package backup

import (
	"archive/zip"
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	release "debtik"
)

const (
	DefaultDebtikDir   = "/etc/debtik"
	DefaultNetworkDir  = "/etc/network/interfaces.d"
	DefaultBackupStore = "/var/lib/debtik/backups"

	MaxArchiveEntries = 5000
	MaxArchiveBytes   = 100 * 1024 * 1024 // 100 MB max uncompressed
	BackupFormatVer   = "1.0"
)

// Manager handles backup generation, inspection, restoration, and local retention.
type Manager struct {
	debtikDir   string
	networkDir  string
	backupStore string
	restartFunc func() error
	mu          sync.Mutex
}

// NewManager creates a new backup Manager with the provided or default directories.
func NewManager(debtikDir, networkDir, backupStore string, restartFunc func() error) *Manager {
	if debtikDir == "" {
		debtikDir = DefaultDebtikDir
	}
	if networkDir == "" {
		networkDir = DefaultNetworkDir
	}
	if backupStore == "" {
		backupStore = DefaultBackupStore
	}
	return &Manager{
		debtikDir:   filepath.Clean(debtikDir),
		networkDir:  filepath.Clean(networkDir),
		backupStore: filepath.Clean(backupStore),
		restartFunc: restartFunc,
	}
}

// CreateBackup generates an in-memory zip archive containing all DebTik configurations.
func (m *Manager) CreateBackup(comment string) ([]byte, *Manifest, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.createBackupLocked(comment)
}

func (m *Manager) createBackupLocked(comment string) ([]byte, *Manifest, error) {
	hostname, _ := os.Hostname()
	if hostname == "" {
		hostname = "DebTik"
	}

	manifest := &Manifest{
		Version:       BackupFormatVer,
		DebTikVersion: release.Version(),
		Hostname:      hostname,
		CreatedAt:     time.Now().UTC(),
		Comment:       strings.TrimSpace(comment),
		Files:         make([]FileInfo, 0),
	}

	buf := new(bytes.Buffer)
	zw := zip.NewWriter(buf)

	// 1. Collect /etc/debtik configuration tree
	if err := m.archiveDebtikTree(zw, manifest); err != nil {
		_ = zw.Close()
		return nil, nil, fmt.Errorf("failed archiving debtik config tree: %w", err)
	}

	// 2. Collect /etc/network/interfaces.d configuration files
	if err := m.archiveNetworkFiles(zw, manifest); err != nil {
		_ = zw.Close()
		return nil, nil, fmt.Errorf("failed archiving network config files: %w", err)
	}

	// 3. Write manifest.json
	manifestBytes, err := json.MarshalIndent(manifest, "", "  ")
	if err != nil {
		_ = zw.Close()
		return nil, nil, fmt.Errorf("failed serializing manifest: %w", err)
	}

	manifestHeader := &zip.FileHeader{
		Name:     "manifest.json",
		Method:   zip.Deflate,
		Modified: manifest.CreatedAt,
	}
	manifestHeader.SetMode(0644)
	w, err := zw.CreateHeader(manifestHeader)
	if err != nil {
		_ = zw.Close()
		return nil, nil, fmt.Errorf("failed creating manifest in zip: %w", err)
	}
	if _, err := w.Write(manifestBytes); err != nil {
		_ = zw.Close()
		return nil, nil, fmt.Errorf("failed writing manifest to zip: %w", err)
	}

	if err := zw.Close(); err != nil {
		return nil, nil, fmt.Errorf("failed finalizing zip archive: %w", err)
	}

	return buf.Bytes(), manifest, nil
}

func (m *Manager) archiveDebtikTree(zw *zip.Writer, manifest *Manifest) error {
	if _, err := os.Stat(m.debtikDir); os.IsNotExist(err) {
		return nil
	}

	return filepath.Walk(m.debtikDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsDir() {
			return nil
		}
		// Skip sockets, named pipes, etc.
		if !info.Mode().IsRegular() {
			return nil
		}

		rel, err := filepath.Rel(m.debtikDir, path)
		if err != nil {
			return err
		}
		rel = filepath.ToSlash(rel)
		zipPath := "debtik/" + rel

		data, err := os.ReadFile(path)
		if err != nil {
			return fmt.Errorf("cannot read file %s: %w", path, err)
		}

		hash := sha256.Sum256(data)
		hashStr := hex.EncodeToString(hash[:])

		hdr := &zip.FileHeader{
			Name:     zipPath,
			Method:   zip.Deflate,
			Modified: info.ModTime().UTC(),
		}
		hdr.SetMode(info.Mode().Perm())

		w, err := zw.CreateHeader(hdr)
		if err != nil {
			return err
		}
		if _, err := w.Write(data); err != nil {
			return err
		}

		manifest.Files = append(manifest.Files, FileInfo{
			Path:   zipPath,
			Size:   int64(len(data)),
			Mode:   uint32(info.Mode().Perm()),
			SHA256: hashStr,
		})
		return nil
	})
}

func (m *Manager) archiveNetworkFiles(zw *zip.Writer, manifest *Manifest) error {
	if _, err := os.Stat(m.networkDir); os.IsNotExist(err) {
		return nil
	}

	entries, err := os.ReadDir(m.networkDir)
	if err != nil {
		return nil
	}

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		// Only archive .cfg files (e.g. interfaces.cfg, vlans.cfg)
		if !strings.HasSuffix(name, ".cfg") {
			continue
		}

		filePath := filepath.Join(m.networkDir, name)
		info, err := entry.Info()
		if err != nil || !info.Mode().IsRegular() {
			continue
		}

		data, err := os.ReadFile(filePath)
		if err != nil {
			continue
		}

		hash := sha256.Sum256(data)
		hashStr := hex.EncodeToString(hash[:])

		zipPath := "network/" + name
		hdr := &zip.FileHeader{
			Name:     zipPath,
			Method:   zip.Deflate,
			Modified: info.ModTime().UTC(),
		}
		hdr.SetMode(info.Mode().Perm())

		w, err := zw.CreateHeader(hdr)
		if err != nil {
			return err
		}
		if _, err := w.Write(data); err != nil {
			return err
		}

		manifest.Files = append(manifest.Files, FileInfo{
			Path:   zipPath,
			Size:   int64(len(data)),
			Mode:   uint32(info.Mode().Perm()),
			SHA256: hashStr,
		})
	}

	return nil
}

// SaveBackup creates a backup and saves it to the local backupStore directory.
func (m *Manager) SaveBackup(name, comment string) (string, *Manifest, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.saveBackupLocked(name, comment)
}

func (m *Manager) saveBackupLocked(name, comment string) (string, *Manifest, error) {
	if err := os.MkdirAll(m.backupStore, 0700); err != nil {
		return "", nil, fmt.Errorf("failed creating backup storage directory: %w", err)
	}

	data, manifest, err := m.createBackupLocked(comment)
	if err != nil {
		return "", nil, err
	}

	if name == "" {
		name = fmt.Sprintf("debtik-backup-%s-%s.zip", sanitizeFilename(manifest.Hostname), manifest.CreatedAt.Format("20060102-150405"))
	}
	if !strings.HasSuffix(name, ".zip") {
		name += ".zip"
	}
	name = sanitizeFilename(name)
	targetPath := filepath.Join(m.backupStore, name)

	if err := os.WriteFile(targetPath, data, 0600); err != nil {
		return "", nil, fmt.Errorf("failed writing backup file: %w", err)
	}

	return targetPath, manifest, nil
}

// CreatePreRestoreBackup creates a safety backup before applying any restored configurations.
// It keeps the latest 5 pre-restore backups, pruning older ones.
func (m *Manager) CreatePreRestoreBackup() (string, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.createPreRestoreBackupLocked()
}

func (m *Manager) createPreRestoreBackupLocked() (string, error) {
	if err := os.MkdirAll(m.backupStore, 0700); err != nil {
		return "", err
	}

	hostname, _ := os.Hostname()
	if hostname == "" {
		hostname = "DebTik"
	}
	fileName := fmt.Sprintf("pre-restore-%s-%s-%d.zip", sanitizeFilename(hostname), time.Now().UTC().Format("20060102-150405"), time.Now().UnixNano()%1000000)
	savedPath, _, err := m.saveBackupLocked(fileName, "Automatic pre-restore safety fallback")
	if err != nil {
		return "", err
	}

	// Prune older pre-restore backups, keeping latest 5
	m.prunePreRestoreBackups(5)

	return savedPath, nil
}

func (m *Manager) prunePreRestoreBackups(keep int) {
	entries, err := os.ReadDir(m.backupStore)
	if err != nil {
		return
	}

	type fileItem struct {
		name    string
		modTime time.Time
	}
	var preRestores []fileItem

	for _, e := range entries {
		if e.IsDir() || !strings.HasPrefix(e.Name(), "pre-restore-") || !strings.HasSuffix(e.Name(), ".zip") {
			continue
		}
		info, err := e.Info()
		if err == nil {
			preRestores = append(preRestores, fileItem{name: e.Name(), modTime: info.ModTime()})
		}
	}

	if len(preRestores) <= keep {
		return
	}

	sort.Slice(preRestores, func(i, j int) bool {
		return preRestores[i].modTime.After(preRestores[j].modTime)
	})

	for i := keep; i < len(preRestores); i++ {
		_ = os.Remove(filepath.Join(m.backupStore, preRestores[i].name))
	}
}

// InspectBackup verifies the integrity of an archive and extracts its manifest without restoring.
func (m *Manager) InspectBackup(r io.ReaderAt, size int64) (*Manifest, error) {
	zr, err := zip.NewReader(r, size)
	if err != nil {
		return nil, fmt.Errorf("invalid zip archive: %w", err)
	}

	if len(zr.File) > MaxArchiveEntries {
		return nil, fmt.Errorf("archive contains too many entries (%d > %d)", len(zr.File), MaxArchiveEntries)
	}

	var totalUncompressed int64
	var manifestFile *zip.File

	for _, f := range zr.File {
		cleanName := filepath.Clean(f.Name)

		// Prevent Zip Slip / Path Traversal
		if strings.HasPrefix(cleanName, "..") || strings.HasPrefix(cleanName, "/") || strings.HasPrefix(cleanName, "\\") {
			return nil, fmt.Errorf("illegal entry path: %s", f.Name)
		}
		if !strings.HasPrefix(cleanName, "debtik/") &&
			!strings.HasPrefix(cleanName, "network/") &&
			cleanName != "manifest.json" &&
			cleanName != "debtik" &&
			cleanName != "network" {
			return nil, fmt.Errorf("unrecognized file outside allowed prefixes: %s", cleanName)
		}

		totalUncompressed += int64(f.UncompressedSize64)
		if totalUncompressed > MaxArchiveBytes {
			return nil, fmt.Errorf("archive uncompressed size exceeds maximum allowed (%d bytes)", MaxArchiveBytes)
		}

		if cleanName == "manifest.json" {
			manifestFile = f
		}
	}

	if manifestFile == nil {
		return nil, errors.New("archive is missing manifest.json")
	}

	rc, err := manifestFile.Open()
	if err != nil {
		return nil, fmt.Errorf("cannot read manifest.json: %w", err)
	}
	defer rc.Close()

	var manifest Manifest
	if err := json.NewDecoder(rc).Decode(&manifest); err != nil {
		return nil, fmt.Errorf("invalid manifest.json format: %w", err)
	}

	if manifest.Version == "" {
		return nil, errors.New("manifest version is missing")
	}

	return &manifest, nil
}

// RestoreBackup inspects, creates a pre-restore safety copy, stages, and restores configurations.
func (m *Manager) RestoreBackup(r io.ReaderAt, size int64) (*RestoreResult, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	// 1. Inspect and validate zip structure
	manifest, err := m.InspectBackup(r, size)
	if err != nil {
		return nil, fmt.Errorf("backup validation failed: %w", err)
	}

	// 2. Create pre-restore safety backup of active config
	safetyBackupPath, err := m.createPreRestoreBackupLocked()
	if err != nil {
		log.Printf("[Backup] Warning: failed creating pre-restore safety backup: %v", err)
	} else {
		log.Printf("[Backup] Created pre-restore fallback backup: %s", safetyBackupPath)
	}

	// 3. Extract to staging directory
	stagingDir, err := os.MkdirTemp("", "debtik-restore-stage-*")
	if err != nil {
		return nil, fmt.Errorf("failed creating staging directory: %w", err)
	}
	defer os.RemoveAll(stagingDir)

	zr, err := zip.NewReader(r, size)
	if err != nil {
		return nil, err
	}

	for _, f := range zr.File {
		cleanName := filepath.Clean(f.Name)
		if cleanName == "manifest.json" {
			continue
		}
		if f.FileInfo().IsDir() {
			continue
		}

		destPath := filepath.Join(stagingDir, cleanName)
		// Ensure destination path strictly within stagingDir
		if !strings.HasPrefix(destPath, stagingDir+string(filepath.Separator)) {
			return nil, fmt.Errorf("illegal path traversal detected in %s", f.Name)
		}

		if err := os.MkdirAll(filepath.Dir(destPath), 0755); err != nil {
			return nil, fmt.Errorf("failed creating staging subdir: %w", err)
		}

		rc, err := f.Open()
		if err != nil {
			return nil, fmt.Errorf("failed opening entry %s: %w", f.Name, err)
		}

		content, err := io.ReadAll(rc)
		_ = rc.Close()
		if err != nil {
			return nil, fmt.Errorf("failed reading entry %s: %w", f.Name, err)
		}

		// Determine safe mode
		mode := os.FileMode(0644)
		lower := strings.ToLower(cleanName)
		if strings.Contains(lower, "key") || strings.Contains(lower, "users.json") || strings.Contains(lower, "ppp_secrets.json") {
			mode = 0600
		} else if f.Mode().Perm() != 0 {
			mode = f.Mode().Perm()
		}

		if err := os.WriteFile(destPath, content, mode); err != nil {
			return nil, fmt.Errorf("failed writing staged file %s: %w", f.Name, err)
		}
	}

	// 4. Apply DebTik directory (/etc/debtik)
	stagedDebtik := filepath.Join(stagingDir, "debtik")
	if info, err := os.Stat(stagedDebtik); err == nil && info.IsDir() {
		// Clean and replace /etc/debtik contents
		if err := m.syncDirectory(stagedDebtik, m.debtikDir); err != nil {
			return nil, fmt.Errorf("failed restoring debtik configuration: %w", err)
		}
	}

	// 5. Apply Network directory (/etc/network/interfaces.d)
	stagedNetwork := filepath.Join(stagingDir, "network")
	if info, err := os.Stat(stagedNetwork); err == nil && info.IsDir() {
		if err := os.MkdirAll(m.networkDir, 0755); err != nil {
			return nil, fmt.Errorf("failed ensuring network config dir: %w", err)
		}
		entries, _ := os.ReadDir(stagedNetwork)
		for _, entry := range entries {
			if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".cfg") {
				src := filepath.Join(stagedNetwork, entry.Name())
				dst := filepath.Join(m.networkDir, entry.Name())
				data, err := os.ReadFile(src)
				if err == nil {
					_ = os.WriteFile(dst, data, 0644)
				}
			}
		}
	}

	result := &RestoreResult{
		Success:      true,
		Message:      "Configuration restored successfully. Reloading appliance controller...",
		Manifest:     manifest,
		SafetyBackup: safetyBackupPath,
		RestoredAt:   time.Now().UTC(),
	}

	return result, nil
}

// syncDirectory copies srcDir into dstDir, cleaning obsolete files while preserving security permissions.
func (m *Manager) syncDirectory(srcDir, dstDir string) error {
	if err := os.MkdirAll(dstDir, 0755); err != nil {
		return err
	}

	// Wipe existing files in dstDir to avoid stale or orphaned configs
	existing, err := os.ReadDir(dstDir)
	if err == nil {
		for _, e := range existing {
			_ = os.RemoveAll(filepath.Join(dstDir, e.Name()))
		}
	}

	return filepath.Walk(srcDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		rel, err := filepath.Rel(srcDir, path)
		if err != nil {
			return err
		}
		target := filepath.Join(dstDir, rel)

		if info.IsDir() {
			dirPerm := os.FileMode(0755)
			if strings.Contains(rel, "certs") {
				dirPerm = 0700
			}
			return os.MkdirAll(target, dirPerm)
		}

		data, err := os.ReadFile(path)
		if err != nil {
			return err
		}

		mode := info.Mode().Perm()
		lower := strings.ToLower(rel)
		if strings.Contains(lower, "key") || strings.Contains(lower, "users.json") || strings.Contains(lower, "ppp_secrets.json") {
			mode = 0600
		} else if mode == 0 {
			mode = 0644
		}

		return os.WriteFile(target, data, mode)
	})
}

// TriggerRestart initiates an asynchronous service reload or restart.
func (m *Manager) TriggerRestart(delay time.Duration) {
	go func() {
		time.Sleep(delay)
		log.Printf("[Backup] Initiating controller restart following configuration restore...")
		if m.restartFunc != nil {
			if err := m.restartFunc(); err != nil {
				log.Printf("[Backup] Restart hook returned error: %v", err)
			}
			return
		}
		cmd := exec.Command("systemctl", "restart", "debtik")
		if err := cmd.Run(); err != nil {
			log.Printf("[Backup] systemctl restart debtik failed: %v", err)
		}
	}()
}

// ListLocalBackups returns a list of stored backups in the backupStore.
func (m *Manager) ListLocalBackups() ([]BackupInfo, error) {
	if err := os.MkdirAll(m.backupStore, 0700); err != nil {
		return nil, err
	}

	entries, err := os.ReadDir(m.backupStore)
	if err != nil {
		return nil, err
	}

	var results []BackupInfo
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".zip") {
			continue
		}

		info, err := e.Info()
		if err != nil {
			continue
		}

		filePath := filepath.Join(m.backupStore, e.Name())
		bInfo := BackupInfo{
			Filename: e.Name(),
			Size:     info.Size(),
			ModTime:  info.ModTime().UTC(),
		}

		// Attempt reading manifest for richer metadata
		if f, err := os.Open(filePath); err == nil {
			if zr, err := zip.NewReader(f, info.Size()); err == nil {
				for _, zf := range zr.File {
					if zf.Name == "manifest.json" {
						if rc, err := zf.Open(); err == nil {
							var mf Manifest
							if err := json.NewDecoder(rc).Decode(&mf); err == nil {
								bInfo.DebTikVersion = mf.DebTikVersion
								bInfo.Hostname = mf.Hostname
								bInfo.Comment = mf.Comment
							}
							_ = rc.Close()
						}
						break
					}
				}
			}
			_ = f.Close()
		}

		results = append(results, bInfo)
	}

	sort.Slice(results, func(i, j int) bool {
		return results[i].ModTime.After(results[j].ModTime)
	})

	return results, nil
}

// GetLocalBackup returns the full path of a stored backup file after sanitization.
func (m *Manager) GetLocalBackup(filename string) (string, error) {
	cleanName := sanitizeFilename(filename)
	if !strings.HasSuffix(cleanName, ".zip") {
		return "", errors.New("backup filename must have .zip extension")
	}

	fullPath := filepath.Join(m.backupStore, cleanName)
	if info, err := os.Stat(fullPath); err != nil || info.IsDir() {
		return "", fmt.Errorf("backup file %q not found", cleanName)
	}

	return fullPath, nil
}

// sanitizeFilename restricts filenames to safe alphanumeric characters, dashes, underscores, and dots.
func sanitizeFilename(name string) string {
	name = filepath.Base(name)
	var b strings.Builder
	for _, r := range name {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '-' || r == '_' || r == '.' {
			b.WriteRune(r)
		} else {
			b.WriteRune('_')
		}
	}
	res := b.String()
	if res == "" || res == "." || res == ".." {
		return "backup.zip"
	}
	return res
}