// Copyright (C) 2014 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.change;

import com.google.auto.value.AutoValue;
import com.google.common.base.Function;
import com.google.common.collect.Collections2;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;
import com.google.common.collect.MultimapBuilder;
import com.google.common.collect.Ordering;
import com.google.gerrit.common.Nullable;
import com.google.gerrit.extensions.api.changes.FixInput;
import com.google.gerrit.extensions.common.ProblemInfo;
import com.google.gerrit.extensions.common.ProblemInfo.Status;
import com.google.gerrit.reviewdb.client.Change;
import com.google.gerrit.reviewdb.client.PatchSet;
import com.google.gerrit.reviewdb.client.Project;
import com.google.gerrit.reviewdb.server.ReviewDb;
import com.google.gerrit.server.CurrentUser;
import com.google.gerrit.server.GerritPersonIdent;
import com.google.gerrit.server.IdentifiedUser;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.patch.PatchSetInfoFactory;
import com.google.gerrit.server.patch.PatchSetInfoNotAvailableException;
import com.google.gerrit.server.query.change.ChangeData;
import com.google.gwtorm.server.AtomicUpdate;
import com.google.gwtorm.server.OrmException;
import com.google.inject.Inject;
import com.google.inject.Provider;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.PersonIdent;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.RefUpdate;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;

/**
 * Checks changes for various kinds of inconsistency and corruption.
 * <p>
 * A single instance may be reused for checking multiple changes, but not
 * concurrently.
 */
public class ConsistencyChecker {
  private static final Logger log =
      LoggerFactory.getLogger(ConsistencyChecker.class);

  @AutoValue
  public abstract static class Result {
    private static Result create(Change.Id id, List<ProblemInfo> problems) {
      return new AutoValue_ConsistencyChecker_Result(id, null, problems);
    }

    private static Result create(Change c, List<ProblemInfo> problems) {
      return new AutoValue_ConsistencyChecker_Result(c.getId(), c, problems);
    }

    public abstract Change.Id id();

    @Nullable
    public abstract Change change();

    public abstract List<ProblemInfo> problems();
  }

  private final Provider<ReviewDb> db;
  private final GitRepositoryManager repoManager;
  private final Provider<CurrentUser> user;
  private final Provider<PersonIdent> serverIdent;
  private final PatchSetInfoFactory patchSetInfoFactory;

  private FixInput fix;
  private Change change;
  private Repository repo;
  private RevWalk rw;

  private PatchSet currPs;
  private RevCommit currPsCommit;

  private List<ProblemInfo> problems;

  @Inject
  ConsistencyChecker(Provider<ReviewDb> db,
      GitRepositoryManager repoManager,
      Provider<CurrentUser> user,
      @GerritPersonIdent Provider<PersonIdent> serverIdent,
      PatchSetInfoFactory patchSetInfoFactory) {
    this.db = db;
    this.repoManager = repoManager;
    this.user = user;
    this.serverIdent = serverIdent;
    this.patchSetInfoFactory = patchSetInfoFactory;
    reset();
  }

  private void reset() {
    change = null;
    repo = null;
    rw = null;
    problems = new ArrayList<>();
  }

  public Result check(ChangeData cd) {
    return check(cd, null);
  }

  public Result check(ChangeData cd, @Nullable FixInput f) {
    reset();
    try {
      return check(cd.change(), f);
    } catch (OrmException e) {
      error("Error looking up change", e);
      return Result.create(cd.getId(), problems);
    }
  }

  public Result check(Change c) {
    return check(c, null);
  }

  public Result check(Change c, @Nullable FixInput f) {
    reset();
    fix = f;
    change = c;
    try {
      checkImpl();
      return Result.create(c, problems);
    } finally {
      if (rw != null) {
        rw.release();
      }
      if (repo != null) {
        repo.close();
      }
    }
  }

  private void checkImpl() {
    checkOwner();
    checkCurrentPatchSetEntity();

    // All checks that require the repo.
    if (!openRepo()) {
      return;
    }
    if (!checkPatchSets()) {
      return;
    }
    checkMerged();
  }

  private void checkOwner() {
    try {
      if (db.get().accounts().get(change.getOwner()) == null) {
        problem("Missing change owner: " + change.getOwner());
      }
    } catch (OrmException e) {
      error("Failed to look up owner", e);
    }
  }

  private void checkCurrentPatchSetEntity() {
    try {
      PatchSet.Id psId = change.currentPatchSetId();
      currPs = db.get().patchSets().get(psId);
      if (currPs == null) {
        problem(String.format("Current patch set %d not found", psId.get()));
      }
    } catch (OrmException e) {
      error("Failed to look up current patch set", e);
    }
  }

  private boolean openRepo() {
    Project.NameKey project = change.getDest().getParentKey();
    try {
      repo = repoManager.openRepository(project);
      rw = new RevWalk(repo);
      return true;
    } catch (RepositoryNotFoundException e) {
      return error("Destination repository not found: " + project, e);
    } catch (IOException e) {
      return error("Failed to open repository: " + project, e);
    }
  }

  private static final Function<PatchSet, Integer> TO_PS_ID =
      new Function<PatchSet, Integer>() {
        @Override
        public Integer apply(PatchSet in) {
          return in.getId().get();
        }
      };

  private static final Ordering<PatchSet> PS_ID_ORDER = Ordering.natural()
    .onResultOf(TO_PS_ID);

  private boolean checkPatchSets() {
    List<PatchSet> all;
    try {
      all = Lists.newArrayList(db.get().patchSets().byChange(change.getId()));
    } catch (OrmException e) {
      return error("Failed to look up patch sets", e);
    }
    // Iterate in descending order so deletePatchSet can assume the latest patch
    // set exists.
    Collections.sort(all, PS_ID_ORDER.reverse());
    Multimap<ObjectId, PatchSet> bySha = MultimapBuilder.hashKeys(all.size())
        .treeSetValues(PS_ID_ORDER)
        .build();
    for (PatchSet ps : all) {
      // Check revision format.
      ObjectId objId;
      String rev = ps.getRevision().get();
      int psNum = ps.getId().get();
      String refName = ps.getId().toRefName();
      try {
        objId = ObjectId.fromString(rev);
      } catch (IllegalArgumentException e) {
        error(String.format("Invalid revision on patch set %d: %s", psNum, rev),
            e);
        continue;
      }
      bySha.put(objId, ps);

      // Check ref existence.
      ProblemInfo refProblem = null;
      try {
        Ref ref = repo.getRef(refName);
        if (ref == null) {
          refProblem = problem("Ref missing: " + refName);
        } else if (!objId.equals(ref.getObjectId())) {
          String actual = ref.getObjectId() != null
              ? ref.getObjectId().name()
              : "null";
          refProblem = problem(String.format(
              "Expected %s to point to %s, found %s",
              ref.getName(), objId.name(), actual));
        }
      } catch (IOException e) {
        error("Error reading ref: " + refName, e);
        refProblem = lastProblem();
      }

      // Check object existence.
      RevCommit psCommit = parseCommit(
          objId, String.format("patch set %d", psNum));
      if (psCommit == null) {
        if (fix != null && fix.deletePatchSetIfCommitMissing) {
          deletePatchSet(lastProblem(), ps.getId());
        }
        continue;
      } else if (refProblem != null && fix != null) {
        fixPatchSetRef(refProblem, ps);
      }
      if (ps.getId().equals(change.currentPatchSetId())) {
        currPsCommit = psCommit;
      }
    }

    // Check for duplicates.
    for (Map.Entry<ObjectId, Collection<PatchSet>> e
        : bySha.asMap().entrySet()) {
      if (e.getValue().size() > 1) {
        problem(String.format("Multiple patch sets pointing to %s: %s",
            e.getKey().name(),
            Collections2.transform(e.getValue(), TO_PS_ID)));
      }
    }

    return currPs != null && currPsCommit != null;
  }

  private void checkMerged() {
    String refName = change.getDest().get();
    Ref dest;
    try {
      dest = repo.getRef(refName);
    } catch (IOException e) {
      problem("Failed to look up destination ref: " + refName);
      return;
    }
    if (dest == null) {
      problem("Destination ref not found (may be new branch): "
          + change.getDest().get());
      return;
    }
    RevCommit tip = parseCommit(dest.getObjectId(),
        "destination ref " + refName);
    if (tip == null) {
      return;
    }
    boolean merged;
    try {
      merged = rw.isMergedInto(currPsCommit, tip);
    } catch (IOException e) {
      problem("Error checking whether patch set " + currPs.getId().get()
          + " is merged");
      return;
    }
    if (merged && change.getStatus() != Change.Status.MERGED) {
      ProblemInfo p = problem(String.format(
          "Patch set %d (%s) is merged into destination ref %s (%s), but change"
          + " status is %s", currPs.getId().get(), currPsCommit.name(),
          refName, tip.name(), change.getStatus()));
      if (fix != null) {
        fixMerged(p);
      }
    } else if (!merged && change.getStatus() == Change.Status.MERGED) {
      problem(String.format("Patch set %d (%s) is not merged into"
            + " destination ref %s (%s), but change status is %s",
            currPs.getId().get(), currPsCommit.name(), refName, tip.name(),
            change.getStatus()));
    }
  }

  private void fixMerged(ProblemInfo p) {
    try {
      change = db.get().changes().atomicUpdate(change.getId(),
          new AtomicUpdate<Change>() {
            @Override
            public Change update(Change c) {
              c.setStatus(Change.Status.MERGED);
              return c;
            }
          });
      p.status = Status.FIXED;
      p.outcome = "Marked change as merged";
    } catch (OrmException e) {
      log.warn("Error marking " + change.getId() + "as merged", e);
      p.status = Status.FIX_FAILED;
      p.outcome = "Error updating status to merged";
    }
  }

  private void fixPatchSetRef(ProblemInfo p, PatchSet ps) {
    try {
      RefUpdate ru = repo.updateRef(ps.getId().toRefName());
      ru.setForceUpdate(true);
      ru.setNewObjectId(ObjectId.fromString(ps.getRevision().get()));
      ru.setRefLogIdent(newRefLogIdent());
      ru.setRefLogMessage("Repair patch set ref", true);
      RefUpdate.Result result = ru.update();
      switch (result) {
        case NEW:
        case FORCED:
        case FAST_FORWARD:
        case NO_CHANGE:
          p.status = Status.FIXED;
          p.outcome = "Repaired patch set ref";
          return;
        default:
          p.status = Status.FIX_FAILED;
          p.outcome = "Failed to update patch set ref: " + result;
          return;
      }
    } catch (IOException e) {
      String msg = "Error fixing patch set ref";
      log.warn(msg + ' ' + ps.getId().toRefName(), e);
      p.status = Status.FIX_FAILED;
      p.outcome = msg;
    }
  }

  private void deletePatchSet(ProblemInfo p, PatchSet.Id psId) {
    ReviewDb db = this.db.get();
    Change.Id cid = psId.getParentKey();
    try {
      db.changes().beginTransaction(cid);
      try {
        Change c = db.changes().get(cid);
        if (c == null) {
          throw new OrmException("Change missing: " + cid);
        }

        if (psId.equals(c.currentPatchSetId())) {
          List<PatchSet> all = Lists.newArrayList(db.patchSets().byChange(cid));
          if (all.size() == 1 && all.get(0).getId().equals(psId)) {
            p.status = Status.FIX_FAILED;
            p.outcome = "Cannot delete patch set; no patch sets would remain";
            return;
          }
          // If there were multiple missing patch sets, assumes deletePatchSet
          // has been called in decreasing order, so the max remaining PatchSet
          // is the effective current patch set.
          Collections.sort(all, PS_ID_ORDER.reverse());
          PatchSet.Id latest = null;
          for (PatchSet ps : all) {
            latest = ps.getId();
            if (!ps.getId().equals(psId)) {
              break;
            }
          }
          c.setCurrentPatchSet(patchSetInfoFactory.get(db, latest));
          db.changes().update(Collections.singleton(c));
        }

        // Delete dangling primary key references. Don't delete ChangeMessages,
        // which don't use patch sets as a primary key, and may provide useful
        // historical information.
        db.accountPatchReviews().delete(
            db.accountPatchReviews().byPatchSet(psId));
        db.patchSetAncestors().delete(
            db.patchSetAncestors().byPatchSet(psId));
        db.patchSetApprovals().delete(
            db.patchSetApprovals().byPatchSet(psId));
        db.patchComments().delete(
            db.patchComments().byPatchSet(psId));
        db.patchSets().deleteKeys(Collections.singleton(psId));
        db.commit();

        p.status = Status.FIXED;
        p.outcome = "Deleted patch set";
      } finally {
        db.rollback();
      }
    } catch (PatchSetInfoNotAvailableException | OrmException e) {
      String msg = "Error deleting patch set";
      log.warn(msg + ' ' + psId, e);
      p.status = Status.FIX_FAILED;
      p.outcome = msg;
    }
  }

  private PersonIdent newRefLogIdent() {
    CurrentUser u = user.get();
    if (u.isIdentifiedUser()) {
      return ((IdentifiedUser) u).newRefLogIdent();
    } else {
      return serverIdent.get();
    }
  }

  private RevCommit parseCommit(ObjectId objId, String desc) {
    try {
      return rw.parseCommit(objId);
    } catch (MissingObjectException e) {
      problem(String.format("Object missing: %s: %s", desc, objId.name()));
    } catch (IncorrectObjectTypeException e) {
      problem(String.format("Not a commit: %s: %s", desc, objId.name()));
    } catch (IOException e) {
      problem(String.format("Failed to look up: %s: %s", desc, objId.name()));
    }
    return null;
  }

  private ProblemInfo problem(String msg) {
    ProblemInfo p = new ProblemInfo();
    p.message = msg;
    problems.add(p);
    return p;
  }

  private ProblemInfo lastProblem() {
    return problems.get(problems.size() - 1);
  }

  private boolean error(String msg, Throwable t) {
    problem(msg);
    // TODO(dborowitz): Expose stack trace to administrators.
    log.warn("Error in consistency check of change " + change.getId(), t);
    return false;
  }
}