feat: add the nextjs starter template to examples/ dir

examples/agent-kit-nextjs-langchain/app/api/chat/route.ts

@@ -0,0 +1,71 @@
+import { NextRequest, NextResponse } from "next/server";
+import { ChatOpenAI } from "@langchain/openai";
+import { MemorySaver } from "@langchain/langgraph";
+import { createReactAgent } from "@langchain/langgraph/prebuilt";
+import { SolanaAgentKit, createSolanaTools } from "solana-agent-kit";
+
+const llm = new ChatOpenAI({
+	temperature: 0.7,
+	model: "gpt-4o-mini",
+});
+
+const solanaAgent = new SolanaAgentKit(
+	process.env.SOLANA_PRIVATE_KEY!,
+	process.env.RPC_URL,
+	process.env.OPENAI_API_KEY!,
+);
+
+const tools = createSolanaTools(solanaAgent);
+const memory = new MemorySaver();
+
+const agent = createReactAgent({
+	llm,
+	tools,
+	checkpointSaver: memory,
+	messageModifier: `
+      You are a helpful agent that can interact onchain using the Solana Agent Kit. You are
+      empowered to interact onchain using your tools. If you ever need funds, you can request them from the
+      faucet. If not, you can provide your wallet details and request funds from the user. If there is a 5XX
+      (internal) HTTP error code, ask the user to try again later. If someone asks you to do something you
+      can't do with your currently available tools, you must say so, and encourage them to implement it
+      themselves using the Solana Agent Kit, recommend they go to https://www.solanaagentkit.xyz for more information. Be
+      concise and helpful with your responses. Refrain from restating your tools' descriptions unless it is explicitly requested.
+    `,
+});
+
+export async function POST(req: NextRequest) {
+	try {
+		const body = await req.json();
+		const messages = body.messages ?? [];
+
+		const eventStream = agent.streamEvents(
+			{
+				messages,
+			},
+			{
+				version: "v2",
+				configurable: {
+					thread_id: "Solana Agent Kit!",
+				},
+			},
+		);
+
+		const textEncoder = new TextEncoder();
+		const transformStream = new ReadableStream({
+			async start(controller) {
+				for await (const { event, data } of eventStream) {
+					if (event === "on_chat_model_stream") {
+						if (!!data.chunk.content) {
+							controller.enqueue(textEncoder.encode(data.chunk.content));
+						}
+					}
+				}
+				controller.close();
+			},
+		});
+
+		return new Response(transformStream);
+	} catch (e: any) {
+		return NextResponse.json({ error: e.message }, { status: e.status ?? 500 });
+	}
+}