileSystem(getFileSystem());
      return path;
    }

    if (other.isEmpty()) {
      // An empty component MUST refer to a directory.
      other = "/";
    }

    if (object.isEmpty()) {
      return new GcsPath(fs, bucket, other);
    } else if (object.endsWith("/")) {
      return new GcsPath(fs, bucket, object + other);
    } else {
      return new GcsPath(fs, bucket, object + "/" + other);
    }
  }

  @Override
  public Path resolveSibling(Path other) {
    throw new UnsupportedOperationException();
  }

  @Override
  public Path resolveSibling(String other) {
    if (getNameCount() < 2) {
      throw new UnsupportedOperationException("Can't resolve the sibling of a root path: " + this);
    }
    GcsPath parent = getParent();
    return (parent == null) ? fromUri(other) : parent.resolve(other);
  }

  @Override
  public Path relativize(Path other) {
    throw new UnsupportedOperationException();
  }

  @Override
  public GcsPath toAbsolutePath() {
    return this;
  }

  @Override
  public GcsPath toRealPath(LinkOption... options) throws IOException {
    return this;
  }

  @Override
  public File toFile() {
    throw new UnsupportedOperationException();
  }

  @Override
  public WatchKey register(WatchService watcher, WatchEvent.Kind<?>[] events,
      WatchEvent.Modifier... modifiers) throws IOException {
    throw new UnsupportedOperationException();
  }

  @Override
  public WatchKey register(WatchService watcher, WatchEvent.Kind<?>... events)
      throws IOException {
    throw new UnsupportedOperationException();
  }

  @Override
  public Iterator<Path> iterator() {
    return new NameIterator(fs, !bucket.isEmpty(), bucketAndObject());
  }

  private static class NameIterator implements Iterator<Path> {
    private final FileSystem fs;
    private boolean fullPath;
    private String name;

    NameIterator(FileSystem fs, boolean fullPath, String name) {
      this.fs = fs;
      this.fullPath = fullPath;
      this.name = name;
    }

    @Override
    public boolean hasNext() {
      return !isNullOrEmpty(name);
    }

    @Override
    public GcsPath next() {
      int i = name.indexOf('/');
      String component;
      if (i >= 0) {
        component = name.substring(0, i);
        name = name.substring(i + 1);
      } else {
        component = name;
        name = null;
      }
      if (fullPath) {
        fullPath = false;
        return new GcsPath(fs, component, "");
      } else {
        // Relative paths have no bucket.
        return new GcsPath(fs, "", component);
      }
    }

    @Override
    public void remove() {
      throw new UnsupportedOperationException();
    }
  }

  @Override
  public int compareTo(Path other) {
    if (!(other instanceof GcsPath)) {
      throw new ClassCastException();
    }

    GcsPath path = (GcsPath) other;
    int b = bucket.compareTo(path.bucket);
    if (b != 0) {
      return b;
    }

    // Compare a component at a time, so that the separator char doesn't
    // get compared against component contents.  Eg, "a/b" < "a-1/b".
    Iterator<Path> left = iterator();
    Iterator<Path> right = path.iterator();

    while (left.hasNext() && right.hasNext()) {
      String leftStr = left.next().toString();
      String rightStr = right.next().toString();
      int c = leftStr.compareTo(rightStr);
      if (c != 0) {
        return c;
      }
    }

    if (!left.hasNext() && !right.hasNext()) {
      return 0;
    } else {
      return left.hasNext() ? 1 : -1;
    }
  }

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

    GcsPath paths = (GcsPath) o;
    return bucket.equals(paths.bucket) && object.equals(paths.object);
  }

  @Override
  public int hashCode() {
    int result = bucket.hashCode();
    result = 31 * result + object.hashCode();
    return result;
  }

  @Override
  public String toString() {
    if (!isAbsolute()) {
      return object;
    }
    StringBuilder sb = new StringBuilder();
    sb.append(SCHEME)
        .append("://");
    if (!bucket.isEmpty()) {
      sb.append(bucket)
          .append('/');
    }
    sb.append(object);
    return sb.toString();
  }

  // TODO: Consider using resource names for all GCS paths used by the SDK.
  public String toResourceName() {
    StringBuilder sb = new StringBuilder();
    sb.append("storage.googleapis.com/");
    if (!bucket.isEmpty()) {
      sb.append(bucket).append('/');
    }
    sb.append(object);
    return sb.toString();
  }

  @Override
  public URI toUri() {
    try {
      return new URI(SCHEME, "//" + bucketAndObject(), null);
    } catch (URISyntaxException e) {
      throw new RuntimeException("Unable to create URI for GCS path " + this);
    }
  }

  private String bucketAndObject() {
    if (bucket.isEmpty()) {
      return object;
    } else {
      return bucket + "/" + object;
    }
  }
}
