// Copyright (C) 2018 The Android Open Source Project
//
// 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.googlesource.gerrit.plugins.replication;

import static java.nio.charset.StandardCharsets.UTF_8;

import com.google.auto.value.AutoValue;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableSet;
import com.google.common.flogger.FluentLogger;
import com.google.common.hash.Hashing;
import com.google.gerrit.common.Nullable;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;
import com.google.inject.Inject;
import com.google.inject.ProvisionException;
import com.google.inject.Singleton;
import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.file.Files;
import java.nio.file.NoSuchFileException;
import java.nio.file.NotDirectoryException;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.util.HashSet;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Stream;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.transport.URIish;

/**
 * A persistent store for replication tasks.
 *
 * <p>The data of this store lives under <replication_data>/ref-updates where replication_data is
 * determined by the replication.eventsDirectory config option and defaults to
 * <site_dir>/data/replication. Atomic renames must be supported from anywhere within the store to
 * anywhere within the store. This generally means that all the contents of the store needs to live
 * on the same filesystem.
 *
 * <p>Individual tasks are stored in files under the following directories using the sha1 of the
 * task:
 *
 * <p><code>
 *   .../building/<tmp_name>                       new replication tasks under construction
 *   .../running/<sha1>                            running replication tasks
 *   .../waiting/<task_sha1>  outstanding replication tasks
 * </code>
 *
 * <p>Tasks are moved atomically via a rename between those directories to indicate the current
 * state of each task.
 */
@Singleton
public class ReplicationTasksStorage {
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();

  @AutoValue
  public abstract static class ReplicateRefUpdate {
    public static Optional<ReplicateRefUpdate> createOptionally(Path file, Gson gson) {
      try {
        return Optional.ofNullable(create(file, gson));
      } catch (NoSuchFileException e) {
        logger.atFine().log("File %s not found while reading task", file);
      } catch (IOException e) {
        logger.atSevere().withCause(e).log("Error while reading task %s", file);
      }
      return Optional.empty();
    }

    public static ReplicateRefUpdate create(Path file, Gson gson) throws IOException {
      String json = new String(Files.readAllBytes(file), UTF_8);
      return create(gson.fromJson(json, ReplicateRefUpdate.class), file.getFileName().toString());
    }

    public static ReplicateRefUpdate create(
        String project, Set<String> refs, URIish uri, String remote) {
      return new AutoValue_ReplicationTasksStorage_ReplicateRefUpdate(
          project,
          ImmutableSet.copyOf(refs),
          uri.toASCIIString(),
          remote,
          sha1(project, ImmutableSet.copyOf(refs), uri.toASCIIString(), remote));
    }

    public static ReplicateRefUpdate create(ReplicateRefUpdate u, String filename) {
      return new AutoValue_ReplicationTasksStorage_ReplicateRefUpdate(
          u.project(), u.refs(), u.uri(), u.remote(), filename);
    }

    public abstract String project();

    public abstract ImmutableSet<String> refs();

    public abstract String uri();

    public abstract String remote();

    public abstract String sha1();

    private static String sha1(String project, Set<String> refs, String uri, String remote) {
      return ReplicationTasksStorage.sha1(
              project + "\n" + refs.toString() + "\n" + uri + "\n" + remote)
          .name();
    }

    @Override
    public final String toString() {
      return "ref-update "
          + project()
          + ":"
          + refs().toString()
          + " uri:"
          + uri()
          + " remote:"
          + remote();
    }

    public static TypeAdapter<ReplicateRefUpdate> typeAdapter(Gson gson) {
      return new AutoValue_ReplicationTasksStorage_ReplicateRefUpdate.GsonTypeAdapter(gson);
    }
  }

  private final Gson gson;

  private final Path buildingUpdates;
  private final Path runningUpdates;
  private final Path waitingUpdates;

  private boolean isMultiPrimary;

  @Inject
  ReplicationTasksStorage(ReplicationConfig config) {
    this(config.getEventsDirectory().resolve("ref-updates"));
    isMultiPrimary = config.getDistributionInterval() != 0;
  }

  @VisibleForTesting
  public ReplicationTasksStorage(Path refUpdates) {
    buildingUpdates = refUpdates.resolve("building");
    runningUpdates = refUpdates.resolve("running");
    waitingUpdates = refUpdates.resolve("waiting");
    gson =
        new GsonBuilder()
            .registerTypeAdapterFactory(new ReplicateRefUpdateTypeAdapterFactory())
            .create();
  }

  private boolean isMultiPrimary() {
    return isMultiPrimary;
  }

  public synchronized String create(ReplicateRefUpdate r) {
    return new Task(r).create();
  }

  public synchronized Set<ImmutableSet<String>> start(UriUpdates uriUpdates) {
    Set<ImmutableSet<String>> startedRefs = new HashSet<>();
    for (ReplicateRefUpdate update : uriUpdates.getReplicateRefUpdates()) {
      Task t = new Task(update);
      if (t.start()) {
        startedRefs.add(t.update.refs());
      }
    }
    return startedRefs;
  }

  public synchronized void reset(UriUpdates uriUpdates) {
    for (ReplicateRefUpdate update : uriUpdates.getReplicateRefUpdates()) {
      new Task(update).reset();
    }
  }

  public synchronized void recoverAll() {
    streamRunning().forEach(r -> new Task(r).recover());
  }

  public boolean isWaiting(UriUpdates uriUpdates) {
    return uriUpdates.getReplicateRefUpdates().stream()
        .map(update -> new Task(update))
        .anyMatch(Task::isWaiting);
  }

  public void finish(UriUpdates uriUpdates) {
    for (ReplicateRefUpdate update : uriUpdates.getReplicateRefUpdates()) {
      new Task(update).finish();
    }
  }

  public Stream<ReplicateRefUpdate> streamWaiting() {
    return streamRecursive(createDir(waitingUpdates));
  }

  public Stream<ReplicateRefUpdate> streamRunning() {
    return streamRecursive(createDir(runningUpdates));
  }

  private Stream<ReplicateRefUpdate> streamRecursive(Path dir) {
    return walkNonDirs(dir)
        .map(path -> ReplicateRefUpdate.createOptionally(path, gson))
        .filter(Optional::isPresent)
        .map(Optional::get);
  }

  private Stream<Path> walkNonDirs(Path path) {
    try {
      return Files.list(path).flatMap(sub -> walkNonDirs(sub));
    } catch (NotDirectoryException e) {
      return Stream.of(path);
    } catch (Exception e) {
      String message = "Error while walking directory %s";
      if (isMultiPrimary() && e instanceof NoSuchFileException) {
        logger.atFine().log(
            message + " (expected regularly with multi-primaries and distributor enabled)", path);
      } else {
        logger.atSevere().withCause(e).log(message, path);
      }
      return Stream.empty();
    }
  }

  @SuppressWarnings("deprecation")
  private static ObjectId sha1(String s) {
    return ObjectId.fromRaw(Hashing.sha1().hashString(s, UTF_8).asBytes());
  }

  private static Path createDir(Path dir) {
    try {
      return Files.createDirectories(dir);
    } catch (IOException e) {
      throw new ProvisionException(String.format("Couldn't create %s", dir), e);
    }
  }

  public static final class ReplicateRefUpdateTypeAdapterFactory implements TypeAdapterFactory {
    static class ReplicateRefUpdateTypeAdapter<T> extends TypeAdapter<ReplicateRefUpdate> {

      @Override
      public void write(JsonWriter out, ReplicateRefUpdate value) throws IOException {
        if (value == null) {
          out.nullValue();
          return;
        }
        out.beginObject();

        out.name("project");
        out.value(value.project());

        out.name("refs");
        out.beginArray();
        for (String ref : value.refs()) {
          out.value(ref);
        }
        out.endArray();

        out.name("uri");
        out.value(value.uri());

        out.name("remote");
        out.value(value.remote());

        out.endObject();
      }

      @Nullable
      @Override
      public ReplicateRefUpdate read(JsonReader in) throws IOException {
        if (in.peek() == JsonToken.NULL) {
          in.nextNull();
          return null;
        }
        String project = null;
        Set<String> refs = new HashSet<>();
        URIish uri = null;
        String remote = null;

        String fieldname = null;
        in.beginObject();

        while (in.hasNext()) {
          JsonToken token = in.peek();

          if (token.equals(JsonToken.NAME)) {
            fieldname = in.nextName();
          }

          switch (fieldname) {
            case "project":
              project = in.nextString();
              break;
            case "refs":
              in.beginArray();
              while (in.hasNext()) {
                refs.add(in.nextString());
              }
              in.endArray();
              break;
            case "ref":
              refs.add(in.nextString());
              break;
            case "uri":
              try {
                uri = new URIish(in.nextString());
              } catch (URISyntaxException e) {
                throw new IOException("Unable to parse remote URI", e);
              }
              break;
            case "remote":
              remote = in.nextString();
              break;
            default:
              throw new IOException(String.format("Unknown field in stored task: %s", fieldname));
          }
        }

        in.endObject();
        return ReplicateRefUpdate.create(project, refs, uri, remote);
      }
    }

    @SuppressWarnings("unchecked")
    @Nullable
    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
      if (type.equals(TypeToken.get(AutoValue_ReplicationTasksStorage_ReplicateRefUpdate.class))
          || type.equals(TypeToken.get(ReplicateRefUpdate.class))) {
        return (TypeAdapter<T>) new ReplicateRefUpdateTypeAdapter<T>();
      }
      return null;
    }
  }

  @VisibleForTesting
  class Task {
    public final ReplicateRefUpdate update;
    public final String taskKey;
    public final Path running;
    public final Path waiting;

    public Task(ReplicateRefUpdate update) {
      this.update = update;
      taskKey = update.sha1();
      running = createDir(runningUpdates).resolve(taskKey);
      waiting = createDir(waitingUpdates).resolve(taskKey);
    }

    public String create() {
      if (Files.exists(waiting)) {
        return taskKey;
      }

      String json = gson.toJson(update) + "\n";
      try {
        Path tmp = Files.createTempFile(createDir(buildingUpdates), taskKey, null);
        logger.atFine().log("CREATE %s %s", tmp, updateLog());
        Files.write(tmp, json.getBytes(UTF_8));
        logger.atFine().log("RENAME %s %s %s", tmp, waiting, updateLog());
        rename(tmp, waiting);
      } catch (IOException e) {
        logger.atWarning().withCause(e).log("Couldn't create task %s", json);
      }
      return taskKey;
    }

    public boolean start() {
      return rename(waiting, running);
    }

    public void reset() {
      rename(running, waiting);
    }

    public void recover() {
      rename(running, waiting);
    }

    public boolean isWaiting() {
      return Files.exists(waiting);
    }

    public void finish() {
      try {
        logger.atFine().log("DELETE %s %s", running, updateLog());
        Files.delete(running);
      } catch (IOException e) {
        logger.atSevere().withCause(e).log("Error while deleting task %s", taskKey);
      }
    }

    @VisibleForTesting
    boolean rename(Path from, Path to) {
      try {
        logger.atFine().log("RENAME %s to %s %s", from, to, updateLog());
        Files.move(from, to, StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
        return true;
      } catch (IOException e) {
        String message = "Error while renaming task %s";
        if (isMultiPrimary() && e instanceof NoSuchFileException) {
          logger.atFine().log(
              message + " (expected regularly with multi-primaries and distributor enabled)",
              taskKey);
        } else {
          logger.atSevere().withCause(e).log(message, taskKey);
        }
        return false;
      }
    }

    private String updateLog() {
      return String.format("(%s:%s => %s)", update.project(), update.refs(), update.uri());
    }
  }
}