Simplify GeminiClient (#101)

Doing some more clean-up:
* Remove confusing continue/break
* Handle empty result
* Rename the file just client.js

packages/server/src/core/client.ts

@@ -0,0 +1,162 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  GenerateContentConfig,
+  GoogleGenAI,
+  Part,
+  Chat,
+  SchemaUnion,
+  PartListUnion,
+  Content,
+  FunctionDeclaration,
+  Tool,
+} from '@google/genai';
+import { CoreSystemPrompt } from './prompts.js';
+import process from 'node:process';
+import { getFolderStructure } from '../utils/getFolderStructure.js';
+import { Turn, ServerTool, ServerGeminiStreamEvent } from './turn.js';
+
+export class GeminiClient {
+  private client: GoogleGenAI;
+  private model: string;
+  private generateContentConfig: GenerateContentConfig = {
+    temperature: 0,
+    topP: 1,
+  };
+  private readonly MAX_TURNS = 100;
+
+  constructor(apiKey: string, model: string) {
+    this.client = new GoogleGenAI({ apiKey: apiKey });
+    this.model = model;
+  }
+
+  private async getEnvironment(): Promise<Part> {
+    const cwd = process.cwd();
+    const today = new Date().toLocaleDateString(undefined, {
+      weekday: 'long',
+      year: 'numeric',
+      month: 'long',
+      day: 'numeric',
+    });
+    const platform = process.platform;
+    const folderStructure = await getFolderStructure(cwd);
+    const context = `
+  Okay, just setting up the context for our chat.
+  Today is ${today}.
+  My operating system is: ${platform}
+  I'm currently working in the directory: ${cwd}
+  ${folderStructure}
+          `.trim();
+    return { text: context };
+  }
+
+  async startChat(toolDeclarations: FunctionDeclaration[]): Promise<Chat> {
+    const envPart = await this.getEnvironment();
+    const tools: Tool[] = [{ functionDeclarations: toolDeclarations }];
+    try {
+      return this.client.chats.create({
+        model: this.model,
+        config: {
+          systemInstruction: CoreSystemPrompt,
+          ...this.generateContentConfig,
+          tools: tools,
+        },
+        history: [
+          {
+            role: 'user',
+            parts: [envPart],
+          },
+          {
+            role: 'model',
+            parts: [{ text: 'Got it. Thanks for the context!' }],
+          },
+        ],
+      });
+    } catch (error) {
+      console.error('Error initializing Gemini chat session:', error);
+      const message = error instanceof Error ? error.message : 'Unknown error.';
+      throw new Error(`Failed to initialize chat: ${message}`);
+    }
+  }
+
+  async *sendMessageStream(
+    chat: Chat,
+    request: PartListUnion,
+    availableTools: ServerTool[],
+    signal?: AbortSignal,
+  ): AsyncGenerator<ServerGeminiStreamEvent> {
+    let turns = 0;
+    try {
+      while (turns < this.MAX_TURNS) {
+        turns++;
+        const turn = new Turn(chat, availableTools);
+        const resultStream = turn.run(request, signal);
+        for await (const event of resultStream) {
+          yield event;
+        }
+
+        const confirmations = turn.getConfirmationDetails();
+        if (confirmations.length > 0) {
+          break;
+        }
+
+        // What do we do when we have both function responses and confirmations?
+        const fnResponses = turn.getFunctionResponses();
+        if (fnResponses.length == 0) {
+          break; // user's turn to respond
+        }
+        request = fnResponses;
+      }
+      if (turns >= this.MAX_TURNS) {
+        console.warn(
+          'sendMessageStream: Reached maximum tool call turns limit.',
+        );
+      }
+    } catch (error: unknown) {
+      if (error instanceof Error && error.name === 'AbortError') {
+        console.log('Gemini stream request aborted by user.');
+        throw error;
+      }
+      console.error(`Error during Gemini stream or tool interaction:`, error);
+      throw error;
+    }
+  }
+
+  async generateJson(
+    contents: Content[],
+    schema: SchemaUnion,
+  ): Promise<Record<string, unknown>> {
+    try {
+      const result = await this.client.models.generateContent({
+        model: this.model,
+        config: {
+          ...this.generateContentConfig,
+          systemInstruction: CoreSystemPrompt,
+          responseSchema: schema,
+          responseMimeType: 'application/json',
+        },
+        contents,
+      });
+      if (!result || !result.text) {
+        throw new Error('API returned an empty response.');
+      }
+      try {
+        return JSON.parse(result.text);
+      } catch (parseError) {
+        console.error('Failed to parse JSON response:', result.text);
+        throw new Error(
+          `Failed to parse API response as JSON: ${parseError instanceof Error ? parseError.message : String(parseError)}`,
+        );
+      }
+    } catch (error) {
+      console.error('Error generating JSON content:', error);
+      const message =
+        error instanceof Error ? error.message : 'Unknown API error.';
+      throw new Error(`Failed to generate JSON content: ${message}`);
+    }
+  }
+}