source: node_modules/type-fest/ts41/camel-case.d.ts

import {WordSeparators} from '../source/utilities';

/**
Recursively split a string literal into two parts on the first occurence of the given string, returning an array literal of all the separate parts.
*/
export type Split<S extends string, D extends string> =
        string extends S ? string[] :
        S extends '' ? [] :
        S extends `${infer T}${D}${infer U}` ? [T, ...Split<U, D>] :
        [S];

/**
Step by step takes the first item in an array literal, formats it and adds it to a string literal, and then recursively appends the remainder.

Only to be used by `CamelCaseStringArray<>`.

@see CamelCaseStringArray
*/
type InnerCamelCaseStringArray<Parts extends any[], PreviousPart> =
        Parts extends [`${infer FirstPart}`, ...infer RemainingParts]
                ? FirstPart extends undefined
                        ? ''
                        : FirstPart extends ''
                                        ? InnerCamelCaseStringArray<RemainingParts, PreviousPart>
                                        : `${PreviousPart extends '' ? FirstPart : Capitalize<FirstPart>}${InnerCamelCaseStringArray<RemainingParts, FirstPart>}`
                : '';

/**
Starts fusing the output of `Split<>`, an array literal of strings, into a camel-cased string literal.

It's separate from `InnerCamelCaseStringArray<>` to keep a clean API outwards to the rest of the code.

@see Split
*/
type CamelCaseStringArray<Parts extends string[]> =
        Parts extends [`${infer FirstPart}`, ...infer RemainingParts]
                ? Uncapitalize<`${FirstPart}${InnerCamelCaseStringArray<RemainingParts, FirstPart>}`>
                : never;

/**
Convert a string literal to camel-case.

This can be useful when, for example, converting some kebab-cased command-line flags or a snake-cased database result.

@example
```
import {CamelCase} from 'type-fest';

// Simple

const someVariable: CamelCase<'foo-bar'> = 'fooBar';

// Advanced

type CamelCasedProps<T> = {
        [K in keyof T as CamelCase<K>]: T[K]
};

interface RawOptions {
        'dry-run': boolean;
        'full_family_name': string;
        foo: number;
}

const dbResult: CamelCasedProps<ModelProps> = {
        dryRun: true,
        fullFamilyName: 'bar.js',
        foo: 123
};
```
*/
export type CamelCase<K> = K extends string ? CamelCaseStringArray<Split<K, WordSeparators>> : K;