The SinchService.js module handles sending SMS messages. It uses Axios to make POST requests to the Sinch API with recipient numbers, message content, and optionally a sender number. The sendSms function manages single messages, while sendSmsBatch (to be implemented) will handle sending to multiple recipients.

Prisma is used as an Object-Relational Mapper (ORM) to simplify database interactions. It allows the application to interact with the PostgreSQL database using JavaScript objects and functions instead of raw SQL queries, making the code cleaner and easier to manage.

Express.js is a minimalist web framework for Node.js that makes it easy to build APIs and handle HTTP requests. It provides a structure for routing, middleware, and request handling, making the backend code more organized and manageable.

Ngrok is essential during development to test webhooks locally. It creates a public URL that forwards requests to your local server, allowing Sinch to deliver webhook events even when your app isn't publicly deployed.

The current example code does not directly support scheduling but includes placeholders for this functionality. You would need to implement database fields (like scheduleAt) and background processes to check and trigger sending at the right time.

You'll need Node.js v18 or later, npm, a Sinch account (free or paid), PostgreSQL database access, ngrok for webhook testing, and basic knowledge of Node.js, Express, REST APIs, and SQL.

While the code doesn't show it yet, delivery reports are handled through Sinch webhooks. The Express app must expose a webhook endpoint to receive these updates and update message status in the database accordingly.

Express-validator is middleware for validating user inputs before they reach controllers. This helps ensure data integrity and prevents unexpected errors. It allows for flexible validation using rules and sanitization methods.

The provided examples don't implement contact lists, but they can be added. You would define database models to represent lists, link contacts to lists, and modify controllers to handle list creation, assignment, and fetching contacts from specified lists for campaigns.

A POST request to the /api/campaigns endpoint with the campaign name, message body, and optional target list ID creates a new campaign marked with the initial status 'DRAFT'. Validation is performed using express-validator.

The hardcoded recipient is a temporary placeholder for initial testing. It is critically important to replace this part with proper contact list fetching logic before using the app for real campaigns.

The application uses PostgreSQL, a robust open-source relational database, to store contact information, campaign details, and message logs. The DATABASE_URL environment variable configures the connection.

Ngrok allows you to expose your local development server to the internet. This enables Sinch webhooks to reach your application during testing, even before deploying it to a public server.

The code enforces a maximum of 1600 characters for the message body, as longer messages may be split into multiple parts. However, this limit can be adjusted as needed or based on limitations of Sinch or mobile carriers.