// Copyright (C) 2012 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.git;

import com.google.gerrit.server.git.CodeReviewCommit.CodeReviewRevWalk;

import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevFlag;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

public class RebaseSorter {
  private final CodeReviewRevWalk rw;
  private final RevFlag canMergeFlag;
  private final RevCommit initialTip;
  private final Set<RevCommit> alreadyAccepted;

  public RebaseSorter(CodeReviewRevWalk rw, RevCommit initialTip,
      Set<RevCommit> alreadyAccepted, RevFlag canMergeFlag) {
    this.rw = rw;
    this.canMergeFlag = canMergeFlag;
    this.initialTip = initialTip;
    this.alreadyAccepted = alreadyAccepted;
  }

  public List<CodeReviewCommit> sort(Collection<CodeReviewCommit> incoming)
      throws IOException {
    final List<CodeReviewCommit> sorted = new ArrayList<>();
    final Set<CodeReviewCommit> sort = new HashSet<>(incoming);
    while (!sort.isEmpty()) {
      final CodeReviewCommit n = removeOne(sort);

      rw.resetRetain(canMergeFlag);
      rw.markStart(n);
      if (initialTip != null) {
        rw.markUninteresting(initialTip);
      }

      CodeReviewCommit c;
      final List<CodeReviewCommit> contents = new ArrayList<>();
      while ((c = rw.next()) != null) {
        if (!c.has(canMergeFlag) || !incoming.contains(c)) {
          if (isAlreadyMerged(c)) {
            rw.markUninteresting(c);
            break;
          }
          // We cannot merge n as it would bring something we
          // aren't permitted to merge at this time. Drop n.
          //
          if (n.missing == null) {
            n.setStatusCode(CommitMergeStatus.MISSING_DEPENDENCY);
            n.missing = new ArrayList<>();
          }
          n.missing.add(c);
        } else {
          contents.add(c);
        }
      }

      if (n.getStatusCode() == CommitMergeStatus.MISSING_DEPENDENCY) {
        continue;
      }

      sort.removeAll(contents);
      Collections.reverse(contents);
      sorted.removeAll(contents);
      sorted.addAll(contents);
    }
    return sorted;
  }

  private boolean isAlreadyMerged(CodeReviewCommit commit) throws IOException {
    try (CodeReviewRevWalk mirw =
        CodeReviewCommit.newRevWalk(rw.getObjectReader())) {
      mirw.reset();
      mirw.markStart(commit);
      for (RevCommit accepted : alreadyAccepted) {
        if (mirw.isMergedInto(mirw.parseCommit(commit),
            mirw.parseCommit(accepted))) {
          return true;
        }
      }
    }
    return false;
  }

  private static <T> T removeOne(final Collection<T> c) {
    final Iterator<T> i = c.iterator();
    final T r = i.next();
    i.remove();
    return r;
  }
}