From 8b851bfd3c0a072a86ba213dde50af890b2e9316 Mon Sep 17 00:00:00 2001
From: Bauke <me@bauke.xyz>
Date: Wed, 31 May 2023 17:19:57 +0200
Subject: [PATCH] Add the DateWrapper code.

---
 source/date/date.test.ts | 48 ++++++++++++++++++++++++++++
 source/date/date.ts      | 68 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 source/date/date.test.ts
 create mode 100644 source/date/date.ts

diff --git a/source/date/date.test.ts b/source/date/date.test.ts
new file mode 100644
index 0000000..cb051e1
--- /dev/null
+++ b/source/date/date.test.ts
@@ -0,0 +1,48 @@
+// Third-party imports.
+import {setup} from "@holllo/test";
+// First-party imports.
+import {DateWrapper} from "./date.js";
+
+await setup("DateWrapper", async (group) => {
+  group.test("Add Days", async (test) => {
+    const samples = [
+      [1, 23],
+      [10, 1],
+      [-1, 21],
+      [-10, 12],
+    ];
+    for (const [daysToAdd, expectedDay] of samples) {
+      const wrapper = new DateWrapper("2023-05-22T12:00:00Z");
+      wrapper.addDays(daysToAdd);
+      test.equals(wrapper.date.getDate(), expectedDay, wrapper.iso());
+    }
+  });
+
+  group.test("Constructor", async (test) => {
+    const stringConstructor = new DateWrapper("2023-05-22T12:00:00Z");
+    test.true(stringConstructor.date instanceof Date, "String constructor");
+    const dateConstructor = new DateWrapper(new Date("2023-05-22T12:00:00Z"));
+    test.true(dateConstructor.date instanceof Date, "Date constructor");
+  });
+
+  group.test("Day of the Week", async (test) => {
+    const wrapper = new DateWrapper("2023-05-22T12:00:00Z");
+    for (let expected = 1; expected <= 7; expected++) {
+      test.equals(wrapper.dayOfTheWeek(), expected, wrapper.iso());
+      wrapper.addDays(1);
+    }
+  });
+
+  group.test("Padded Functions", async (test) => {
+    const samples: Array<[DateWrapper, string, string]> = [
+      [new DateWrapper("2023-05-02T12:00:00Z"), "05", "02"],
+      [new DateWrapper("2023-05-22T12:00:00Z"), "05", "22"],
+      [new DateWrapper("2023-11-02T12:00:00Z"), "11", "02"],
+      [new DateWrapper("2023-11-22T12:00:00Z"), "11", "22"],
+    ];
+    for (const [wrapper, month, day] of samples) {
+      test.equals(wrapper.paddedMonth(), month, wrapper.iso());
+      test.equals(wrapper.paddedDay(), day, wrapper.iso());
+    }
+  });
+});
diff --git a/source/date/date.ts b/source/date/date.ts
new file mode 100644
index 0000000..963fe73
--- /dev/null
+++ b/source/date/date.ts
@@ -0,0 +1,68 @@
+export class DateWrapper {
+  public date: Date;
+
+  constructor(date: Date | string) {
+    this.date = date instanceof Date ? date : new Date(date);
+  }
+
+  /**
+   * Adds the specified number of days to the inner date.
+   *
+   * @param days The amount of days to add, can also be negative to subtract.
+   */
+  public addDays(days: number): void {
+    this.date.setDate(this.date.getDate() + days);
+  }
+
+  /** Clone the current date and return a completely new DateWrapper. */
+  public clone(): DateWrapper {
+    return new DateWrapper(new Date(this.iso()));
+  }
+
+  /** Get the day of the week with Monday starting as 1. */
+  public dayOfTheWeek(): number {
+    const day = this.date.getDay();
+    return day === 0 ? 7 : day;
+  }
+
+  /** Get the date as an ISO-formatted string. */
+  public iso(): string {
+    return this.date.toISOString();
+  }
+
+  /** Get the day padded with a leading zero when necessary. */
+  public paddedDay(): string {
+    const day = this.date.getDate();
+    return day.toString().padStart(2, "0");
+  }
+
+  /** Get the month padded with a leading zero when necessary. */
+  public paddedMonth(): string {
+    const month = this.date.getMonth() + 1;
+    return month.toString().padStart(2, "0");
+  }
+
+  /**
+   * Get the week of the year the date is in.
+   *
+   * Code adapted from https://weeknumber.net/how-to/javascript.
+   * */
+  public week(): number {
+    const date = new Date(this.date.getTime());
+    date.setHours(0, 0, 0, 0);
+
+    // Thursday in the current week decides the year.
+    date.setDate(date.getDate() + 3 - ((date.getDay() + 6) % 7));
+
+    // January 4 is always in week 1.
+    const firstWeek = new Date(date.getFullYear(), 0, 4);
+
+    // Get the difference between the first week and the current date in days.
+    const dayDifference = (date.getTime() - firstWeek.getTime()) / 86_400_000;
+
+    // Adjust the day difference to Thursday and then get the number of weeks.
+    return (
+      1 + Math.round((dayDifference - 3 + ((firstWeek.getDay() + 6) % 7)) / 7)
+    );
+  }
+}