// Package task provides asynchronous task processing with handler factory pattern
package task

import (
	"context"
	"fmt"
	"sync"
	"time"

	"modelRT/database"
	"modelRT/logger"
	"modelRT/orm"

	"github.com/gofrs/uuid"
	"gorm.io/gorm"
)

// TaskHandler defines the interface for task processors
type TaskHandler interface {
	// Execute processes a task with the given ID, type, and params from the MQ message
	Execute(ctx context.Context, taskID uuid.UUID, taskType TaskType, params map[string]any, db *gorm.DB) error
	// CanHandle returns true if this handler can process the given task type
	CanHandle(taskType TaskType) bool
	// Name returns the name of the handler for logging and metrics
	Name() string
}

// HandlerFactory creates task handlers based on task type
type HandlerFactory struct {
	handlers map[TaskType]TaskHandler
	mu       sync.RWMutex
}

// NewHandlerFactory creates a new HandlerFactory
func NewHandlerFactory() *HandlerFactory {
	return &HandlerFactory{
		handlers: make(map[TaskType]TaskHandler),
	}
}

// RegisterHandler registers a handler for a specific task type
func (f *HandlerFactory) RegisterHandler(ctx context.Context, taskType TaskType, handler TaskHandler) {
	f.mu.Lock()
	defer f.mu.Unlock()

	f.handlers[taskType] = handler
	logger.Info(ctx, "Handler registered",
		"task_type", taskType,
		"handler_name", handler.Name(),
	)
}

// GetHandler returns a handler for the given task type
func (f *HandlerFactory) GetHandler(taskType TaskType) (TaskHandler, error) {
	f.mu.RLock()
	handler, exists := f.handlers[taskType]
	f.mu.RUnlock()

	if !exists {
		return nil, fmt.Errorf("no handler registered for task type: %s", taskType)
	}

	return handler, nil
}

// CreateDefaultHandlers registers all default task handlers
func (f *HandlerFactory) CreateDefaultHandlers(ctx context.Context) {
	f.RegisterHandler(ctx, TypeTopologyAnalysis, &TopologyAnalysisHandler{})
	f.RegisterHandler(ctx, TypeEventAnalysis, &EventAnalysisHandler{})
	f.RegisterHandler(ctx, TypeBatchImport, &BatchImportHandler{})
	f.RegisterHandler(ctx, TaskType(TaskTypeTest), NewTestTaskHandler())
}

// BaseHandler provides common functionality for all task handlers
type BaseHandler struct {
	name string
}

// NewBaseHandler creates a new BaseHandler
func NewBaseHandler(name string) *BaseHandler {
	return &BaseHandler{name: name}
}

// Name returns the handler name
func (h *BaseHandler) Name() string {
	return h.name
}

// TopologyAnalysisHandler handles topology analysis tasks
type TopologyAnalysisHandler struct {
	BaseHandler
}

// NewTopologyAnalysisHandler creates a new TopologyAnalysisHandler
func NewTopologyAnalysisHandler() *TopologyAnalysisHandler {
	return &TopologyAnalysisHandler{
		BaseHandler: *NewBaseHandler("topology_analysis_handler"),
	}
}

// Execute processes a topology analysis task.
// Params (all sourced from the MQ message, no DB lookup needed):
//   - start_component_uuid (string, required): BFS origin
//   - end_component_uuid   (string, required): reachability target
//   - check_in_service     (bool,   optional, default true): skip out-of-service components
func (h *TopologyAnalysisHandler) Execute(ctx context.Context, taskID uuid.UUID, taskType TaskType, params map[string]any, db *gorm.DB) error {
	logger.Info(ctx, "topology analysis started", "task_id", taskID)

	// Phase 1: parse params from MQ message
	startComponentUUID, endComponentUUID, checkInService, err := parseTopologyAnalysisParams(params)
	if err != nil {
		return fmt.Errorf("invalid topology analysis params: %w", err)
	}

	logger.Info(ctx, "topology params parsed",
		"task_id", taskID,
		"start", startComponentUUID,
		"end", endComponentUUID,
		"check_in_service", checkInService,
	)

	if err := database.UpdateAsyncTaskProgress(ctx, db, taskID, 20); err != nil {
		logger.Warn(ctx, "update progress failed", "task_id", taskID, "progress", 20, "error", err)
	}

	// Phase 2: query topology edges from startComponentUUID, build adjacency list
	topoEdges, err := database.QueryTopologicByStartUUID(ctx, db, startComponentUUID)
	if err != nil {
		return fmt.Errorf("query topology from start node: %w", err)
	}

	// adjacency list: uuid_from → []uuid_to
	adjMap := make(map[uuid.UUID][]uuid.UUID, len(topoEdges))
	// collect all UUIDs for batch InService query
	allUUIDs := make(map[uuid.UUID]struct{}, len(topoEdges)*2)
	allUUIDs[startComponentUUID] = struct{}{}
	for _, edge := range topoEdges {
		adjMap[edge.UUIDFrom] = append(adjMap[edge.UUIDFrom], edge.UUIDTo)
		allUUIDs[edge.UUIDFrom] = struct{}{}
		allUUIDs[edge.UUIDTo] = struct{}{}
	}

	if err := database.UpdateAsyncTaskProgress(ctx, db, taskID, 40); err != nil {
		logger.Warn(ctx, "update progress failed", "task_id", taskID, "progress", 40, "error", err)
	}

	// Phase 3: batch-load InService status (only when checkInService is true)
	inServiceMap := make(map[uuid.UUID]bool)
	if checkInService {
		uuidSlice := make([]uuid.UUID, 0, len(allUUIDs))
		for id := range allUUIDs {
			uuidSlice = append(uuidSlice, id)
		}
		inServiceMap, err = database.QueryComponentsInServiceByUUIDs(ctx, db, uuidSlice)
		if err != nil {
			return fmt.Errorf("query component in_service status: %w", err)
		}

		// check the start node itself before BFS
		if !inServiceMap[startComponentUUID] {
			return persistTopologyResult(ctx, db, taskID, startComponentUUID, endComponentUUID,
				checkInService, false, nil, &startComponentUUID)
		}
	}

	if err := database.UpdateAsyncTaskProgress(ctx, db, taskID, 60); err != nil {
		logger.Warn(ctx, "update progress failed", "task_id", taskID, "progress", 60, "error", err)
	}

	// Phase 4: BFS reachability check
	visited := make(map[uuid.UUID]struct{})
	parent := make(map[uuid.UUID]uuid.UUID) // for path reconstruction
	queue := []uuid.UUID{startComponentUUID}
	visited[startComponentUUID] = struct{}{}
	isReachable := false
	var blockedBy *uuid.UUID

	for len(queue) > 0 {
		cur := queue[0]
		queue = queue[1:]

		if cur == endComponentUUID {
			isReachable = true
			break
		}

		for _, next := range adjMap[cur] {
			if _, seen := visited[next]; seen {
				continue
			}
			if checkInService && !inServiceMap[next] {
				// record first out-of-service blocker but keep searching other branches
				if blockedBy == nil {
					id := next
					blockedBy = &id
				}
				continue
			}
			visited[next] = struct{}{}
			parent[next] = cur
			queue = append(queue, next)
		}
	}

	if err := database.UpdateAsyncTaskProgress(ctx, db, taskID, 80); err != nil {
		logger.Warn(ctx, "update progress failed", "task_id", taskID, "progress", 80, "error", err)
	}

	// Phase 5: reconstruct path (if reachable) and persist result
	var path []uuid.UUID
	if isReachable {
		blockedBy = nil // reachable path found — clear any partial blocker
		path = reconstructPath(parent, startComponentUUID, endComponentUUID)
	}

	return persistTopologyResult(ctx, db, taskID, startComponentUUID, endComponentUUID,
		checkInService, isReachable, path, blockedBy)
}

// parseTopologyAnalysisParams extracts and validates the three required fields.
// check_in_service defaults to true when absent.
func parseTopologyAnalysisParams(params map[string]any) (startID, endID uuid.UUID, checkInService bool, err error) {
	startStr, ok := params["start_component_uuid"].(string)
	if !ok || startStr == "" {
		err = fmt.Errorf("missing or invalid start_component_uuid")
		return
	}
	endStr, ok := params["end_component_uuid"].(string)
	if !ok || endStr == "" {
		err = fmt.Errorf("missing or invalid end_component_uuid")
		return
	}
	startID, err = uuid.FromString(startStr)
	if err != nil {
		err = fmt.Errorf("parse start_component_uuid %q: %w", startStr, err)
		return
	}
	endID, err = uuid.FromString(endStr)
	if err != nil {
		err = fmt.Errorf("parse end_component_uuid %q: %w", endStr, err)
		return
	}

	// check_in_service defaults to true
	checkInService = true
	if v, exists := params["check_in_service"]; exists {
		if b, isBool := v.(bool); isBool {
			checkInService = b
		}
	}
	return
}

// reconstructPath walks the parent map backwards from end to start.
func reconstructPath(parent map[uuid.UUID]uuid.UUID, start, end uuid.UUID) []uuid.UUID {
	var path []uuid.UUID
	for cur := end; cur != start; cur = parent[cur] {
		path = append(path, cur)
	}
	path = append(path, start)
	// reverse: path was built end→start
	for i, j := 0, len(path)-1; i < j; i, j = i+1, j-1 {
		path[i], path[j] = path[j], path[i]
	}
	return path
}

// persistTopologyResult serialises the analysis outcome and writes it to async_task_result.
func persistTopologyResult(
	ctx context.Context, db *gorm.DB, taskID uuid.UUID,
	startID, endID uuid.UUID, checkInService, isReachable bool,
	path []uuid.UUID, blockedBy *uuid.UUID,
) error {
	pathStrs := make([]string, 0, len(path))
	for _, id := range path {
		pathStrs = append(pathStrs, id.String())
	}

	result := orm.JSONMap{
		"start_component_uuid": startID.String(),
		"end_component_uuid":   endID.String(),
		"check_in_service":     checkInService,
		"is_reachable":         isReachable,
		"path":                 pathStrs,
		"computed_at":          time.Now().Unix(),
	}
	if blockedBy != nil {
		result["blocked_by"] = blockedBy.String()
	}

	if err := database.CreateAsyncTaskResult(ctx, db, taskID, result); err != nil {
		return fmt.Errorf("save task result: %w", err)
	}

	logger.Info(ctx, "topology analysis completed",
		"task_id", taskID,
		"is_reachable", isReachable,
		"path_length", len(path),
	)
	return nil
}

// CanHandle returns true for topology analysis tasks
func (h *TopologyAnalysisHandler) CanHandle(taskType TaskType) bool {
	return taskType == TypeTopologyAnalysis
}

// EventAnalysisHandler handles event analysis tasks
type EventAnalysisHandler struct {
	BaseHandler
}

// NewEventAnalysisHandler creates a new EventAnalysisHandler
func NewEventAnalysisHandler() *EventAnalysisHandler {
	return &EventAnalysisHandler{
		BaseHandler: *NewBaseHandler("event_analysis_handler"),
	}
}

// Execute processes an event analysis task
func (h *EventAnalysisHandler) Execute(ctx context.Context, taskID uuid.UUID, taskType TaskType, params map[string]any, db *gorm.DB) error {
	logger.Info(ctx, "Starting event analysis",
		"task_id", taskID,
		"task_type", taskType,
	)

	// TODO: Implement actual event analysis logic
	// This would typically involve:
	// 1. Fetching motor and trigger information
	// 2. Analyzing events within the specified duration
	// 3. Generating analysis report
	// 4. Storing results in database

	// Simulate work
	logger.Info(ctx, "Event analysis completed",
		"task_id", taskID,
		"task_type", taskType,
	)

	return nil
}

// CanHandle returns true for event analysis tasks
func (h *EventAnalysisHandler) CanHandle(taskType TaskType) bool {
	return taskType == TypeEventAnalysis
}

// BatchImportHandler handles batch import tasks
type BatchImportHandler struct {
	BaseHandler
}

// NewBatchImportHandler creates a new BatchImportHandler
func NewBatchImportHandler() *BatchImportHandler {
	return &BatchImportHandler{
		BaseHandler: *NewBaseHandler("batch_import_handler"),
	}
}

// Execute processes a batch import task
func (h *BatchImportHandler) Execute(ctx context.Context, taskID uuid.UUID, taskType TaskType, params map[string]any, db *gorm.DB) error {
	logger.Info(ctx, "Starting batch import",
		"task_id", taskID,
		"task_type", taskType,
	)

	// TODO: Implement actual batch import logic
	// This would typically involve:
	// 1. Reading file from specified path
	// 2. Parsing file content (CSV, Excel, etc.)
	// 3. Validating and importing data into database
	// 4. Generating import report

	// Simulate work
	logger.Info(ctx, "Batch import completed",
		"task_id", taskID,
		"task_type", taskType,
	)

	return nil
}

// CanHandle returns true for batch import tasks
func (h *BatchImportHandler) CanHandle(taskType TaskType) bool {
	return taskType == TypeBatchImport
}

// CompositeHandler can handle multiple task types by delegating to appropriate handlers
type CompositeHandler struct {
	factory *HandlerFactory
}

// NewCompositeHandler creates a new CompositeHandler
func NewCompositeHandler(factory *HandlerFactory) *CompositeHandler {
	return &CompositeHandler{factory: factory}
}

// Execute delegates task execution to the appropriate handler
func (h *CompositeHandler) Execute(ctx context.Context, taskID uuid.UUID, taskType TaskType, params map[string]any, db *gorm.DB) error {
	handler, err := h.factory.GetHandler(taskType)
	if err != nil {
		return fmt.Errorf("failed to get handler for task type %s: %w", taskType, err)
	}

	return handler.Execute(ctx, taskID, taskType, params, db)
}

// CanHandle returns true if any registered handler can handle the task type
func (h *CompositeHandler) CanHandle(taskType TaskType) bool {
	_, err := h.factory.GetHandler(taskType)
	return err == nil
}

// Name returns the composite handler name
func (h *CompositeHandler) Name() string {
	return "composite_handler"
}

// DefaultHandlerFactory returns a HandlerFactory with all default handlers registered
func DefaultHandlerFactory(ctx context.Context) *HandlerFactory {
	factory := NewHandlerFactory()
	factory.CreateDefaultHandlers(ctx)
	return factory
}

// DefaultCompositeHandler returns a CompositeHandler with all default handlers
func DefaultCompositeHandler(ctx context.Context) TaskHandler {
	factory := DefaultHandlerFactory(ctx)
	return NewCompositeHandler(factory)
}