import {CamelCase, PascalCase} from 'type-fest';

// eslint-disable-next-line @typescript-eslint/ban-types
type EmptyTuple = [];

/**
Return a default type if input type is nil.

@template T - Input type.
@template U - Default type.
*/
type WithDefault<T, U extends T> = T extends undefined | void | null ? U : T; // eslint-disable-line @typescript-eslint/ban-types

// TODO: Replace this with https://github.com/sindresorhus/type-fest/blob/main/source/includes.d.ts
/**
Check if an element is included in a tuple.
*/
type IsInclude<List extends readonly unknown[], Target> = List extends undefined
	? false
	: List extends Readonly<EmptyTuple>
		? false
		: List extends readonly [infer First, ...infer Rest]
			? First extends Target
				? true
				: IsInclude<Rest, Target>
			: boolean;

/**
Append a segment to dot-notation path.
*/
type AppendPath<S extends string, Last extends string> = S extends ''
	? Last
	: `${S}.${Last}`;

/**
Convert keys of an object to camelcase strings.
*/
export type CamelCaseKeys<
	T extends Record<string, any> | readonly any[],
	Deep extends boolean = false,
	IsPascalCase extends boolean = false,
	Exclude extends readonly unknown[] = EmptyTuple,
	StopPaths extends readonly string[] = EmptyTuple,
	Path extends string = '',
> = T extends readonly any[]
	// Handle arrays or tuples.
	? {
		[P in keyof T]: T[P] extends Record<string, any> | readonly any[]
		// eslint-disable-next-line @typescript-eslint/ban-types
			? {} extends CamelCaseKeys<T[P]>
				? T[P]
				: CamelCaseKeys<
				T[P],
				Deep,
				IsPascalCase,
				Exclude,
				StopPaths
				>
			: T[P];
	}
	: T extends Record<string, any>
		// Handle objects.
		? {
			[P in keyof T as [IsInclude<Exclude, P>] extends [true]
				? P
				: [IsPascalCase] extends [true]
					? PascalCase<P>
					: CamelCase<P>]: [IsInclude<StopPaths, AppendPath<Path, P & string>>] extends [
				true,
			]
				? T[P]
				// eslint-disable-next-line @typescript-eslint/ban-types
				: {} extends CamelCaseKeys<T[P]>
					? T[P]
					: [Deep] extends [true]
						? CamelCaseKeys<
						T[P],
						Deep,
						IsPascalCase,
						Exclude,
						StopPaths,
						AppendPath<Path, P & string>
						>
						: T[P];
		}
		// Return anything else as-is.
		: T;

type Options = {
	/**
	Recurse nested objects and objects in arrays.

	@default false
	*/
	readonly deep?: boolean;

	/**
	Exclude keys from being camel-cased.

	If this option can be statically determined, it's recommended to add `as const` to it.

	@default []
	*/
	readonly exclude?: ReadonlyArray<string | RegExp>;

	/**
	Exclude children at the given object paths in dot-notation from being camel-cased. For example, with an object like `{a: {b: '🦄'}}`, the object path to reach the unicorn is `'a.b'`.

	If this option can be statically determined, it's recommended to add `as const` to it.

	@default []

	@example
	```
	import camelcaseKeys from 'camelcase-keys';

	camelcaseKeys({
		a_b: 1,
		a_c: {
			c_d: 1,
			c_e: {
				e_f: 1
			}
		}
	}, {
		deep: true,
		stopPaths: [
			'a_c.c_e'
		]
	}),
	// {
	// 	aB: 1,
	// 	aC: {
	// 		cD: 1,
	// 		cE: {
	// 			e_f: 1
	// 		}
	// 	}
	// }
	```
	*/
	readonly stopPaths?: readonly string[];

	/**
	Uppercase the first character as in `bye-bye` → `ByeBye`.

	@default false
	*/
	readonly pascalCase?: boolean;
};

/**
Convert object keys to camel case using [`camelcase`](https://github.com/sindresorhus/camelcase).

@param input - Object or array of objects to camel-case.

@example
```
import camelcaseKeys from 'camelcase-keys';

// Convert an object
camelcaseKeys({'foo-bar': true});
//=> {fooBar: true}

// Convert an array of objects
camelcaseKeys([{'foo-bar': true}, {'bar-foo': false}]);
//=> [{fooBar: true}, {barFoo: false}]

camelcaseKeys({'foo-bar': true, nested: {unicorn_rainbow: true}}, {deep: true});
//=> {fooBar: true, nested: {unicornRainbow: true}}

camelcaseKeys({a_b: 1, a_c: {c_d: 1, c_e: {e_f: 1}}}, {deep: true, stopPaths: ['a_c.c_e']}),
//=> {aB: 1, aC: {cD: 1, cE: {e_f: 1}}}

// Convert object keys to pascal case
camelcaseKeys({'foo-bar': true, nested: {unicorn_rainbow: true}}, {deep: true, pascalCase: true});
//=> {FooBar: true, Nested: {UnicornRainbow: true}}
```

@example
```
import {parseArgs} from 'node:utils';
import camelcaseKeys from 'camelcase-keys';

const commandLineArguments = parseArgs();
//=> {_: [], 'foo-bar': true}

camelcaseKeys(commandLineArguments);
//=> {_: [], fooBar: true}
```
*/
export default function camelcaseKeys<
	T extends Record<string, any> | readonly any[],
	OptionsType extends Options = Options,
>(
	input: T,
	options?: OptionsType
): CamelCaseKeys<
T,
WithDefault<OptionsType['deep'], false>,
WithDefault<OptionsType['pascalCase'], false>,
WithDefault<OptionsType['exclude'], EmptyTuple>,
WithDefault<OptionsType['stopPaths'], EmptyTuple>
>;