package gitbucket.core.service

import gitbucket.core.model.Account
import gitbucket.core.util.Directory._
import gitbucket.core.util.SyntaxSugars._
import org.eclipse.jgit.merge.{MergeStrategy, Merger, RecursiveMerger}
import org.eclipse.jgit.api.Git
import org.eclipse.jgit.transport.RefSpec
import org.eclipse.jgit.errors.NoMergeBaseException
import org.eclipse.jgit.lib.{CommitBuilder, ObjectId, PersonIdent, Repository}
import org.eclipse.jgit.revwalk.{RevCommit, RevWalk}

import scala.collection.JavaConverters._

trait MergeService {
  import MergeService._

  /**
   * Checks whether conflict will be caused in merging within pull request.
   * Returns true if conflict will be caused.
   */
  def checkConflict(userName: String, repositoryName: String, branch: String, issueId: Int): Option[String] = {
    using(Git.open(getRepositoryDir(userName, repositoryName))) { git =>
      new MergeCacheInfo(git, branch, issueId).checkConflict()
    }
  }

  /**
   * Checks whether conflict will be caused in merging within pull request.
   * only cache check.
   * Returns Some(true) if conflict will be caused.
   * Returns None if cache has not created yet.
   */
  def checkConflictCache(
    userName: String,
    repositoryName: String,
    branch: String,
    issueId: Int
  ): Option[Option[String]] = {
    using(Git.open(getRepositoryDir(userName, repositoryName))) { git =>
      new MergeCacheInfo(git, branch, issueId).checkConflictCache()
    }
  }

  /** merge the pull request with a merge commit */
  def mergePullRequest(git: Git, branch: String, issueId: Int, message: String, committer: PersonIdent): Unit = {
    new MergeCacheInfo(git, branch, issueId).merge(message, committer)
  }

  /** rebase to the head of the pull request branch */
  def rebasePullRequest(
    git: Git,
    branch: String,
    issueId: Int,
    commits: Seq[RevCommit],
    committer: PersonIdent
  ): Unit = {
    new MergeCacheInfo(git, branch, issueId).rebase(committer, commits)
  }

  /** squash commits in the pull request and append it */
  def squashPullRequest(git: Git, branch: String, issueId: Int, message: String, committer: PersonIdent): Unit = {
    new MergeCacheInfo(git, branch, issueId).squash(message, committer)
  }

  /** fetch remote branch to my repository refs/pull/{issueId}/head */
  def fetchAsPullRequest(
    userName: String,
    repositoryName: String,
    requestUserName: String,
    requestRepositoryName: String,
    requestBranch: String,
    issueId: Int
  ) {
    using(Git.open(getRepositoryDir(userName, repositoryName))) { git =>
      git.fetch
        .setRemote(getRepositoryDir(requestUserName, requestRepositoryName).toURI.toString)
        .setRefSpecs(new RefSpec(s"refs/heads/${requestBranch}:refs/pull/${issueId}/head"))
        .call
    }
  }

  /**
   * Checks whether conflict will be caused in merging. Returns true if conflict will be caused.
   */
  def tryMergeRemote(
    localUserName: String,
    localRepositoryName: String,
    localBranch: String,
    remoteUserName: String,
    remoteRepositoryName: String,
    remoteBranch: String
  ): Either[String, (ObjectId, ObjectId, ObjectId)] = {
    using(Git.open(getRepositoryDir(localUserName, localRepositoryName))) { git =>
      val remoteRefName = s"refs/heads/${remoteBranch}"
      val tmpRefName = s"refs/remote-temp/${remoteUserName}/${remoteRepositoryName}/${remoteBranch}"
      val refSpec = new RefSpec(s"${remoteRefName}:${tmpRefName}").setForceUpdate(true)
      try {
        // fetch objects from origin repository branch
        git.fetch
          .setRemote(getRepositoryDir(remoteUserName, remoteRepositoryName).toURI.toString)
          .setRefSpecs(refSpec)
          .call
        // merge conflict check
        val merger = MergeStrategy.RECURSIVE.newMerger(git.getRepository, true)
        val mergeBaseTip = git.getRepository.resolve(s"refs/heads/${localBranch}")
        val mergeTip = git.getRepository.resolve(tmpRefName)
        try {
          if (merger.merge(mergeBaseTip, mergeTip)) {
            Right((merger.getResultTreeId, mergeBaseTip, mergeTip))
          } else {
            Left(createConflictMessage(mergeTip, mergeBaseTip, merger))
          }
        } catch {
          case e: NoMergeBaseException => Left(e.toString)
        }
      } finally {
        val refUpdate = git.getRepository.updateRef(refSpec.getDestination)
        refUpdate.setForceUpdate(true)
        refUpdate.delete()
      }
    }
  }

  /**
   * Checks whether conflict will be caused in merging. Returns `Some(errorMessage)` if conflict will be caused.
   */
  def checkConflict(
    userName: String,
    repositoryName: String,
    branch: String,
    requestUserName: String,
    requestRepositoryName: String,
    requestBranch: String
  ): Option[String] =
    tryMergeRemote(userName, repositoryName, branch, requestUserName, requestRepositoryName, requestBranch).left.toOption

  def pullRemote(
    localUserName: String,
    localRepositoryName: String,
    localBranch: String,
    remoteUserName: String,
    remoteRepositoryName: String,
    remoteBranch: String,
    loginAccount: Account,
    message: String
  ): Option[ObjectId] = {
    tryMergeRemote(localUserName, localRepositoryName, localBranch, remoteUserName, remoteRepositoryName, remoteBranch).map {
      case (newTreeId, oldBaseId, oldHeadId) =>
        using(Git.open(getRepositoryDir(localUserName, localRepositoryName))) { git =>
          val committer = new PersonIdent(loginAccount.fullName, loginAccount.mailAddress)
          val newCommit =
            Util.createMergeCommit(git.getRepository, newTreeId, committer, message, Seq(oldBaseId, oldHeadId))
          Util.updateRefs(git.getRepository, s"refs/heads/${localBranch}", newCommit, false, committer, Some("merge"))
        }
        oldBaseId
    }.toOption
  }

}

object MergeService {

  object Util {
    // return merge commit id
    def createMergeCommit(
      repository: Repository,
      treeId: ObjectId,
      committer: PersonIdent,
      message: String,
      parents: Seq[ObjectId]
    ): ObjectId = {
      val mergeCommit = new CommitBuilder()
      mergeCommit.setTreeId(treeId)
      mergeCommit.setParentIds(parents: _*)
      mergeCommit.setAuthor(committer)
      mergeCommit.setCommitter(committer)
      mergeCommit.setMessage(message)
      // insertObject and got mergeCommit Object Id
      using(repository.newObjectInserter) { inserter =>
        val mergeCommitId = inserter.insert(mergeCommit)
        inserter.flush()
        mergeCommitId
      }
    }

    def updateRefs(
      repository: Repository,
      ref: String,
      newObjectId: ObjectId,
      force: Boolean,
      committer: PersonIdent,
      refLogMessage: Option[String] = None
    ): Unit = {
      val refUpdate = repository.updateRef(ref)
      refUpdate.setNewObjectId(newObjectId)
      refUpdate.setForceUpdate(force)
      refUpdate.setRefLogIdent(committer)
      refLogMessage.map(refUpdate.setRefLogMessage(_, true))
      refUpdate.update()
    }
  }

  class MergeCacheInfo(git: Git, branch: String, issueId: Int) {

    private val repository = git.getRepository

    private val mergedBranchName = s"refs/pull/${issueId}/merge"
    private val conflictedBranchName = s"refs/pull/${issueId}/conflict"

    lazy val mergeBaseTip = repository.resolve(s"refs/heads/${branch}")
    lazy val mergeTip = repository.resolve(s"refs/pull/${issueId}/head")

    def checkConflictCache(): Option[Option[String]] = {
      Option(repository.resolve(mergedBranchName))
        .flatMap { merged =>
          if (parseCommit(merged).getParents().toSet == Set(mergeBaseTip, mergeTip)) {
            // merged branch exists
            Some(None)
          } else {
            None
          }
        }
        .orElse(Option(repository.resolve(conflictedBranchName)).flatMap { conflicted =>
          val commit = parseCommit(conflicted)
          if (commit.getParents().toSet == Set(mergeBaseTip, mergeTip)) {
            // conflict branch exists
            Some(Some(commit.getFullMessage))
          } else {
            None
          }
        })
    }

    def checkConflict(): Option[String] = {
      checkConflictCache.getOrElse(checkConflictForce)
    }

    def checkConflictForce(): Option[String] = {
      val merger = MergeStrategy.RECURSIVE.newMerger(repository, true)
      val conflicted = try {
        !merger.merge(mergeBaseTip, mergeTip)
      } catch {
        case e: NoMergeBaseException => true
      }
      val mergeTipCommit = using(new RevWalk(repository))(_.parseCommit(mergeTip))
      val committer = mergeTipCommit.getCommitterIdent

      def _updateBranch(treeId: ObjectId, message: String, branchName: String) {
        // creates merge commit
        val mergeCommitId = createMergeCommit(treeId, committer, message)
        Util.updateRefs(repository, branchName, mergeCommitId, true, committer)
      }

      if (!conflicted) {
        _updateBranch(merger.getResultTreeId, s"Merge ${mergeTip.name} into ${mergeBaseTip.name}", mergedBranchName)
        git.branchDelete().setForce(true).setBranchNames(conflictedBranchName).call()
        None
      } else {
        val message = createConflictMessage(mergeTip, mergeBaseTip, merger)
        _updateBranch(mergeTipCommit.getTree().getId(), message, conflictedBranchName)
        git.branchDelete().setForce(true).setBranchNames(mergedBranchName).call()
        Some(message)
      }
    }

    // update branch from cache
    def merge(message: String, committer: PersonIdent) = {
      if (checkConflict().isDefined) {
        throw new RuntimeException("This pull request can't merge automatically.")
      }
      val mergeResultCommit = parseCommit(Option(repository.resolve(mergedBranchName)).getOrElse {
        throw new RuntimeException(s"Not found branch ${mergedBranchName}")
      })
      // creates merge commit
      val mergeCommitId = createMergeCommit(mergeResultCommit.getTree().getId(), committer, message)
      // update refs
      Util.updateRefs(repository, s"refs/heads/${branch}", mergeCommitId, false, committer, Some("merged"))
    }

    def rebase(committer: PersonIdent, commits: Seq[RevCommit]): Unit = {
      if (checkConflict().isDefined) {
        throw new RuntimeException("This pull request can't merge automatically.")
      }

      def _cloneCommit(commit: RevCommit, parentId: ObjectId, baseId: ObjectId): CommitBuilder = {
        val merger = MergeStrategy.RECURSIVE.newMerger(repository, true)
        merger.merge(commit.toObjectId, baseId)

        val newCommit = new CommitBuilder()
        newCommit.setTreeId(merger.getResultTreeId)
        newCommit.addParentId(parentId)
        newCommit.setAuthor(commit.getAuthorIdent)
        newCommit.setCommitter(committer)
        newCommit.setMessage(commit.getFullMessage)
        newCommit
      }

      val mergeBaseTipCommit = using(new RevWalk(repository))(_.parseCommit(mergeBaseTip))
      var previousId = mergeBaseTipCommit.getId

      using(repository.newObjectInserter) { inserter =>
        commits.foreach { commit =>
          val nextCommit = _cloneCommit(commit, previousId, mergeBaseTipCommit.getId)
          previousId = inserter.insert(nextCommit)
        }
        inserter.flush()
      }

      Util.updateRefs(repository, s"refs/heads/${branch}", previousId, false, committer, Some("rebased"))
    }

    def squash(message: String, committer: PersonIdent): Unit = {
      if (checkConflict().isDefined) {
        throw new RuntimeException("This pull request can't merge automatically.")
      }

      val mergeBaseTipCommit = using(new RevWalk(repository))(_.parseCommit(mergeBaseTip))
      val mergeBranchHeadCommit = using(new RevWalk(repository))(_.parseCommit(repository.resolve(mergedBranchName)))

      // Create squash commit
      val mergeCommit = new CommitBuilder()
      mergeCommit.setTreeId(mergeBranchHeadCommit.getTree.getId)
      mergeCommit.setParentId(mergeBaseTipCommit)
      mergeCommit.setAuthor(mergeBranchHeadCommit.getAuthorIdent)
      mergeCommit.setCommitter(committer)
      mergeCommit.setMessage(message)

      // insertObject and got squash commit Object Id
      val newCommitId = using(repository.newObjectInserter) { inserter =>
        val newCommitId = inserter.insert(mergeCommit)
        inserter.flush()
        newCommitId
      }

      Util.updateRefs(repository, mergedBranchName, newCommitId, true, committer)

      // rebase to squash commit
      Util.updateRefs(
        repository,
        s"refs/heads/${branch}",
        repository.resolve(mergedBranchName),
        false,
        committer,
        Some("squashed")
      )
    }

    // return treeId
    private def createMergeCommit(treeId: ObjectId, committer: PersonIdent, message: String) =
      Util.createMergeCommit(repository, treeId, committer, message, Seq[ObjectId](mergeBaseTip, mergeTip))

    private def parseCommit(id: ObjectId) = using(new RevWalk(repository))(_.parseCommit(id))

  }

  private def createConflictMessage(mergeTip: ObjectId, mergeBaseTip: ObjectId, merger: Merger): String = {
    val mergeResults = merger.asInstanceOf[RecursiveMerger].getMergeResults

    s"Can't merge ${mergeTip.name} into ${mergeBaseTip.name}\n\n" +
      "Conflicting files:\n" +
      mergeResults.asScala.map { case (key, _) => "- `" + key + "`\n" }.mkString
  }

}