Add cached Langfuse PromptService

test/core/langfuse/PromptService.test.ts

@@ -0,0 +1,64 @@
+import { describe, expect, it, vi } from 'vitest';
+import { PromptService } from '../../../src/core/langfuse/PromptService';
+import type { PromptFetcher, RawPrompt } from '../../../src/core/langfuse/PromptGateway';
+
+function makeRawPrompt(name: string, version = 1): RawPrompt {
+  return {
+    name,
+    version,
+    config: { model: 'gpt-4o-mini' },
+    compile: (variables) => [{ role: 'user', content: `hello ${String(variables.who)}` }],
+  };
+}
+
+describe('PromptService', () => {
+  it('fetches once and reuses the cache on subsequent calls when caching is enabled', async () => {
+    const fetch = vi.fn().mockResolvedValue(makeRawPrompt('greet'));
+    const fetcher: PromptFetcher = { fetch };
+    const service = new PromptService(fetcher, true);
+
+    await service.getCompiled('greet', { who: 'a' });
+    const compiled = await service.getCompiled('greet', { who: 'b' });
+
+    expect(fetch).toHaveBeenCalledTimes(1);
+    expect(compiled.messages).toEqual([{ role: 'user', content: 'hello b' }]);
+    expect(compiled.config).toEqual({ model: 'gpt-4o-mini' });
+  });
+
+  it('always refetches when caching is disabled', async () => {
+    const fetch = vi.fn().mockResolvedValue(makeRawPrompt('greet'));
+    const fetcher: PromptFetcher = { fetch };
+    const service = new PromptService(fetcher, false);
+
+    await service.getCompiled('greet', { who: 'a' });
+    await service.getCompiled('greet', { who: 'b' });
+
+    expect(fetch).toHaveBeenCalledTimes(2);
+  });
+
+  it('invalidate(name) forces a refetch for that name only', async () => {
+    const fetch = vi.fn().mockResolvedValue(makeRawPrompt('greet'));
+    const fetcher: PromptFetcher = { fetch };
+    const service = new PromptService(fetcher, true);
+
+    await service.getCompiled('greet', {});
+    service.invalidate('greet');
+    await service.getCompiled('greet', {});
+
+    expect(fetch).toHaveBeenCalledTimes(2);
+  });
+
+  it('invalidate() with no name clears the whole cache', async () => {
+    const fetch = vi.fn().mockImplementation((name: string) => Promise.resolve(makeRawPrompt(name)));
+    const fetcher: PromptFetcher = { fetch };
+    const service = new PromptService(fetcher, true);
+
+    await service.getCompiled('a', {});
+    await service.getCompiled('b', {});
+    service.invalidate();
+    await service.getCompiled('a', {});
+    await service.getCompiled('b', {});
+
+    expect(fetch).toHaveBeenCalledTimes(4);
+  });
+});