// Copyright (C) 2019 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.analytics.common

import com.google.common.cache.CacheLoader
import com.google.gerrit.extensions.api.projects.CommentLinkInfo
import com.google.gerrit.reviewdb.client.Project
import com.google.gerrit.server.git.GitRepositoryManager
import com.google.gerrit.server.project.ProjectCache
import com.google.inject.Inject
import com.googlesource.gerrit.plugins.analytics.{CommitInfo, IssueInfo}
import com.googlesource.gerrit.plugins.analytics.common.ManagedResource.use
import org.eclipse.jgit.diff.{DiffFormatter, RawTextComparator}
import org.eclipse.jgit.revwalk.RevWalk
import org.eclipse.jgit.treewalk.{CanonicalTreeParser, EmptyTreeIterator}
import org.eclipse.jgit.util.io.DisabledOutputStream

import scala.collection.JavaConverters._
import scala.util.matching.Regex

class CommitsStatisticsLoader @Inject() (gitRepositoryManager: GitRepositoryManager, projectCache: ProjectCache, botLikeExtractor: BotLikeExtractor) extends CacheLoader[CommitsStatisticsCacheKey, CommitsStatistics] {

  override def load(cacheKey: CommitsStatisticsCacheKey): CommitsStatistics = {
    import RevisionBrowsingSupport._

    val objectId = cacheKey.commitId
    val nameKey = new Project.NameKey(cacheKey.projectName)
    val commentInfoList: Seq[CommentLinkInfo] = projectCache.get(nameKey).getCommentLinks.asScala
    val replacers = commentInfoList.map(info =>
      Replacer(
        info.`match`.r,
        Option(info.link).getOrElse(info.html)))

    use(gitRepositoryManager.openRepository(nameKey)) { repo =>

      // I can imagine this kind of statistics is already being available in Gerrit but couldn't understand how to access it
      // which Injection can be useful for this task?
        use(new RevWalk(repo)) { rw =>
          val reader = repo.newObjectReader()
          val commit = rw.parseCommit(objectId)
          val commitMessage = commit.getFullMessage

          val oldTree = {
            // protects against initial commit
            if (commit.getParentCount == 0)
              new EmptyTreeIterator
            else
              new CanonicalTreeParser(null, reader, rw.parseCommit(commit.getParent(0).getId).getTree)
          }

          val newTree = new CanonicalTreeParser(null, reader, commit.getTree)

          val df = new DiffFormatter(DisabledOutputStream.INSTANCE)
          df.setRepository(repo)
          df.setDiffComparator(RawTextComparator.DEFAULT)
          df.setDetectRenames(true)
          val diffs = df.scan(oldTree, newTree).asScala

          val lines = (for {
            diff <- diffs
            edit <- df.toFileHeader(diff).toEditList.asScala
          } yield Lines(edit.getEndA - edit.getBeginA, edit.getEndB - edit.getBeginB)).fold(Lines(0, 0))(_ + _)

          val files: Set[String] = diffs.map(df.toFileHeader(_).getNewPath).toSet

          val commitInfo = CommitInfo(objectId.getName, commit.getAuthorIdent.getWhen.getTime, commit.isMerge, botLikeExtractor.isBotLike(files), files)
          val commitsStats = CommitsStatistics(lines.added, lines.deleted, commitInfo.merge, commitInfo.botLike, List(commitInfo), extractIssues(commitMessage, replacers).toList)

          commitsStats
        }
    }
  }

  private def extractIssues(commitMessage: String, replacers: Seq[Replacer]): Seq[IssueInfo] =
    replacers.flatMap {
      case Replacer(pattern, replaced) =>
        pattern.findAllIn(commitMessage)
          .map(code => {
            val transformed = pattern.replaceAllIn(code, replaced)
            IssueInfo(code, transformed)
          })
    }


  final private case class Replacer(pattern: Regex, replaced: String)

  final private case class Lines(deleted: Int, added: Int) {
    def +(other: Lines) = Lines(deleted + other.deleted, added + other.added)
  }
}