From 0573b777d837ba6373057a8e33decb5e089d81dd Mon Sep 17 00:00:00 2001
From: Silei <silei@stanford.edu>
Date: Fri, 5 Mar 2021 14:43:08 -0800
Subject: [PATCH] Implement WeekDayDate: turn weekday into actual date

---
 lib/utils/date_utils.ts | 25 +++++++++++++++++++++----
 test/test_date_utils.js | 14 +++++++++++++-
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/lib/utils/date_utils.ts b/lib/utils/date_utils.ts
index 0d5c8715..bf4ee3c5 100644
--- a/lib/utils/date_utils.ts
+++ b/lib/utils/date_utils.ts
@@ -20,7 +20,7 @@
 
 import assert from 'assert';
 
-import { DateEdge, DatePiece, WeekDayDate, AbsoluteTime } from '../ast/values';
+import { DateEdge, DatePiece, WeekDayDate, AbsoluteTime, WeekDay } from '../ast';
 
 const TIME_UNITS = ['ms', 's', 'min', 'h', 'day', 'week', 'mon', 'year'];
 const SET_ZERO : Array<(d : Date) => void> = [(d) => {},
@@ -112,10 +112,27 @@ function createDatePiece(year : number|null, month : number|null, day : number|n
     return date;
 }
 
-function createWeekDayDate(weekday : string, time : AbsoluteTime|null) {
-    const date = new Date;
+function weekdayToNumber(weekday : WeekDay) : number {
+    switch (weekday) {
+        case "monday": return 1;
+        case "tuesday": return 2;
+        case "wednesday": return 3;
+        case "thursday": return 4;
+        case "friday": return 5;
+        case "saturday": return 6;
+        case "sunday": return 7;
+    }
+    throw new Error(`Invalid weekday: ${weekday}`);
+}
 
-    // FIXME: implement this
+function createWeekDayDate(weekday : WeekDay, time : AbsoluteTime|null) {
+    const date = new Date;
+    const weekdayNumber = weekdayToNumber(weekday);
+    const diff = (weekdayNumber - date.getDay()) % 7;
+    // get the date of next specified weekday, today excluded
+    date.setDate(date.getDate() + (diff > 0 ? diff : diff + 7));
+    if (time)
+        date.setHours(time.hour, time.minute, time.second, 0);
     return date;
 }
 
diff --git a/test/test_date_utils.js b/test/test_date_utils.js
index 26e6cc7e..ac9c47b8 100644
--- a/test/test_date_utils.js
+++ b/test/test_date_utils.js
@@ -18,7 +18,7 @@
 
 import assert from 'assert';
 
-import { DateEdge, DatePiece, Time } from '../lib/ast';
+import { DateEdge, DatePiece, Time, WeekDayDate } from '../lib/ast';
 import { parseDate, normalizeDate } from '../lib/utils/date_utils';
 
 function test(value, expected) {
@@ -111,6 +111,18 @@ export default function main() {
     eleven_thirty.setSeconds(0);
     eleven_thirty.setMilliseconds(0);
     test(new DatePiece(null, null, 25, new Time.Absolute(11, 30, 0)), eleven_thirty);
+
+    const weekdays = ['sunday', 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday'];
+    for (let j = 0; j < 7; j++) {
+        const date = new Date;
+        date.setHours(12, 0, 0, 0);
+        const weekday = weekdays[j];
+        const nextweekday = date;
+        nextweekday.setDate(nextweekday.getDate() + 1);
+        while (nextweekday.getDay() !== j)
+            nextweekday.setDate(nextweekday.getDate() + 1);
+        test(new WeekDayDate(weekday, new Time.Absolute(12, 0, 0)), nextweekday);
+    }
 }
 if (!module.parent)
     main();