feat(manip): addDuration and subDuration

.eslintrc.js

@@ -12,7 +12,7 @@ module.exports = {
     sourceType: 'module', // Allows for the use of imports
   },
   rules: {
-    '@typescript-eslint/explicit-module-boundary-types': 'error', // makes code-reviews easier + code quality better by explicitly defining outputs of exported functions+classes
+    '@typescript-eslint/explicit-module-boundary-types': 'warn', // makes code-reviews easier + code quality better by explicitly defining outputs of exported functions+classes
     '@typescript-eslint/explicit-function-return-type': 'off', // prefer '@typescript-eslint/explicit-module-boundary-types' since it only requires the check on exported functions+classes
     'sort-imports': 'off',
     'import/prefer-default-export': 'off', // default export = bad

src/index.ts

@@ -4,3 +4,5 @@ export * from './utils/sleep';
 export * from './checks/isUniDate';
 export * from './checks/isUniDateTime';
 export * from './casts/toMillisecondsSinceEpoch';
+export * from './manipulate/addDuration';
+export * from './manipulate/subDuration';

src/manipulate/addDuration.ts

@@ -0,0 +1,21 @@
+import { parseISO, subMilliseconds } from 'date-fns';
+import { PickOne } from 'type-fns';
+
+import { asUniDate, isUniDate } from '../checks/isUniDate';
+import { asUniDateTime } from '../checks/isUniDateTime';
+import { UniDate, UniDateTime } from '../domain/UniDateTime';
+import { UniDuration, toMilliseconds } from '../domain/UniDuration';
+
+/**
+ * subtract a duration from a datetime
+ */
+export const subDuration = (
+  ...args:
+    | [UniDateTime, UniDuration]
+    | [UniDate, PickOne<Pick<Required<UniDuration>, 'days'>>]
+) =>
+  isUniDate(args[0])
+    ? asUniDate(subMilliseconds(parseISO(args[0]), toMilliseconds(args[1])))
+    : asUniDateTime(
+        subMilliseconds(parseISO(args[0]), toMilliseconds(args[1])),
+      );

src/manipulate/subDuration.ts

@@ -0,0 +1,21 @@
+import { addMilliseconds, parseISO } from 'date-fns';
+import { PickOne } from 'type-fns';
+
+import { asUniDate, isUniDate } from '../checks/isUniDate';
+import { asUniDateTime } from '../checks/isUniDateTime';
+import { UniDate, UniDateTime } from '../domain/UniDateTime';
+import { UniDuration, toMilliseconds } from '../domain/UniDuration';
+
+/**
+ * add a duration to a datetime
+ */
+export const addDuration = (
+  ...args:
+    | [UniDateTime, UniDuration]
+    | [UniDate, PickOne<Pick<Required<UniDuration>, 'days'>>]
+) =>
+  isUniDate(args[0])
+    ? asUniDate(addMilliseconds(parseISO(args[0]), toMilliseconds(args[1])))
+    : asUniDateTime(
+        addMilliseconds(parseISO(args[0]), toMilliseconds(args[1])),
+      );