Requirements

• Register a vending machine with a unique machine id.
• Create a lease agreement between a customer and an available vending machine.
• Use currentMonth to decide whether a lease is active, upcoming, expired, or ended.
• Do not allow overlapping lease periods for the same vending machine.
• Track the current state of each vending machine.
• Allow state changes between Idle, OutOfStock, and Maintenance.
• Allow payments to be calculated based on the payment strategy chosen for the lease.
• Support querying lease and machine details.

Important Rules

• A lease has a fixed month range represented by startMonth and endMonth.
• A lease is considered active at currentMonth if it has not been manually ended and startMonth ≤ currentMonth ≤ endMonth.
• A lease is considered upcoming at currentMonth if it has not been manually ended and currentMonth < startMonth.
• A lease is considered expired at currentMonth if it has not been manually ended and currentMonth > endMonth.
• A lease is considered ended if endLease has been called for that lease.
• A vending machine cannot have two non-ended leases with overlapping month ranges.
• Expired leases are still considered non-ended leases. Therefore, an expired lease can still block creation of another overlapping lease unless it was manually ended.
• Two lease ranges overlap if max(startMonth1,startMonth2) ≤ min(endMonth1,endMonth2).
• A vending machine can be leased only if its current machine state is Idle.
• Creating or ending a lease does not automatically change the machine state.
• Upcoming leases do not make the machine's leasedStatus equal to "LEASED". Only active leases count.
• Manual ending does not change the result of calculatePayment. Payment is always calculated using the original lease period and original payment strategy.
• The system only stores whether a lease was manually ended. It does not need to return the month when it was ended.
• State names and payment strategy names are case-sensitive.
• When multiple error conditions apply, return the error for the first matching condition in the order listed for that method.

Machine States

• Idle: The machine is working normally and is not under maintenance or out of stock. A machine in Idle state may still be leased. Leasing status is tracked separately from machine state.
• OutOfStock: The machine has no inventory available and cannot be leased for a new lease while it remains in this state.
• Maintenance: The machine is temporarily unavailable because it needs service and cannot be leased for a new lease while it remains in this state.

Payment Strategies

• MONTHLY: The lease amount is calculated as amount * numberOfMonths. Here, amount represents the monthly lease amount.
• ONE_TIME: The lease amount is calculated as the fixed amount. Here, amount represents the total fixed lease amount.

Method Signatures

Constructor

Register Machine

• If machineId is already registered, return "Machine already exists".
• Otherwise, add the machine in Idle state and return "Machine registered".

Create Lease

• If leaseId already exists, return "Lease already exists".
• If machineId is not registered, return "Machine not found".
• If endMonth < currentMonth, return "Lease period already expired".
• If the machine has any non-ended lease whose month range overlaps with [startMonth,endMonth], return "Machine already leased for this period".
• If the machine state is not Idle, return "Machine not available".
• Otherwise, create the lease and return "Lease created".

Change Machine State

• If machineId is not registered, return "Machine not found".
• Otherwise, update the machine state and return "State changed".

Calculate Payment

• If leaseId does not exist, return -1.
• For "MONTHLY", return amount * (endMonth - startMonth + 1).
• For "ONE_TIME", return amount.

End Lease

• If leaseId does not exist, return "Lease not found".
• If the lease has already been manually ended, return "Lease already ended".
• If currentMonth < startMonth, return "Lease not started".
• Otherwise, mark the lease as ended and return "Lease ended".

Get Machine Details

• If machineId is not registered, return "Machine not found".
• Otherwise, return the machine details in the format "machineId,location,state,leasedStatus".
• leasedStatus must be "LEASED" if the machine has a lease that is active at currentMonth.
• leasedStatus must be "AVAILABLE" if the machine has no lease that is active at currentMonth.

Get Lease Details

• If leaseId does not exist, return "Lease not found".
• Otherwise, return the lease details in the format "leaseId,machineId,customerId,startMonth,endMonth,paymentStrategy,amount,status".
• status must be "ACTIVE" if the lease is active at currentMonth.
• status must be "UPCOMING" if the lease has not started yet at currentMonth.
• status must be "EXPIRED" if the lease period has passed at currentMonth and the lease was not manually ended.
• status must be "ENDED" if the lease was manually ended using endLease.

Constraints

• 1 ≤ machineId.length() ≤ 50
• 1 ≤ leaseId.length() ≤ 50
• 1 ≤ customerId.length() ≤ 50
• 1 ≤ location.length() ≤ 100
• 1 ≤ startMonth ≤ endMonth ≤ 120
• 1 ≤ currentMonth ≤ 120
• 1 ≤ amount ≤ 1,000,000
• paymentStrategy will always be either "MONTHLY" or "ONE_TIME".
• newState will always be one of "Idle", "OutOfStock", or "Maintenance".
• All string parameters will be non-null and will satisfy their length constraints.
• The system will receive at most 104 method calls.
• Test cases will never pass invalid parameter values such as null strings, empty ids, invalid month ranges, invalid payment strategies, invalid machine states, negative amounts, or values outside the stated constraints.

Examples

Example 1

Example 2

Example 3

Example 4