End-User / Customer Operations

• Optional - Register onto the platform. In the current scope we don’t have to worry about authentication.
• View the workout slots availability/unavailability for the day - filter by workout type (sorted by start time in ASC order).
• View the workout slots availability/unavailability for the day - filter by workout type and center name (sorted by seats available in ASC order).
• Book a workout slot for a user if seats are available at that time.
• Cancel the booked workout slot.
• Optional - Notify me feature: If a user is interested in some particular slot of a center and seats are unavailable, he can choose to be part of the interest list for that slot. Once any other user cancels that particular slot the interested users can be notified. Notification will be pushed to all the interested users. You can use logs to model the notification.

1) Onboard a Center

• centerName is unique for a center (acts as identifier).
• centerTimings contains time ranges for the day; each element is a string like "6-9" or "18-21". Time is an integer for the current scope (single day).
• workoutTypes contains allowed workouts for the center, e.g. "Weights", "Cardio", "Yoga", "Swimming".
• Adding newer workouts in the future should be supported by allowing new strings in workoutTypes.

2) Admin Defines a Workout Slot

• startTime and endTime are integers for a day-only scope, e.g. 6 to 7.
• startTime < endTime and totalSeats > 0.
• The slot must lie fully inside at least one of the center timing ranges defined during onboarding.
• The workoutType must be one of the allowed types for that center.
• At any point in time for a center, there is just one workout: slots must not overlap in time for the same center.
• Update is out of scope: once a slot is created, it cannot be modified (you may reject duplicate/overlapping re-definitions).
• Return true if the slot is created; otherwise return false (invalid center, invalid time, invalid workout type, overlaps, etc.).

3) View Workout Availability (Sorted by Start Time)

• Returns slot availability for the day filtered by workoutType.
• If centerName is empty or "*", include all centers; otherwise restrict to that center.
• Sort the results by slot startTime and then lexicographically in ascending order.
• Return each slot as a single string: "centerName|workoutType|startTime|endTime|seatsAvailable"

4) View Workout Availability (Sorted by Seats Available)

• Returns slot availability for the day filtered by workoutType and centerName.
• centerName must be provided (cannot be empty or "*").
• Sort the results by seatsAvailable and then lexicographicaly in ascending order.
• Return each slot as a single string: "centerName|workoutType|startTime|endTime|seatsAvailable"

• Book a slot
  String bookSession(String userId, String centerName, String workoutType, int startTime, int endTime)
  • Books exactly one seat for the identified slot: (centerName, workoutType, startTime, endTime).
  • Return values:
    • "BOOKED" on success
    • "NO_SEATS" if slot exists but has 0 seats available
    • "SLOT_NOT_FOUND" if the slot does not exist
    • "ALREADY_BOOKED" if the same user already booked the same slot
• Cancel a booking
  String cancelSession(String userId, String centerName, String workoutType, int startTime, int endTime)
  • Cancels the user’s booking for the identified slot and restores exactly one seat.
  • Return values:
    • "CANCELLED" on success
    • "BOOKING_NOT_FOUND" if user has no booking for that slot
    • "SLOT_NOT_FOUND" if the slot does not exist
  • If notify-me is enabled, after cancellation notifyInterestedUsers() will return notification logs for interested users.
• Notify-me / Interest list
  String addToInterestList(String userId, String centerName, String workoutType, int startTime, int endTime)
  • Adds the user to the interest list for the identified slot when the slot is currently full.
  • Return values:
    • "INTEREST_ADDED" if user was added
    • "ALREADY_INTERESTED" if user is already in the list
    • "SEATS_AVAILABLE" if slot currently has seats (so interest is not needed)
    • "SLOT_NOT_FOUND" if the slot does not exist
• Notification dispatch
  List<String> notifyInterestedUsers(String centerName, String workoutType, int startTime, int endTime)
  • Called after a successful cancellation when a seat becomes available.
  • Returns log lines like: "NOTIFY|<userId>|<centerName>|<workoutType>|<startTime>-<endTime>".

Constraints

• Time is an integer for a single day only (e.g. 6 means 6 AM, 18 means 6 PM).
• centerTimings.size() >= 1 and each timing string is a range "start-end" with start < end.
• workoutTypes.size() >= 1.
• totalSeats > 0.
• No external databases allowed; use only in-memory data structures.
• All operations are for one day only, but design should be extensible to multiple days with minimal changes.
• Identifiers are unique and lowercase (you may treat centerName and userId as unique identifiers).

Functional Notes

• Admin can define slots only for the same day; updates to already-created slots are out of scope.
• A center cannot create a workout slot outside its onboarded timings.
• A center cannot create a workout slot for a workout type not onboarded for that center.
• Within a center, workout slots must not overlap in time (one workout at one point of time).
• For notifications, you can model notification as logs printed when cancellation happens.

Examples

Example 1: Center Onboarding + Slot Definition

Example 2: View Availability (Sorted by Start Time)

Example 3: Book Session + Verify Updated Seats + Prevent Double Booking

Example 4: View Availability (Sorted by Seats Available)

Example 5: Cancel Restores Seat + Notify-Me Flow