package hold

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"log"
	"sync"
	"time"

	"github.com/google/uuid"
)

// MultipartMode indicates how multipart uploads are handled
type MultipartMode int

const (
	// S3Native uses S3's native multipart API with presigned URLs
	S3Native MultipartMode = iota
	// Buffered buffers parts in memory and assembles them in the hold service
	Buffered
)

// CompletedPart represents an uploaded part with its ETag
type CompletedPart struct {
	PartNumber int    `json:"part_number"`
	ETag       string `json:"etag"`
}

// MultipartSession tracks an in-progress multipart upload
type MultipartSession struct {
	UploadID     string                 // Unique upload ID
	Digest       string                 // Target digest path
	Mode         MultipartMode          // Upload mode (S3Native or Buffered)
	S3UploadID   string                 // S3 upload ID (for S3Native mode)
	Parts        map[int]*MultipartPart // Buffered parts (for Buffered mode)
	CreatedAt    time.Time              // When upload started
	LastActivity time.Time              // Last part upload
	mu           sync.RWMutex           // Protects Parts map
}

// MultipartPart represents a single part in a multipart upload
type MultipartPart struct {
	PartNumber int       // Part number (1-indexed)
	Data       []byte    // Part data (for Buffered mode)
	ETag       string    // ETag from S3 or computed hash
	Size       int64     // Part size in bytes
	UploadedAt time.Time // When part was uploaded
}

// MultipartManager manages multipart upload sessions
type MultipartManager struct {
	sessions map[string]*MultipartSession // uploadID -> session
	mu       sync.RWMutex                 // Protects sessions map
}

// NewMultipartManager creates a new multipart manager
func NewMultipartManager() *MultipartManager {
	mgr := &MultipartManager{
		sessions: make(map[string]*MultipartSession),
	}

	// Start cleanup goroutine for abandoned uploads
	go mgr.cleanupLoop()

	return mgr
}

// cleanupLoop periodically cleans up expired sessions
func (m *MultipartManager) cleanupLoop() {
	ticker := time.NewTicker(15 * time.Minute)
	defer ticker.Stop()

	for range ticker.C {
		m.cleanupExpiredSessions()
	}
}

// cleanupExpiredSessions removes sessions inactive for >24 hours
func (m *MultipartManager) cleanupExpiredSessions() {
	m.mu.Lock()
	defer m.mu.Unlock()

	now := time.Now()
	for uploadID, session := range m.sessions {
		if now.Sub(session.LastActivity) > 24*time.Hour {
			log.Printf("Cleaning up expired multipart session: uploadID=%s, age=%v", uploadID, now.Sub(session.CreatedAt))
			delete(m.sessions, uploadID)
		}
	}
}

// CreateSession creates a new multipart upload session
func (m *MultipartManager) CreateSession(digest string, mode MultipartMode, s3UploadID string) *MultipartSession {
	uploadID := uuid.New().String()

	session := &MultipartSession{
		UploadID:     uploadID,
		Digest:       digest,
		Mode:         mode,
		S3UploadID:   s3UploadID,
		Parts:        make(map[int]*MultipartPart),
		CreatedAt:    time.Now(),
		LastActivity: time.Now(),
	}

	m.mu.Lock()
	m.sessions[uploadID] = session
	m.mu.Unlock()

	log.Printf("Created multipart session: uploadID=%s, digest=%s, mode=%v", uploadID, digest, mode)
	return session
}

// GetSession retrieves a multipart session by upload ID
func (m *MultipartManager) GetSession(uploadID string) (*MultipartSession, error) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	session, ok := m.sessions[uploadID]
	if !ok {
		return nil, fmt.Errorf("multipart session not found: %s", uploadID)
	}

	return session, nil
}

// DeleteSession removes a multipart session
func (m *MultipartManager) DeleteSession(uploadID string) {
	m.mu.Lock()
	defer m.mu.Unlock()

	delete(m.sessions, uploadID)
	log.Printf("Deleted multipart session: uploadID=%s", uploadID)
}

// StorePart stores a part in the session (for Buffered mode)
func (s *MultipartSession) StorePart(partNumber int, data []byte) string {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Compute ETag as SHA256 hash of part data
	hash := sha256.Sum256(data)
	etag := hex.EncodeToString(hash[:])

	part := &MultipartPart{
		PartNumber: partNumber,
		Data:       data,
		ETag:       etag,
		Size:       int64(len(data)),
		UploadedAt: time.Now(),
	}

	s.Parts[partNumber] = part
	s.LastActivity = time.Now()

	log.Printf("Stored part: uploadID=%s, part=%d, size=%d bytes, etag=%s", s.UploadID, partNumber, len(data), etag)
	return etag
}

// RecordS3Part records a part uploaded to S3 (for S3Native mode)
func (s *MultipartSession) RecordS3Part(partNumber int, etag string, size int64) {
	s.mu.Lock()
	defer s.mu.Unlock()

	part := &MultipartPart{
		PartNumber: partNumber,
		ETag:       etag,
		Size:       size,
		UploadedAt: time.Now(),
	}

	s.Parts[partNumber] = part
	s.LastActivity = time.Now()

	log.Printf("Recorded S3 part: uploadID=%s, part=%d, size=%d bytes, etag=%s", s.UploadID, partNumber, size, etag)
}

// AssembleBufferedParts assembles all buffered parts into a single blob
// Returns the complete data and total size
func (s *MultipartSession) AssembleBufferedParts() ([]byte, int64, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	if s.Mode != Buffered {
		return nil, 0, fmt.Errorf("session is not in buffered mode")
	}

	// Calculate total size
	var totalSize int64
	maxPart := 0
	for partNum, part := range s.Parts {
		totalSize += part.Size
		if partNum > maxPart {
			maxPart = partNum
		}
	}

	// Check for missing parts
	for i := 1; i <= maxPart; i++ {
		if _, ok := s.Parts[i]; !ok {
			return nil, 0, fmt.Errorf("missing part %d", i)
		}
	}

	// Assemble parts in order
	assembled := make([]byte, 0, totalSize)
	for i := 1; i <= maxPart; i++ {
		part := s.Parts[i]
		assembled = append(assembled, part.Data...)
	}

	log.Printf("Assembled buffered parts: uploadID=%s, parts=%d, totalSize=%d bytes", s.UploadID, maxPart, totalSize)
	return assembled, totalSize, nil
}

// GetCompletedParts returns the list of completed parts for S3 multipart completion
func (s *MultipartSession) GetCompletedParts() []CompletedPart {
	s.mu.RLock()
	defer s.mu.RUnlock()

	parts := make([]CompletedPart, 0, len(s.Parts))
	for _, part := range s.Parts {
		parts = append(parts, CompletedPart{
			PartNumber: part.PartNumber,
			ETag:       part.ETag,
		})
	}

	return parts
}

// StartMultipartUploadWithManager initiates a multipart upload using the manager
// Returns uploadID and mode
func (s *HoldService) StartMultipartUploadWithManager(ctx context.Context, digest string, manager *MultipartManager) (string, MultipartMode, error) {
	// Check if presigned URLs are disabled for testing
	if s.config.Server.DisablePresignedURLs {
		log.Printf("Presigned URLs disabled (DISABLE_PRESIGNED_URLS=true), using buffered mode")
		session := manager.CreateSession(digest, Buffered, "")
		log.Printf("Started buffered multipart: uploadID=%s", session.UploadID)
		return session.UploadID, Buffered, nil
	}

	// Try S3 native multipart first
	if s.s3Client != nil {
		s3UploadID, err := s.startMultipartUpload(ctx, digest)
		if err == nil {
			// S3 native multipart succeeded
			session := manager.CreateSession(digest, S3Native, s3UploadID)
			log.Printf("Started S3 native multipart: uploadID=%s, s3UploadID=%s", session.UploadID, s3UploadID)
			return session.UploadID, S3Native, nil
		}
		log.Printf("S3 native multipart failed, falling back to buffered mode: %v", err)
	}

	// Fallback to buffered mode
	session := manager.CreateSession(digest, Buffered, "")
	log.Printf("Started buffered multipart: uploadID=%s", session.UploadID)
	return session.UploadID, Buffered, nil
}

// GetPartUploadURL generates a presigned URL for uploading a part
// Only used for S3Native mode - Buffered mode is handled by blobstore adapter
func (s *HoldService) GetPartUploadURL(ctx context.Context, session *MultipartSession, partNumber int, did string) (string, error) {
	if session.Mode != S3Native {
		return "", fmt.Errorf("GetPartUploadURL only supports S3Native mode")
	}

	// Generate S3 presigned URL for this part
	url, err := s.getPartPresignedURL(ctx, session.Digest, session.S3UploadID, partNumber)
	if err != nil {
		return "", fmt.Errorf("failed to generate S3 part URL: %w", err)
	}
	return url, nil
}

// CompleteMultipartUploadWithManager completes a multipart upload
func (s *HoldService) CompleteMultipartUploadWithManager(ctx context.Context, session *MultipartSession, manager *MultipartManager) error {
	defer manager.DeleteSession(session.UploadID)

	if session.Mode == S3Native {
		// Complete S3 multipart upload
		parts := session.GetCompletedParts()
		if err := s.completeMultipartUpload(ctx, session.Digest, session.S3UploadID, parts); err != nil {
			return fmt.Errorf("failed to complete S3 multipart: %w", err)
		}
		log.Printf("Completed S3 native multipart: uploadID=%s, parts=%d", session.UploadID, len(parts))
		return nil
	}

	// Buffered mode: assemble parts and write via driver
	data, size, err := session.AssembleBufferedParts()
	if err != nil {
		return fmt.Errorf("failed to assemble parts: %w", err)
	}

	// Write assembled blob to storage
	path := blobPath(session.Digest)
	writer, err := s.driver.Writer(ctx, path, false)
	if err != nil {
		return fmt.Errorf("failed to create writer: %w", err)
	}

	written, err := writer.Write(data)
	if err != nil {
		writer.Cancel(ctx)
		return fmt.Errorf("failed to write blob: %w", err)
	}

	if err := writer.Commit(ctx); err != nil {
		return fmt.Errorf("failed to commit blob: %w", err)
	}

	log.Printf("Completed buffered multipart: uploadID=%s, size=%d bytes, written=%d", session.UploadID, size, written)
	return nil
}

// AbortMultipartUploadWithManager aborts a multipart upload
func (s *HoldService) AbortMultipartUploadWithManager(ctx context.Context, session *MultipartSession, manager *MultipartManager) error {
	defer manager.DeleteSession(session.UploadID)

	if session.Mode == S3Native {
		// Abort S3 multipart upload
		if err := s.abortMultipartUpload(ctx, session.Digest, session.S3UploadID); err != nil {
			return fmt.Errorf("failed to abort S3 multipart: %w", err)
		}
		log.Printf("Aborted S3 native multipart: uploadID=%s", session.UploadID)
		return nil
	}

	// Buffered mode: just delete the session (parts are in memory)
	log.Printf("Aborted buffered multipart: uploadID=%s", session.UploadID)
	return nil
}