Add all my notes

imperfect_notes/pragy/LLD 5.md

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+LLD 5
+-----
+
+- some have still not submitted the BookMyShow diagram
+- So postpone it to next class
+- For now, BookMyShow
+
+
+Hotel Management System
+-----------------------
+
+- support booking different room types
+    - suite
+    - king size
+    - delux
+    - **Entities:**
+        - booking
+        - room
+    - **Relations:**
+        - booking-room
+        - room-subclass
+- search and book rooms for a guest
+    - **Entities:**
+        - search interface
+        - guest
+    - who else can use search? We can not only book rooms online. People also visit the frontdesk and book rooms
+    - **Relationships**
+        - guest uses search interface
+        - Receptionist
+- Who booked a particular room, say 1004
+    - **Relation:**
+        - room booking has multiple guests
+        - one guest can only bok one room
+- cancel a booking
+    - behavior. no new entity / relation here
+- track housekeeping tasks
+    - **Entities:**
+        - housekeeing task
+        - housekeeper
+    - **Relation:**
+        - housekeeper can perform * tasks
+- customer can ask for room service
+    - room service is different from house keeping
+    - don't have to pay for housekeeping
+    - have to pay for roomservice
+    - order food/drinks in roomservice
+    - **Entities:**
+        - room service
+- payment should be supported through various modes
+    - card
+    - cash
+
+-- --
+
+How should we start?
+- from building
+- from brand
+
+```python
+class HotelBranch:
+    name: str
+    
+    def get_number_of_centers():
+    def add_location():
+    
+class HotelCenter: # actual physical building
+    location: Address
+    name: str
+    
+    def get_rooms():
+```
+
+HotelBrand  1 <>----- * HotelBranch
+
+```python
+class Room:
+    room_number: str
+    room_type: str  # or subclass
+    price: float
+    is_booked: bool
+    
+    def check_in():
+    def check_out():
+```
+HotelCenter 1 <>----- * Room
+
+-- --
+
+How will you get into your room?
+Do you need something?
+Each room can have multiple keys, right?
+
+```python
+class RoomKey:
+    id: str
+    barcode: str
+    issued_at_date: Date
+    is_active: bool
+```
+
+Room 1 <>----- * Key
+
+-- --
+
+Humans
+- guest
+- receptionist
+- housekeeper
+- manager
+
+
+```python
+class Person:
+    name: str
+    phone_number: str
+    email_id: str
+
+class Guest(Person):
+    def create_booking():
+
+class Receptionist(Person):
+    def create_booking():
+    
+class Housekeeper(Person): # or servant. Or differnt subclasses of servant - cleaner / food server / masseur
+    def add_service_charge(): # for services they offer
+    # no def create_booking()
+```
+
+Person <--- ext --- Guest
+Person <--- ext --- Receptionist
+Person <--- ext --- Housekeeper
+
+-- --
+
+How do you track / manage these people?
+Account
+
+```python
+class Account:
+    name: str
+    email: str
+    password: str
+```
+
+Person 1 <>------ 1 Account
+
+-- --
+
+How do you track of your sales?
+Booking
+
+What is it that you book? Brand/Hotel/Room?
+Room
+
+```python
+class Booking:
+    booking_number: str
+    start_time: DateTime
+    end_time: DateTime
+    status: successfull / failed
+    
+    def modify():
+    def cancel():
+```
+
+Can there be multiple bookings for a particular room?
+- Yes, for different times. All bookings can exist simultaneously
+
+
+Room 1 ---- * Booking
+- Composition or Association?
+- If room goes bad - leaking / haunted / something not working
+- Would you cancel my booking? No - reassign to a room of the same type
+- Association
+Room ---> Booking
+
+
+Booking * ------> 1 Guest
+
+Does not need to be composition, because room can be booked for a friend. Could be though depending on the case
+
+-- --
+
+What does a housekeeper do?
+- various housekeeping tasks
+
+```python
+class HouseKeepingTask:  # or record
+    description: str
+    start_time: DateTime
+    duration: Time 
+```
+
+HouseKeeper 1 -----> * HouseKeepingTask
+
+Not a composition
+
+HouseKeepingTask * <------ Room
+Same room could have multiple tasks that were/need to be done
+
+What if room is destroyed? Should destroy previous tasks?
+- no
+- but what about foriegn keys?
+- keep a note in room saying invalid or something
+- depends on requirements
+- We will discuss DB schema design later in LLD
+
+-- --
+
+RoomService (not the same as housekeeping)
+
+```python
+class FoodService:
+    
+class MassageService:
+```
+
+HouseKeeper 1 ------- * Service
+
+-- --
+
+Now, each service will need some payment.
+Invoice
+
+```python
+class InvoiceItem:
+    amount: float
+    time: DateTime
+```
+
+InvoiceItem  1 ------- 1 Service
+Each instance of service associated with each instance of invoiceitem
+Or we could make Service objects static
+Then, Invoice * ------ 1 Service
+
+InvoiceItem * ------ RoomBooking
+Same room can request multiple services
+
+-- --
+
+All invoiceitems associated with an invoice
+
+```python
+class Invoice:
+    
+```
+
+Do you always charge money all the time? No. at the end
+RoomBooking 1 -------> 1 Invoice
+
+InvoiceItem * ------<> 1 Invoice
+
+-- --
+
+Searching
+
+```python
+<<interface>> Search:
+    search_by_room_type()
+    search_by_floor()
+```
+
+have catalogues of rooms and mapping that we need
+Who can use this?
+Receptionist
+
+**Why is search an interface?**
+Because search can be done on various things - users, rooms, tasks ..
+So, the common functionality of search is an interface. Then there are several modules that implement that interface
+
+-- --
+
+going forward, we will look at DB schema design for things like this
+
+-- --
+