// 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 sharedrepo

import (
	"bufio"
	"bytes"
	"context"
	"crypto/rand"
	"encoding/base32"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strings"

	"github.com/harness/gitness/errors"
	"github.com/harness/gitness/git/command"
	"github.com/harness/gitness/git/tempdir"
	"github.com/harness/gitness/git/types"

	"github.com/rs/zerolog/log"
)

type SharedRepo struct {
	temporaryPath  string
	repositoryPath string
}

// NewSharedRepo creates a new temporary bare repository.
func NewSharedRepo(
	baseTmpDir string,
	repositoryPath string,
) (*SharedRepo, error) {
	var buf [5]byte
	_, _ = rand.Read(buf[:])
	id := base32.StdEncoding.EncodeToString(buf[:])

	temporaryPath, err := tempdir.CreateTemporaryPath(baseTmpDir, id)
	if err != nil {
		return nil, fmt.Errorf("failed to create shared repository directory: %w", err)
	}

	t := &SharedRepo{
		temporaryPath:  temporaryPath,
		repositoryPath: repositoryPath,
	}

	return t, nil
}

func (r *SharedRepo) Close(ctx context.Context) {
	if err := tempdir.RemoveTemporaryPath(r.temporaryPath); err != nil {
		log.Ctx(ctx).Err(err).
			Str("path", r.temporaryPath).
			Msg("Failed to remove temporary shared directory")
	}
}

func (r *SharedRepo) InitAsBare(ctx context.Context) error {
	cmd := command.New("init", command.WithFlag("--bare"))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath)); err != nil {
		return fmt.Errorf("failed to initialize bare git repository directory: %w", err)
	}

	if err := func() error {
		alternates := filepath.Join(r.temporaryPath, "objects", "info", "alternates")
		f, err := os.OpenFile(alternates, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
		if err != nil {
			return fmt.Errorf("failed to create alternates file: %w", err)
		}

		defer func() { _ = f.Close() }()

		data := filepath.Join(r.repositoryPath, "objects")
		if _, err = fmt.Fprintln(f, data); err != nil {
			return fmt.Errorf("failed to write alternates file: %w", err)
		}

		return nil
	}(); err != nil {
		return fmt.Errorf("failed to make the alternates file in shared repository: %w", err)
	}

	return nil
}

func (r *SharedRepo) Directory() string {
	return r.temporaryPath
}

// SetDefaultIndex sets the git index to our HEAD.
func (r *SharedRepo) SetDefaultIndex(ctx context.Context) error {
	cmd := command.New("read-tree", command.WithArg("HEAD"))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath)); err != nil {
		return fmt.Errorf("failed to initialize shared repository index to HEAD: %w", err)
	}

	return nil
}

// SetIndex sets the git index to the provided treeish.
func (r *SharedRepo) SetIndex(ctx context.Context, treeish string) error {
	cmd := command.New("read-tree", command.WithArg(treeish))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath)); err != nil {
		return fmt.Errorf("failed to initialize shared repository index to %q: %w", treeish, err)
	}

	return nil
}

// ClearIndex clears the git index.
func (r *SharedRepo) ClearIndex(ctx context.Context) error {
	cmd := command.New("read-tree", command.WithFlag("--empty"))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath)); err != nil {
		return fmt.Errorf("failed to clear shared repository index: %w", err)
	}

	return nil
}

// LsFiles checks if the given filename arguments are in the index.
func (r *SharedRepo) LsFiles(
	ctx context.Context,
	filenames ...string,
) ([]string, error) {
	cmd := command.New("ls-files", command.WithFlag("-z"), command.WithPostSepArg(filenames...))

	stdout := bytes.NewBuffer(nil)

	err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdout(stdout))
	if err != nil {
		return nil, fmt.Errorf("failed to list files in shared repository's git index: %w", err)
	}

	files := make([]string, 0)
	for _, line := range bytes.Split(stdout.Bytes(), []byte{'\000'}) {
		files = append(files, string(line))
	}

	return files, nil
}

// RemoveFilesFromIndex removes the given files from the index.
func (r *SharedRepo) RemoveFilesFromIndex(
	ctx context.Context,
	filenames ...string,
) error {
	cmd := command.New("update-index",
		command.WithFlag("--remove"),
		command.WithFlag("-z"),
		command.WithFlag("--index-info"))

	stdin := bytes.NewBuffer(nil)
	for _, file := range filenames {
		if file != "" {
			stdin.WriteString("0 0000000000000000000000000000000000000000\t")
			stdin.WriteString(file)
			stdin.WriteByte('\000')
		}
	}

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdin(stdin)); err != nil {
		return fmt.Errorf("failed to update-index in shared repo: %w", err)
	}

	return nil
}

// WriteGitObject writes the provided content to the object db and returns its hash.
func (r *SharedRepo) WriteGitObject(
	ctx context.Context,
	content io.Reader,
) (string, error) {
	cmd := command.New("hash-object",
		command.WithFlag("-w"),
		command.WithFlag("--stdin"))

	stdout := bytes.NewBuffer(nil)

	err := cmd.Run(ctx,
		command.WithDir(r.temporaryPath),
		command.WithStdin(content),
		command.WithStdout(stdout))
	if err != nil {
		return "", fmt.Errorf("failed to hash-object in shared repo: %w", err)
	}

	return strings.TrimSpace(stdout.String()), nil
}

// ShowFile dumps show file and write to io.Writer.
func (r *SharedRepo) ShowFile(
	ctx context.Context,
	filePath string,
	rev string,
	writer io.Writer,
) error {
	file := strings.TrimSpace(rev) + ":" + strings.TrimSpace(filePath)

	cmd := command.New("show", command.WithArg(file))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdout(writer)); err != nil {
		return fmt.Errorf("failed to show file in shared repo: %w", err)
	}

	return nil
}

// AddObjectToIndex adds the provided object hash to the index with the provided mode and path.
func (r *SharedRepo) AddObjectToIndex(
	ctx context.Context,
	mode string,
	objectHash string,
	objectPath string,
) error {
	cmd := command.New("update-index",
		command.WithFlag("--add"),
		command.WithFlag("--replace"),
		command.WithFlag("--cacheinfo", mode, objectHash, objectPath))

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath)); err != nil {
		if matched, _ := regexp.MatchString(".*Invalid path '.*", err.Error()); matched {
			return errors.InvalidArgument("invalid path '%s'", objectPath)
		}
		return fmt.Errorf("failed to add object to index in shared repo (path=%s): %w", objectPath, err)
	}

	return nil
}

// WriteTree writes the current index as a tree to the object db and returns its hash.
func (r *SharedRepo) WriteTree(ctx context.Context) (string, error) {
	cmd := command.New("write-tree")

	stdout := bytes.NewBuffer(nil)

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdout(stdout)); err != nil {
		return "", fmt.Errorf("failed to write-tree in shared repo: %w", err)
	}

	return strings.TrimSpace(stdout.String()), nil
}

// MergeTree merges commits in git index.
func (r *SharedRepo) MergeTree(
	ctx context.Context,
	commitMergeBase, commitTarget, commitSource string,
) (string, []string, error) {
	cmd := command.New("merge-tree",
		command.WithFlag("--write-tree"),
		command.WithFlag("--name-only"),
		command.WithFlag("--no-messages"),
		command.WithArg(commitTarget),
		command.WithArg(commitSource))

	if commitMergeBase != "" {
		cmd.Add(command.WithFlag("--merge-base=" + commitMergeBase))
	}

	stdout := bytes.NewBuffer(nil)

	err := cmd.Run(ctx,
		command.WithDir(r.temporaryPath),
		command.WithStdout(stdout))

	// no error: the output is just the tree object SHA
	if err == nil {
		return strings.TrimSpace(stdout.String()), nil, nil
	}

	// exit code=1: the output is the tree object SHA, and list of files in conflict.
	if cErr := command.AsError(err); cErr != nil && cErr.ExitCode() == 1 {
		output := strings.TrimSpace(stdout.String())
		lines := strings.Split(output, "\n")
		if len(lines) < 2 {
			log.Ctx(ctx).Err(err).Str("output", output).Msg("unexpected output of merge-tree in shared repo")
			return "", nil, fmt.Errorf("unexpected output of merge-tree in shared repo: %w", err)
		}
		return lines[0], lines[1:], nil
	}

	return "", nil, fmt.Errorf("failed to merge-tree in shared repo: %w", err)
}

// CommitTree creates a commit from a given tree for the user with provided message.
func (r *SharedRepo) CommitTree(
	ctx context.Context,
	author, committer *types.Signature,
	treeHash, message string,
	signoff bool,
	parentCommits ...string,
) (string, error) {
	cmd := command.New("commit-tree",
		command.WithArg(treeHash),
		command.WithAuthorAndDate(
			author.Identity.Name,
			author.Identity.Email,
			author.When,
		),
		command.WithCommitterAndDate(
			committer.Identity.Name,
			committer.Identity.Email,
			committer.When,
		),
	)

	for _, parentCommit := range parentCommits {
		cmd.Add(command.WithFlag("-p", parentCommit))
	}

	// temporary no signing
	cmd.Add(command.WithFlag("--no-gpg-sign"))

	messageBytes := new(bytes.Buffer)
	_, _ = messageBytes.WriteString(message)
	_, _ = messageBytes.WriteString("\n")

	if signoff {
		// Signed-off-by
		_, _ = messageBytes.WriteString("\n")
		_, _ = messageBytes.WriteString("Signed-off-by: ")
		_, _ = messageBytes.WriteString(fmt.Sprintf("%s <%s>", committer.Identity.Name, committer.Identity.Email))
	}

	stdout := bytes.NewBuffer(nil)

	err := cmd.Run(ctx,
		command.WithDir(r.temporaryPath),
		command.WithStdout(stdout),
		command.WithStdin(messageBytes))
	if err != nil {
		return "", fmt.Errorf("failed to commit-tree in shared repo: %w", err)
	}

	return strings.TrimSpace(stdout.String()), nil
}

// CommitSHAList returns list of SHAs of the commits between the two git revisions.
func (r *SharedRepo) CommitSHAList(
	ctx context.Context,
	start, end string,
) ([]string, error) {
	cmd := command.New("rev-list", command.WithArg(start+".."+end))

	stdout := bytes.NewBuffer(nil)

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdout(stdout)); err != nil {
		return nil, fmt.Errorf("failed to rev-list in shared repo: %w", err)
	}

	var commitSHAs []string

	scan := bufio.NewScanner(stdout)
	for scan.Scan() {
		commitSHA := scan.Text()
		commitSHAs = append(commitSHAs, commitSHA)
	}
	if err := scan.Err(); err != nil {
		return nil, fmt.Errorf("failed to scan rev-list output in shared repo: %w", err)
	}

	return commitSHAs, nil
}

// MergeBase returns number of commits between the two git revisions.
func (r *SharedRepo) MergeBase(
	ctx context.Context,
	rev1, rev2 string,
) (string, error) {
	cmd := command.New("merge-base", command.WithArg(rev1), command.WithArg(rev2))

	stdout := bytes.NewBuffer(nil)

	if err := cmd.Run(ctx, command.WithDir(r.temporaryPath), command.WithStdout(stdout)); err != nil {
		return "", fmt.Errorf("failed to merge-base in shared repo: %w", err)
	}

	return strings.TrimSpace(stdout.String()), nil
}

// MoveObjects moves git object from the shared repository to the original repository.
func (r *SharedRepo) MoveObjects(ctx context.Context) error {
	srcDir := path.Join(r.temporaryPath, "objects")
	dstDir := path.Join(r.repositoryPath, "objects")

	var files []fileEntry

	err := filepath.WalkDir(srcDir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		if d.IsDir() {
			return nil
		}

		relPath, err := filepath.Rel(srcDir, path)
		if err != nil {
			return fmt.Errorf("failed to get relative path: %w", err)
		}

		// avoid coping anything in the info/
		if strings.HasPrefix(relPath, "info/") {
			return nil
		}

		fileName := filepath.Base(relPath)

		files = append(files, fileEntry{
			fileName: fileName,
			fullPath: path,
			relPath:  relPath,
			priority: filePriority(fileName),
		})

		return nil
	})
	if err != nil {
		return fmt.Errorf("failed to list files of shared repository directory: %w", err)
	}

	sort.Slice(files, func(i, j int) bool {
		return files[i].priority < files[j].priority // 0 is top priority, 5 is lowest priority
	})

	for _, f := range files {
		dstPath := filepath.Join(dstDir, f.relPath)

		err = os.MkdirAll(filepath.Dir(dstPath), os.ModePerm)
		if err != nil {
			return fmt.Errorf("failed to create directory for git object: %w", err)
		}

		// Try to move the file

		errRename := os.Rename(f.fullPath, dstPath)
		if errRename == nil {
			log.Ctx(ctx).Debug().
				Str("object", f.relPath).
				Msg("moved git object")
			continue
		}

		// Try to copy the file

		copyError := func() error {
			srcFile, err := os.Open(f.fullPath)
			if err != nil {
				return fmt.Errorf("failed to open source file: %w", err)
			}
			defer func() { _ = srcFile.Close() }()

			dstFile, err := os.Create(dstPath)
			if err != nil {
				return fmt.Errorf("failed to create target file: %w", err)
			}
			defer func() { _ = dstFile.Close() }()

			_, err = io.Copy(dstFile, srcFile)
			if err != nil {
				return fmt.Errorf("failed to copy file content: %w", err)
			}

			return nil
		}()
		if copyError != nil {
			log.Ctx(ctx).Err(copyError).
				Str("object", f.relPath).
				Str("renameErr", errRename.Error()).
				Msg("failed to move or copy git object")
			return fmt.Errorf("failed to move or copy git object: %w", copyError)
		}

		log.Ctx(ctx).Warn().
			Str("object", f.relPath).
			Str("renameErr", errRename.Error()).
			Msg("copied git object")
	}

	return nil
}

// filePriority is based on https://github.com/git/git/blob/master/tmp-objdir.c#L168
func filePriority(name string) int {
	switch {
	case !strings.HasPrefix(name, "pack"):
		return 0
	case strings.HasSuffix(name, ".keep"):
		return 1
	case strings.HasSuffix(name, ".pack"):
		return 2
	case strings.HasSuffix(name, ".rev"):
		return 3
	case strings.HasSuffix(name, ".idx"):
		return 4
	default:
		return 5
	}
}

type fileEntry struct {
	fileName string
	fullPath string
	relPath  string
	priority int
}