package api

import (
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"time"

	"github.com/ant0ine/go-json-rest/rest"
	"github.com/openaccounting/oa-server/core/model"
	"github.com/openaccounting/oa-server/core/model/types"
	"github.com/openaccounting/oa-server/core/storage"
	"github.com/openaccounting/oa-server/core/util"
	"github.com/openaccounting/oa-server/core/util/id"
)

// AttachmentHandler handles attachment operations with configurable storage
type AttachmentHandler struct {
	storage storage.Storage
}

// Global attachment handler instance (will be initialized during server startup)
var attachmentHandler *AttachmentHandler

// InitializeAttachmentHandler initializes the global attachment handler with storage backend
func InitializeAttachmentHandler(storageConfig storage.Config) error {
	storageBackend, err := storage.NewStorage(storageConfig)
	if err != nil {
		return fmt.Errorf("failed to initialize storage backend: %w", err)
	}
	
	attachmentHandler = &AttachmentHandler{
		storage: storageBackend,
	}
	
	return nil
}

// PostAttachmentWithStorage handles file upload using the configured storage backend
func PostAttachmentWithStorage(w rest.ResponseWriter, r *rest.Request) {
	if attachmentHandler == nil {
		rest.Error(w, "Storage backend not initialized", http.StatusInternalServerError)
		return
	}
	
	transactionId := r.FormValue("transactionId")
	if transactionId == "" {
		rest.Error(w, "Transaction ID is required", http.StatusBadRequest)
		return
	}

	if !util.IsValidUUID(transactionId) {
		rest.Error(w, "Invalid transaction ID format", http.StatusBadRequest)
		return
	}

	user := r.Env["USER"].(*types.User)

	// Parse multipart form
	err := r.ParseMultipartForm(MaxFileSize)
	if err != nil {
		rest.Error(w, "Failed to parse multipart form", http.StatusBadRequest)
		return
	}

	files := r.MultipartForm.File["file"]
	if len(files) == 0 {
		rest.Error(w, "No file provided", http.StatusBadRequest)
		return
	}

	fileHeader := files[0] // Take the first file

	// Verify transaction exists and user has permission
	tx, err := model.Instance.GetTransaction(transactionId, "", user.Id)
	if err != nil {
		rest.Error(w, "Transaction not found", http.StatusNotFound)
		return
	}
	if tx == nil {
		rest.Error(w, "Transaction not found", http.StatusNotFound)
		return
	}

	// Process the file upload
	attachment, err := attachmentHandler.processFileUploadWithStorage(fileHeader, transactionId, tx.OrgId, user.Id, r.FormValue("description"))
	if err != nil {
		rest.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	// Save attachment to database
	createdAttachment, err := model.Instance.CreateAttachment(attachment)
	if err != nil {
		// Clean up the stored file on database error
		attachmentHandler.storage.Delete(attachment.FilePath)
		rest.Error(w, "Failed to save attachment", http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusCreated)
	w.WriteJson(createdAttachment)
}

// GetAttachmentWithStorage retrieves an attachment using the configured storage backend
func GetAttachmentWithStorage(w rest.ResponseWriter, r *rest.Request) {
	if attachmentHandler == nil {
		rest.Error(w, "Storage backend not initialized", http.StatusInternalServerError)
		return
	}
	
	attachmentId := r.PathParam("id")
	if !util.IsValidUUID(attachmentId) {
		rest.Error(w, "Invalid attachment ID format", http.StatusBadRequest)
		return
	}

	user := r.Env["USER"].(*types.User)

	// Get attachment from database
	attachment, err := model.Instance.GetAttachment(attachmentId, "", "", user.Id)
	if err != nil {
		rest.Error(w, "Attachment not found", http.StatusNotFound)
		return
	}

	// Check if this is a download request
	if r.URL.Query().Get("download") == "true" {
		// Stream the file directly to the client
		err := attachmentHandler.streamFile(w, attachment)
		if err != nil {
			rest.Error(w, "Failed to retrieve file", http.StatusInternalServerError)
			return
		}
		return
	}

	// Return attachment metadata
	w.WriteJson(attachment)
}

// GetAttachmentDownloadURL returns a download URL for an attachment
func GetAttachmentDownloadURL(w rest.ResponseWriter, r *rest.Request) {
	if attachmentHandler == nil {
		rest.Error(w, "Storage backend not initialized", http.StatusInternalServerError)
		return
	}
	
	attachmentId := r.PathParam("id")
	if !util.IsValidUUID(attachmentId) {
		rest.Error(w, "Invalid attachment ID format", http.StatusBadRequest)
		return
	}

	user := r.Env["USER"].(*types.User)

	// Get attachment from database
	attachment, err := model.Instance.GetAttachment(attachmentId, "", "", user.Id)
	if err != nil {
		rest.Error(w, "Attachment not found", http.StatusNotFound)
		return
	}

	// Generate download URL (valid for 1 hour)
	url, err := attachmentHandler.storage.GetURL(attachment.FilePath, time.Hour)
	if err != nil {
		rest.Error(w, "Failed to generate download URL", http.StatusInternalServerError)
		return
	}

	response := map[string]string{
		"url":       url,
		"expiresIn": "3600", // 1 hour in seconds
	}

	w.WriteJson(response)
}

// DeleteAttachmentWithStorage deletes an attachment using the configured storage backend
func DeleteAttachmentWithStorage(w rest.ResponseWriter, r *rest.Request) {
	if attachmentHandler == nil {
		rest.Error(w, "Storage backend not initialized", http.StatusInternalServerError)
		return
	}
	
	attachmentId := r.PathParam("id")
	if !util.IsValidUUID(attachmentId) {
		rest.Error(w, "Invalid attachment ID format", http.StatusBadRequest)
		return
	}

	user := r.Env["USER"].(*types.User)

	// Get attachment from database first
	attachment, err := model.Instance.GetAttachment(attachmentId, "", "", user.Id)
	if err != nil {
		rest.Error(w, "Attachment not found", http.StatusNotFound)
		return
	}

	// Delete from database (soft delete)
	err = model.Instance.DeleteAttachment(attachmentId, attachment.TransactionId, attachment.OrgId, user.Id)
	if err != nil {
		rest.Error(w, "Failed to delete attachment", http.StatusInternalServerError)
		return
	}

	// Delete from storage backend
	// Note: For production, you might want to delay physical deletion
	// and run a cleanup job later to handle any issues
	err = attachmentHandler.storage.Delete(attachment.FilePath)
	if err != nil {
		// Log the error but don't fail the request since database deletion succeeded
		// The file can be cleaned up later by a maintenance job
		fmt.Printf("Warning: Failed to delete file from storage: %v\n", err)
	}

	w.WriteHeader(http.StatusOK)
	w.WriteJson(map[string]string{"status": "deleted"})
}

// processFileUploadWithStorage processes a file upload using the storage backend
func (h *AttachmentHandler) processFileUploadWithStorage(fileHeader *multipart.FileHeader, transactionId, orgId, userId, description string) (*types.Attachment, error) {
	// Validate file size
	if fileHeader.Size > MaxFileSize {
		return nil, fmt.Errorf("file too large. Maximum size is %d bytes", MaxFileSize)
	}

	// Validate content type
	contentType := fileHeader.Header.Get("Content-Type")
	if !AllowedMimeTypes[contentType] {
		return nil, fmt.Errorf("unsupported file type: %s", contentType)
	}

	// Open the file
	file, err := fileHeader.Open()
	if err != nil {
		return nil, fmt.Errorf("failed to open uploaded file: %w", err)
	}
	defer file.Close()

	// Store the file using the storage backend
	storagePath, err := h.storage.Store(fileHeader.Filename, file, contentType)
	if err != nil {
		return nil, fmt.Errorf("failed to store file: %w", err)
	}

	// Create attachment record
	attachment := &types.Attachment{
		Id:            id.String(id.New()),
		TransactionId: transactionId,
		OrgId:         orgId,
		UserId:        userId,
		FileName:      storagePath, // Store the storage path/key
		OriginalName:  fileHeader.Filename,
		ContentType:   contentType,
		FileSize:      fileHeader.Size,
		FilePath:      storagePath, // For backward compatibility
		Description:   description,
		Uploaded:      time.Now(),
		Deleted:       false,
	}

	return attachment, nil
}

// streamFile streams a file from storage to the HTTP response
func (h *AttachmentHandler) streamFile(w rest.ResponseWriter, attachment *types.Attachment) error {
	// Get file from storage
	reader, err := h.storage.Retrieve(attachment.FilePath)
	if err != nil {
		return fmt.Errorf("failed to retrieve file: %w", err)
	}
	defer reader.Close()

	// Set appropriate headers
	w.Header().Set("Content-Type", attachment.ContentType)
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", attachment.OriginalName))
	
	// If we know the file size, set Content-Length
	if attachment.FileSize > 0 {
		w.Header().Set("Content-Length", fmt.Sprintf("%d", attachment.FileSize))
	}

	// Stream the file to the client
	_, err = io.Copy(w.(http.ResponseWriter), reader)
	return err
}