backend-service/internal/repositories/schedule_repository.go

package repositories

import (
	"errors"
	"fmt"
	"time"

	"attune-heart-therapy/internal/models"

	"gorm.io/gorm"
)

// scheduleRepository implements the ScheduleRepository interface
type scheduleRepository struct {
	db *gorm.DB
}

// NewScheduleRepository creates a new instance of ScheduleRepository
func NewScheduleRepository(db *gorm.DB) ScheduleRepository {
	return &scheduleRepository{
		db: db,
	}
}

// Create creates a new schedule slot in the database
func (r *scheduleRepository) Create(schedule *models.Schedule) error {
	if schedule == nil {
		return errors.New("schedule cannot be nil")
	}

	// Check for overlapping schedules
	var count int64
	if err := r.db.Model(&models.Schedule{}).
		Where("((start_time <= ? AND end_time > ?) OR (start_time < ? AND end_time >= ?)) AND is_available = ?",
			schedule.StartTime, schedule.StartTime, schedule.EndTime, schedule.EndTime, true).
		Count(&count).Error; err != nil {
		return fmt.Errorf("failed to check for overlapping schedules: %w", err)
	}

	if count > 0 {
		return errors.New("schedule slot overlaps with existing available slot")
	}

	if err := r.db.Create(schedule).Error; err != nil {
		return fmt.Errorf("failed to create schedule: %w", err)
	}

	return nil
}

// GetAvailable retrieves all available schedule slots for a specific date
func (r *scheduleRepository) GetAvailable(date time.Time) ([]models.Schedule, error) {
	var schedules []models.Schedule

	// Get the start and end of the day
	startOfDay := time.Date(date.Year(), date.Month(), date.Day(), 0, 0, 0, 0, date.Location())
	endOfDay := startOfDay.Add(24 * time.Hour)

	if err := r.db.Where("is_available = ? AND start_time >= ? AND start_time < ? AND booked_count < max_bookings",
		true, startOfDay, endOfDay).
		Order("start_time ASC").
		Find(&schedules).Error; err != nil {
		return nil, fmt.Errorf("failed to get available schedules for date %s: %w", date.Format("2006-01-02"), err)
	}

	// Filter out slots that are in the past
	now := time.Now()
	var availableSchedules []models.Schedule
	for _, schedule := range schedules {
		if schedule.StartTime.After(now) && schedule.IsAvailableForBooking() {
			availableSchedules = append(availableSchedules, schedule)
		}
	}

	return availableSchedules, nil
}

// Update updates an existing schedule slot in the database
func (r *scheduleRepository) Update(schedule *models.Schedule) error {
	if schedule == nil {
		return errors.New("schedule cannot be nil")
	}

	if schedule.ID == 0 {
		return errors.New("schedule ID is required for update")
	}

	// Check if schedule exists
	var existingSchedule models.Schedule
	if err := r.db.First(&existingSchedule, schedule.ID).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return fmt.Errorf("schedule with ID %d not found", schedule.ID)
		}
		return fmt.Errorf("failed to check schedule existence: %w", err)
	}

	// If updating time slots, check for overlaps (excluding current schedule)
	if schedule.StartTime != existingSchedule.StartTime || schedule.EndTime != existingSchedule.EndTime {
		var count int64
		if err := r.db.Model(&models.Schedule{}).
			Where("id != ? AND ((start_time <= ? AND end_time > ?) OR (start_time < ? AND end_time >= ?)) AND is_available = ?",
				schedule.ID, schedule.StartTime, schedule.StartTime, schedule.EndTime, schedule.EndTime, true).
			Count(&count).Error; err != nil {
			return fmt.Errorf("failed to check for overlapping schedules: %w", err)
		}

		if count > 0 {
			return errors.New("updated schedule slot would overlap with existing available slot")
		}
	}

	// Update the schedule
	if err := r.db.Save(schedule).Error; err != nil {
		return fmt.Errorf("failed to update schedule: %w", err)
	}

	return nil
}

// GetByID retrieves a schedule slot by its ID
func (r *scheduleRepository) GetByID(id uint) (*models.Schedule, error) {
	if id == 0 {
		return nil, errors.New("invalid schedule ID")
	}

	var schedule models.Schedule
	if err := r.db.First(&schedule, id).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, fmt.Errorf("schedule with ID %d not found", id)
		}
		return nil, fmt.Errorf("failed to get schedule by ID: %w", err)
	}

	return &schedule, nil
}

// IncrementBookedCount atomically increments the booked count for a schedule slot
// This method handles concurrent booking scenarios
func (r *scheduleRepository) IncrementBookedCount(scheduleID uint) error {
	if scheduleID == 0 {
		return errors.New("invalid schedule ID")
	}

	// Use a transaction to ensure atomicity
	return r.db.Transaction(func(tx *gorm.DB) error {
		var schedule models.Schedule

		// Lock the row for update to prevent race conditions
		if err := tx.Set("gorm:query_option", "FOR UPDATE").First(&schedule, scheduleID).Error; err != nil {
			if errors.Is(err, gorm.ErrRecordNotFound) {
				return fmt.Errorf("schedule with ID %d not found", scheduleID)
			}
			return fmt.Errorf("failed to get schedule for update: %w", err)
		}

		// Check if slot is still available
		if !schedule.IsAvailableForBooking() {
			return errors.New("schedule slot is no longer available for booking")
		}

		// Increment booked count
		schedule.BookedCount++

		if err := tx.Save(&schedule).Error; err != nil {
			return fmt.Errorf("failed to increment booked count: %w", err)
		}

		return nil
	})
}

// DecrementBookedCount atomically decrements the booked count for a schedule slot
// This method is used when a booking is cancelled
func (r *scheduleRepository) DecrementBookedCount(scheduleID uint) error {
	if scheduleID == 0 {
		return errors.New("invalid schedule ID")
	}

	// Use a transaction to ensure atomicity
	return r.db.Transaction(func(tx *gorm.DB) error {
		var schedule models.Schedule

		// Lock the row for update to prevent race conditions
		if err := tx.Set("gorm:query_option", "FOR UPDATE").First(&schedule, scheduleID).Error; err != nil {
			if errors.Is(err, gorm.ErrRecordNotFound) {
				return fmt.Errorf("schedule with ID %d not found", scheduleID)
			}
			return fmt.Errorf("failed to get schedule for update: %w", err)
		}

		// Check if booked count can be decremented
		if schedule.BookedCount <= 0 {
			return errors.New("booked count is already zero")
		}

		// Decrement booked count
		schedule.BookedCount--

		if err := tx.Save(&schedule).Error; err != nil {
			return fmt.Errorf("failed to decrement booked count: %w", err)
		}

		return nil
	})
}