Calendar/src/storage/BaseEntityService.ts

import { ISync, EntityType, SyncStatus, IEventBus } from '../types/CalendarTypes';
import { IEntityService } from './IEntityService';
import { SyncPlugin } from './SyncPlugin';
import { IndexedDBContext } from './IndexedDBContext';
import { CoreEvents } from '../constants/CoreEvents';
import { diff } from 'json-diff-ts';
import { IEntitySavedPayload, IEntityDeletedPayload } from '../types/EventTypes';

/**
 * BaseEntityService<T extends ISync> - Abstract base class for all entity services
 *
 * HYBRID PATTERN: Inheritance + Composition
 * - Services EXTEND this base class (inheritance for structure)
 * - Sync logic is COMPOSED via SyncPlugin (pluggable)
 *
 * PROVIDES:
 * - Generic CRUD operations (get, getAll, save, delete)
 * - Sync status management (delegates to SyncPlugin)
 * - Serialization hooks (override in subclass if needed)
 * - Lazy database access via IndexedDBContext
 *
 * SUBCLASSES MUST IMPLEMENT:
 * - storeName: string (IndexedDB object store name)
 * - entityType: EntityType (for runtime routing)
 *
 * SUBCLASSES MAY OVERRIDE:
 * - serialize(entity: T): any (default: no serialization)
 * - deserialize(data: any): T (default: no deserialization)
 *
 * BENEFITS:
 * - DRY: Single source of truth for CRUD logic
 * - Type safety: Generic T ensures compile-time checking
 * - Pluggable: SyncPlugin can be swapped for testing/different implementations
 * - Open/Closed: New entities just extend this class
 * - Lazy database access: db requested when needed, not at construction time
 */
export abstract class BaseEntityService<T extends ISync> implements IEntityService<T> {
  // Abstract properties - must be implemented by subclasses
  abstract readonly storeName: string;
  abstract readonly entityType: EntityType;

  // Internal composition - sync functionality
  private syncPlugin: SyncPlugin<T>;

  // IndexedDB context - provides database connection
  private context: IndexedDBContext;

  // EventBus for emitting entity events
  protected eventBus: IEventBus;

  /**
   * @param context - IndexedDBContext instance (injected dependency)
   * @param eventBus - EventBus for emitting entity events
   */
  constructor(context: IndexedDBContext, eventBus: IEventBus) {
    this.context = context;
    this.eventBus = eventBus;
    this.syncPlugin = new SyncPlugin<T>(this);
  }

  /**
   * Get IDBDatabase instance (lazy access)
   * Protected getter accessible to subclasses and methods in this class
   */
  protected get db(): IDBDatabase {
    return this.context.getDatabase();
  }

  /**
   * Serialize entity before storing in IndexedDB
   * Override in subclass if entity has Date fields or needs transformation
   *
   * @param entity - Entity to serialize
   * @returns Serialized data (default: entity itself)
   */
  protected serialize(entity: T): any {
    return entity; // Default: no serialization
  }

  /**
   * Deserialize data from IndexedDB back to entity
   * Override in subclass if entity has Date fields or needs transformation
   *
   * @param data - Raw data from IndexedDB
   * @returns Deserialized entity (default: data itself)
   */
  protected deserialize(data: any): T {
    return data as T; // Default: no deserialization
  }

  /**
   * Get a single entity by ID
   *
   * @param id - Entity ID
   * @returns Entity or null if not found
   */
  async get(id: string): Promise<T | null> {
    return new Promise((resolve, reject) => {
      const transaction = this.db.transaction([this.storeName], 'readonly');
      const store = transaction.objectStore(this.storeName);
      const request = store.get(id);

      request.onsuccess = () => {
        const data = request.result;
        if (data) {
          resolve(this.deserialize(data));
        } else {
          resolve(null);
        }
      };

      request.onerror = () => {
        reject(new Error(`Failed to get ${this.entityType} ${id}: ${request.error}`));
      };
    });
  }

  /**
   * Get all entities
   *
   * @returns Array of all entities
   */
  async getAll(): Promise<T[]> {
    return new Promise((resolve, reject) => {
      const transaction = this.db.transaction([this.storeName], 'readonly');
      const store = transaction.objectStore(this.storeName);
      const request = store.getAll();

      request.onsuccess = () => {
        const data = request.result as any[];
        const entities = data.map(item => this.deserialize(item));
        resolve(entities);
      };

      request.onerror = () => {
        reject(new Error(`Failed to get all ${this.entityType}s: ${request.error}`));
      };
    });
  }

  /**
   * Save an entity (create or update)
   * Emits ENTITY_SAVED event with operation type and changes
   *
   * @param entity - Entity to save
   */
  async save(entity: T): Promise<void> {
    const entityId = (entity as any).id;

    // Check if entity exists to determine create vs update
    const existingEntity = await this.get(entityId);
    const isCreate = existingEntity === null;

    // Calculate changes: full entity for create, diff for update
    let changes: any;
    if (isCreate) {
      changes = entity;
    } else {
      // Calculate diff between existing and new entity
      const existingSerialized = this.serialize(existingEntity);
      const newSerialized = this.serialize(entity);
      changes = diff(existingSerialized, newSerialized);
    }

    const serialized = this.serialize(entity);

    return new Promise((resolve, reject) => {
      const transaction = this.db.transaction([this.storeName], 'readwrite');
      const store = transaction.objectStore(this.storeName);
      const request = store.put(serialized);

      request.onsuccess = () => {
        // Emit ENTITY_SAVED event
        const payload: IEntitySavedPayload = {
          entityType: this.entityType,
          entityId,
          operation: isCreate ? 'create' : 'update',
          changes,
          timestamp: Date.now()
        };
        this.eventBus.emit(CoreEvents.ENTITY_SAVED, payload);
        resolve();
      };

      request.onerror = () => {
        reject(new Error(`Failed to save ${this.entityType} ${entityId}: ${request.error}`));
      };
    });
  }

  /**
   * Delete an entity
   * Emits ENTITY_DELETED event
   *
   * @param id - Entity ID to delete
   */
  async delete(id: string): Promise<void> {
    return new Promise((resolve, reject) => {
      const transaction = this.db.transaction([this.storeName], 'readwrite');
      const store = transaction.objectStore(this.storeName);
      const request = store.delete(id);

      request.onsuccess = () => {
        // Emit ENTITY_DELETED event
        const payload: IEntityDeletedPayload = {
          entityType: this.entityType,
          entityId: id,
          operation: 'delete',
          timestamp: Date.now()
        };
        this.eventBus.emit(CoreEvents.ENTITY_DELETED, payload);
        resolve();
      };

      request.onerror = () => {
        reject(new Error(`Failed to delete ${this.entityType} ${id}: ${request.error}`));
      };
    });
  }

  // ============================================================================
  // SYNC METHODS (IEntityService implementation) - Delegates to SyncPlugin
  // ============================================================================

  /**
   * Mark entity as successfully synced (IEntityService implementation)
   * Delegates to SyncPlugin
   *
   * @param id - Entity ID
   */
  async markAsSynced(id: string): Promise<void> {
    return this.syncPlugin.markAsSynced(id);
  }

  /**
   * Mark entity as sync error (IEntityService implementation)
   * Delegates to SyncPlugin
   *
   * @param id - Entity ID
   */
  async markAsError(id: string): Promise<void> {
    return this.syncPlugin.markAsError(id);
  }

  /**
   * Get sync status for an entity (IEntityService implementation)
   * Delegates to SyncPlugin
   *
   * @param id - Entity ID
   * @returns SyncStatus or null if entity not found
   */
  async getSyncStatus(id: string): Promise<SyncStatus | null> {
    return this.syncPlugin.getSyncStatus(id);
  }

  /**
   * Get entities by sync status
   * Delegates to SyncPlugin - uses IndexedDB syncStatus index
   *
   * @param syncStatus - Sync status ('synced', 'pending', 'error')
   * @returns Array of entities with this sync status
   */
  async getBySyncStatus(syncStatus: string): Promise<T[]> {
    return this.syncPlugin.getBySyncStatus(syncStatus);
  }
}