perf: Optimize getSlots function to handle large dateRanges arrays efficiently (#21371)

* perf: Optimize getSlots function to handle large dateRanges arrays efficiently

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* Update packages/lib/slots.test.ts

* test: Update performance test to use 2000 date ranges

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

* test: Update performance test to process 2000 date ranges across multiple days

Co-Authored-By: keith@cal.com <keithwillcode@gmail.com>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: keith@cal.com <keithwillcode@gmail.com>

packages/lib/slots.test.ts

@@ -350,3 +350,52 @@ describe("Tests the slot logic with custom env variable", () => {
     ).toHaveLength(11);
   });
 });
+
+describe("Tests the slots function performance", () => {
+  it("handles hundreds of date ranges efficiently", async () => {
+    const startTime = process.hrtime();
+
+    const startDay = dayjs.utc().add(1, "day").startOf("day");
+    const dateRanges: DateRange[] = [];
+
+    for (let day = 0; day < 7; day++) {
+      const currentDay = startDay.add(day, "day");
+
+      for (let hour = 0; hour < 24; hour++) {
+        for (let minute = 0; minute < 60; minute += 5) {
+          if (dateRanges.length >= 2000) break;
+
+          dateRanges.push({
+            start: currentDay.hour(hour).minute(minute),
+            end: currentDay
+              .hour(hour)
+              .minute(minute + 4)
+              .second(59),
+          });
+        }
+        if (dateRanges.length >= 2000) break;
+      }
+      if (dateRanges.length >= 2000) break;
+    }
+
+    const result = getSlots({
+      inviteeDate: startDay,
+      frequency: 5,
+      minimumBookingNotice: 0,
+      dateRanges: dateRanges,
+      eventLength: 5,
+      offsetStart: 0,
+    });
+
+    expect(result.length).toBeGreaterThan(0);
+
+    const endTime = process.hrtime(startTime);
+    const executionTimeInMs = endTime[0] * 1000 + endTime[1] / 1000000;
+
+    expect(executionTimeInMs).toBeLessThan(2000); // less than 2 seconds for 2000 date ranges
+
+    console.log(
+      `Performance test completed in ${executionTimeInMs}ms with ${result.length} slots generated from ${dateRanges.length} date ranges`
+    );
+  });
+});

packages/lib/slots.ts

@@ -40,6 +40,9 @@ function buildSlotsWithDateRanges({
   frequency = minimumOfOne(frequency);
   eventLength = minimumOfOne(eventLength);
   offsetStart = offsetStart ? minimumOfOne(offsetStart) : 0;
+
+  const orderedDateRanges = dateRanges.sort((a, b) => a.start.valueOf() - b.start.valueOf());
+
   // there can only ever be one slot at a given start time, and based on duration also only a single length.
   const slots = new Map<
     string,
@@ -66,7 +69,8 @@ function buildSlotsWithDateRanges({
 
   const startTimeWithMinNotice = dayjs.utc().add(minimumBookingNotice, "minute");
 
-  const orderedDateRanges = dateRanges.sort((a, b) => a.start.valueOf() - b.start.valueOf());
+  const slotBoundaries = new Map<string, true>();
+
   orderedDateRanges.forEach((range) => {
     const dateYYYYMMDD = range.start.format("YYYY-MM-DD");
 
@@ -81,32 +85,41 @@ function buildSlotsWithDateRanges({
 
     slotStartTime = slotStartTime.add(offsetStart ?? 0, "minutes").tz(timeZone);
 
-    // if the slotStartTime is between an existing slot, we need to adjust to the begin of the existing slot
-    // but that adjusted startTime must be legal.
-    const iterator = slots.keys();
-    let result = iterator.next();
+    // Find the nearest appropriate slot boundary if this time falls within an existing slot
+    const slotBoundariesArray = Array.from(slotBoundaries.keys()).map((t) => dayjs(t));
+    if (slotBoundariesArray.length > 0) {
+      slotBoundariesArray.sort((a, b) => a.valueOf() - b.valueOf());
 
-    while (!result.done) {
-      const utcResultValue = dayjs.utc(result.value);
-      // if the slotStartTime is between an existing slot, we need to adjust to the begin of the existing slot
-      if (
-        utcResultValue.isBefore(slotStartTime) &&
-        utcResultValue.add(frequency + (offsetStart ?? 0), "minutes").isAfter(slotStartTime)
-      ) {
-        // however, the slot can now be before the start of this date range.
-        if (!utcResultValue.isBefore(range.start)) {
-          // it is between, if possible floor down to the start of the existing slot
-          slotStartTime = utcResultValue;
-        } else {
-          // if not possible to floor, we need to ceil up to the next slot.
-          slotStartTime = utcResultValue.add(frequency + (offsetStart ?? 0), "minutes");
+      let prevBoundary = null;
+      for (let i = slotBoundariesArray.length - 1; i >= 0; i--) {
+        if (slotBoundariesArray[i].isBefore(slotStartTime)) {
+          prevBoundary = slotBoundariesArray[i];
+          break;
+        }
+      }
+
+      if (prevBoundary) {
+        const prevBoundaryEnd = prevBoundary.add(frequency + (offsetStart ?? 0), "minutes");
+        if (prevBoundaryEnd.isAfter(slotStartTime)) {
+          if (!prevBoundary.isBefore(range.start)) {
+            slotStartTime = prevBoundary;
+          } else {
+            slotStartTime = prevBoundaryEnd;
+          }
+          slotStartTime = slotStartTime.tz(timeZone);
         }
-        // and then convert to the correct timezone - UTC mode is just for performance.
-        slotStartTime = slotStartTime.tz(timeZone);
       }
-      result = iterator.next();
     }
+
     while (!slotStartTime.add(eventLength, "minutes").subtract(1, "second").utc().isAfter(range.end)) {
+      const slotKey = slotStartTime.toISOString();
+      if (slots.has(slotKey)) {
+        slotStartTime = slotStartTime.add(frequency + (offsetStart ?? 0), "minutes");
+        continue;
+      }
+
+      slotBoundaries.set(slotKey, true);
+
       const dateOutOfOfficeExists = datesOutOfOffice?.[dateYYYYMMDD];
       let slotData: {
         time: Dayjs;
@@ -133,7 +146,7 @@ function buildSlotsWithDateRanges({
         };
       }
 
-      slots.set(slotData.time.toISOString(), slotData);
+      slots.set(slotKey, slotData);
       slotStartTime = slotStartTime.add(frequency + (offsetStart ?? 0), "minutes");
     }
   });