scheduling conflict

Hi, I’m working on a Laravel project for managing physiotherapy treatments for uni. I need to prevent scheduling conflicts, so that the same room, physiotherapist, or patient cannot be booked for overlapping time slots on the same day.

This is a simplified version of my controller code for reference, but i don't understand why it doesn't work correctly:

class TreatmentController extends Controller { // ...existing index method...

public function store(StoreTrattamentiRequest $request)
{
    Gate::authorize('create', Treatment::class);
    DB::beginTransaction();
    $user_id = UserService::getUser()['id'];
    $request->merge(['user_id' => $user_id]);
    try {
        $price = floatval($request->input('prezzo'));
        $paid = floatval($request->input('importo_pagato'));

        // PAID IN FULL
        if ($paid == $price) {
            $status = TreatmentStatus::where('nome', 'Saldato')->firstOrFail();
            $request->merge(['stato_trattamento_id' => $status->id, 'importo_da_pagare' => 0]);
        }

        // NOT PAID
        if ($paid == 0) {
            $status = TreatmentStatus::where('nome', 'Non saldato')->firstOrFail();
            $request->merge(['stato_trattamento_id' => $status->id, 'importo_da_pagare' => $price]);
        }

        // DISCOUNTED OR PARTIALLY PAID
        else {
            $status_id = $request->input('stato_trattamento_id');
            $status = TreatmentStatus::find($status_id);
            $remaining = $status->nome === 'Sconto' ? 0 : ($price - $paid);
            $request->merge(['importo_da_pagare' => $remaining]);
            if (!$status_id) {
                return response()->json([
                    'message' => 'For partial payments, please specify if this is a discount or partial payment.'
                ], 422);
            }
        }

        $patientIds = $this->getPatients($request);

        
        if ($this->conflictRoom($request)) {
            return response()->json(['message' => 'The room is already booked for the selected time slot'], 409);
        }
        if ($this->conflictPhysiotherapist($request)) {
            return response()->json(['message' => 'The physiotherapist is already booked for the selected time slot'], 409);
        }
        if ($this->conflictPatient($patientIds, $request)) {
            return response()->json(['message' => 'The patient is already booked for the selected time slot'], 409);
        }
        if ($this->conflictTime($request)) {
            return response()->json(['message' => 'End time cannot be earlier than start time'], 409);
        }
        // --- END CONCURRENCY ---

        $treatment = Treatment::create($request->all());
        $treatment->patients()->attach($patientIds);
        DB::commit();
    } catch (Throwable $e) {
        DB::rollBack();
        throw $e;
    }
    return response()->json(compact('treatment'));
}

private function getPatients(Request $request): array
{
    $ids = [];
    foreach ($request->input('pazienti') as $patient) {
        $ids[] = $patient['id'];
    }
    return $ids;
}

private function checkConflict(Builder $query, Request $request, $excludeId = null): void
{
    $start = $request->input('ora_inizio');
    $end = $request->input('ora_fine');

    $query->where(function ($subQuery) use ($start, $end) {
        $subQuery->where('ora_inizio', '<', $end)
                 ->where('ora_fine', '>', $start);
    });

    
    if ($excludeId) {
        $query->where('id', '!=', $excludeId);
    }
}

private function conflictRoom(Request $request, $excludeId = null): bool
{
    $date = $request->input('data');
    $roomId = $request->input('stanza_id');
    $query = Treatment::where('data', $date)->where('stanza_id', $roomId);
    $this->checkConflict($query, $request, $excludeId);
    return $query->exists();
}

private function conflictPhysiotherapist(Request $request, $excludeId = null): bool
{
    $date = $request->input('data');
    $physioId = $request->input('fisioterapista_id');
    $query = Treatment::where('data', $date)->where('fisioterapista_id', $physioId);
    $this->checkConflict($query, $request, $excludeId);
    return $query->exists();
}

private function conflictPatient(array $patients, Request $request, $excludeId = null): bool
{
    $date = $request->input('data');
    if ($patients != null) {
        foreach ($patients as $patientId) {
            $query = Treatment::where('data', $date)
                ->whereHas('patients', function ($subQuery) use ($patientId) {
                    $subQuery->where('paziente_id', $patientId);
                });
            $this->checkConflict($query, $request, $excludeId);
            if ($query->exists()) {
                return true;
            }
        }
    }
    return false;
}

private function conflictTime(Request $request): bool
{
    $start = $request->input('ora_inizio');
    $end = $request->input('ora_fine');
    return $start >= $end;
}