# NestJS Time-Slot & Scheduling System Analysis

## Executive Summary

This is a comprehensive analysis of the pilates studio booking system's time-slot generation and scheduling backend. The system automatically generates time slots from reusable weekly templates, maintains their lifecycle, and integrates tightly with the booking and membership management systems.

---

## 1. Data Models (Prisma Schema)

### 1.1 WeekTemplate Model
**Location:** `packages/server/prisma/schema.prisma` (lines 113-126)

```prisma
model WeekTemplate {
  id        String   @id @default(uuid())
  dayOfWeek Int      @map("day_of_week")           // 1=Mon, 7=Sun (ISO standard)
  startTime String   @map("start_time")            // e.g., "09:00"
  endTime   String   @map("end_time")              // e.g., "10:00"
  capacity  Int      @default(1)                   // Max participants
  isActive  Boolean  @default(true)                // Enable/disable template
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt

  timeSlots TimeSlot[]                             // Generated slots from this template
}
```

**Purpose:**
- Defines recurring time slots by day of week and time
- Used as blueprint for automatic slot generation
- Capacity defines how many people can book each slot

**Key Constraints:**
- `dayOfWeek` uses **ISO 8601 standard** (1=Monday through 7=Sunday)
- NOT JavaScript getDay() (0=Sunday)
- Conversion happens in SlotGeneratorService.toIsoWeekday()

---

### 1.2 TimeSlot Model
**Location:** `packages/server/prisma/schema.prisma` (lines 128-148)

```prisma
model TimeSlot {
  id          String         @id @default(uuid())
  date        DateTime       @db.Date              // Calendar date (midnight UTC)
  startTime   String         @map("start_time")    // "HH:mm" format
  endTime     String         @map("end_time")      // "HH:mm" format
  capacity    Int            @default(1)           // Max participants
  bookedCount Int            @default(0)           // Current bookings
  status      TimeSlotStatus @default(OPEN)        // OPEN | FULL | CLOSED
  source      TimeSlotSource @default(TEMPLATE)    // TEMPLATE | MANUAL
  templateId  String?        @map("template_id")   // Reference to WeekTemplate
  createdAt   DateTime       @default(now())
  updatedAt   DateTime       @updatedAt

  template WeekTemplate?  @relation(fields: [templateId], references: [id])
  bookings Booking[]

  @@unique([date, startTime, endTime])            // Prevent duplicate slots
  @@index([date])
  @@index([status])
}
```

**Status Lifecycle:**
- **OPEN**: Accepts bookings, bookedCount < capacity
- **FULL**: No more bookings, bookedCount >= capacity
- **CLOSED**: Past date or manually closed, no bookings allowed

**Source Types:**
- **TEMPLATE**: Auto-generated from WeekTemplate
- **MANUAL**: Created directly by admin

---

### 1.3 Booking Model
**Location:** `packages/server/prisma/schema.prisma` (lines 150-168)

```prisma
model Booking {
  id           String        @id @default(uuid())
  userId       String        @map("user_id")
  timeSlotId   String        @map("time_slot_id")
  membershipId String        @map("membership_id")
  status       BookingStatus @default(CONFIRMED)
  cancelledAt  DateTime?     @map("cancelled_at")
  createdAt    DateTime      @default(now())
  updatedAt    DateTime      @updatedAt

  user       User       @relation(fields: [userId], references: [id])
  timeSlot   TimeSlot   @relation(fields: [timeSlotId], references: [id])
  membership Membership @relation(fields: [membershipId], references: [id])

  @@unique([userId, timeSlotId])                  // One booking per user per slot
  @@index([userId])
  @@index([status])
}
```

**Booking Status Values:**
- **CONFIRMED**: Active reservation
- **CANCELLED**: User cancelled
- **COMPLETED**: Slot time has passed
- **NO_SHOW**: Marked manually if user didn't attend

---

## 2. SlotGeneratorService

**Location:** `packages/server/src/time-slot/slot-generator.service.ts`

### 2.1 Service Overview

Core service responsible for:
1. **Generating** time slots from WeekTemplate
2. **Cleaning up** expired slots
3. **Managing** membership expiration
4. **Marking** past bookings as completed

### 2.2 Key Methods

#### `generateSlots(daysAhead: number = 14): Promise<number>`

**Purpose:** Creates time slots for the next N days based on active WeekTemplates.

**Algorithm:**
```
1. Fetch all active WeekTemplates (isActive = true)
2. Calculate tomorrow at midnight UTC as start date
3. For each day in [tomorrow, tomorrow + daysAhead):
   a. Get ISO weekday (1-7) from JavaScript date
   b. Find matching templates for this weekday
   c. For each matching template, create slot data:
      - date: UTC midnight
      - startTime/endTime: from template
      - capacity: from template
      - source: TimeSlotSource.TEMPLATE
      - templateId: template.id
4. Batch create all slots using createMany() with skipDuplicates: true
5. Return count of newly created slots
```

**Key Features:**
- **Idempotent:** Re-running is safe; duplicate date+startTime+endTime combos are skipped
- **Timezone Aware:** Uses UTC midnight for dates
- **Weekday Mapping:** Converts JS getDay() → ISO weekday
- **Batch Insert:** Creates all slots in single database operation

**Example Execution:**
- Today: Monday, April 7, 2026
- Daylight: 14 days
- Template: Monday 09:00-10:00, Friday 18:00-19:00
- Result: 2 slots tomorrow (Monday), 0 Wed-Thu, 1 Friday, repeat pattern

---

#### `cleanupExpiredSlots(): Promise<number>`

**Purpose:** Marks all OPEN slots with dates before today as CLOSED.

**Logic:**
```sql
UPDATE time_slots
SET status = 'CLOSED'
WHERE status = 'OPEN' AND date < TODAY_MIDNIGHT_UTC
```

**Returns:** Count of slots closed.

---

#### `checkExpiredMemberships(): Promise<number>`

**Purpose:** Manages membership expiration in two ways:

1. **By Expiration Date:**
   ```
   WHERE status = ACTIVE AND expireDate < NOW
   SET status = EXPIRED
   ```

2. **By Used-Up Sessions:**
   ```
   WHERE status = ACTIVE AND remainingTimes = 0
   SET status = USED_UP
   ```

**Returns:** Total count of memberships updated.

---

#### `completeBookings(): Promise<number>`

**Purpose:** Marks CONFIRMED bookings for past time slots as COMPLETED.

**Logic:**
```sql
UPDATE bookings
SET status = 'COMPLETED'
WHERE status = 'CONFIRMED' 
  AND timeSlot.date < TODAY_MIDNIGHT_UTC
```

---

## 3. TimeSlotService

**Location:** `packages/server/src/time-slot/time-slot.service.ts`

### 3.1 Service Overview

Handles time slot queries and management for both members and admins.

### 3.2 Key Methods

#### `getAvailableSlots(date: string, userId?: string): Promise<TimeSlotWithBookingStatus[]>`

**Purpose:** Retrieve all non-closed slots for a specific date, optionally including user's booking status.

**Query Logic:**
```
1. Parse date string to Date object
2. Find all slots for that calendar day:
   - WHERE status != CLOSED
   - ORDER BY startTime ASC
3. If userId provided:
   - Include bookings where userId=X AND status=CONFIRMED
   - Map to "isBookedByMe" and "myBookingId" fields
4. Return TimeSlotWithBookingStatus[]
```

**Response Type:**
```typescript
interface TimeSlotWithBookingStatus {
  id: string
  date: string                    // ISO date "YYYY-MM-DD"
  startTime: string               // "HH:mm"
  endTime: string
  capacity: number
  bookedCount: number
  status: TimeSlotStatus          // OPEN | FULL | CLOSED
  source: TimeSlotSource          // TEMPLATE | MANUAL
  templateId: string | null
  createdAt: string               // ISO datetime
  updatedAt: string
  isBookedByMe: boolean           // Current user's booking?
  myBookingId: string | null      // For cancellation
}
```

---

#### `getSlotById(id: string): Promise<TimeSlot>`

Returns full slot details including all bookings. Throws NotFoundException if not found.

---

#### `createManualSlot(dto: CreateManualSlotDto): Promise<TimeSlot>`

**Purpose:** Allow admins to create one-off time slots outside templates.

**DTO:**
```typescript
class CreateManualSlotDto {
  date: string              // "YYYY-MM-DD"
  startTime: string         // "HH:mm"
  endTime: string           // "HH:mm"
  capacity?: number         // Defaults to DEFAULT_SLOT_CAPACITY (1)
}
```

**Creates slot with:**
- `source: TimeSlotSource.MANUAL`
- `templateId: null`

---

#### `closeSlot(id: string): Promise<TimeSlot>`

Sets slot status to CLOSED. Prevents new bookings but keeps existing ones.

---

#### `getWeekTemplates(): Promise<WeekTemplate[]>`

Lists all templates ordered by dayOfWeek and startTime.

---

#### `replaceWeekTemplates(items: WeekTemplateItemDto[]): Promise<CreateBatchPayload>`

**Purpose:** Atomic replacement of all templates (used during admin config).

**Transaction:**
```
1. DELETE FROM week_templates (all rows)
2. CREATE week_templates with new items
3. Return count
```

---

## 4. TimeSlotController & AdminTimeSlotController

**Location:** `packages/server/src/time-slot/time-slot.controller.ts`

### 4.1 Member Endpoints

#### `GET /time-slot/available?date=YYYY-MM-DD`
- Returns available slots for the date
- Includes current user's booking status
- Requires JWT authentication

#### `GET /time-slot/:id`
- Returns full slot details with all bookings
- Requires JWT authentication

---

### 4.2 Admin Endpoints

All require `@Roles(UserRole.ADMIN)` and JWT auth.

#### `GET /admin/week-template`
Lists all WeekTemplate entries.

#### `PUT /admin/week-template`
Replaces all templates. Request body:
```json
{
  "templates": [
    {
      "dayOfWeek": 1,
      "startTime": "09:00",
      "endTime": "10:00",
      "capacity": 1,
      "isActive": true
    }
  ]
}
```

#### `POST /admin/time-slot/manual`
Creates a manual slot. Request body:
```json
{
  "date": "2026-04-10",
  "startTime": "14:00",
  "endTime": "15:00",
  "capacity": 2
}
```

#### `PUT /admin/time-slot/:id/close`
Closes a specific slot.

#### `POST /admin/generate-slots`
Manually trigger slot generation (default 14 days ahead).

---

## 5. SchedulerService - Automated Jobs

**Location:** `packages/server/src/scheduler/scheduler.service.ts`

### 5.1 Overview

Uses `@nestjs/schedule` to run daily maintenance tasks. All times in UTC.

### 5.2 Cron Jobs

#### Job 1: Slot Generation
```
@Cron('0 2 * * *')  // 02:00 UTC daily
async handleSlotGeneration()
```
- Calls: `slotGenerator.generateSlots(14)`
- Generates slots 14 days ahead
- Purpose: Keep pipeline filled

---

#### Job 2: Slot Cleanup
```
@Cron('30 2 * * *')  // 02:30 UTC daily
async handleCleanupSlots()
```
- Calls: `slotGenerator.cleanupExpiredSlots()`
- Marks past OPEN slots as CLOSED

---

#### Job 3: Membership Check
```
@Cron('0 3 * * *')   // 03:00 UTC daily
async handleCheckMemberships()
```
- Calls: `slotGenerator.checkExpiredMemberships()`
- Expires memberships by date or used-up sessions

---

#### Job 4: Booking Completion
```
@Cron('0 22 * * *')  // 22:00 UTC daily
async handleCompleteBookings()
```
- Calls: `slotGenerator.completeBookings()`
- Marks past CONFIRMED bookings as COMPLETED

---

## 6. BookingService - Integration with TimeSlots

**Location:** `packages/server/src/booking/booking.service.ts`

### 6.1 Key Integration Points

#### `createBooking(userId: string, dto: CreateBookingDto): Promise<BookingWithRelations>`

**DTO:**
```typescript
class CreateBookingDto {
  timeSlotId: string   // UUID of TimeSlot
  membershipId: string // UUID of Membership
}
```

**Transaction Flow:**
```
1. Fetch TimeSlot - validate status = OPEN
2. Check unique constraint - user not already booked this slot
3. Fetch Membership - validate:
   - Belongs to user
   - Status = ACTIVE
   - Has remaining capacity:
     * TIMES/TRIAL: remainingTimes > 0
     * DURATION: not expired
4. Create Booking(userId, timeSlotId, membershipId) → CONFIRMED
5. Update TimeSlot:
   - bookedCount++
   - If bookedCount >= capacity, set status = FULL
6. Update Membership (if time-based):
   - remainingTimes--
   - If remainingTimes = 0, set status = USED_UP
7. Return booking with relations
```

**Error Handling:**
- TimeSlot not OPEN → BadRequestException
- Duplicate booking → ConflictException
- Invalid membership → ForbiddenException
- No remaining sessions → BadRequestException

---

#### `cancelBooking(userId: string, bookingId: string): Promise<CancelBookingResult>`

**Refund Logic:**
```
cancelHoursLimit = StudioConfig.cancelHoursLimit (default 2 hours)
slotStartMs = Date(date).setUTC Hours + startTime
deadlineMs = NOW + (cancelHoursLimit * 3600 * 1000)
withinLimit = slotStartMs >= deadlineMs

IF withinLimit:
  Restore membership.remainingTimes++
ELSE:
  No refund
```

**Transaction Flow:**
```
1. Mark Booking → CANCELLED, set cancelledAt
2. Decrement TimeSlot.bookedCount
3. If slot was FULL, restore to OPEN
4. If within cancel window:
   - For TIMES/TRIAL: increment remainingTimes
   - Restore membership status if was USED_UP
```

---

#### `getMyBookings(userId: string, status?, page, limit): Promise<PaginatedResult>`

Lists user's bookings with pagination, optionally filtered by status.

---

#### `getUpcomingBookings(userId: string): Promise<BookingWithRelations[]>`

Returns all CONFIRMED bookings for dates >= today, ordered by date.

---

## 7. Data Flow Diagrams

### 7.1 Slot Generation Flow

```
Daily 02:00 UTC
       ↓
SchedulerService.handleSlotGeneration()
       ↓
SlotGeneratorService.generateSlots(14)
       ↓
1. Query WeekTemplate (isActive=true)
2. For next 14 days:
   - Match templates by ISO weekday
   - Create TimeSlot entries
3. Use createMany(skipDuplicates: true)
       ↓
Database: Insert new TimeSlot records
       ↓
Return: count of new slots
```

---

### 7.2 Booking Flow

```
User Action
       ↓
POST /booking
  timeSlotId: UUID
  membershipId: UUID
       ↓
BookingService.createBooking()
       ↓
START TRANSACTION
  ├─ Validate TimeSlot (status=OPEN)
  ├─ Check unique(userId, timeSlotId)
  ├─ Validate Membership (ACTIVE, not expired)
  ├─ CREATE Booking(CONFIRMED)
  ├─ UPDATE TimeSlot(bookedCount++, status=?)
  └─ UPDATE Membership(remainingTimes--)
COMMIT
       ↓
Return: BookingWithRelations
```

---

### 7.3 Cancellation Flow

```
User Action
       ↓
PUT /booking/:id/cancel
       ↓
BookingService.cancelBooking()
       ↓
Check: Now vs Slot Time + cancelHoursLimit
       ↓
START TRANSACTION
  ├─ UPDATE Booking(CANCELLED, cancelledAt=NOW)
  ├─ UPDATE TimeSlot(bookedCount--, status=?)
  └─ IF within cancel window:
     └─ UPDATE Membership(remainingTimes++)
COMMIT
       ↓
Return: { booking, refunded: boolean }
```

---

## 8. DTOs & Request/Response

### 8.1 Time Slot DTOs

**Location:** `packages/server/src/time-slot/dto/`

#### `QuerySlotsDto`
```typescript
class QuerySlotsDto {
  @IsDateString()
  date!: string  // Format: YYYY-MM-DD
}
```

#### `CreateManualSlotDto`
```typescript
class CreateManualSlotDto {
  @IsDateString()
  date!: string
  @IsString()
  startTime!: string
  @IsString()
  endTime!: string
  @IsOptional()
  @IsInt()
  @Min(1)
  capacity?: number
}
```

#### `WeekTemplateItemDto` & `UpdateWeekTemplateDto`
```typescript
class WeekTemplateItemDto {
  @IsInt()
  @Min(1)
  @Max(7)
  dayOfWeek!: number  // ISO: 1=Mon, 7=Sun
  @IsString()
  startTime!: string
  @IsString()
  endTime!: string
  @IsOptional()
  capacity?: number
  @IsOptional()
  isActive?: boolean
}

class UpdateWeekTemplateDto {
  @ArrayNotEmpty()
  templates!: WeekTemplateItemDto[]
}
```

---

## 9. Shared Constants & Enums

**Location:** `packages/shared/src/`

### 9.1 Constants

```typescript
// constants.ts
export const DEFAULT_CANCEL_HOURS_LIMIT = 2
export const DEFAULT_SLOT_CAPACITY = 1
export const SLOT_GENERATION_DAYS = 14
export const TIME_PERIODS = {
  MORNING: { label: '上午', start: '06:00', end: '12:00' },
  AFTERNOON: { label: '下午', start: '12:00', end: '18:00' },
  EVENING: { label: '晚上', start: '18:00', end: '22:00' },
}
export const DATE_SELECTOR_DAYS = 7
export const WEEKDAY_LABELS = ['', '周一', '周二', '周三', '周四', '周五', '周六', '周日']
```

### 9.2 Enums

```typescript
// enums.ts
enum TimeSlotStatus {
  OPEN = 'OPEN',
  FULL = 'FULL',
  CLOSED = 'CLOSED',
}

enum TimeSlotSource {
  TEMPLATE = 'TEMPLATE',
  MANUAL = 'MANUAL',
}

enum BookingStatus {
  CONFIRMED = 'CONFIRMED',
  CANCELLED = 'CANCELLED',
  COMPLETED = 'COMPLETED',
  NO_SHOW = 'NO_SHOW',
}

enum MembershipStatus {
  ACTIVE = 'ACTIVE',
  EXPIRED = 'EXPIRED',
  USED_UP = 'USED_UP',
}
```

---

## 10. File Structure Summary

```
packages/server/src/
├── time-slot/
│   ├── __tests__/
│   │   ├── slot-generator.service.spec.ts  (170 lines, comprehensive tests)
│   │   └── time-slot.service.spec.ts
│   ├── dto/
│   │   ├── query-slots.dto.ts
│   │   ├── create-manual-slot.dto.ts
│   │   └── week-template.dto.ts
│   ├── slot-generator.service.ts           (172 lines, 4 key methods)
│   ├── time-slot.service.ts                (142 lines)
│   ├── time-slot.controller.ts             (93 lines, 2 controllers)
│   └── time-slot.module.ts
│
├── scheduler/
│   ├── __tests__/
│   │   └── scheduler.service.spec.ts
│   ├── scheduler.service.ts                (55 lines, 4 cron jobs)
│   └── scheduler.module.ts
│
├── booking/
│   ├── __tests__/
│   │   └── booking.service.spec.ts
│   ├── dto/
│   │   └── create-booking.dto.ts
│   ├── booking.service.ts                  (367 lines)
│   ├── booking.controller.ts               (82 lines)
│   └── booking.module.ts
│
├── prisma/
│   └── schema.prisma                       (205 lines, includes models)
│
└── app.module.ts                           (imports TimeSlotModule, SchedulerModule)

packages/shared/src/
├── types/
│   ├── time-slot.ts
│   └── (others)
├── constants.ts                            (22 lines)
├── enums.ts                                (47 lines)
└── index.ts
```

---

## 11. Key Architectural Patterns

### 11.1 Idempotent Slot Generation

**Problem:** If scheduler crashes or delays, slots might not be generated.
**Solution:** 
- Use `createMany(skipDuplicates: true)` with unique constraint on `[date, startTime, endTime]`
- Safe to re-run multiple times
- Only inserts new combinations

---

### 11.2 Atomic Transactions

**For Booking Creation:**
- Create booking, update slot, update membership in single transaction
- All-or-nothing: ensures consistency if any step fails

**For Cancellation:**
- Cancel booking, restore slot, conditionally restore membership
- Prevents race conditions

---

### 11.3 ISO Weekday Mapping

**Problem:** JavaScript `Date.getDay()` uses 0=Sunday, but WeekTemplate uses ISO 8601 (1=Monday).

**Solution:** Helper function `toIsoWeekday()`:
```typescript
function toIsoWeekday(jsDay: number): number {
  return jsDay === 0 ? 7 : jsDay
}
```

---

### 11.4 Membership Type Handling

**TIMES/TRIAL cardType:**
- Deduct `remainingTimes--` on booking
- Mark USED_UP when remainingTimes = 0
- Refund if cancelled within window

**DURATION cardType:**
- Check `expireDate` not passed
- No deduction; just check validity
- No refund on cancellation

---

## 12. Example Scenarios

### Scenario 1: Setup Studio with Mon-Fri Classes

**Admin Actions:**
```json
PUT /admin/week-template
{
  "templates": [
    { "dayOfWeek": 1, "startTime": "09:00", "endTime": "10:00", "capacity": 1 },
    { "dayOfWeek": 1, "startTime": "10:30", "endTime": "11:30", "capacity": 1 },
    { "dayOfWeek": 2, "startTime": "09:00", "endTime": "10:00", "capacity": 1 },
    { "dayOfWeek": 3, "startTime": "09:00", "endTime": "10:00", "capacity": 1 },
    { "dayOfWeek": 4, "startTime": "09:00", "endTime": "10:00", "capacity": 1 },
    { "dayOfWeek": 5, "startTime": "09:00", "endTime": "10:00", "capacity": 1 },
    { "dayOfWeek": 5, "startTime": "18:00", "endTime": "19:00", "capacity": 1 }
  ]
}
```

**Next Day (02:00 UTC):**
- Scheduler auto-generates 14 days of slots
- Result: 14 Mon morning + 14 Mon mid-morning + 14 Tue morning + ... + 14 Fri evening

**Member Action (View Availability):**
```
GET /time-slot/available?date=2026-04-10
→ Returns all slots for April 10 (Friday)
→ Includes bookings for current user
```

---

### Scenario 2: Member Books, Then Cancels

**Member Books:**
```
POST /booking
{
  "timeSlotId": "slot-123",
  "membershipId": "mem-456"
}
```

**System:**
1. Validates slot is OPEN, membership is ACTIVE with remaining sessions
2. Creates Booking(CONFIRMED)
3. Increments slot.bookedCount (1 → 2)
4. If now at capacity, sets slot.status = FULL
5. Decrements membership.remainingTimes (5 → 4)

**Member Cancels (within 2-hour window):**
```
PUT /booking/booking-789/cancel
```

**System:**
1. Checks if NOW + 2 hours ≤ slot start time ✓
2. Sets booking.status = CANCELLED
3. Decrements slot.bookedCount (2 → 1)
4. If slot was FULL, restores to OPEN
5. Increments membership.remainingTimes (4 → 5) ✓ refunded

---

### Scenario 3: Membership Expires

**Overnight at 03:00 UTC:**
- Scheduler runs `handleCheckMemberships()`
- Updates all ACTIVE memberships where `expireDate < NOW` to EXPIRED
- User tries to book → BadRequestException "Membership is not active (status: EXPIRED)"

---

## 13. Testing Guide

### Key Test Files

1. **`slot-generator.service.spec.ts`** (310 lines)
   - Tests slot generation from templates
   - Tests weekday mapping (JS vs ISO)
   - Tests cleanup and expiration logic
   - Tests membership and booking expiration

2. **`time-slot.service.spec.ts`** (existing)
   - Tests getAvailableSlots with user booking status
   - Tests manual slot creation

3. **`booking.service.spec.ts`** (existing)
   - Tests booking creation with all validations
   - Tests cancellation with refund logic

---

## 14. Configuration & Environment

### Required Env Variables
```
DATABASE_URL=mysql://...
```

### Studio Config (StudioConfig table)
- `cancelHoursLimit`: Hours before slot to allow free cancellation (default 2)

### Constants (shared package)
- `SLOT_GENERATION_DAYS`: 14 (days ahead to generate)
- `DEFAULT_SLOT_CAPACITY`: 1 (private lessons)
- `DEFAULT_CANCEL_HOURS_LIMIT`: 2

---

## 15. Performance Considerations

### Database Indexes
- `TimeSlot(date)` - for date range queries
- `TimeSlot(status)` - for status filtering
- `Booking(userId)` - for user's bookings
- `Booking(status)` - for status filtering

### Batch Operations
- Slot generation uses `createMany()` for efficiency
- Expiration checks use `updateMany()` instead of loops

### Transaction Isolation
- All booking/cancellation operations wrapped in transactions
- Prevents race conditions on bookedCount and remainingTimes

---

## 16. Security Notes

### Authorization
- JWT guard on all endpoints
- RolesGuard for admin endpoints (only ADMIN role)
- Users can only modify their own bookings/memberships

### Validation
- All DTOs have class-validator decorators
- UUID validation on foreign keys
- Date string validation (YYYY-MM-DD format)

### Data Integrity
- Unique constraint on `[userId, timeSlotId]` prevents duplicate bookings
- Unique constraint on `[date, startTime, endTime]` prevents duplicate slots
- Foreign key constraints on relations

---

## 17. Future Enhancement Ideas

1. **Overbooking Buffer:**
   - Allow configurable overbooking ratio (e.g., 110% capacity)

2. **Waitlist Support:**
   - Add BookingStatus.WAITLISTED
   - Auto-promote when slot opens

3. **Recurring Cancellation:**
   - Cancel all future bookings of a series
   - Batch refunds

4. **Slot Availability Notifications:**
   - Alert users when slots available
   - Implement notification queue

5. **Dynamic Pricing:**
   - Peak vs off-peak pricing
   - Last-minute discounts

---

## Summary

This time-slot and scheduling system is well-architected with:

✅ **Idempotent slot generation** - Safe to re-run
✅ **Atomic transactions** - ACID compliance for bookings
✅ **Automatic maintenance** - 4 daily cron jobs
✅ **Flexible membership types** - TIMES, DURATION, TRIAL
✅ **Refund policy** - Configurable cancellation window
✅ **ISO weekday standard** - Proper international support
✅ **Comprehensive validation** - DTOs with decorators
✅ **Role-based access** - Admin vs member endpoints

The system handles:
- Auto-generating 14 days of slots nightly
- Accepting bookings with capacity management
- Canceling with conditional refunds
- Expiring memberships and marking past bookings
- All with transactional integrity and concurrent safety.