// Package client provides ZFS snapshot backup client functionality.
// This file contains snapshot management functions including creation,
// bookmarking, and rotation similar to zfs-auto-snapshot.
package client

import (
	"bytes"
	"compress/gzip"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"os/exec"
	"sort"
	"strings"
	"time"

	"github.com/mistifyio/go-zfs"
)

// SnapshotPolicy defines retention settings for automatic snapshots.
type SnapshotPolicy struct {
	// KeepHourly is the number of hourly snapshots to keep
	KeepHourly int
	// KeepDaily is the number of daily snapshots to keep
	KeepDaily int
	// KeepWeekly is the number of weekly snapshots to keep
	KeepWeekly int
	// KeepMonthly is the number of monthly snapshots to keep
	KeepMonthly int
}

// DefaultPolicy returns the default snapshot retention policy.
func DefaultPolicy() *SnapshotPolicy {
	return &SnapshotPolicy{
		KeepHourly:  24,
		KeepDaily:   7,
		KeepWeekly:  4,
		KeepMonthly: 12,
	}
}

// SnapshotType represents the type of snapshot (hourly, daily, etc.)
type SnapshotType string

const (
	SnapshotHourly  SnapshotType = "hourly"
	SnapshotDaily   SnapshotType = "daily"
	SnapshotWeekly  SnapshotType = "weekly"
	SnapshotMonthly SnapshotType = "monthly"
	SnapshotManual  SnapshotType = "manual"
)

// CreateSnapshotWithType creates a snapshot with a specific type label.
// The snapshot name follows the pattern: zfs-backup-<type>-<timestamp>
func (c *Client) CreateSnapshotWithType(snapshotType SnapshotType) (*zfs.Dataset, error) {
	ds, err := zfs.GetDataset(c.config.LocalDataset)
	if err != nil {
		return nil, fmt.Errorf("failed to get dataset: %v", err)
	}

	timestamp := time.Now().Format("2006-01-02_15-04-05")
	snapshotName := fmt.Sprintf("zfs-backup-%s-%s", snapshotType, timestamp)

	snapshot, err := ds.Snapshot(snapshotName, false)
	if err != nil {
		return nil, fmt.Errorf("failed to create snapshot: %v", err)
	}

	fmt.Printf("✓ Created %s snapshot: %s@%s\n", snapshotType, c.config.LocalDataset, snapshotName)
	return snapshot, nil
}

// CreateBookmark creates a ZFS bookmark from a snapshot.
// Bookmarks allow incremental sends even after the source snapshot is deleted.
func (c *Client) CreateBookmark(snapshot *zfs.Dataset) error {
	// Extract snapshot name from full path (dataset@snapshot -> snapshot)
	parts := strings.Split(snapshot.Name, "@")
	if len(parts) != 2 {
		return fmt.Errorf("invalid snapshot name format: %s", snapshot.Name)
	}
	snapshotName := parts[1]
	bookmarkName := fmt.Sprintf("%s#%s", c.config.LocalDataset, snapshotName)

	// Create bookmark using zfs command
	cmd := exec.Command("zfs", "bookmark", snapshot.Name, bookmarkName)
	output, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("failed to create bookmark: %v: %s", err, string(output))
	}

	fmt.Printf("✓ Created bookmark: %s\n", bookmarkName)
	return nil
}

// GetLastBookmark returns the most recent bookmark for the dataset.
// Bookmarks are used as the base for incremental sends.
func (c *Client) GetLastBookmark() (string, error) {
	// List all bookmarks for the dataset
	cmd := exec.Command("zfs", "list", "-t", "bookmark", "-o", "name", "-H", "-r", c.config.LocalDataset)
	output, err := cmd.Output()
	if err != nil {
		return "", nil // No bookmarks yet
	}

	bookmarks := strings.Split(strings.TrimSpace(string(output)), "\n")
	if len(bookmarks) == 0 || bookmarks[0] == "" {
		return "", nil
	}

	// Return the last bookmark (most recent)
	return bookmarks[len(bookmarks)-1], nil
}

// GetLastSnapshot returns the most recent snapshot for the dataset.
func (c *Client) GetLastSnapshot() (*zfs.Dataset, error) {
	ds, err := zfs.GetDataset(c.config.LocalDataset)
	if err != nil {
		return nil, fmt.Errorf("failed to get dataset: %v", err)
	}

	snapshots, err := ds.Snapshots()
	if err != nil {
		return nil, fmt.Errorf("failed to list snapshots: %v", err)
	}

	if len(snapshots) == 0 {
		return nil, nil
	}

	// Return the last snapshot (most recent)
	return snapshots[len(snapshots)-1], nil
}

// SendIncremental sends an incremental stream from a bookmark or snapshot.
// If base is empty, sends a full stream.
func (c *Client) SendIncremental(snapshot *zfs.Dataset, base string) error {
	estimatedSize := c.GetSnapshotSize(snapshot)

	// Determine if this is incremental or full
	isIncremental := base != ""
	var uploadMethod string
	if isIncremental {
		uploadMethod = "incremental"
	} else {
		uploadMethod = "full"
	}

	// Request upload authorization from server
	uploadReq := map[string]interface{}{
		"client_id":      c.config.ClientID,
		"api_key":        c.config.APIKey,
		"dataset_name":   c.config.LocalDataset,
		"timestamp":      time.Now().Format(time.RFC3339),
		"compressed":     c.config.Compress,
		"estimated_size": estimatedSize,
		"incremental":    isIncremental,
		"base_snapshot":  base,
	}

	reqBody, _ := json.Marshal(uploadReq)
	resp, err := http.Post(c.config.ServerURL+"/upload", "application/json", bytes.NewBuffer(reqBody))
	if err != nil {
		return fmt.Errorf("failed to request upload: %v", err)
	}
	defer resp.Body.Close()

	var uploadResp struct {
		Success      bool   `json:"success"`
		Message      string `json:"message"`
		UploadURL    string `json:"upload_url"`
		UploadMethod string `json:"upload_method"`
		StorageKey   string `json:"storage_key"`
	}

	if err := json.NewDecoder(resp.Body).Decode(&uploadResp); err != nil {
		return fmt.Errorf("failed to decode response: %v", err)
	}

	if !uploadResp.Success {
		return fmt.Errorf("upload not authorized: %s", uploadResp.Message)
	}

	fmt.Printf("→ Upload authorized\n")
	fmt.Printf("  Method: %s\n", uploadResp.UploadMethod)
	fmt.Printf("  Type: %s\n", uploadMethod)
	fmt.Printf("  Storage key: %s\n", uploadResp.StorageKey)

	// Choose upload method based on server response
	if uploadResp.UploadMethod == "s3" {
		return c.streamIncrementalToS3(snapshot, base, uploadResp.UploadURL, uploadResp.StorageKey)
	}
	return c.sendIncrementalViaZFS(snapshot, base, uploadResp.StorageKey)
}

// streamIncrementalToS3 streams an incremental ZFS snapshot to S3.
func (c *Client) streamIncrementalToS3(snapshot *zfs.Dataset, base, uploadURL, storageKey string) error {
	fmt.Printf("→ Streaming snapshot to S3...\n")

	// Create ZFS send command
	var cmd *exec.Cmd
	if base != "" {
		// Incremental send from bookmark or snapshot
		fmt.Printf("  Base: %s\n", base)
		cmd = exec.Command("zfs", "send", "-i", base, snapshot.Name)
	} else {
		// Full send
		cmd = exec.Command("zfs", "send", snapshot.Name)
	}

	zfsOut, err := cmd.StdoutPipe()
	if err != nil {
		return fmt.Errorf("failed to create pipe: %v", err)
	}

	if err := cmd.Start(); err != nil {
		return fmt.Errorf("failed to start zfs send: %v", err)
	}

	var reader io.Reader = zfsOut

	// Apply gzip compression if enabled
	if c.config.Compress {
		fmt.Printf("  Compressing with gzip...\n")
		pr, pw := io.Pipe()
		gzWriter := gzip.NewWriter(pw)

		go func() {
			// Copy zfs output to gzip writer
			io.Copy(gzWriter, zfsOut)
			// Close gzip writer first to flush footer, then close pipe
			gzWriter.Close()
			pw.Close()
		}()

		reader = pr
	}

	// Create HTTP request
	req, err := http.NewRequest("POST", c.config.ServerURL+uploadURL, reader)
	if err != nil {
		return fmt.Errorf("failed to create request: %v", err)
	}

	// Set required headers
	req.Header.Set("X-API-Key", c.config.APIKey)
	req.Header.Set("X-Storage-Key", storageKey)
	req.Header.Set("X-Dataset-Name", c.config.LocalDataset)
	req.Header.Set("X-Compressed", fmt.Sprintf("%v", c.config.Compress))
	req.Header.Set("X-Incremental", fmt.Sprintf("%v", base != ""))
	if base != "" {
		req.Header.Set("X-Base-Snapshot", base)
	}
	req.Header.Set("Content-Type", "application/octet-stream")

	// Send request with no timeout for large uploads
	client := &http.Client{
		Timeout: 0,
	}

	httpResp, err := client.Do(req)
	if err != nil {
		cmd.Process.Kill()
		return fmt.Errorf("failed to upload: %v", err)
	}
	defer httpResp.Body.Close()

	if httpResp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(httpResp.Body)
		return fmt.Errorf("upload failed with status %d: %s", httpResp.StatusCode, body)
	}

	if err := cmd.Wait(); err != nil {
		return fmt.Errorf("zfs send failed: %v", err)
	}

	// Parse response
	var result struct {
		Success bool   `json:"success"`
		Message string `json:"message"`
		Size    int64  `json:"size"`
	}

	if err := json.NewDecoder(httpResp.Body).Decode(&result); err != nil {
		return fmt.Errorf("failed to decode response: %v", err)
	}

	if !result.Success {
		return fmt.Errorf("upload failed: %s", result.Message)
	}

	fmt.Printf("✓ Snapshot uploaded successfully!\n")
	fmt.Printf("  Size: %.2f MB\n", float64(result.Size)/(1024*1024))

	return nil
}

// sendIncrementalViaZFS sends an incremental snapshot via ZFS send/receive over SSH.
// This method is used when the server uses local ZFS storage.
func (c *Client) sendIncrementalViaZFS(snapshot *zfs.Dataset, base, receivePath string) error {
	fmt.Printf("-> Sending via ZFS send/receive...\n")

	// Extract server host from URL
	serverHost := c.config.ServerURL
	if len(serverHost) > 7 && strings.HasPrefix(serverHost, "http://") {
		serverHost = serverHost[7:]
	} else if len(serverHost) > 8 && strings.HasPrefix(serverHost, "https://") {
		serverHost = serverHost[8:]
	}

	// Remove port if present
	if idx := strings.LastIndex(serverHost, ":"); idx > 0 {
		serverHost = serverHost[:idx]
	}

	// Build zfs send command
	var zfsSendCmd string
	if base != "" {
		// Incremental send
		fmt.Printf("  Base: %s\n", base)
		zfsSendCmd = fmt.Sprintf("zfs send -i %s %s", base, snapshot.Name)
	} else {
		// Full send
		zfsSendCmd = fmt.Sprintf("zfs send %s", snapshot.Name)
	}

	// Execute ZFS send over SSH
	cmd := exec.Command("sh", "-c",
		fmt.Sprintf("%s | ssh %s 'zfs recv -F %s'", zfsSendCmd, serverHost, receivePath))

	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	if err := cmd.Run(); err != nil {
		return fmt.Errorf("failed to send snapshot: %v", err)
	}

	fmt.Printf("Snapshot sent successfully!\n")
	return nil
}

// RotateLocalSnapshots removes old snapshots based on the retention policy.
// This is similar to zfs-auto-snapshot's rotation behavior.
func (c *Client) RotateLocalSnapshots(policy *SnapshotPolicy) error {
	ds, err := zfs.GetDataset(c.config.LocalDataset)
	if err != nil {
		return fmt.Errorf("failed to get dataset: %v", err)
	}

	snapshots, err := ds.Snapshots()
	if err != nil {
		return fmt.Errorf("failed to list snapshots: %v", err)
	}

	// Group snapshots by type
	groups := make(map[SnapshotType][]*zfs.Dataset)
	for _, snap := range snapshots {
		snapType := parseSnapshotType(snap.Name)
		groups[snapType] = append(groups[snapType], snap)
	}

	// Apply retention policy
	deletedCount := 0
	keepCount := map[SnapshotType]int{
		SnapshotHourly:  policy.KeepHourly,
		SnapshotDaily:   policy.KeepDaily,
		SnapshotWeekly:  policy.KeepWeekly,
		SnapshotMonthly: policy.KeepMonthly,
		SnapshotManual:  -1, // Keep all manual snapshots
	}

	for snapType, snaps := range groups {
		maxKeep := keepCount[snapType]
		if maxKeep < 0 {
			continue // Keep all
		}

		// Sort by creation time (oldest first)
		sortSnapshotsByTime(snaps)

		// Delete oldest snapshots exceeding the limit
		if len(snaps) > maxKeep {
			toDelete := snaps[:len(snaps)-maxKeep]
			for _, snap := range toDelete {
				fmt.Printf("  Deleting old snapshot: %s\n", snap.Name)
				if err := snap.Destroy(zfs.DestroyDefault); err != nil {
					fmt.Printf("  Warning: failed to delete %s: %v\n", snap.Name, err)
				} else {
					deletedCount++
				}
			}
		}
	}

	if deletedCount > 0 {
		fmt.Printf("✓ Rotated %d local snapshots\n", deletedCount)
	}

	return nil
}

// parseSnapshotType extracts the snapshot type from the snapshot name.
func parseSnapshotType(name string) SnapshotType {
	if strings.Contains(name, "hourly") {
		return SnapshotHourly
	}
	if strings.Contains(name, "daily") {
		return SnapshotDaily
	}
	if strings.Contains(name, "weekly") {
		return SnapshotWeekly
	}
	if strings.Contains(name, "monthly") {
		return SnapshotMonthly
	}
	return SnapshotManual
}

// sortSnapshotsByTime sorts snapshots by creation time (oldest first).
// Uses the snapshot name which contains timestamp for sorting.
func sortSnapshotsByTime(snaps []*zfs.Dataset) {
	sort.Slice(snaps, func(i, j int) bool {
		// Extract timestamp from snapshot name for comparison
		// Names are like: dataset@zfs-backup-hourly-2006-01-02_15-04-05
		return snaps[i].Name < snaps[j].Name
	})
}