--- /dev/null
+import {UpperCaseCharacters, WordSeparators} from '../source/utilities';
+
+/**
+Unlike a simpler split, this one includes the delimiter splitted on in the resulting array literal. This is to enable splitting on, for example, upper-case characters.
+*/
+export type SplitIncludingDelimiters<Source extends string, Delimiter extends string> =
+ Source extends '' ? [] :
+ Source extends `${infer FirstPart}${Delimiter}${infer SecondPart}` ?
+ (
+ Source extends `${FirstPart}${infer UsedDelimiter}${SecondPart}`
+ ? UsedDelimiter extends Delimiter
+ ? Source extends `${infer FirstPart}${UsedDelimiter}${infer SecondPart}`
+ ? [...SplitIncludingDelimiters<FirstPart, Delimiter>, UsedDelimiter, ...SplitIncludingDelimiters<SecondPart, Delimiter>]
+ : never
+ : never
+ : never
+ ) :
+ [Source];
+
+/**
+Format a specific part of the splitted string literal that `StringArrayToDelimiterCase<>` fuses together, ensuring desired casing.
+
+@see StringArrayToDelimiterCase
+*/
+type StringPartToDelimiterCase<StringPart extends string, UsedWordSeparators extends string, UsedUpperCaseCharacters extends string, Delimiter extends string> =
+ StringPart extends UsedWordSeparators ? Delimiter :
+ StringPart extends UsedUpperCaseCharacters ? `${Delimiter}${Lowercase<StringPart>}` :
+ StringPart;
+
+/**
+Takes the result of a splitted string literal and recursively concatenates it together into the desired casing.
+
+It receives `UsedWordSeparators` and `UsedUpperCaseCharacters` as input to ensure it's fully encapsulated.
+
+@see SplitIncludingDelimiters
+*/
+type StringArrayToDelimiterCase<Parts extends any[], UsedWordSeparators extends string, UsedUpperCaseCharacters extends string, Delimiter extends string> =
+ Parts extends [`${infer FirstPart}`, ...infer RemainingParts]
+ ? `${StringPartToDelimiterCase<FirstPart, UsedWordSeparators, UsedUpperCaseCharacters, Delimiter>}${StringArrayToDelimiterCase<RemainingParts, UsedWordSeparators, UsedUpperCaseCharacters, Delimiter>}`
+ : '';
+
+/**
+Convert a string literal to a custom string delimiter casing.
+
+This can be useful when, for example, converting a camel-cased object property to an oddly cased one.
+
+@see KebabCase
+@see SnakeCase
+
+@example
+```
+import {DelimiterCase} from 'type-fest';
+
+// Simple
+
+const someVariable: DelimiterCase<'fooBar', '#'> = 'foo#bar';
+
+// Advanced
+
+type OddlyCasedProps<T> = {
+ [K in keyof T as DelimiterCase<K, '#'>]: T[K]
+};
+
+interface SomeOptions {
+ dryRun: boolean;
+ includeFile: string;
+ foo: number;
+}
+
+const rawCliOptions: OddlyCasedProps<SomeOptions> = {
+ 'dry#run': true,
+ 'include#file': 'bar.js',
+ foo: 123
+};
+```
+*/
+
+export type DelimiterCase<Value, Delimiter extends string> = Value extends string
+ ? StringArrayToDelimiterCase<
+ SplitIncludingDelimiters<Value, WordSeparators | UpperCaseCharacters>,
+ WordSeparators,
+ UpperCaseCharacters,
+ Delimiter
+ >
+ : Value;