How to develop a What’s App BOT in C#

To design and develop a WhatsApp bot using C#, you need to understand how to interact with the WhatsApp Business API, as WhatsApp doesn’t provide direct access for bot development through a regular WhatsApp account. Here’s a step-by-step guide on building a WhatsApp bot using C#, including setting up your environment and coding an example.

Steps Overview:

1. Setup WhatsApp Business API: Set up and configure the WhatsApp Business API.
2. Setup Webhook Receiver: Configure a webhook to receive messages from WhatsApp.
3. Send & Receive Messages: Implement message-sending and handling in C#.

Prerequisites

1. WhatsApp Business Account: You’ll need a WhatsApp Business account to access the API.
2. Facebook Developer Account: Create a Facebook Developer account if you don’t have one.
3. WhatsApp Cloud API Access: Sign up for WhatsApp's Cloud API or use WhatsApp's Business API on-premises. This example assumes you are using the Cloud API, which is easier for testing and development.

Setting Up the WhatsApp Cloud API

1. Go to the Meta for Developers website and create an app.
2. Add "WhatsApp" as a product and create a test WhatsApp number.
3. Get your API key/token from the "WhatsApp" section under the app settings.
4. Note your API_TOKEN, PHONE_NUMBER_ID, and BUSINESS_ACCOUNT_ID as they will be required to send and receive messages.

Step 1: Create a C# Project

Create a new C# console or web application (e.g., ASP.NET Core Web API) to serve as your bot backend.

Step 2: Setup Webhook to Receive Messages

WhatsApp Cloud API sends incoming messages to a webhook. Here’s how to set up a simple webhook in ASP.NET Core.

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using Microsoft.AspNetCore.Mvc;

using System.Text.Json;

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[ApiController]

[Route("api/whatsapp")]

public class WhatsAppWebhookController : ControllerBase

{

??? [HttpPost("webhook")]

??? public IActionResult ReceiveMessage([FromBody] JsonDocument incomingMessage)

??? {

??????? // Log incoming message for debugging

??????? Console.WriteLine("Received Message: " + incomingMessage);

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??????? // Process the message

??????? var message = incomingMessage.RootElement.GetProperty("entry")[0]

???????????????????????? .GetProperty("changes")[0]

???????????????????????? .GetProperty("value")

????????????????????? ???.GetProperty("messages")[0];

??????? var from = message.GetProperty("from").GetString();

??????? var text = message.GetProperty("text").GetProperty("body").GetString();

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??????? Console.WriteLine($"Message from {from}: {text}");

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??????? // Respond with a success status

??????? return Ok();

??? }

}

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Step 3: Sending Messages from the Bot

You can send messages using WhatsApp’s API endpoint. Use HttpClient to call the API.

1. Install the System.Net.Http.Json package if needed.
2. Create a method to send messages.

Example Code to Send a Message

using System.Net.Http;

using System.Net.Http.Headers;

using System.Text.Json;

using System.Text;

using System.Threading.Tasks;

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public class WhatsAppBotService

{

??? private readonly HttpClient _httpClient;

??? private readonly string apiUrl = "https://graph.facebook.com/v16.0/PHONENUMBER_ID/messages";? // Replace PHONE_NUMBER_ID

??? private readonly string apiToken = "YOURAPI_TOKEN"; // Replace YOUR_API_TOKEN

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??? public WhatsAppBotService()

??? {

??????? _httpClient = new HttpClient();

??????? httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", apiToken);

??? }

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??? public async Task SendMessageAsync(string recipientPhoneNumber, string messageText)

??? {

??????? var messageData = new

??????? {

??????????? messaging_product = "whatsapp",

??????????? to = recipientPhoneNumber,

??????????? text = new { body = messageText },

??????????? type = "text"

??????? };

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??????? var content = new StringContent(JsonSerializer.Serialize(messageData), Encoding.UTF8, "application/json");

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??????? var response = await httpClient.PostAsync(apiUrl, content);

??????? response.EnsureSuccessStatusCode();

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??????? var responseContent = await response.Content.ReadAsStringAsync();

??????? Console.WriteLine("Message sent. Response: " + responseContent);

??? }

}

Step 4: Calling the Send Method in Response to an Incoming Message

Modify the ReceiveMessage method to send a reply message.

?[HttpPost("webhook")]

public async Task<IActionResult> ReceiveMessage([FromBody] JsonDocument incomingMessage)

{

??? var message = incomingMessage.RootElement.GetProperty("entry")[0]

???????????????????? .GetProperty("changes")[0]

???????????????????? .GetProperty("value")

???????????????????? .GetProperty("messages")[0];

??? var from = message.GetProperty("from").GetString();

??? var text = message.GetProperty("text").GetProperty("body").GetString();

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??? Console.WriteLine($"Message from {from}: {text}");

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??? // Process received message and send response

??? var botService = new WhatsAppBotService();

??? await botService.SendMessageAsync(from, "Hello! This is an automated reply from our bot.");

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??? return Ok();

}

Step 5: Run the Bot

1. Run your ASP.NET Core Web API locally.
2. Use a tunneling tool like ngrok to expose your localhost to the internet:

bash

Copy code

ngrok http 5000

1. Copy the public URL from ngrok and paste it as the webhook URL in your WhatsApp Cloud API settings. Example webhook URL: https://your-ngrok-url/api/whatsapp/webhook
2. Verify the Webhook: WhatsApp will send a verification request to your webhook. Handle this by modifying the webhook endpoint to accept and respond to the verification challenge.

Optional: Webhook Verification Example

Add the following code to handle webhook verification requests from WhatsApp.

?[HttpGet("webhook")]

public IActionResult VerifyWebhook([FromQuery] string hub_mode, [FromQuery] string hub_challenge, [FromQuery] string hub_verify_token)

{

??? var verifyToken = "YOUR_VERIFY_TOKEN"; // Set this token in WhatsApp API settings

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??? if (hub_mode == "subscribe" && hub_verify_token == verifyToken)

??? {

??????? return Ok(hub_challenge);

??? }

??? return Unauthorized();

}

Replace "YOUR_VERIFY_TOKEN" with a token you set in WhatsApp’s API settings.

Full Example Structure

1. WhatsAppWebhookController.cs: Receives incoming messages and triggers response.
2. WhatsAppBotService.cs: Contains logic to send messages through WhatsApp API.
3. Program.cs: Sets up and runs the application.

Running and Testing

1. Run the application and ensure it’s connected to ngrok.
2. Send a test message to your WhatsApp number, and the bot should respond with the configured message.

Notes

• This bot only supports simple text responses. To add more capabilities like sending images or templates, modify the messageData object in SendMessageAsync.
• Make sure to follow Meta’s policies and guidelines for WhatsApp bots to avoid restrictions on your account.

With this setup, you now have a working WhatsApp bot in C#.