ESP Integration API

Accomplishments

• Built a Node.js + TypeScript REST API that integrates internal applications with external Email Service Providers (Mailchimp and GetResponse) through a single unified interface.
• Implemented a POST /api/integrations/esp endpoint that validates ESP API keys in real time against the provider before persisting them, rejecting invalid providers and bad keys.
• Implemented a GET /api/integrations/esp/lists endpoint that fetches mailing lists (Mailchimp audiences / GetResponse campaigns) for a given userId and provider via query params.
• Normalized disparate ESP response formats into a consistent schema (id, name, created_at, subscriber_count/contact_count) so clients get a uniform structure regardless of provider.
• Integrated Mailchimp via HTTP Basic Auth, dynamically deriving the datacenter from the API key (the "-dc" suffix) to build the correct regional API URL.
• Integrated GetResponse via the X-Auth-Token header, verifying credentials against the /v3/accounts endpoint and fetching campaigns from /v3/campaigns.
• Added resilient error handling that maps external ESP failures to proper HTTP status codes: 401 for invalid keys, 429 for rate-limit exceeded, and 500 for network/server errors.
• Used safe fallbacks (e.g. subscriber_count defaulting to 0) to prevent crashes when optional fields are missing from ESP responses.
• Persisted integration credentials in MongoDB via a Mongoose Integration model with an enum-constrained provider field and automatic timestamps.
• Structured the codebase into a clean layered architecture (config, routes, controllers, services, models) with separate server bootstrap (server.ts) and app setup (app.ts).
• Configured a TypeScript dev/build/start workflow using nodemon + ts-node for development and tsc for production builds, with CORS and dotenv-based environment config.
• Developed the project through a PR-based workflow (dev → main), iterating on features like MongoDB integration, rate-limit checks, and the created_at field before documenting it all in the README.