Build an Amazon locker system

• A locker station has compartments of sizes small, medium and large; each compartment is free, occupied or out of service
• deposit(packageId, size) assigns the smallest free compartment that fits (a small package may use a medium one if no small is free), opens it and returns a one-time pickup code; if none fits, it fails clearly
• pickup(code) verifies the code, opens the compartment, frees it and marks the package collected; codes are single use, and wrong codes are counted with a lockout after several attempts
• Packages expire after a configurable number of days (injectable clock): expired packages cannot be picked up with the code, and returnExpired() frees those compartments and lists the packages for return to the sender
• Pickup codes are random, unique among active packages and not derived from the package id
• Concurrent deposits never assign the same compartment, and the state of every compartment can be inspected

Only after every requirement works.

• Multiple stations with nearest-station assignment
• Notification to the customer on deposit and before expiry
• Reserve a compartment ahead of time