// Copyright 2023 Harness, Inc.
//
// 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 service

import (
	"context"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/harness/gitness/gitrpc/enum"
	"github.com/harness/gitness/gitrpc/internal/tempdir"
	"github.com/harness/gitness/gitrpc/internal/types"
	"github.com/harness/gitness/gitrpc/rpc"

	"github.com/rs/zerolog/log"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

type MergeService struct {
	rpc.UnimplementedMergeServiceServer
	adapter      GitAdapter
	reposRoot    string
	reposTempDir string
}

var _ rpc.MergeServiceServer = (*MergeService)(nil)

func NewMergeService(adapter GitAdapter, reposRoot, reposTempDir string) (*MergeService, error) {
	return &MergeService{
		adapter:      adapter,
		reposRoot:    reposRoot,
		reposTempDir: reposTempDir,
	}, nil
}

//nolint:funlen,gocognit // maybe some refactoring when we add fast forward merging
func (s MergeService) Merge(
	ctx context.Context,
	request *rpc.MergeRequest,
) (*rpc.MergeResponse, error) {
	if err := validateMergeRequest(request); err != nil {
		return nil, err
	}

	base := request.Base
	repoPath := getFullPathForRepo(s.reposRoot, base.RepoUid)

	baseBranch := "base"
	trackingBranch := "tracking"

	pr := &types.PullRequest{
		BaseRepoPath: repoPath,
		BaseBranch:   request.BaseBranch,
		HeadBranch:   request.HeadBranch,
	}

	// Clone base repo.
	tmpRepo, err := s.adapter.CreateTemporaryRepoForPR(ctx, s.reposTempDir, pr, baseBranch, trackingBranch)
	if err != nil {
		return nil, processGitErrorf(err, "failed to initialize temporary repo")
	}
	defer func() {
		rmErr := tempdir.RemoveTemporaryPath(tmpRepo.Path)
		if rmErr != nil {
			log.Ctx(ctx).Warn().Msgf("Removing temporary location %s for merge operation was not successful", tmpRepo.Path)
		}
	}()

	mergeBaseCommitSHA, _, err := s.adapter.GetMergeBase(ctx, tmpRepo.Path, "origin", baseBranch, trackingBranch)
	if err != nil {
		return nil, fmt.Errorf("failed to get merge base: %w", err)
	}

	if tmpRepo.HeadSHA == mergeBaseCommitSHA {
		return nil, ErrInvalidArgumentf("no changes between head branch %s and base branch %s",
			request.HeadBranch, request.BaseBranch)
	}

	if request.HeadExpectedSha != "" && request.HeadExpectedSha != tmpRepo.HeadSHA {
		return nil, status.Errorf(
			codes.FailedPrecondition,
			"head branch '%s' is on SHA '%s' which doesn't match expected SHA '%s'.",
			request.HeadBranch,
			tmpRepo.HeadSHA,
			request.HeadExpectedSha)
	}

	var outbuf, errbuf strings.Builder
	// Enable sparse-checkout
	sparseCheckoutList, err := s.adapter.GetDiffTree(ctx, tmpRepo.Path, baseBranch, trackingBranch)
	if err != nil {
		return nil, fmt.Errorf("execution of GetDiffTree failed: %w", err)
	}

	infoPath := filepath.Join(tmpRepo.Path, ".git", "info")
	if err = os.MkdirAll(infoPath, 0o700); err != nil {
		return nil, fmt.Errorf("unable to create .git/info in tmpRepo.Path: %w", err)
	}

	sparseCheckoutListPath := filepath.Join(infoPath, "sparse-checkout")
	if err = os.WriteFile(sparseCheckoutListPath, []byte(sparseCheckoutList), 0o600); err != nil {
		return nil,
			fmt.Errorf("unable to write .git/info/sparse-checkout file in tmpRepo.Path: %w", err)
	}

	// Switch off LFS process (set required, clean and smudge here also)
	if err = s.adapter.Config(ctx, tmpRepo.Path, "filter.lfs.process", ""); err != nil {
		return nil, err
	}

	if err = s.adapter.Config(ctx, tmpRepo.Path, "filter.lfs.required", "false"); err != nil {
		return nil, err
	}

	if err = s.adapter.Config(ctx, tmpRepo.Path, "filter.lfs.clean", ""); err != nil {
		return nil, err
	}

	if err = s.adapter.Config(ctx, tmpRepo.Path, "filter.lfs.smudge", ""); err != nil {
		return nil, err
	}

	if err = s.adapter.Config(ctx, tmpRepo.Path, "core.sparseCheckout", "true"); err != nil {
		return nil, err
	}

	// Read base branch index
	if err = s.adapter.ReadTree(ctx, tmpRepo.Path, "HEAD", io.Discard); err != nil {
		return nil, fmt.Errorf("failed to read tree: %w", err)
	}
	outbuf.Reset()
	errbuf.Reset()

	committer := base.GetActor()
	if request.GetCommitter() != nil {
		committer = request.GetCommitter()
	}
	committerDate := time.Now().UTC()
	if request.GetAuthorDate() != 0 {
		committerDate = time.Unix(request.GetCommitterDate(), 0)
	}

	author := committer
	if request.GetAuthor() != nil {
		author = request.GetAuthor()
	}
	authorDate := committerDate
	if request.GetAuthorDate() != 0 {
		authorDate = time.Unix(request.GetAuthorDate(), 0)
	}

	// Because this may call hooks we should pass in the environment
	// TODO: merge specific envars should be set by the adapter impl.
	env := append(CreateEnvironmentForPush(ctx, base),
		"GIT_AUTHOR_NAME="+author.Name,
		"GIT_AUTHOR_EMAIL="+author.Email,
		"GIT_AUTHOR_DATE="+authorDate.Format(time.RFC3339),
		"GIT_COMMITTER_NAME="+committer.Name,
		"GIT_COMMITTER_EMAIL="+committer.Email,
		"GIT_COMMITTER_DATE="+committerDate.Format(time.RFC3339),
	)

	mergeMsg := strings.TrimSpace(request.Title)
	if len(request.Message) > 0 {
		mergeMsg += "\n\n" + strings.TrimSpace(request.Message)
	}

	if err = s.adapter.Merge(
		ctx,
		pr,
		enum.MergeMethodFromRPC(request.Method),
		baseBranch,
		trackingBranch,
		tmpRepo.Path,
		mergeMsg,
		env,
		&types.Identity{
			Name:  author.Name,
			Email: author.Email,
		}); err != nil {
		return nil, processGitErrorf(err, "merge failed")
	}

	mergeCommitSHA, err := s.adapter.GetFullCommitID(ctx, tmpRepo.Path, baseBranch)
	if err != nil {
		return nil, fmt.Errorf("failed to get full commit id for the new merge: %w", err)
	}

	refType := enum.RefFromRPC(request.RefType)
	if refType == enum.RefTypeUndefined {
		return &rpc.MergeResponse{
			BaseSha:      tmpRepo.BaseSHA,
			HeadSha:      tmpRepo.HeadSHA,
			MergeBaseSha: mergeBaseCommitSHA,
			MergeSha:     mergeCommitSHA,
		}, nil
	}

	refPath, err := GetRefPath(request.RefName, refType)
	if err != nil {
		return nil, fmt.Errorf("failed to generate full reference for type '%s' and name '%s' for merge operation: %w",
			request.RefType, request.RefName, err)
	}
	pushRef := baseBranch + ":" + refPath

	if err = s.adapter.Push(ctx, tmpRepo.Path, types.PushOptions{
		Remote: "origin",
		Branch: pushRef,
		Force:  request.Force,
		Env:    env,
	}); err != nil {
		return nil, fmt.Errorf("failed to push merge commit to ref '%s': %w", refPath, err)
	}

	return &rpc.MergeResponse{
		BaseSha:      tmpRepo.BaseSHA,
		HeadSha:      tmpRepo.HeadSHA,
		MergeBaseSha: mergeBaseCommitSHA,
		MergeSha:     mergeCommitSHA,
	}, nil
}

func validateMergeRequest(request *rpc.MergeRequest) error {
	base := request.Base
	if base == nil {
		return types.ErrBaseCannotBeEmpty
	}

	author := base.Actor
	if author == nil {
		return fmt.Errorf("empty actor")
	}

	if len(author.Email) == 0 {
		return fmt.Errorf("empty user email")
	}

	if len(author.Name) == 0 {
		return fmt.Errorf("empty user name")
	}

	if len(request.BaseBranch) == 0 {
		return fmt.Errorf("empty branch name")
	}

	if len(request.HeadBranch) == 0 {
		return fmt.Errorf("empty head branch name")
	}

	if request.RefType != rpc.RefType_Undefined && len(request.RefName) == 0 {
		return fmt.Errorf("ref name has to be provided if type is defined")
	}

	return nil
}