Code Archaeology: How to Reverse-Engineer a Complex Operation

You join a project mid-flight. There’s a complex operation that creates records, updates statuses, sends notifications, and touches three different services. You need to build the reverse of it. Nobody wrote docs.

Welcome to code archaeology.

The Approach That Actually Works

Don’t start by reading the code top-to-bottom. Start by finding the entry point and tracing outward.

# Find where the operation starts
grep -rn "createOrder\|placeOrder\|submitOrder" app/ --include="*.php" -l

# Find what events it fires
grep -rn "event(\|dispatch(" app/Services/OrderService.php

# Find what listeners react
grep -rn "OrderCreated\|OrderPlaced" app/Listeners/ -l

Build a map as you go. I literally open a scratch file and write:

OrderService::create()
  -> validates input
  -> creates DB record
  -> fires OrderCreated event
     -> SendConfirmationEmail (listener)
     -> UpdateInventory (listener)
     -> NotifyWarehouse (listener)
  -> returns response

Repository Pattern Makes This Harder

If the codebase uses the repository pattern, the actual logic might be buried two or three layers deep. The controller calls the service, the service calls the repository, the repository has the Eloquent query. Grep is your best friend here.

# When you can't find where the actual DB write happens
grep -rn "->save()\|->create(\|->insert(" app/Repositories/ --include="*.php"

The Undo Operation

Once you have the map, building the reverse is mechanical. Each step in the forward operation needs a corresponding undo step, executed in reverse order. The hard part was never the coding. It was understanding what the original code actually does.

Next time you’re staring at a method that calls six other methods across four files, resist the urge to “just figure it out” in your head. Write the map. It takes five minutes and saves five hours.