September 2017 Update

Task/Find-the-last-Sunday-of-each-month/JavaScript/find-the-last-sunday-of-each-month-3.js

@@ -0,0 +1,55 @@
+(() => {
+    'use strict'
+
+    // lastWeekDaysOfYear :: Int -> Int -> [Date]
+    const lastWeekDaysOfYear = (iWeekDay, y) => [
+            31,
+            0 === y % 4 && 0 !== y % 100 || 0 === y % 400 ? 29 : 28,
+            31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+        ]
+        .map((d, m) =>
+            new Date(Date.UTC(
+                y, m, d - ((new Date(Date.UTC(y, m, d))
+                    .getDay() + (7 - iWeekDay)) % 7))));
+
+    const days = {
+        sunday: 0,
+        monday: 1,
+        tuesday: 2,
+        wednesday: 3,
+        thursday: 4,
+        friday: 5,
+        saturday: 6
+    };
+
+    // GENERIC FUNCTIONS
+
+    // curry :: ((a, b) -> c) -> a -> b -> c
+    const curry = f => a => b => f(a, b);
+
+    // isoDateString :: Date -> String
+    const isoDateString = dte =>
+        dte.toISOString()
+        .substr(0, 10);
+
+    // range :: Int -> Int -> [Int]
+    const range = (m, n) =>
+        Array.from({
+            length: Math.floor(n - m) + 1
+        }, (_, i) => m + i);
+
+    // transpose :: [[a]] -> [[a]]
+    const transpose = lst =>
+        lst[0].map((_, iCol) =>
+            lst.map(row => row[iCol]));
+
+    // TEST
+    return transpose(
+            range(2015, 2019)
+            .map(curry(lastWeekDaysOfYear)(days.sunday))
+        )
+        .map(row => row
+            .map(isoDateString)
+            .join('\t'))
+        .join('\n');
+})();