Building flexible approval workflows for any business process.

I designed and built this approval workflow engine from scratch. The goal was creating something flexible enough to handle different approval processes across different modules—leave requests, loan applications, purchase requisitions—without duplicating code.

I implemented this using the Strategy Pattern combined with a State Machine. Organizations can configure approval chains—how many levels, who approves at each level, whether approvals are sequential or parallel. The system tracks state transitions, handles escalations, and sends real-time notifications.

The challenging part was making it truly reusable. The workflow engine doesn't care what it's approving—it works with any entity that implements the IApprovable interface. This meant leave requests, loans, and purchase orders could all use the same workflow logic.

Every organization has different approval rules. Some need sequential approvals—manager, then director, then CEO. Others want parallel approvals—any one of these three people can approve. Some have escalation rules—if not approved in 48 hours, escalate to the next level.

And different processes have different needs. Leave requests might need 2 levels of approval. Loan applications might need 4. Purchase requisitions might need approvals based on amount—small purchases need one approval, large ones need three.

For employees: They wanted transparency. Where is my request? Who's reviewing it? Why is it taking so long?

For approvers: They needed context. What am I approving? What's the impact? Can I delegate this? Can I reject with comments?

For HR/Admin: They needed control. Set approval chains once, have them apply automatically. Track bottlenecks, identify delays, generate audit trails.

The technical reality: We needed a state machine to track workflow states, a strategy pattern for different approval methods, real-time notifications, escalation handling, and complete audit trails. And it all had to be reusable across modules.

I built the workflow engine using a combination of State Machine pattern (for tracking states) and Strategy Pattern (for different approval methods). This made the system both flexible and maintainable.

The state machine: Every approvable item goes through states—Pending, In Review, Approved, Rejected. The state machine ensures valid transitions and prevents invalid states. You can't approve something already rejected. You can't reject something already approved.

Sequential vs Parallel approvals: I implemented two strategies. Sequential means approvals must happen in order—level 1, then level 2, then level 3. Parallel means any approver at a level can approve. Organizations configure which strategy per workflow.

Real-time notifications: Using SignalR for real-time updates. When someone approves/rejects, the requester gets notified immediately. When a request lands on your desk, you get notified. No more email delays.

Escalation handling: Configurable escalation rules. If an approval sits pending for X hours, it automatically escalates to the next level or notifies supervisors. Prevents requests from getting stuck.