db layer implemented

using sqlite

apps/admin/src/lib/database/index.ts

@@ -0,0 +1,87 @@
+import { IDatabase, DatabaseConfig } from './types'
+import { SQLiteDatabase } from './sqlite'
+
+// Database factory - creates appropriate database instance based on config
+export class DatabaseFactory {
+  private static instance: IDatabase | null = null
+  private static config: DatabaseConfig | null = null
+
+  static async initialize(config: DatabaseConfig): Promise<IDatabase> {
+    if (this.instance && this.config && this.isSameConfig(config)) {
+      return this.instance
+    }
+
+    // Close existing connection if different config
+    if (this.instance) {
+      await this.instance.disconnect()
+      this.instance = null
+    }
+
+    // Create new database instance based on type
+    switch (config.type) {
+      case 'sqlite':
+        this.instance = new SQLiteDatabase(config)
+        break
+      
+      case 'postgresql':
+        // TODO: Implement PostgreSQLDatabase
+        throw new Error('PostgreSQL implementation not yet available')
+      
+      case 'mysql':
+        // TODO: Implement MySQLDatabase
+        throw new Error('MySQL implementation not yet available')
+      
+      case 'mongodb':
+        // TODO: Implement MongoDBDatabase
+        throw new Error('MongoDB implementation not yet available')
+      
+      default:
+        throw new Error(`Unsupported database type: ${config.type}`)
+    }
+
+    await this.instance.connect()
+    this.config = config
+    
+    return this.instance
+  }
+
+  static getInstance(): IDatabase {
+    if (!this.instance) {
+      throw new Error('Database not initialized. Call initialize() first.')
+    }
+    return this.instance
+  }
+
+  static async disconnect(): Promise<void> {
+    if (this.instance) {
+      await this.instance.disconnect()
+      this.instance = null
+      this.config = null
+    }
+  }
+
+  private static isSameConfig(config: DatabaseConfig): boolean {
+    if (!this.config) return false
+    
+    return (
+      this.config.type === config.type &&
+      JSON.stringify(this.config.connection) === JSON.stringify(config.connection)
+    )
+  }
+}
+
+// Default configuration
+export const defaultDatabaseConfig: DatabaseConfig = {
+  type: 'sqlite',
+  connection: {
+    filename: './data/fitai.db'
+  },
+  options: {
+    logging: process.env.NODE_ENV === 'development'
+  }
+}
+
+// Convenience function to get database instance
+export async function getDatabase(): Promise<IDatabase> {
+  return await DatabaseFactory.initialize(defaultDatabaseConfig)
+}