Let's build a simplified Application Tracking System (ATS), similar to Greenhouse, to manage job applications. Imagine you're building this from scratch. The core of this system needs to handle various stages of the application process, from initial submission to offer and eventual hiring. We'll focus on the core application lifecycle, candidate management, and interview scheduling. Our system won't handle external integrations (e.g., LinkedIn, Indeed) or complex reporting features for now. The goal is to create a clean, extensible, and maintainable design that can gracefully accommodate future features.

A crucial aspect of the ATS is efficiently managing the flow of candidates through various stages of the hiring pipeline. Each role will have a defined pipeline, and candidates will progress through these stages. The system should also support different types of interviews and allow interviewers to provide feedback, which should be stored and accessible to the hiring team. We also need to consider that multiple users might be accessing the system concurrently, leading to potential race conditions and data inconsistencies.

Requirements