package store

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

// Validatable interface for entities that can validate themselves
type Validatable interface {
	Validate() error
}

// IndexBuilder function type for building custom indices
type IndexBuilder[T any] func(allItems map[int]*T) any

// BaseStore provides generic storage with index management
type BaseStore[T any] struct {
	items         map[int]*T
	maxID         int
	mu            sync.RWMutex
	itemType      reflect.Type
	indices       map[string]any
	indexBuilders map[string]IndexBuilder[T]
}

// 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),
		indices:       make(map[string]any),
		indexBuilders: make(map[string]IndexBuilder[T]),
	}
}

// RegisterIndex registers an index builder function
func (bs *BaseStore[T]) RegisterIndex(name string, builder IndexBuilder[T]) {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	bs.indexBuilders[name] = builder
}

// GetIndex retrieves a named index
func (bs *BaseStore[T]) GetIndex(name string) (any, bool) {
	bs.mu.RLock()
	defer bs.mu.RUnlock()
	index, exists := bs.indices[name]
	return index, exists
}

// RebuildIndices rebuilds all registered indices
func (bs *BaseStore[T]) RebuildIndices() {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	bs.rebuildIndicesUnsafe()
}

func (bs *BaseStore[T]) rebuildIndicesUnsafe() {
	allItems := make(map[int]*T, len(bs.items))
	maps.Copy(allItems, bs.items)

	for name, builder := range bs.indexBuilders {
		bs.indices[name] = builder(allItems)
	}
}

// AddWithRebuild adds item with validation and index rebuild
func (bs *BaseStore[T]) AddWithRebuild(id int, item *T) error {
	bs.mu.Lock()
	defer bs.mu.Unlock()

	if validatable, ok := any(item).(Validatable); ok {
		if err := validatable.Validate(); err != nil {
			return err
		}
	}

	bs.items[id] = item
	if id > bs.maxID {
		bs.maxID = id
	}

	bs.rebuildIndicesUnsafe()
	return nil
}

// RemoveWithRebuild removes item and rebuilds indices
func (bs *BaseStore[T]) RemoveWithRebuild(id int) {
	bs.mu.Lock()
	defer bs.mu.Unlock()
	delete(bs.items, id)
	bs.rebuildIndicesUnsafe()
}

// UpdateWithRebuild updates item with validation and index rebuild
func (bs *BaseStore[T]) UpdateWithRebuild(id int, item *T) error {
	return bs.AddWithRebuild(id, item)
}

// Common Query Methods

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

// AllSorted returns all items using named sorted index
func (bs *BaseStore[T]) AllSorted(indexName string) []*T {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	if index, exists := bs.indices[indexName]; exists {
		if sortedIDs, ok := index.([]int); ok {
			result := make([]*T, 0, len(sortedIDs))
			for _, id := range sortedIDs {
				if item, exists := bs.items[id]; exists {
					result = append(result, item)
				}
			}
			return result
		}
	}

	// Fallback: return all items by ID order
	ids := make([]int, 0, len(bs.items))
	for id := range bs.items {
		ids = append(ids, id)
	}
	sort.Ints(ids)

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

// LookupByIndex finds single item using string lookup index
func (bs *BaseStore[T]) LookupByIndex(indexName, key string) (*T, bool) {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	if index, exists := bs.indices[indexName]; exists {
		if lookupMap, ok := index.(map[string]int); ok {
			if id, found := lookupMap[key]; found {
				if item, exists := bs.items[id]; exists {
					return item, true
				}
			}
		}
	}
	return nil, false
}

// GroupByIndex returns items grouped by key
func (bs *BaseStore[T]) GroupByIndex(indexName string, key any) []*T {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	if index, exists := bs.indices[indexName]; exists {
		switch groupMap := index.(type) {
		case map[int][]int:
			if intKey, ok := key.(int); ok {
				if ids, found := groupMap[intKey]; found {
					result := make([]*T, 0, len(ids))
					for _, id := range ids {
						if item, exists := bs.items[id]; exists {
							result = append(result, item)
						}
					}
					return result
				}
			}
		case map[string][]int:
			if strKey, ok := key.(string); ok {
				if ids, found := groupMap[strKey]; found {
					result := make([]*T, 0, len(ids))
					for _, id := range ids {
						if item, exists := bs.items[id]; exists {
							result = append(result, item)
						}
					}
					return result
				}
			}
		}
	}
	return []*T{}
}

// FilterByIndex returns items matching filter criteria
func (bs *BaseStore[T]) FilterByIndex(indexName string, filterFunc func(*T) bool) []*T {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	var sourceIDs []int

	if index, exists := bs.indices[indexName]; exists {
		if sortedIDs, ok := index.([]int); ok {
			sourceIDs = sortedIDs
		}
	}

	if sourceIDs == nil {
		for id := range bs.items {
			sourceIDs = append(sourceIDs, id)
		}
		sort.Ints(sourceIDs)
	}

	var result []*T
	for _, id := range sourceIDs {
		if item, exists := bs.items[id]; exists && filterFunc(item) {
			result = append(result, item)
		}
	}
	return result
}

// BuildStringLookupIndex creates string-to-ID mapping
func BuildStringLookupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[string]int)
		for id, item := range allItems {
			key := keyFunc(item)
			index[key] = id
		}
		return index
	}
}

// BuildCaseInsensitiveLookupIndex creates lowercase string-to-ID mapping
func BuildCaseInsensitiveLookupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[string]int)
		for id, item := range allItems {
			key := strings.ToLower(keyFunc(item))
			index[key] = id
		}
		return index
	}
}

// BuildIntGroupIndex creates int-to-[]ID mapping
func BuildIntGroupIndex[T any](keyFunc func(*T) int) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[int][]int)
		for id, item := range allItems {
			key := keyFunc(item)
			index[key] = append(index[key], id)
		}

		// Sort each group by ID
		for key := range index {
			sort.Ints(index[key])
		}

		return index
	}
}

// BuildStringGroupIndex creates string-to-[]ID mapping
func BuildStringGroupIndex[T any](keyFunc func(*T) string) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[string][]int)
		for id, item := range allItems {
			key := keyFunc(item)
			index[key] = append(index[key], id)
		}

		// Sort each group by ID
		for key := range index {
			sort.Ints(index[key])
		}

		return index
	}
}

// BuildSortedListIndex creates sorted []ID list
func BuildSortedListIndex[T any](sortFunc func(*T, *T) bool) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		ids := make([]int, 0, len(allItems))
		for id := range allItems {
			ids = append(ids, id)
		}

		sort.Slice(ids, func(i, j int) bool {
			return sortFunc(allItems[ids[i]], allItems[ids[j]])
		})

		return ids
	}
}

// NewSingleton creates singleton store pattern with sync.Once
func NewSingleton[S any](initFunc func() *S) func() *S {
	var store *S
	var once sync.Once

	return func() *S {
		once.Do(func() {
			store = initFunc()
		})
		return store
	}
}

// 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) {
	return bs.Find(id)
}

// 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))
	maps.Copy(result, bs.items)
	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
	bs.rebuildIndicesUnsafe()
}

// 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 with consistent ID ordering
func (bs *BaseStore[T]) SaveToJSON(filename string) error {
	bs.mu.RLock()
	defer bs.mu.RUnlock()

	// Get sorted IDs for consistent ordering
	ids := make([]int, 0, len(bs.items))
	for id := range bs.items {
		ids = append(ids, id)
	}
	sort.Ints(ids)

	// Build items slice in ID order
	items := make([]*T, 0, len(bs.items))
	for _, id := range ids {
		items = append(items, bs.items[id])
	}

	data, err := json.MarshalIndent(items, "", "\t")
	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 %s\n", len(bs.items), dataPath)
	bs.RebuildIndices() // Rebuild indices after loading
	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 %s\n", len(bs.items), dataPath)
	return nil
}

// BuildFilteredIntGroupIndex creates int-to-[]ID mapping for items passing filter
func BuildFilteredIntGroupIndex[T any](filterFunc func(*T) bool, keyFunc func(*T) int) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[int][]int)
		for id, item := range allItems {
			if filterFunc(item) {
				key := keyFunc(item)
				index[key] = append(index[key], id)
			}
		}

		// Sort each group by ID
		for key := range index {
			sort.Ints(index[key])
		}

		return index
	}
}

// BuildFilteredStringGroupIndex creates string-to-[]ID mapping for items passing filter
func BuildFilteredStringGroupIndex[T any](filterFunc func(*T) bool, keyFunc func(*T) string) IndexBuilder[T] {
	return func(allItems map[int]*T) any {
		index := make(map[string][]int)
		for id, item := range allItems {
			if filterFunc(item) {
				key := keyFunc(item)
				index[key] = append(index[key], id)
			}
		}

		// Sort each group by ID
		for key := range index {
			sort.Ints(index[key])
		}

		return index
	}
}