package store

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"reflect"
	"sync"
)

// Store provides generic storage operations
type Store[T any] interface {
	LoadFromJSON(filename string) error
	SaveToJSON(filename string) error
	LoadData(dataPath string) error
	SaveData(dataPath string) error
}

// BaseStore provides generic JSON persistence
type BaseStore[T any] struct {
	items    map[int]*T
	maxID    int
	mu       sync.RWMutex
	itemType reflect.Type
}

// NewBaseStore creates a new base store for type T
func NewBaseStore[T any]() *BaseStore[T] {
	var zero T
	return &BaseStore[T]{
		items:    make(map[int]*T),
		maxID:    0,
		itemType: reflect.TypeOf(zero),
	}
}

// GetNextID returns the next available ID atomically
func (bs *BaseStore[T]) GetNextID() int {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	bs.maxID++
	return bs.maxID
}

// GetByID retrieves an item by ID
func (bs *BaseStore[T]) GetByID(id int) (*T, bool) {
	bs.mu.RLock()
	defer bs.mu.RUnlock()
	item, exists := bs.items[id]
	return item, exists
}

// Add adds an item to the store
func (bs *BaseStore[T]) Add(id int, item *T) {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	bs.items[id] = item
	if id > bs.maxID {
		bs.maxID = id
	}
}

// Remove removes an item from the store
func (bs *BaseStore[T]) Remove(id int) {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	delete(bs.items, id)
}

// GetAll returns all items
func (bs *BaseStore[T]) GetAll() map[int]*T {
	bs.mu.RLock()
	defer bs.mu.RUnlock()
	result := make(map[int]*T, len(bs.items))
	for k, v := range bs.items {
		result[k] = v
	}
	return result
}

// Clear removes all items
func (bs *BaseStore[T]) Clear() {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	bs.items = make(map[int]*T)
	bs.maxID = 0
}

// LoadFromJSON loads items from JSON using reflection
func (bs *BaseStore[T]) LoadFromJSON(filename string) error {
	bs.mu.Lock()
	defer bs.mu.Unlock()

	data, err := os.ReadFile(filename)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("failed to read JSON: %w", err)
	}

	if len(data) == 0 {
		return nil
	}

	// Create slice of pointers to T
	sliceType := reflect.SliceOf(reflect.PointerTo(bs.itemType))
	slicePtr := reflect.New(sliceType)

	if err := json.Unmarshal(data, slicePtr.Interface()); err != nil {
		return fmt.Errorf("failed to unmarshal JSON: %w", err)
	}

	// Clear existing data
	bs.items = make(map[int]*T)
	bs.maxID = 0

	// Extract items using reflection
	slice := slicePtr.Elem()
	for i := 0; i < slice.Len(); i++ {
		item := slice.Index(i).Interface().(*T)

		// Get ID using reflection
		itemValue := reflect.ValueOf(item).Elem()
		idField := itemValue.FieldByName("ID")
		if !idField.IsValid() {
			return fmt.Errorf("item type must have an ID field")
		}

		id := int(idField.Int())
		bs.items[id] = item
		if id > bs.maxID {
			bs.maxID = id
		}
	}

	return nil
}

// SaveToJSON saves items to JSON atomically
func (bs *BaseStore[T]) SaveToJSON(filename string) error {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	items := make([]*T, 0, len(bs.items))
	for _, item := range bs.items {
		items = append(items, item)
	}

	data, err := json.MarshalIndent(items, "", "  ")
	if err != nil {
		return fmt.Errorf("failed to marshal to JSON: %w", err)
	}

	// Atomic write
	tempFile := filename + ".tmp"
	if err := os.WriteFile(tempFile, data, 0644); err != nil {
		return fmt.Errorf("failed to write temp JSON: %w", err)
	}

	if err := os.Rename(tempFile, filename); err != nil {
		os.Remove(tempFile)
		return fmt.Errorf("failed to rename temp JSON: %w", err)
	}

	return nil
}

// LoadData loads from JSON file or starts empty
func (bs *BaseStore[T]) LoadData(dataPath string) error {
	if err := bs.LoadFromJSON(dataPath); err != nil {
		if os.IsNotExist(err) {
			fmt.Println("No existing data found, starting with empty store")
			return nil
		}
		return fmt.Errorf("failed to load from JSON: %w", err)
	}

	fmt.Printf("Loaded %d items from JSON\n", len(bs.items))
	return nil
}

// SaveData saves to JSON file
func (bs *BaseStore[T]) SaveData(dataPath string) error {
	// Ensure directory exists
	dataDir := filepath.Dir(dataPath)
	if err := os.MkdirAll(dataDir, 0755); err != nil {
		return fmt.Errorf("failed to create data directory: %w", err)
	}

	if err := bs.SaveToJSON(dataPath); err != nil {
		return fmt.Errorf("failed to save to JSON: %w", err)
	}

	fmt.Printf("Saved %d items to JSON\n", len(bs.items))
	return nil
}