// Package client provides ZFS snapshot backup client functionality.
// It handles creating snapshots and uploading them to a remote server.
package client

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"os/exec"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/credentials"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	"github.com/mistifyio/go-zfs"
	"github.com/pierrec/lz4/v4"
)

// Client handles snapshot backup operations to a remote server.
// It manages creating local ZFS snapshots and transmitting them
// to the backup server via HTTP or SSH.
type Client struct {
	config *Config
}

// New creates a new Client instance with the provided configuration.
func New(config *Config) *Client {
	return &Client{config: config}
}

// CreateSnapshot creates a local ZFS snapshot of the configured dataset.
// The snapshot is named with a timestamp for easy identification.
// Returns the created snapshot dataset or an error.
func (c *Client) CreateSnapshot() (*zfs.Dataset, error) {
	// Get the local dataset
	ds, err := zfs.GetDataset(c.config.LocalDataset)
	if err != nil {
		return nil, fmt.Errorf("failed to get dataset: %v", err)
	}

	// Generate snapshot name with timestamp
	timestamp := time.Now().Format("2006-01-02_15:04:05")
	snapshotName := fmt.Sprintf("backup_%s", timestamp)

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

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

// GetSnapshotSize returns the used size of a snapshot in bytes.
func (c *Client) GetSnapshotSize(snapshot *zfs.Dataset) int64 {
	return int64(snapshot.Used)
}

// SendSnapshot sends a snapshot to the backup server.
// It first requests upload authorization, then streams the snapshot
// using the appropriate method (S3 or ZFS receive).
func (c *Client) SendSnapshot(snapshot *zfs.Dataset) error {
	estimatedSize := c.GetSnapshotSize(snapshot)

	// 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,
	}

	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()

	// Parse server response
	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("  Storage key: %s\n", uploadResp.StorageKey)

	// Choose upload method based on server response
	if uploadResp.UploadMethod == "s3" {
		return c.streamToS3(snapshot, uploadResp.UploadURL, uploadResp.StorageKey)
	}
	return c.sendViaZFS(snapshot, uploadResp.StorageKey)
}

// streamToS3 streams a ZFS snapshot to S3 storage using AWS SDK.
// The snapshot is optionally compressed with LZ4 before transmission.
func (c *Client) streamToS3(snapshot *zfs.Dataset, uploadURL, storageKey string) error {
	fmt.Printf("→ Uploading snapshot to S3...\n")

	// Ensure endpoint has valid URI scheme
	endpoint := c.config.S3Endpoint
	if endpoint != "" && !strings.HasPrefix(endpoint, "http://") && !strings.HasPrefix(endpoint, "https://") {
		endpoint = "http://" + endpoint
	}

	// Create AWS config
	awsCfg, err := config.LoadDefaultConfig(context.TODO(),
		config.WithRegion(c.config.S3Region),
		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(
			c.config.S3AccessKey,
			c.config.S3SecretKey,
			"",
		)),
	)
	if err != nil {
		return fmt.Errorf("failed to load AWS config: %v", err)
	}

	// Determine if using custom endpoint (non-AWS)
	customEndpoint := endpoint != "" && endpoint != "http://s3.amazonaws.com" && endpoint != "https://s3.amazonaws.com"

	// Create S3 client
	s3Client := s3.NewFromConfig(awsCfg, func(o *s3.Options) {
		if customEndpoint {
			o.BaseEndpoint = aws.String(endpoint)
			o.UsePathStyle = true // Required for MinIO compatible storage
		}
	})

	// Create ZFS send command
	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 LZ4 compression if enabled
	if c.config.Compress {
		fmt.Printf("  Compressing with LZ4...\n")
		pr, pw := io.Pipe()
		lz4Writer := lz4.NewWriter(pw)
		lz4Writer.Apply(lz4.BlockSizeOption(lz4.BlockSize(4 * 1024 * 1024))) // 4MB blocks for better performance

		go func() {
			// Copy zfs output to LZ4 writer
			io.Copy(lz4Writer, zfsOut)
			// Close LZ4 writer first to flush, then close pipe
			lz4Writer.Close()
			pw.Close()
		}()

		reader = pr
	}

	// Upload to S3 using PutObject
	_, err = s3Client.PutObject(context.TODO(), &s3.PutObjectInput{
		Bucket:      aws.String(c.config.S3Bucket),
		Key:         aws.String(storageKey),
		Body:        reader,
		ContentType: aws.String("application/octet-stream"),
	})

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

	if err != nil {
		return fmt.Errorf("failed to upload to S3: %v", err)
	}

	fmt.Printf("✓ Snapshot uploaded to S3 successfully!\n")

	return nil
}

// sendViaZFS sends a snapshot via traditional ZFS send/receive over SSH.
// This method is used when the server uses local ZFS storage.
func (c *Client) sendViaZFS(snapshot *zfs.Dataset, 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]
	}

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

// SnapshotResult contains the result of a snapshot creation and send operation.
type SnapshotResult struct {
	FullBackup bool
	Snapshot   *zfs.Dataset
}

// CreateAndSend creates a snapshot and sends it to the backup server.
// It automatically detects if this is a full or incremental backup:
// - If no bookmark exists, does a full backup
// - If bookmark exists, does an incremental backup from the bookmark
func (c *Client) CreateAndSend() (*SnapshotResult, error) {
	// Check for existing bookmark to determine backup type
	lastBookmark, err := c.GetLastBookmark()
	if err != nil {
		return nil, fmt.Errorf("failed to check bookmarks: %v", err)
	}

	// Create new snapshot
	snapshot, err := c.CreateSnapshot()
	if err != nil {
		return nil, fmt.Errorf("failed to create snapshot: %v", err)
	}

	isFullBackup := lastBookmark == ""
	if isFullBackup {
		fmt.Println("→ No previous backup found, doing FULL backup...")
		// Send as full (no base)
		if err := c.SendIncremental(snapshot, ""); err != nil {
			return nil, fmt.Errorf("failed to send snapshot: %v", err)
		}
	} else {
		fmt.Printf("→ Found previous backup, doing INCREMENTAL from %s...", lastBookmark)
		// Send as incremental from bookmark
		if err := c.SendIncremental(snapshot, lastBookmark); err != nil {
			return nil, fmt.Errorf("failed to send incremental: %v", err)
		}
	}

	// Create bookmark for future incremental backups
	if err := c.CreateBookmark(snapshot); err != nil {
		fmt.Printf("Warning: failed to create bookmark: %v\n", err)
	}

	return &SnapshotResult{
		FullBackup: isFullBackup,
		Snapshot:   snapshot,
	}, nil
}

// GetStatus retrieves and displays the client's backup status from the server.
// Shows storage usage, quota, and snapshot count.
func (c *Client) GetStatus() error {
	url := fmt.Sprintf("%s/status?client_id=%s&api_key=%s",
		c.config.ServerURL, c.config.ClientID, c.config.APIKey)

	resp, err := http.Get(url)
	if err != nil {
		return fmt.Errorf("failed to get status: %v", err)
	}
	defer resp.Body.Close()

	var status struct {
		Success        bool    `json:"success"`
		TotalSnapshots int     `json:"total_snapshots"`
		UsedBytes      int64   `json:"used_bytes"`
		MaxBytes       int64   `json:"max_bytes"`
		PercentUsed    float64 `json:"percent_used"`
		StorageType    string  `json:"storage_type"`
	}

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

	if !status.Success {
		return fmt.Errorf("status check failed")
	}

	fmt.Printf("\n=== Server Status ===\n")
	fmt.Printf("Storage Type: %s\n", status.StorageType)
	fmt.Printf("Total Snapshots: %d\n", status.TotalSnapshots)
	fmt.Printf("Used: %.2f GB / %.2f GB (%.1f%%)\n",
		float64(status.UsedBytes)/(1024*1024*1024),
		float64(status.MaxBytes)/(1024*1024*1024),
		status.PercentUsed)

	return nil
}