// Copyright (C) 2017 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.google.gerrit.server.schema;

import com.google.common.base.Stopwatch;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import com.google.gerrit.reviewdb.client.Account;
import com.google.gerrit.reviewdb.client.RefNames;
import com.google.gerrit.reviewdb.server.ReviewDb;
import com.google.gerrit.server.GerritPersonIdent;
import com.google.gerrit.server.config.AllUsersName;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gwtorm.server.OrmException;
import com.google.inject.Inject;
import com.google.inject.Provider;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Timestamp;
import java.text.ParseException;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
import org.eclipse.jgit.internal.storage.file.FileRepository;
import org.eclipse.jgit.internal.storage.file.GC;
import org.eclipse.jgit.lib.CommitBuilder;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.PersonIdent;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.RefUpdate;
import org.eclipse.jgit.lib.RefUpdate.Result;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.lib.TextProgressMonitor;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevSort;
import org.eclipse.jgit.revwalk.RevWalk;

/**
 * Make sure that for every account a user branch exists that has an initial empty commit with the
 * registration date as commit time.
 *
 * <p>For accounts that don't have a user branch yet the user branch is created with an initial
 * empty commit that has the registration date as commit time.
 *
 * <p>For accounts that already have a user branch the user branch is rewritten and an initial empty
 * commit with the registration date as commit time is inserted (if such a commit doesn't exist
 * yet).
 */
public class Schema_146 extends SchemaVersion {
  private static final String CREATE_ACCOUNT_MSG = "Create Account";

  private final GitRepositoryManager repoManager;
  private final AllUsersName allUsersName;
  private final PersonIdent serverIdent;
  private AtomicInteger i = new AtomicInteger();
  private Stopwatch sw = Stopwatch.createStarted();
  ReentrantLock gcLock = new ReentrantLock();
  private int size;

  @Inject
  Schema_146(
      Provider<Schema_145> prior,
      GitRepositoryManager repoManager,
      AllUsersName allUsersName,
      @GerritPersonIdent PersonIdent serverIdent) {
    super(prior);
    this.repoManager = repoManager;
    this.allUsersName = allUsersName;
    this.serverIdent = serverIdent;
  }

  @Override
  protected void migrateData(ReviewDb db, UpdateUI ui) throws OrmException, SQLException {
    ui.message("Migrating accounts");
    Set<Entry<Account.Id, Timestamp>> accounts = scanAccounts(db, ui).entrySet();
    gc(ui);
    Set<List<Entry<Account.Id, Timestamp>>> batches =
        Sets.newHashSet(Iterables.partition(accounts, 500));
    ExecutorService pool = createExecutor(ui);
    try {
      batches.stream().forEach(batch -> pool.submit(() -> processBatch(batch, ui)));
      pool.shutdown();
      pool.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
    } catch (InterruptedException e) {
      throw new RuntimeException(e);
    }
    ui.message(
        String.format("... (%.3f s) Migrated all %d accounts to schema 146", elapsed(), i.get()));
  }

  private ExecutorService createExecutor(UpdateUI ui) {
    int threads;
    try {
      threads = Integer.parseInt(System.getProperty("threadcount"));
    } catch (NumberFormatException e) {
      threads = Runtime.getRuntime().availableProcessors();
    }
    ui.message(String.format("... using %d threads ...", threads));
    return Executors.newFixedThreadPool(threads);
  }

  private void processBatch(List<Entry<Account.Id, Timestamp>> batch, UpdateUI ui) {
    try (Repository repo = repoManager.openRepository(allUsersName);
        RevWalk rw = new RevWalk(repo);
        ObjectInserter oi = repo.newObjectInserter()) {
      ObjectId emptyTree = emptyTree(oi);

      for (Map.Entry<Account.Id, Timestamp> e : batch) {
        String refName = RefNames.refsUsers(e.getKey());
        Ref ref = repo.exactRef(refName);
        if (ref != null) {
          rewriteUserBranch(repo, rw, oi, emptyTree, ref, e.getValue());
        } else {
          createUserBranch(repo, oi, emptyTree, e.getKey(), e.getValue());
        }
        int count = i.incrementAndGet();
        showProgress(ui, count);
        if (count % 1000 == 0) {
          gc(repo, true, ui);
        }
      }
    } catch (IOException e) {
      throw new UncheckedIOException(e);
    }
  }

  private double elapsed() {
    return sw.elapsed(TimeUnit.MILLISECONDS) / 1000d;
  }

  private void showProgress(UpdateUI ui, int count) {
    if (count % 100 == 0) {
      ui.message(
          String.format(
              "... (%.3f s) migrated %d%% (%d/%d) accounts",
              elapsed(), Math.round(100.0 * count / size), count, size));
    }
  }

  private void gc(UpdateUI ui) {
    try (Repository repo = repoManager.openRepository(allUsersName)) {
      gc(repo, false, ui);
    } catch (IOException e) {
      throw new UncheckedIOException(e);
    }
  }

  private void gc(Repository repo, boolean refsOnly, UpdateUI ui) {
    if (repo instanceof FileRepository && gcLock.tryLock()) {
      ProgressMonitor pm = null;
      try {
        pm = new TextProgressMonitor();
        FileRepository r = (FileRepository) repo;
        GC gc = new GC(r);
        gc.setProgressMonitor(pm);
        pm.beginTask("gc", ProgressMonitor.UNKNOWN);
        if (refsOnly) {
          ui.message(String.format("... (%.3f s) pack refs", elapsed()));
          gc.packRefs();
        } else {
          ui.message(String.format("... (%.3f s) gc --prune=now", elapsed()));
          gc.setExpire(new Date());
          gc.gc();
        }
      } catch (IOException | ParseException e) {
        throw new RuntimeException(e);
      } finally {
        gcLock.unlock();
        if (pm != null) {
          pm.endTask();
        }
      }
    }
  }

  private void rewriteUserBranch(
      Repository repo,
      RevWalk rw,
      ObjectInserter oi,
      ObjectId emptyTree,
      Ref ref,
      Timestamp registeredOn)
      throws IOException {
    ObjectId current = createInitialEmptyCommit(oi, emptyTree, registeredOn);

    rw.reset();
    rw.sort(RevSort.TOPO);
    rw.sort(RevSort.REVERSE, true);
    rw.markStart(rw.parseCommit(ref.getObjectId()));

    RevCommit c;
    while ((c = rw.next()) != null) {
      if (isInitialEmptyCommit(emptyTree, c)) {
        return;
      }

      CommitBuilder cb = new CommitBuilder();
      cb.setParentId(current);
      cb.setTreeId(c.getTree());
      cb.setAuthor(c.getAuthorIdent());
      cb.setCommitter(c.getCommitterIdent());
      cb.setMessage(c.getFullMessage());
      cb.setEncoding(c.getEncoding());
      current = oi.insert(cb);
    }

    oi.flush();

    RefUpdate ru = repo.updateRef(ref.getName());
    ru.setExpectedOldObjectId(ref.getObjectId());
    ru.setNewObjectId(current);
    ru.setForceUpdate(true);
    ru.setRefLogIdent(serverIdent);
    ru.setRefLogMessage(getClass().getSimpleName(), true);
    Result result = ru.update();
    if (result != Result.FORCED) {
      throw new IOException(
          String.format("Failed to update ref %s: %s", ref.getName(), result.name()));
    }
  }

  public void createUserBranch(
      Repository repo,
      ObjectInserter oi,
      ObjectId emptyTree,
      Account.Id accountId,
      Timestamp registeredOn)
      throws IOException {
    ObjectId id = createInitialEmptyCommit(oi, emptyTree, registeredOn);

    String refName = RefNames.refsUsers(accountId);
    RefUpdate ru = repo.updateRef(refName);
    ru.setExpectedOldObjectId(ObjectId.zeroId());
    ru.setNewObjectId(id);
    ru.setRefLogIdent(serverIdent);
    ru.setRefLogMessage(CREATE_ACCOUNT_MSG, false);
    Result result = ru.update();
    if (result != Result.NEW) {
      throw new IOException(String.format("Failed to update ref %s: %s", refName, result.name()));
    }
  }

  private ObjectId createInitialEmptyCommit(
      ObjectInserter oi, ObjectId emptyTree, Timestamp registrationDate) throws IOException {
    PersonIdent ident = new PersonIdent(serverIdent, registrationDate);

    CommitBuilder cb = new CommitBuilder();
    cb.setTreeId(emptyTree);
    cb.setCommitter(ident);
    cb.setAuthor(ident);
    cb.setMessage(CREATE_ACCOUNT_MSG);
    return oi.insert(cb);
  }

  private boolean isInitialEmptyCommit(ObjectId emptyTree, RevCommit c) {
    return c.getParentCount() == 0
        && c.getTree().equals(emptyTree)
        && c.getShortMessage().equals(CREATE_ACCOUNT_MSG);
  }

  private static ObjectId emptyTree(ObjectInserter oi) throws IOException {
    return oi.insert(Constants.OBJ_TREE, new byte[] {});
  }

  private Map<Account.Id, Timestamp> scanAccounts(ReviewDb db, UpdateUI ui) throws SQLException {
    ui.message(String.format("... (%.3f s) scan accounts", elapsed()));
    try (Statement stmt = newStatement(db);
        ResultSet rs = stmt.executeQuery("SELECT account_id, registered_on FROM accounts")) {
      HashMap<Account.Id, Timestamp> m = new HashMap<>();
      while (rs.next()) {
        m.put(new Account.Id(rs.getInt(1)), rs.getTimestamp(2));
      }
      size = m.size();
      return m;
    }
  }
}