erDiagram
    %% SHARED COMPONENT (All Members)
    %% User Management is central to the system
    USERS {
        ObjectId _id PK
        string name
        string email
        string password
        string role "Admin, HospitalStaff, Public"
        string nic "National ID"
        string phone
        string address
        date createdAt
    }

    %% MODULE 1: VACCINE SUPPLY CHAIN (Minidu)
    %% Manages the abstract vaccine types and specific physical batches
    VACCINE {
        ObjectId _id PK
        string name "e.g., Pfizer, Sinopharm"
        string manufacturer
        string description
        int dosesRequired
        int daysBetweenDoses
        string imageUrl "Cloudinary URL"
    }

    BATCH {
        ObjectId _id PK
        ObjectId vaccineId FK
        ObjectId hospitalId FK
        string batchNumber
        int quantity
        date expiryDate
        date arrivalDate
        string status "Available, Expired, Depleted"
    }

    %% MODULE 2: CLINIC MANAGEMENT (Nethmi)
    %% Manages the physical locations and time slots
    HOSPITAL {
        ObjectId _id PK
        string name
        string district
        string city
        object location "Lat/Lng from LocationIQ"
        string contactNumber
        string type "Govt, Private"
    }

    CLINIC {
        ObjectId _id PK
        ObjectId hospitalId FK
        ObjectId vaccineId FK
        date date
        string timeSlot "08:00-12:00"
        int maxCapacity
        int currentBookings
        string status "Scheduled, Active, Completed, Cancelled"
    }

    %% MODULE 3: APPOINTMENT ENGINE (Saniru)
    %% Manages the booking transaction and queue
    APPOINTMENT {
        ObjectId _id PK
        ObjectId clinicId FK
        ObjectId userId FK
        int queueNumber
        string status "Pending, Completed, Cancelled, No-Show"
        string qrCodeUrl "QR API Generated"
        date bookedAt
    }

    %% MODULE 4: PATIENT RECORDS & HISTORY (Kaveen)
    %% Manages the permanent medical history and post-vax data
    RECORD {
        ObjectId _id PK
        ObjectId userId FK
        ObjectId appointmentId FK
        ObjectId batchId FK "Traceability"
        date vaccinationDate
        string notes
        date nextDoseDate
        string certificateUrl "Generated PDF"
    }

    %% RELATIONSHIPS
    %% Linking the specific modules together

    %% Minidu's Relationships
    VACCINE ||--o{ BATCH : "has many batches"

    %% Nethmi's Relationships
    HOSPITAL ||--o{ CLINIC : "hosts"
    HOSPITAL ||--o{ BATCH : "stocks"

    %% Saniru's Relationships
    CLINIC ||--o{ APPOINTMENT : "has bookings"
    USERS ||--o{ APPOINTMENT : "makes"

    %% Kaveen's Relationships
    APPOINTMENT ||--|| RECORD : "generates"
    USERS ||--o{ RECORD : "has history"
    BATCH ||--o{ RECORD : "used in"

    %% Cross-Module Links
    VACCINE ||--o{ CLINIC : "offered at"