From 7723f551c80ae18b240a8f258fe6cce0571978a8 Mon Sep 17 00:00:00 2001
From: Varun Patil <varunpatil@ucla.edu>
Date: Sat, 15 Oct 2022 11:00:24 -0700
Subject: [PATCH] scroller: use binary search for moveHoverCursor

---
 src/components/ScrollerManager.vue | 12 +++++-----
 src/mixins/GlobalMixin.ts          |  1 +
 src/services/Utils.ts              | 35 +++++++++++++++++++++++++++++-
 3 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/src/components/ScrollerManager.vue b/src/components/ScrollerManager.vue
index c4cf9385..a1cf194a 100644
--- a/src/components/ScrollerManager.vue
+++ b/src/components/ScrollerManager.vue
@@ -206,7 +206,7 @@ export default class ScrollerManager extends Mixins(GlobalMixin) {
         // Itearte over rows
         for (const row of this.rows) {
             if (row.type === IRowType.HEAD) {
-                if (Object.values(this.TagDayID).includes(row.dayId)) {
+                if (this.TagDayIDValueSet.has(row.dayId)) {
                     // Blank tick
                     this.ticks.push(getTick(row.dayId));
                 } else {
@@ -234,22 +234,20 @@ export default class ScrollerManager extends Mixins(GlobalMixin) {
         this.hoverCursorY = y;
 
         // Get index of previous tick
-        let idx = this.ticks.findIndex(t => t.top >= y);
+        let idx = utils.binarySearch(this.ticks, y, 'top');
         if (idx === 0) {
             // use this tick
-        } else if (idx >= 1) {
+        } else if (idx >= 1 && idx <= this.ticks.length) {
             idx = idx - 1;
-        } else if (idx === -1 && this.ticks.length > 0) {
-            idx = this.ticks.length - 1;
         } else {
             return;
         }
 
         // DayId of current hover
-        const dayId = this.ticks[idx].dayId
+        const dayId = this.ticks[idx]?.dayId
 
         // Special days
-        if (Object.values(this.TagDayID).includes(dayId)) {
+        if (dayId === undefined || this.TagDayIDValueSet.has(dayId)) {
             this.hoverCursorText = "";
             return;
         }
diff --git a/src/mixins/GlobalMixin.ts b/src/mixins/GlobalMixin.ts
index 492108a4..4ce25188 100644
--- a/src/mixins/GlobalMixin.ts
+++ b/src/mixins/GlobalMixin.ts
@@ -9,4 +9,5 @@ export default class GlobalMixin extends Vue {
 
     public readonly c = constants.c;
     public readonly TagDayID = constants.TagDayID;
+    public readonly TagDayIDValueSet = new Set(Object.values(this.TagDayID));
 }
\ No newline at end of file
diff --git a/src/services/Utils.ts b/src/services/Utils.ts
index c27d8833..adb3702e 100644
--- a/src/services/Utils.ts
+++ b/src/services/Utils.ts
@@ -33,7 +33,7 @@ export function getLongDateStr(date: Date, skipYear=false, time=false) {
  * @return {Number}    A 32bit integer
  * @see http://werxltd.com/wp/2010/05/13/javascript-implementation-of-javas-string-hashcode-method/
  */
- export function hashCode(str: string): number {
+export function hashCode(str: string): number {
     let hash = 0;
     for (let i = 0, len = str.length; i < len; i++) {
         let chr = str.charCodeAt(i);
@@ -43,6 +43,39 @@ export function getLongDateStr(date: Date, skipYear=false, time=false) {
     return hash;
 }
 
+/**
+ * Search for elem in a sorted array of objects
+ * If the object is not found, return the index where it should be inserted
+ *
+ * @param arr Array of objects to search
+ * @param elem Element to search for
+ * @param key Key to use for comparison
+ */
+export function binarySearch(arr: any, elem: any, key?: string) {
+    let minIndex = 0;
+    let maxIndex = arr.length - 1;
+    let currentIndex: number;
+    let currentElement: any;
+
+    while (minIndex <= maxIndex) {
+        currentIndex = (minIndex + maxIndex) / 2 | 0;
+        currentElement = key ? arr[currentIndex][key] : arr[currentIndex];
+
+        if (currentElement < elem) {
+            minIndex = currentIndex + 1;
+        }
+        else if (currentElement > elem) {
+            maxIndex = currentIndex - 1;
+        }
+        else {
+            return currentIndex;
+        }
+    }
+
+    return minIndex;
+}
+
+/** Global constants */
 export const constants = {
     c: {
         FLAG_PLACEHOLDER:   1 << 0,