apps/backend/src/lib/slot-validator.ts

@@ -0,0 +1,34 @@
+function toMinutes(value: string): number {
+  const [hours, minutes] = value.split(':').map((part) => Number(part));
+  return hours * 60 + minutes;
+}
+
+export function isSlotInPast(
+  bookingDate: Date,
+  startTime: string,
+  slotDurationMinutes: number,
+  now?: Date
+): boolean {
+  const currentTime = now ?? new Date();
+
+  const todayStart = new Date(
+    currentTime.getFullYear(),
+    currentTime.getMonth(),
+    currentTime.getDate()
+  );
+
+  const bookingLocalStart = new Date(
+    bookingDate.getUTCFullYear(),
+    bookingDate.getUTCMonth(),
+    bookingDate.getUTCDate()
+  );
+
+  if (bookingLocalStart < todayStart) return true;
+  if (bookingLocalStart > todayStart) return false;
+
+  const currentMinutes = currentTime.getHours() * 60 + currentTime.getMinutes();
+  const slotStartMinutes = toMinutes(startTime);
+  const elapsed = currentMinutes - slotStartMinutes;
+
+  return elapsed > slotDurationMinutes / 2;
+}

apps/backend/src/modules/admin-booking/services/admin-booking.service.ts

@@ -1,6 +1,7 @@
 import { randomInt } from 'node:crypto';
 import { CourtBookingStatus } from '@/generated/prisma/enums';
 import { db } from '@/lib/prisma';
+import { isSlotInPast } from '@/lib/slot-validator';
 import { evaluatePlanUsage, parsePlanRules } from '@/modules/plan/services/plan-rules.service';
 import type { DayOfWeek } from '@repo/api-contract';
 import type {
@@ -361,6 +362,10 @@ export async function createAdminBooking(
     );
   }
 
+  if (isSlotInPast(bookingDate, input.startTime, court.slotDurationMinutes)) {
+    throw new AdminBookingServiceError('No se pueden crear reservas en el pasado.', 400);
+  }
+
   for (let attempt = 0; attempt < 5; attempt += 1) {
     try {
       const booking = await db.$transaction(async (tx) => {

apps/backend/src/modules/public-booking/services/public-booking.service.ts

@@ -1,5 +1,6 @@
 import { randomInt } from 'node:crypto';
 import { db } from '@/lib/prisma';
+import { isSlotInPast } from '@/lib/slot-validator';
 import { evaluatePlanUsage, parsePlanRules } from '@/modules/plan/services/plan-rules.service';
 import type {
   CancelPublicBookingInput,
@@ -574,6 +575,10 @@ export async function createPublicBooking(complexSlug: string, input: CreatePubl
     );
   }
 
+  if (isSlotInPast(bookingDate, input.startTime, selectedCourt.slotDurationMinutes)) {
+    throw new PublicBookingServiceError('No se pueden crear reservas en el pasado.', 400);
+  }
+
   for (let attempt = 0; attempt < 5; attempt += 1) {
     try {
       const booking = await db.$transaction(async (tx) => {

apps/backend/test/public-booking/slot-validator.test.ts

@@ -0,0 +1,90 @@
+import { expect, test } from 'bun:test';
+
+import { isSlotInPast } from '@/lib/slot-validator';
+
+/**
+ * Helper to create a bookingDate like parseIsoDate does (UTC midnight).
+ */
+function bookingDate(year: number, month: number, day: number): Date {
+  return new Date(Date.UTC(year, month - 1, day));
+}
+
+/**
+ * Helper to create a "now" date at a specific local time.
+ * Using local date constructor guarantees the date parts
+ * (getFullYear, getMonth, getDate) match the arguments
+ * regardless of the test runner's timezone.
+ */
+function localDate(year: number, month: number, day: number, hours: number, minutes: number): Date {
+  return new Date(year, month - 1, day, hours, minutes, 0, 0);
+}
+
+test('future date — always allowed', () => {
+  const future = bookingDate(2027, 6, 10); // 2027-06-10
+  const now = localDate(2026, 6, 8, 12, 0); // 2026-06-08 12:00
+
+  expect(isSlotInPast(future, '10:00', 60, now)).toBe(false);
+});
+
+test('past date — rejected', () => {
+  const past = bookingDate(2025, 6, 8); // 2025-06-08
+  const now = localDate(2026, 6, 8, 12, 0); // 2026-06-08 12:00
+
+  expect(isSlotInPast(past, '10:00', 60, now)).toBe(true);
+});
+
+test('today, slot not started yet — allowed', () => {
+  const today = bookingDate(2026, 6, 8); // 2026-06-08
+  const now = localDate(2026, 6, 8, 9, 0); // 09:00, slot empieza a las 10:00
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(false);
+});
+
+test('today, slot in progress less than half elapsed — allowed', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 10, 10); // 10:10, slot 10:00-11:00 (60 min), 10 min elapsed
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(false);
+});
+
+test('today, slot in progress more than half elapsed — rejected', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 10, 40); // 10:40, slot 10:00-11:00 (60 min), 40 min elapsed
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(true);
+});
+
+test('today, slot already ended — rejected', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 11, 1); // 11:01, slot 10:00-11:00 terminó
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(true);
+});
+
+test('today, exactly half elapsed — allowed (inclusive boundary)', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 10, 30); // 10:30, slot 10:00-11:00 (60 min), exactamente 30 min
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(false);
+});
+
+test('today, slot starts exactly now — allowed', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 10, 0); // 10:00 exacto
+
+  expect(isSlotInPast(today, '10:00', 60, now)).toBe(false);
+});
+
+test('90 min slot with 10 min elapsed — allowed', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 12, 10); // 12:10, slot 12:00-13:30, 10/90 elapsed
+
+  expect(isSlotInPast(today, '12:00', 90, now)).toBe(false);
+});
+
+test('90 min slot with 50 min elapsed — rejected', () => {
+  const today = bookingDate(2026, 6, 8);
+  const now = localDate(2026, 6, 8, 12, 50); // 12:50, slot 12:00-13:30, 50/90 elapsed
+
+  expect(isSlotInPast(today, '12:00', 90, now)).toBe(true);
+});