package backup

import (
	"archive/tar"
	"compress/gzip"
	"context"
	"fmt"
	"io"
	"log/slog"
	"os"
	"path/filepath"
	"time"

	"git.misaka.ren/M1saka/docker_backup/internal/config"
)

// Result holds the outcome of backing up a single project.
type Result struct {
	ProjectName string
	Error       error
	BackupPath  string
	FileSize    int64
	Downtime    time.Duration
	Duration    time.Duration
}

// Engine orchestrates backup of Docker Compose projects.
type Engine struct {
	BackupDir string
	TempDir   string
	DryRun    bool
	Logger    *slog.Logger
}

// NewEngine creates a new backup engine.
func NewEngine(backupDir, tempDir string, dryRun bool, logger *slog.Logger) *Engine {
	if logger == nil {
		logger = slog.Default()
	}
	return &Engine{
		BackupDir: backupDir,
		TempDir:   tempDir,
		DryRun:    dryRun,
		Logger:    logger,
	}
}

// Run backs up all configured projects. Results are returned in order.
func (e *Engine) Run(ctx context.Context, projects []config.ProjectConfig) []Result {
	results := make([]Result, 0, len(projects))
	for _, proj := range projects {
		results = append(results, e.backupOne(ctx, proj))
	}
	return results
}

func (e *Engine) backupOne(ctx context.Context, proj config.ProjectConfig) Result {
	start := time.Now()
	result := Result{ProjectName: proj.Name}

	if err := ctx.Err(); err != nil {
		result.Error = err
		result.Duration = time.Since(start)
		return result
	}

	e.Logger.Info("starting backup", "project", proj.Name, "path", proj.Path)

	composeFilePath := filepath.Join(proj.Path, proj.ComposeFile)
	if _, err := os.Stat(composeFilePath); err != nil && !e.DryRun {
		result.Error = fmt.Errorf("compose file not found: %s: %w", composeFilePath, err)
		result.Duration = time.Since(start)
		return result
	}

	backupPath := e.backupPath(proj.Name)
	if e.DryRun {
		result.BackupPath = backupPath
		result.Duration = time.Since(start)
		e.Logger.Info("dry-run: backup plan complete", "project", proj.Name, "file", backupPath)
		return result
	}

	executor := NewComposeExecutor(proj.Path, proj.ComposeFile)

	// 1. Stop the compose project. If the stop is interrupted midway
	// (e.g. the context is cancelled), containers may be left stopped, so
	// always attempt a restart before returning.
	stopStart := time.Now()
	if err := executor.Stop(ctx); err != nil {
		_ = restartCompose(executor)
		result.Error = fmt.Errorf("stop: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	e.Logger.Info("compose stopped", "project", proj.Name)

	// 2. Create a staging directory.
	stagingDir, err := os.MkdirTemp(e.TempDir, "dc-backup-"+proj.Name+"-*")
	if err != nil {
		_ = restartCompose(executor)
		result.Error = fmt.Errorf("create staging dir: %w", err)
		result.Duration = time.Since(start)
		return result
	}

	// 3. Copy project directory to staging.
	copier := &DirectoryCopier{Exclude: proj.Exclude, Context: ctx}
	if err := copier.Copy(proj.Path, stagingDir); err != nil {
		_ = os.RemoveAll(stagingDir)
		_ = restartCompose(executor)
		result.Error = fmt.Errorf("copy: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	e.Logger.Info("files copied to staging", "project", proj.Name, "staging", stagingDir)

	// 4. Immediately restart the compose project.
	if err := restartCompose(executor); err != nil {
		_ = os.RemoveAll(stagingDir)
		result.Error = fmt.Errorf("start: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	result.Downtime = time.Since(stopStart)
	e.Logger.Info("compose restarted", "project", proj.Name, "downtime", result.Downtime)

	// 5. Compress staging directory to the backup destination.
	backupDir := filepath.Dir(backupPath)
	if err := os.MkdirAll(backupDir, 0755); err != nil {
		_ = os.RemoveAll(stagingDir)
		result.Error = fmt.Errorf("create backup dir: %w", err)
		result.Duration = time.Since(start)
		return result
	}

	if err := createTarGz(ctx, stagingDir, backupPath); err != nil {
		_ = os.RemoveAll(stagingDir)
		result.Error = fmt.Errorf("compress: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	e.Logger.Info("backup compressed", "project", proj.Name, "file", backupPath)

	// 6. Clean up staging.
	_ = os.RemoveAll(stagingDir)

	// 7. Record file size.
	if fi, err := os.Stat(backupPath); err == nil {
		result.FileSize = fi.Size()
	}

	result.BackupPath = backupPath
	result.Duration = time.Since(start)
	e.Logger.Info("backup complete", "project", proj.Name, "duration", result.Duration, "size", result.FileSize)
	return result
}

func (e *Engine) backupPath(projectName string) string {
	timestamp := time.Now().Format("20060102-150405.000000000")
	backupFile := fmt.Sprintf("%s-%s.tar.gz", projectName, timestamp)
	return filepath.Join(e.BackupDir, projectName, backupFile)
}

func restartCompose(executor *ComposeExecutor) error {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()
	return executor.Start(ctx)
}

// createTarGz creates a tar.gz archive from a source directory.
func createTarGz(ctx context.Context, srcDir, dstPath string) error {
	f, err := os.Create(dstPath)
	if err != nil {
		return err
	}

	gw := gzip.NewWriter(f)
	tw := tar.NewWriter(gw)

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

		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		rel, err := filepath.Rel(srcDir, path)
		if err != nil {
			return fmt.Errorf("rel: %w", err)
		}
		if rel == "." {
			return nil
		}

		info, err := d.Info()
		if err != nil {
			return err
		}

		linkTarget := ""
		if info.Mode()&os.ModeSymlink != 0 {
			linkTarget, err = os.Readlink(path)
			if err != nil {
				return err
			}
		}

		header, err := tar.FileInfoHeader(info, linkTarget)
		if err != nil {
			return err
		}
		header.Name = filepath.ToSlash(rel)

		if err := tw.WriteHeader(header); err != nil {
			return err
		}

		if d.IsDir() || !info.Mode().IsRegular() {
			return nil
		}

		return copyFileToTar(tw, path)
	})

	closeErr := closeTarGz(tw, gw, f)
	if walkErr != nil {
		_ = os.Remove(dstPath)
		return walkErr
	}
	if closeErr != nil {
		_ = os.Remove(dstPath)
		return closeErr
	}
	return nil
}

func closeTarGz(tw *tar.Writer, gw *gzip.Writer, f *os.File) error {
	if err := tw.Close(); err != nil {
		_ = gw.Close()
		_ = f.Close()
		return fmt.Errorf("close tar: %w", err)
	}
	if err := gw.Close(); err != nil {
		_ = f.Close()
		return fmt.Errorf("close gzip: %w", err)
	}
	if err := f.Close(); err != nil {
		return fmt.Errorf("close file: %w", err)
	}
	return nil
}

// copyFileToTar opens a file and copies it into the tar writer.
// The file is closed before returning — no deferred leak in a loop.
func copyFileToTar(tw *tar.Writer, path string) error {
	srcFile, err := os.Open(path)
	if err != nil {
		return err
	}
	defer srcFile.Close()

	_, err = io.Copy(tw, srcFile)
	return err
}