From 633cfcf713d20ed51287ad6ed1306fb4a2c5c809 Mon Sep 17 00:00:00 2001
From: William Valentin <william.valentin.info@gmail.com>
Date: Mon, 2 Feb 2026 21:10:46 -0800
Subject: [PATCH] feat: add OpenAI client for fallback support

Implements ModelClient interface with OpenAI SDK to support GPT models
as fallback when local inference is unavailable. Includes tests with
mocked OpenAI API responses.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 src/models/index.ts       |  1 +
 src/models/openai.test.ts | 33 ++++++++++++++++++++++++
 src/models/openai.ts      | 54 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 src/models/openai.test.ts
 create mode 100644 src/models/openai.ts

diff --git a/src/models/index.ts b/src/models/index.ts
index 6e2626a..11c7316 100644
--- a/src/models/index.ts
+++ b/src/models/index.ts
@@ -1,2 +1,3 @@
 export { AnthropicClient, type AnthropicClientConfig } from './anthropic.js';
+export { OpenAIClient, type OpenAIClientConfig } from './openai.js';
 export type { Message, ChatRequest, ChatResponse, ModelClient } from './types.js';
diff --git a/src/models/openai.test.ts b/src/models/openai.test.ts
new file mode 100644
index 0000000..1b37a0d
--- /dev/null
+++ b/src/models/openai.test.ts
@@ -0,0 +1,33 @@
+import { describe, it, expect, vi } from 'vitest';
+import { OpenAIClient } from './openai.js';
+
+vi.mock('openai', () => ({
+  default: vi.fn().mockImplementation(() => ({
+    chat: {
+      completions: {
+        create: vi.fn().mockResolvedValue({
+          choices: [{ message: { content: 'Hello from GPT!' }, finish_reason: 'stop' }],
+          usage: { prompt_tokens: 10, completion_tokens: 5 },
+        }),
+      },
+    },
+  })),
+}));
+
+describe('OpenAIClient', () => {
+  it('sends messages and returns response', async () => {
+    const client = new OpenAIClient({
+      apiKey: 'test-key',
+      model: 'gpt-4o',
+    });
+
+    const response = await client.chat({
+      messages: [{ role: 'user', content: 'Hello' }],
+    });
+
+    expect(response.content).toBe('Hello from GPT!');
+    expect(response.stopReason).toBe('stop');
+    expect(response.usage.inputTokens).toBe(10);
+    expect(response.usage.outputTokens).toBe(5);
+  });
+});
diff --git a/src/models/openai.ts b/src/models/openai.ts
new file mode 100644
index 0000000..3b75ca0
--- /dev/null
+++ b/src/models/openai.ts
@@ -0,0 +1,54 @@
+import OpenAI from 'openai';
+import type { ChatRequest, ChatResponse, ModelClient } from './types.js';
+
+export interface OpenAIClientConfig {
+  apiKey?: string;
+  model: string;
+  maxTokens?: number;
+  baseURL?: string;
+}
+
+export class OpenAIClient implements ModelClient {
+  private client: OpenAI;
+  private model: string;
+  private defaultMaxTokens: number;
+
+  constructor(config: OpenAIClientConfig) {
+    this.client = new OpenAI({
+      apiKey: config.apiKey,
+      baseURL: config.baseURL,
+    });
+    this.model = config.model;
+    this.defaultMaxTokens = config.maxTokens ?? 4096;
+  }
+
+  async chat(request: ChatRequest): Promise<ChatResponse> {
+    const messages: OpenAI.ChatCompletionMessageParam[] = [];
+
+    if (request.system) {
+      messages.push({ role: 'system', content: request.system });
+    }
+
+    for (const msg of request.messages) {
+      messages.push({ role: msg.role, content: msg.content });
+    }
+
+    const response = await this.client.chat.completions.create({
+      model: this.model,
+      max_tokens: request.maxTokens ?? this.defaultMaxTokens,
+      messages,
+    });
+
+    const choice = response.choices[0];
+    const content = choice?.message?.content ?? '';
+
+    return {
+      content,
+      stopReason: choice?.finish_reason ?? 'stop',
+      usage: {
+        inputTokens: response.usage?.prompt_tokens ?? 0,
+        outputTokens: response.usage?.completion_tokens ?? 0,
+      },
+    };
+  }
+}