Fixes that sometimes last shown slot was unavailable (#7804)

* fix unavailable slots + add relevant test

* code clean up

---------

Co-authored-by: CarinaWolli <wollencarina@gmail.com>

apps/web/test/lib/slots.test.ts

@@ -112,4 +112,25 @@ describe("Tests the slot logic", () => {
       })
     ).toHaveLength(11);
   });
+
+  it("shows correct time slots for 20 minutes long events with working hours that do not end at a full hour ", async () => {
+    // 72 20-minutes events in a 24h day
+    expect(
+      getSlots({
+        inviteeDate: dayjs.utc().add(1, "day"),
+        frequency: 20,
+        minimumBookingNotice: 0,
+        workingHours: [
+          {
+            userId: 1,
+            days: Array.from(Array(7).keys()),
+            startTime: MINUTES_DAY_START,
+            endTime: MINUTES_DAY_END - 14, // 23:45
+          },
+        ],
+        eventLength: 20,
+        organizerTimeZone: "America/Toronto",
+      })
+    ).toHaveLength(71);
+  });
 });

packages/lib/slots.ts

@@ -87,7 +87,7 @@ function buildSlots({
     for (let slotStart = boundaryStart; slotStart < boundaryEnd; slotStart += frequency) {
       computedLocalAvailability.forEach((item) => {
         // TODO: This logic does not allow for past-midnight bookings.
-        if (slotStart < item.startTime || slotStart > item.endTime + 15 - eventLength) {
+        if (slotStart < item.startTime || slotStart > item.endTime + 1 - eventLength) {
           return;
         }
         slotsTimeFrameAvailable[slotStart.toString()] = {