95 Workday - introduce some comments, and methods; improve some variable names; spotted a bug

95_Weekday/javascript/weekday.js

@@ -46,7 +46,33 @@ function fnb(arg) {
     return Math.floor(arg / 7);
 }
 
-const t = [, 0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5];
+// in a non-leap year the day of the week for the first of each month moves by the following amounts.
+const MONTHLY_DAY_OF_WEEK_OFFSETS = [0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5];
+
+/**
+ * Reads a date, and extracts the date information.
+ * This expects date parts to be comma separated, using US date ordering,
+ * i.e. Month,Day,Year.
+ * @returns {Promise<[number,number,number]>} [year, month, dayOfMonth]
+ */
+async function readDateElements() {
+    let dateString = await input();
+    const month = parseInt(dateString);
+    const dayOfMonth = parseInt(dateString.substr(dateString.indexOf(",") + 1));
+    const year = parseInt(dateString.substr(dateString.lastIndexOf(",") + 1));
+    return [year, month, dayOfMonth];
+}
+
+/**
+ * Returns a US formatted date, i.e. Month/Day/Year.
+ * @param year
+ * @param month
+ * @param dayOfMonth
+ * @returns {string}
+ */
+function getFormattedDate(year, month, dayOfMonth) {
+    return month + "/" + dayOfMonth + "/" + year;
+}
 
 let k5;
 let k6;
@@ -73,6 +99,46 @@ function time_spent(f, a8)
     print(i5 + "\t" + i6 + "\t" + i7 + "\n");
 }
 
+function getDayOfWeek(dobYear, dobMonth, dobDayOfMonth) {
+    const i1 = Math.floor((dobYear - 1500) / 100);
+    let a = i1 * 5 + (i1 + 3) / 4;
+    const i2 = Math.floor(a - fnb(a) * 7);
+    const y2 = Math.floor(dobYear / 100);
+    const y3 = Math.floor(dobYear - y2 * 100);
+    a = y3 / 4 + y3 + dobDayOfMonth + MONTHLY_DAY_OF_WEEK_OFFSETS[dobMonth-1] + i2;
+    let dayOfWeek = Math.floor(a - fnb(a) * 7) + 1;
+    if (dobMonth <= 2) {
+        if (y3 !== 0) {
+            t1 = Math.floor(dobYear - fna(dobYear) * 4);
+        } else {
+            a = i1 - 1;
+            t1 = Math.floor(a - fna(a) * 4);
+        }
+        if (t1 === 0) {
+            if (dayOfWeek === 0) {
+                dayOfWeek = 6;
+            }
+            dayOfWeek--;
+        }
+    }
+    if (dayOfWeek === 0) {
+        dayOfWeek = 7;
+    }
+    return dayOfWeek;
+}
+
+/**
+ * The following performs a special hash on the day parts which guarantees
+ * that different days will return different numbers, and the numbers returned are in ordered.
+ * @param todayYear
+ * @param todayMonth
+ * @param todayDayOfMonth
+ * @returns {*}
+ */
+function getNormalisedDay(todayYear, todayMonth, todayDayOfMonth) {
+    return (todayYear * 12 + todayMonth) * 31 + todayDayOfMonth;
+}
+
 // Main control section
 async function main()
 {
@@ -85,59 +151,38 @@ async function main()
     print("GIVES FACTS ABOUT A DATE OF INTEREST TO YOU.\n");
     print("\n");
     print("ENTER TODAY'S DATE IN THE FORM: 3,24,1979  ");
-    let str = await input();
+    const [todayYear, todayMonth, todayDayOfMonth] = await readDateElements();
-    const m1 = parseInt(str);
-    const d1 = parseInt(str.substr(str.indexOf(",") + 1));
-    const y1 = parseInt(str.substr(str.lastIndexOf(",") + 1));
     // This program determines the day of the week
     //  for a date after 1582
     print("ENTER DAY OF BIRTH (OR OTHER DAY OF INTEREST)");
-    str = await input();
+    const [dobYear, dobMonth, dobDayOfMonth] = await readDateElements();
-    const m = parseInt(str);
-    const d = parseInt(str.substr(str.indexOf(",") + 1));
-    const y = parseInt(str.substr(str.lastIndexOf(",") + 1));
     print("\n");
-    const i1 = Math.floor((y - 1500) / 100);
     // Test for date before current calendar.
-    if (y - 1582 < 0) {
+    // Note: this test is unreliable - the Gregorian calendar was introduced on Friday 15 October 1582
+    // and the weekday algorithm fails for dates prior to that
+    if (dobYear - 1582 < 0) {
         print("NOT PREPARED TO GIVE DAY OF WEEK PRIOR TO MDLXXXII.\n");
     } else {
-        let a = i1 * 5 + (i1 + 3) / 4;
+        const dayOfWeek = getDayOfWeek(dobYear, dobMonth, dobDayOfMonth);
-        const i2 = Math.floor(a - fnb(a) * 7);
+
-        const y2 = Math.floor(y / 100);
+        const normalisedToday = getNormalisedDay(todayYear, todayMonth, todayDayOfMonth);
-        const y3 = Math.floor(y - y2 * 100);
+        const normalisedDob = getNormalisedDay(dobYear, dobMonth, dobDayOfMonth);
-        a = y3 / 4 + y3 + d + t[m] + i2;
+
-        let b = Math.floor(a - fnb(a) * 7) + 1;
+        if (normalisedToday < normalisedDob) {
-        if (m <= 2) {
+            print(getFormattedDate(dobYear, dobMonth, dobDayOfMonth) + " WILL BE A ");
-            if (y3 !== 0) {
+        } else if (normalisedToday === normalisedDob) {
-                t1 = Math.floor(y - fna(y) * 4);
+            print(getFormattedDate(dobYear, dobMonth, dobDayOfMonth) + " IS A ");
-            } else {
-                a = i1 - 1;
-                t1 = Math.floor(a - fna(a) * 4);
-            }
-            if (t1 === 0) {
-                if (b === 0)
-                    b = 6;
-                b--;
-            }
-        }
-        if (b === 0)
-            b = 7;
-        if ((y1 * 12 + m1) * 31 + d1 < (y * 12 + m) * 31 + d) {
-            print(m + "/" + d + "/" + y + " WILL BE A ");
-        } else if ((y1 * 12 + m1) * 31 + d1 === (y * 12 + m) * 31 + d) {
-            print(m + "/" + d + "/" + y + " IS A ");
         } else {
-            print(m + "/" + d + "/" + y + " WAS A ");
+            print(getFormattedDate(dobYear, dobMonth, dobDayOfMonth) + " WAS A ");
         }
-        switch (b) {
+        switch (dayOfWeek) {
             case 1: print("SUNDAY.\n"); break;
             case 2: print("MONDAY.\n"); break;
             case 3: print("TUESDAY.\n"); break;
             case 4: print("WEDNESDAY.\n"); break;
             case 5: print("THURSDAY.\n"); break;
             case 6:
-                if (d === 13) {
+                if (dobDayOfMonth === 13) {
                     print("FRIDAY THE THIRTEENTH---BEWARE!\n");
                 } else {
                     print("FRIDAY.\n");
@@ -145,31 +190,32 @@ async function main()
                 break;
             case 7: print("SATURDAY.\n"); break;
         }
-        if ((y1 * 12 + m1) * 31 + d1 !== (y * 12 + m) * 31 + d) {
+        if (normalisedToday !== normalisedDob) {
-            let i5 = y1 - y;
+            let yearsBetweenDates = todayYear - dobYear;
             print("\n");
-            let i6 = m1 - m;
+            let monthsBetweenDates = todayMonth - dobMonth;
-            let i7 = d1 - d;
+            let daysBetweenDates = todayDayOfMonth - dobDayOfMonth;
-            if (i7 < 0) {
+            if (daysBetweenDates < 0) {
-                i6--;
+                monthsBetweenDates--;
-                i7 += 30;
+                daysBetweenDates += 30;
             }
-            if (i6 < 0) {
+            if (monthsBetweenDates < 0) {
-                i5--;
+                yearsBetweenDates--;
-                i6 += 12;
+                monthsBetweenDates += 12;
             }
-            if (i5 >= 0) {
+            if (yearsBetweenDates >= 0) {
-                if (i7 === 0 && i6 === 0)
+                if (daysBetweenDates === 0 && monthsBetweenDates === 0) {
                     print("***HAPPY BIRTHDAY***\n");
+                }
                 print("                        \tYEARS\tMONTHS\tDAYS\n");
                 print("                        \t-----\t------\t----\n");
-                print("YOUR AGE (IF BIRTHDATE) \t" + i5 + "\t" + i6 + "\t" + i7 + "\n");
+                print("YOUR AGE (IF BIRTHDATE) \t" + yearsBetweenDates + "\t" + monthsBetweenDates + "\t" + daysBetweenDates + "\n");
-                const a8 = (i5 * 365) + (i6 * 30) + i7 + Math.floor(i6 / 2);
+                const a8 = (yearsBetweenDates * 365) + (monthsBetweenDates * 30) + daysBetweenDates + Math.floor(monthsBetweenDates / 2);
-                k5 = i5;
+                k5 = yearsBetweenDates;
-                k6 = i6;
+                k6 = monthsBetweenDates;
-                k7 = i7;
+                k7 = daysBetweenDates;
                 // Calculate retirement date.
-                const e = y + 65;
+                const e = dobYear + 65;
                 // Calculate time spent in the following functions.
                 print("YOU HAVE SLEPT \t\t\t");
                 time_spent(0.35, a8);