// Copyright 2022 Harness Inc. All rights reserved.
// Use of this source code is governed by the Polyform Free Trial License
// that can be found in the LICENSE.md file for this repository.

package pullreq

import (
	"context"
	"fmt"
	"strconv"
	"time"

	"github.com/harness/gitness/events"
	"github.com/harness/gitness/gitrpc"
	gitrpcenum "github.com/harness/gitness/gitrpc/enum"
	pullreqevents "github.com/harness/gitness/internal/events/pullreq"
	"github.com/harness/gitness/pubsub"
	"github.com/harness/gitness/types"
	"github.com/harness/gitness/types/enum"
)

const (
	cancelMergeCheckKey = "cancel_merge_check_for_sha"
	nilSHA              = "0000000000000000000000000000000000000000"
)

// mergeCheckOnCreated handles pull request Created events.
// It creates the PR head git ref.
func (s *Service) mergeCheckOnCreated(ctx context.Context,
	event *events.Event[*pullreqevents.CreatedPayload],
) error {
	return s.updateMergeData(
		ctx,
		event.Payload.TargetRepoID,
		event.Payload.Number,
		nilSHA,
		event.Payload.SourceSHA,
	)
}

// mergeCheckOnBranchUpdate handles pull request Branch Updated events.
// It updates the PR head git ref to point to the latest commit.
func (s *Service) mergeCheckOnBranchUpdate(ctx context.Context,
	event *events.Event[*pullreqevents.BranchUpdatedPayload],
) error {
	return s.updateMergeData(
		ctx,
		event.Payload.TargetRepoID,
		event.Payload.Number,
		event.Payload.OldSHA,
		event.Payload.NewSHA,
	)
}

// mergeCheckOnReopen handles pull request StateChanged events.
// It updates the PR head git ref to point to the source branch commit SHA.
func (s *Service) mergeCheckOnReopen(ctx context.Context,
	event *events.Event[*pullreqevents.ReopenedPayload],
) error {
	return s.updateMergeData(
		ctx,
		event.Payload.TargetRepoID,
		event.Payload.Number,
		"",
		event.Payload.SourceSHA,
	)
}

// mergeCheckOnClosed deletes the merge ref.
func (s *Service) mergeCheckOnClosed(ctx context.Context,
	event *events.Event[*pullreqevents.ClosedPayload],
) error {
	return s.deleteMergeRef(ctx, event.Payload.SourceRepoID, event.Payload.Number)
}

// mergeCheckOnMerged deletes the merge ref.
func (s *Service) mergeCheckOnMerged(ctx context.Context,
	event *events.Event[*pullreqevents.MergedPayload],
) error {
	return s.deleteMergeRef(ctx, event.Payload.SourceRepoID, event.Payload.Number)
}

func (s *Service) deleteMergeRef(ctx context.Context, repoID int64, prNum int64) error {
	repo, err := s.repoGitInfoCache.Get(ctx, repoID)
	if err != nil {
		return fmt.Errorf("failed to get repo with ID %d: %w", repoID, err)
	}

	writeParams, err := createSystemRPCWriteParams(ctx, s.urlProvider, repo.ID, repo.GitUID)
	if err != nil {
		return fmt.Errorf("failed to generate rpc write params: %w", err)
	}

	// TODO: This doesn't work for forked repos
	err = s.gitRPCClient.UpdateRef(ctx, gitrpc.UpdateRefParams{
		WriteParams: writeParams,
		Name:        strconv.Itoa(int(prNum)),
		Type:        gitrpcenum.RefTypePullReqMerge,
		NewValue:    "", // when NewValue is empty gitrpc will delete the ref.
		OldValue:    "", // we don't care about the old value
	})
	if err != nil {
		return fmt.Errorf("failed to remove PR merge ref: %w", err)
	}

	return nil
}

//nolint:funlen // refactor if required.
func (s *Service) updateMergeData(
	ctx context.Context,
	repoID int64,
	prNum int64,
	oldSHA string,
	newSHA string,
) error {
	// TODO: Merge check should not update the merge base.
	// TODO: Instead it should accept it as an argument and fail if it doesn't match.
	// Then is would not longer be necessary to cancel already active mergeability checks.

	pr, err := s.pullreqStore.FindByNumber(ctx, repoID, prNum)
	if err != nil {
		return fmt.Errorf("failed to get pull request number %d: %w", prNum, err)
	}

	if pr.State != enum.PullReqStateOpen {
		return fmt.Errorf("cannot do mergability check on closed PR %d", prNum)
	}

	// cancel all previous mergability work for this PR based on oldSHA
	if err = s.pubsub.Publish(ctx, cancelMergeCheckKey, []byte(oldSHA),
		pubsub.WithPublishNamespace("pullreq")); err != nil {
		return err
	}

	var cancel context.CancelFunc
	ctx, cancel = context.WithCancel(ctx)

	s.cancelMutex.Lock()
	s.cancelMergeability[newSHA] = cancel
	s.cancelMutex.Unlock()

	defer func() {
		cancel()
		s.cancelMutex.Lock()
		delete(s.cancelMergeability, newSHA)
		s.cancelMutex.Unlock()
	}()

	// load repository objects
	targetRepo, err := s.repoGitInfoCache.Get(ctx, pr.TargetRepoID)
	if err != nil {
		return err
	}

	sourceRepo := targetRepo
	if pr.TargetRepoID != pr.SourceRepoID {
		sourceRepo, err = s.repoGitInfoCache.Get(ctx, pr.SourceRepoID)
		if err != nil {
			return err
		}
	}

	writeParams, err := createSystemRPCWriteParams(ctx, s.urlProvider, targetRepo.ID, targetRepo.GitUID)
	if err != nil {
		return fmt.Errorf("failed to generate rpc write params: %w", err)
	}

	// call merge and store output in pr merge reference.
	now := time.Now()
	var output gitrpc.MergeOutput
	output, err = s.gitRPCClient.Merge(ctx, &gitrpc.MergeParams{
		WriteParams:     writeParams,
		BaseBranch:      pr.TargetBranch,
		HeadRepoUID:     sourceRepo.GitUID,
		HeadBranch:      pr.SourceBranch,
		RefType:         gitrpcenum.RefTypePullReqMerge,
		RefName:         strconv.Itoa(int(prNum)),
		HeadExpectedSHA: newSHA,
		Force:           true,

		// set committer date to ensure repeatability of merge commit across replicas
		CommitterDate: &now,
	})
	if gitrpc.ErrorStatus(err) == gitrpc.StatusPreconditionFailed {
		return events.NewDiscardEventErrorf("Source branch '%s' is not on SHA '%s' anymore.",
			pr.SourceBranch, newSHA)
	}

	isNotMergeableError := gitrpc.ErrorStatus(err) == gitrpc.StatusNotMergeable
	if err != nil && !isNotMergeableError {
		return fmt.Errorf("merge check failed for %d:%s and %d:%s with err: %w",
			targetRepo.ID, pr.TargetBranch,
			sourceRepo.ID, pr.SourceBranch,
			err)
	}

	// Update DB in both cases (failure or success)
	_, err = s.pullreqStore.UpdateOptLock(ctx, pr, func(pr *types.PullReq) error {
		if pr.SourceSHA != newSHA {
			return events.NewDiscardEventErrorf("PR SHA %s is newer than %s", pr.SourceSHA, newSHA)
		}

		if isNotMergeableError {
			// TODO: gitrpc should return sha's either way, and also conflicting files!
			pr.MergeCheckStatus = enum.MergeCheckStatusConflict
			pr.MergeTargetSHA = &output.BaseSHA
			pr.MergeSHA = nil
			pr.MergeConflicts = nil
		} else {
			pr.MergeCheckStatus = enum.MergeCheckStatusMergeable
			pr.MergeTargetSHA = &output.BaseSHA
			pr.MergeBaseSHA = output.MergeBaseSHA // TODO: Merge check should not update the merge base.
			pr.MergeSHA = &output.MergeSHA
			pr.MergeConflicts = nil
		}
		return nil
	})
	if err != nil {
		return fmt.Errorf("failed to update PR merge ref in db with error: %w", err)
	}

	return nil
}