add singleton pattern

src/main.ts

@@ -2,6 +2,7 @@ export type CloudProvider = 'google' | 'azure' | 'aws'
 export interface VirtualMachine {}
 export interface Storage {}
 export interface Network {}
+export interface Database {}
 
 export class AzureVirtualMachine implements VirtualMachine {}
 export class GoogleVirtualMachine implements VirtualMachine {}
@@ -15,6 +16,10 @@ export class AzureNetwork implements Network {}
 export class GoogleNetwork implements Network {}
 export class AWSNetwork implements Network {}
 
+export class AzureDatabase implements Database {}
+export class GoogleDatabase implements Database {}
+export class AWSDatabase implements Database {}
+
 export class CloudProviderNotSupportException extends Error {}
 export class VirtualMachineNotSupportedException extends Error {}
 export class NetworkNotSupportedException extends Error {}

src/singleton.test.ts

@@ -0,0 +1,10 @@
+import { describe, it, expect } from "bun:test";
+import { AzureDatabase } from "~/singleton";
+
+describe("AzureDatabase", () => {
+  it("should create only one instance", () => {
+    const instance1 = AzureDatabase.create();
+    const instance2 = AzureDatabase.create();
+    expect(instance1).toBe(instance2);
+  });
+});

src/singleton.ts

@@ -0,0 +1,16 @@
+import { Database } from "~/main"
+
+
+export class AzureDatabase  {
+    private static instance: Database
+
+    private constructor() {}
+
+    static create(): Database {
+        if (!AzureDatabase.instance) {
+            AzureDatabase.instance = new AzureDatabase()
+        }
+
+        return AzureDatabase.instance
+    }
+}