Requirements

Functional Requirements:

• Allow reservation of a parking spot.
• Process payment for the reservation.
• Enable parking of a car in the reserved spot.
• Support early departure before reservation time expires.
• Gate check-in/out.
• Handle no show. Payment to be forfeited, user will be informed of this when making payment. If there is a no-show the user needs to be informed that their payment is forfeited
• Prevent cars from entering the car park if it is full
• % of lots reserved for walk in
• Users cannot unreserve their lots
• If users overstay their time in a reserved lot, they will be fined

Non-Functional Requirements:

• Reliability (most important), cannot show incorrect information, should accurately reflect the number of lots available
• Should remain operational even during peak hour
• Consistent

API Design

/POST: reserve-lot

body: {

startTime: datetime string

endTime: datetime string

lotNumber (optional): int

paymentID: int/string

}

status: 200 OK, 404 Bad request

/POST: leave-early

body: {

lotNumber: int

}

status: 200 OK

/POST: admit-car

status: 200 OK, 404 Bad request

/GET: get-avail-lots

status: 200 OK

High-Level Design

1. Reserving the lot
   1. Client will make a request to the API gateway, which will send the API request to the server
   2. Server will pull necessary info from database to determine if the client can reserve that lot
   3. If the client can reserve the lot, update the database accordingly, return 200 ok
   4. Else, return 404 Bad request
2. Displaying the number of lots available (at all times)
   1. get-avail-lots (this needs to be accurate at all times)
3. Deciding whether or not to admit a car
   1. get-avail-lots
4. No shows
   1. Server needs to send notification to the client
   2. Can use some sort of event handler

Detailed Component Design

1. Reservation System
   1. When a client wants to reserve a lot
      1. Check if a lot is specified, if it is, check if that lot is available/ too many lots are reserved (check the time as well), if it isn't return 404 Bad request. If not mark the lot as reserved in the backend, update the database with the reserved lot, return 200 OK to the client
   2. When a client does not show up
      1. At the stipulated time, the backend will send a notification to the client that their lot has been forfeited. The backend will update its own data as well as the database to say that reservation is essentially 'cancelled'
   3. When a car overstays its reservation period
      1. Send a notification to the client to pay the fine, do not mark the lot as 'vacant' until the car leaves
      2. If there is a reservation right after, 'cancel' that and inform the car, refund that car too
   4. When the client leaves a reserved lot early
      1. a leave-early POST request is sent to the backend. The server marks that lot as 'free' in the backend, updates the database accordingly.
2. Displaying the number of lots available
   1. The backend will pull the number of available lots, what lots are reserved etc. at the beginning of the day. As cars begin to come in, reservations begin to come in, the backend can actually update its local data first before updating the database, this reduces latency.
3. Deciding whether or not to admit a car
   1. the client will use the admit-car endpoint
   2. The backend will check its locally cached data to see if there are any lots available
   3. Return 404 Bad request or 200 OK depending on that

Backend logic

1. At the beginning of day we can pull all reservations from the database, this minimizes the need to make calls to the database
2. We can sort all reservations into a sorted array
3. We can also keep track of the number of available lots at any point in time, let the number of lots be x available at any given point in time

When a reservation comes up

1. same day reservation
   1. since all existing reservations are in a sorted array, we can use binary search to find any conflicting reservations
2. different day reservation
   1. We need to get the data from the database to check if it is valid

When a car enters during its reservation time

1. decrease x by 1

When a car leaves early

1. increase x by 1

When a car overstays its reservation

1. Cancel conflicting reservations that may be affected

When admitting a car

1. check that x > 0
2. if the car is admitted, decrease x by 1