Add addBusinessDays helper

STATUS.md

@@ -65,7 +65,7 @@
 
 ### Day helpers
 
-- [ ] `addBusinessDays`
+- [x] `addBusinessDays`
 - [x] `addDays`
 - [x] `subDays`
 - [ ] `differenceInBusinessDays`

__tests__/addBusinessDays_test.re

@@ -0,0 +1,56 @@
+open Jest;
+
+open Js.Date;
+
+describe("addBusinessDays", () => {
+  open ExpectJs;
+
+  test("adds 0 business days", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=1., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=1., ());
+
+    date |> ReDate.addBusinessDays(0) |> expect |> toEqual(expectedDate);
+  });
+
+  test("adds 1 business day", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=1., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=2., ());
+
+    date |> ReDate.addBusinessDays(1) |> expect |> toEqual(expectedDate);
+  });
+
+  test("adds 100 business days", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=1., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=4., ~date=20., ());
+
+    date |> ReDate.addBusinessDays(100) |> expect |> toEqual(expectedDate);
+  });
+
+  test("handles negative number", () => {
+    let date = makeWithYMD(~year=2020., ~month=4., ~date=20., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=1., ());
+
+    date |> ReDate.addBusinessDays(-100) |> expect |> toEqual(expectedDate);
+  });
+
+  test("returns Monday when 1 day is added on Friday", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=10., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=13., ());
+
+    date |> ReDate.addBusinessDays(1) |> expect |> toEqual(expectedDate);
+  });
+
+  test("returns Monday when 1 day is added on Saturday", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=11., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=13., ());
+
+    date |> ReDate.addBusinessDays(1) |> expect |> toEqual(expectedDate);
+  });
+
+  test("returns Monday when 1 day is added on Sunday", () => {
+    let date = makeWithYMD(~year=2020., ~month=0., ~date=12., ());
+    let expectedDate = makeWithYMD(~year=2020., ~month=0., ~date=13., ());
+
+    date |> ReDate.addBusinessDays(1) |> expect |> toEqual(expectedDate);
+  });
+});

docs/day.md

@@ -12,6 +12,18 @@ let date = Js.Date.makeWithYMD(~year=2018., ~month=0., ~date=1., ());
 date |> ReDate.addDays(5);
 ```
 
+#### addBusinessDays
+
+> Add the specified number of business days to the given date (excluding weekends).
+
+`let addBusinessDays: (int, Js.Date.t) => Js.Date.t`
+
+```reason
+let date = Js.Date.makeWithYMD(~year=2018., ~month=0., ~date=1., ());
+
+date |> ReDate.addBusinessDays(5);
+```
+
 #### subDays
 
 > Subtract the specified number of days from the given date.

src/ReDate.re

@@ -470,6 +470,19 @@ let isSameHour = (fst, snd) =>
 
 let addDays = Internal.addDays;
 
+let rec addBusinessDays = (days, date) => {
+  let next = days < 0 ? succ : pred;
+  let sign = days < 0 ? (-1) : 1;
+  let date = date |> addDays(sign);
+
+  if (Internal.isWeekend(date)) {
+    date |> addBusinessDays(days);
+  } else {
+    days == 0
+      ? date |> addDays(- sign) : date |> addBusinessDays(days |> next);
+  };
+};
+
 let subDays = (days, date) => date |> addDays(- days);
 
 let startOfDay = Internal.makeDateWithStartOfDayHours;

src/ReDate.rei

@@ -98,6 +98,8 @@ let isSameHour: (Js.Date.t, Js.Date.t) => bool;
 
 /* ——[Day helpers——————————— */
 
+let addBusinessDays: (int, Js.Date.t) => Js.Date.t;
+
 let addDays: (int, Js.Date.t) => Js.Date.t;
 
 let subDays: (int, Js.Date.t) => Js.Date.t;