Implemented a Persistance agent (#77)

# Pull Request Description
It adds a Postgres database to have a persistent agent that remembers
chats even when shut and opened again.
## Related Issue
Fixes #76 

## Changes Made
This PR adds the following changes:
- Added an example of how we can integrate a Postgres db so that the
agent remembers its previous chats.
  
## Implementation Details
- included a postgres db to store chat for future reference
- 

## Transaction executed by agent 
NA

## Prompt Used
<img width="936" alt="image"
src="https://github.com/user-attachments/assets/0aa1bed2-e895-41bf-ad37-a52f679db7cf"
/>

see it remebers my name even when i closed it and ran again .

## Additional Notes

https://langchain-ai.github.io/langgraphjs/reference/classes/checkpoint_postgres.PostgresSaver.html

I used this above link to implement the changes.

## Checklist
- [ x ] I have tested these changes locally

examples/persistance-agent/.env.example

@@ -0,0 +1,4 @@
+OPENAI_API_KEY=
+RPC_URL=
+SOLANA_PRIVATE_KEY=
+POSTGRES_DB_URL=

examples/persistance-agent/README.md

@@ -0,0 +1,66 @@
+# Persistent Agent with PostgreSQL
+
+This example showcases a persistent agent that retains memory across sessions using a PostgreSQL database. It ensures that the agent can remember previous conversations even after being restarted, enhancing the user experience in applications requiring long-term context retention.
+[Reference](https://langchain-ai.github.io/langgraphjs/reference/classes/checkpoint_postgres.PostgresSaver.html)
+
+## Key Features
+
+- **Persistent Memory**: The agent stores chat history in a PostgreSQL database, allowing it to remember past interactions across sessions.
+- **Seamless Integration**: Designed to integrate smoothly with existing setups.
+- **Scalable Solution**: Ideal for applications requiring long-term memory capabilities.
+
+## Prerequisites
+
+To use this feature, ensure you have the following:
+
+1. **PostgreSQL Database URL**: Create and host ur PostgreSQL databse and enter the URL. It will be of the format "postgresql://user:password@localhost:5432/db"
+
+## Before applying persistance
+```
+Available modes:
+1. chat
+- Interactive chat mode
+2. auto
+- Autonomous action mode
+Choose a mode (enter number or name: 1
+Starting chat mode... Type 'exit' to end.
+Prompt: i am arpit
+Hello Arpit! How can I assist you today?
+Prompt: ^С
+® arpitsingh Mac persistance-agent & ts-node index.ts
+Starting Agent...
+Available modes:
+1. chat
+- Interactive chat mode
+2. auto
+- Autonomous action mode
+Choose a mode (enter number or name): 1
+Starting chat mode... Type 'exit' to end.
+Prompt: do u know my name
+I don't know your name yet. If you'd like, you can share it.
+```
+## After applying persistence
+```
+Available modes:
+1. chat
+- Interactive chat mode
+2. auto
+- Autonomous action mode
+Choose a mode (enter number or name: 1
+Starting chat mode... Type 'exit' to end.
+Prompt: i am arpit
+Hello Arpit! How can I assist you today?
+Prompt: ^С
+® arpitsingh Mac persistance-agent & ts-node index.ts
+Starting Agent...
+Available modes:
+1. chat
+- Interactive chat mode
+2. auto
+- Autonomous action mode
+Choose a mode (enter number or name): 1
+Starting chat mode... Type 'exit' to end.
+Prompt: do u know my name
+Yes, you mentioned that your name is Arpit. How can I help you today? 
+```
+

examples/persistance-agent/index.ts

@@ -0,0 +1,220 @@
+import { SolanaAgentKit, createSolanaTools } from "solana-agent-kit";
+import { HumanMessage } from "@langchain/core/messages";
+import { createReactAgent } from "@langchain/langgraph/prebuilt";
+import { ChatOpenAI } from "@langchain/openai";
+import * as dotenv from "dotenv";
+import * as fs from "fs";
+import * as readline from "readline";
+import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";
+dotenv.config();
+
+const checkpointer = PostgresSaver.fromConnString(
+    process.env.POSTGRES_DB_URL!
+);
+
+function validateEnvironment(): void {
+    const missingVars: string[] = [];
+    const requiredVars = ["OPENAI_API_KEY", "RPC_URL", "SOLANA_PRIVATE_KEY", "POSTGRES_DB_URL"];
+
+    requiredVars.forEach((varName) => {
+        if (!process.env[varName]) {
+            missingVars.push(varName);
+        }
+    });
+
+    if (missingVars.length > 0) {
+        console.error("Error: Required environment variables are not set");
+        missingVars.forEach((varName) => {
+            console.error(`${varName}=your_${varName.toLowerCase()}_here`);
+        });
+        process.exit(1);
+    }
+}
+
+validateEnvironment();
+
+const WALLET_DATA_FILE = "wallet_data.txt";
+
+async function initializeAgent() {
+    try {
+        const llm = new ChatOpenAI({
+            modelName: "gpt-4o-mini",
+            temperature: 0.7,
+        });
+
+        let walletDataStr: string | null = null;
+
+        if (fs.existsSync(WALLET_DATA_FILE)) {
+            try {
+                walletDataStr = fs.readFileSync(WALLET_DATA_FILE, "utf8");
+            } catch (error) {
+                console.error("Error reading wallet data:", error);
+            }
+        }
+
+        const solanaAgent = new SolanaAgentKit(
+            process.env.SOLANA_PRIVATE_KEY!,
+            process.env.RPC_URL,
+            process.env.OPENAI_API_KEY!,
+        );
+
+        const tools = createSolanaTools(solanaAgent);
+        await checkpointer.setup();
+        const config = { configurable: { thread_id: "Solana Agent Kit!" } };
+
+        const agent = createReactAgent({
+            llm,
+            tools,
+            checkpointSaver: checkpointer,
+            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.
+      `,
+        });
+
+        if (walletDataStr) {
+            fs.writeFileSync(WALLET_DATA_FILE, walletDataStr);
+        }
+
+        return { agent, config };
+    } catch (error) {
+        console.error("Failed to initialize agent:", error);
+        throw error;
+    }
+}
+
+async function runAutonomousMode(agent: any, config: any, interval = 10) {
+    console.log("Starting autonomous mode...");
+
+    while (true) {
+        try {
+            const thought =
+                "Be creative and do something interesting on the blockchain. " +
+                "Choose an action or set of actions and execute it that highlights your abilities.";
+
+            const stream = await agent.stream(
+                { messages: [new HumanMessage(thought)] },
+                config,
+            );
+
+            for await (const chunk of stream) {
+                if ("agent" in chunk) {
+                    console.log(chunk.agent.messages[0].content);
+                } else if ("tools" in chunk) {
+                    console.log(chunk.tools.messages[0].content);
+                }
+                console.log("-------------------");
+            }
+
+            await new Promise((resolve) => setTimeout(resolve, interval * 1000));
+        } catch (error) {
+            if (error instanceof Error) {
+                console.error("Error:", error.message);
+            }
+            process.exit(1);
+        }
+    }
+}
+
+async function runChatMode(agent: any, config: any) {
+    console.log("Starting chat mode... Type 'exit' to end.");
+
+    const rl = readline.createInterface({
+        input: process.stdin,
+        output: process.stdout,
+    });
+
+    const question = (prompt: string): Promise<string> =>
+        new Promise((resolve) => rl.question(prompt, resolve));
+
+    try {
+        while (true) {
+            const userInput = await question("\nPrompt: ");
+
+            if (userInput.toLowerCase() === "exit") {
+                break;
+            }
+
+            const stream = await agent.stream(
+                { messages: [new HumanMessage(userInput)] },
+                config,
+            );
+
+            for await (const chunk of stream) {
+                if ("agent" in chunk) {
+                    console.log(chunk.agent.messages[0].content);
+                } else if ("tools" in chunk) {
+                    console.log(chunk.tools.messages[0].content);
+                }
+                console.log("-------------------");
+            }
+        }
+    } catch (error) {
+        if (error instanceof Error) {
+            console.error("Error:", error.message);
+        }
+        process.exit(1);
+    } finally {
+        rl.close();
+    }
+}
+
+async function chooseMode(): Promise<"chat" | "auto"> {
+    const rl = readline.createInterface({
+        input: process.stdin,
+        output: process.stdout,
+    });
+
+    const question = (prompt: string): Promise<string> =>
+        new Promise((resolve) => rl.question(prompt, resolve));
+
+    while (true) {
+        console.log("\nAvailable modes:");
+        console.log("1. chat    - Interactive chat mode");
+        console.log("2. auto    - Autonomous action mode");
+
+        const choice = (await question("\nChoose a mode (enter number or name): "))
+            .toLowerCase()
+            .trim();
+
+        rl.close();
+
+        if (choice === "1" || choice === "chat") {
+            return "chat";
+        } else if (choice === "2" || choice === "auto") {
+            return "auto";
+        }
+        console.log("Invalid choice. Please try again.");
+    }
+}
+
+async function main() {
+    try {
+        console.log("Starting Agent...");
+        const { agent, config } = await initializeAgent();
+        const mode = await chooseMode();
+
+        if (mode === "chat") {
+            await runChatMode(agent, config);
+        } else {
+            await runAutonomousMode(agent, config);
+        }
+    } catch (error) {
+        if (error instanceof Error) {
+            console.error("Error:", error.message);
+        }
+        process.exit(1);
+    }
+}
+
+if (require.main === module) {
+    main().catch((error) => {
+        console.error("Fatal error:", error);
+        process.exit(1);
+    });
+}

examples/persistance-agent/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "persistance-agent",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "@langchain/langgraph-checkpoint-postgres": "^0.0.2",
+    "solana-agent-kit": "^1.3.0"
+  }
+}