meow

meow: {
    <Flags extends AnyFlags>(
        helpMessage: string,
        options: Options<Flags>
    ): Result<Flags>;
    <Flags extends AnyFlags>(options: Options<Flags>): Result<Flags>;
};

type Flag<PrimitiveType extends FlagType, Type, IsMultiple = false> = {
    /**
	Type of value. (Possible values: `string` `boolean` `number`)
	*/
    readonly type?: PrimitiveType;

    /**
	Limit valid values to a predefined set of choices.

	@example
	```
	unicorn: {
		isMultiple: true,
		choices: ['rainbow', 'cat', 'unicorn']
	}
	```
	*/
    readonly choices?: Type extends unknown[] ? Type : Type[];

    /**
	Default value when the flag is not specified.

	@example
	```
	unicorn: {
		type: 'boolean',
		default: true
	}
	```
	*/
    readonly default?: Type;

    /**
	A short flag alias.

	@example
	```
	unicorn: {
		shortFlag: 'u'
	}
	```
	*/
    readonly shortFlag?: string;

    /**
	Other names for the flag.

	@example
	```
	unicorn: {
		aliases: ['unicorns', 'uni']
	}
	```
	*/
    readonly aliases?: string[];

    /**
	Indicates a flag can be set multiple times. Values are turned into an array.

	Multiple values are provided by specifying the flag multiple times, for example, `$ foo -u rainbow -u cat`. Space- or comma-separated values [currently *not* supported](https://github.com/sindresorhus/meow/issues/164).

	@default false
	*/
    readonly isMultiple?: IsMultiple;

    /**
	Determine if the flag is required.

	If it's only known at runtime whether the flag is required or not you can pass a Function instead of a boolean, which based on the given flags and other non-flag arguments should decide if the flag is required.

	- The first argument is the **flags** object, which contains the flags converted to camel-case excluding aliases.
	- The second argument is the **input** string array, which contains the non-flag arguments.
	- The function should return a `boolean`, true if the flag is required, otherwise false.

	@default false

	@example
	```
	isRequired: (flags, input) => {
		if (flags.otherFlag) {
			return true;
		}

		return false;
	}
	```
	*/
    readonly isRequired?: boolean | IsRequiredPredicate;
};

type FlagType = 'string' | 'boolean' | 'number';

type IsRequiredPredicate = (
    flags: Readonly<AnyFlags>,
    input: readonly string[]
) => boolean;

type Options<Flags extends AnyFlags> = {
    /**
	Pass in [`import.meta`](https://nodejs.org/dist/latest/docs/api/esm.html#esm_import_meta). This is used to find the correct package.json file.
	*/
    readonly importMeta: ImportMeta;

    /**
	Define argument flags.

	The key is the flag name in camel-case and the value is an object with any of:

	- `type`: Type of value. (Possible values: `string` `boolean` `number`)
	- `choices`: Limit valid values to a predefined set of choices.
	- `default`: Default value when the flag is not specified.
	- `shortFlag`: A short flag alias.
	- `aliases`: Other names for the flag.
	- `isMultiple`: Indicates a flag can be set multiple times. Values are turned into an array. (Default: false)
		- Multiple values are provided by specifying the flag multiple times, for example, `$ foo -u rainbow -u cat`. Space- or comma-separated values [currently *not* supported](https://github.com/sindresorhus/meow/issues/164).
	- `isRequired`: Determine if the flag is required. (Default: false)
		- If it's only known at runtime whether the flag is required or not, you can pass a `Function` instead of a `boolean`, which based on the given flags and other non-flag arguments, should decide if the flag is required. Two arguments are passed to the function:
		- The first argument is the **flags** object, which contains the flags converted to camel-case excluding aliases.
		- The second argument is the **input** string array, which contains the non-flag arguments.
		- The function should return a `boolean`, true if the flag is required, otherwise false.

	Note that flags are always defined using a camel-case key (`myKey`), but will match arguments in kebab-case (`--my-key`).

	@example
	```
	flags: {
		unicorn: {
			type: 'string',
			choices: ['rainbow', 'cat', 'unicorn'],
			default: ['rainbow', 'cat'],
			shortFlag: 'u',
			aliases: ['unicorns']
			isMultiple: true,
			isRequired: (flags, input) => {
				if (flags.otherFlag) {
					return true;
				}

				return false;
			}
		}
	}
	```
	*/
    readonly flags?: Flags;

    /**
	Description to show above the help text. Default: The package.json `"description"` property.

	Set it to `false` to disable it altogether.
	*/
    readonly description?: string | false;

    /**
	The help text you want shown.

	The input is reindented and starting/ending newlines are trimmed which means you can use a [template literal](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/template_strings) without having to care about using the correct amount of indent.

	The description will be shown above your help text automatically.

	Set it to `false` to disable it altogether.
	*/
    readonly help?: string | false;

    /**
	Set a custom version output. Default: The package.json `"version"` property.
	*/
    readonly version?: string;

    /**
	Automatically show the help text when the `--help` flag is present. Useful to set this value to `false` when a CLI manages child CLIs with their own help text.

	This option is only considered when there is only one argument in `process.argv`.
	*/
    readonly autoHelp?: boolean;

    /**
	Automatically show the version text when the `--version` flag is present. Useful to set this value to `false` when a CLI manages child CLIs with their own version text.

	This option is only considered when there is only one argument in `process.argv`.
	*/
    readonly autoVersion?: boolean;

    /**
	`package.json` as an `Object`. Default: Closest `package.json` upwards.

	Note: Setting this stops `meow` from finding a package.json.

	_You most likely don't need this option._
	*/
    readonly pkg?: Record<string, unknown>;

    /**
	Custom arguments object.

	@default process.argv.slice(2)
	*/
    readonly argv?: readonly string[];

    /**
	Infer the argument type.

	By default, the argument `5` in `$ foo 5` becomes a string. Enabling this would infer it as a number.

	@default false
	*/
    readonly inferType?: boolean;

    /**
	Value of `boolean` flags not defined in `argv`.

	If set to `undefined`, the flags not defined in `argv` will be excluded from the result. The `default` value set in `boolean` flags take precedence over `booleanDefault`.

	_Note: If used in conjunction with `isMultiple`, the default flag value is set to `[]`._

	__Caution: Explicitly specifying `undefined` for `booleanDefault` has different meaning from omitting key itself.__

	@example
	```
	import meow from 'meow';

	const cli = meow(`
		Usage
			$ foo

		Options
			--rainbow, -r  Include a rainbow
			--unicorn, -u  Include a unicorn
			--no-sparkles  Exclude sparkles

		Examples
			$ foo
			🌈 unicorns✨🌈
	`, {
		importMeta: import.meta,
		booleanDefault: undefined,
		flags: {
			rainbow: {
				type: 'boolean',
				default: true,
				shortFlag: 'r'
			},
				unicorn: {
				type: 'boolean',
				default: false,
				shortFlag: 'u'
			},
			cake: {
				type: 'boolean',
				shortFlag: 'c'
			},
			sparkles: {
				type: 'boolean',
				default: true
			}
		}
	});

	//{
	//	flags: {
	//		rainbow: true,
	//		unicorn: false,
	//		sparkles: true
	//	},
	//	unnormalizedFlags: {
	//		rainbow: true,
	//		r: true,
	//		unicorn: false,
	//		u: false,
	//		sparkles: true
	//	},
	//	…
	//}
	```
	*/
    readonly booleanDefault?: boolean | undefined;

    /**
	Whether to allow unknown flags or not.

	@default true
	*/
    readonly allowUnknownFlags?: boolean;

    /**
	The number of spaces to use for indenting the help text.

	@default 2
	*/
    readonly helpIndent?: number;
};

type Result<Flags extends AnyFlags> = {
    /**
	Non-flag arguments.
	*/
    input: string[];

    /**
	Flags converted to camelCase excluding aliases.
	*/
    flags: CamelCasedProperties<TypedFlags<Flags>> & Record<string, unknown>;

    /**
	Flags converted camelCase including aliases.
	*/
    unnormalizedFlags: TypedFlags<Flags> & Record<string, unknown>;

    /**
	The `package.json` object.
	*/
    pkg: PackageJson;

    /**
	The help text used with `--help`.
	*/
    help: string;

    /**
	Show the help text and exit with code.

	@param exitCode - The exit code to use. Default: `2`.
	*/
    showHelp: (exitCode?: number) => never;

    /**
	Show the version text and exit.
	*/
    showVersion: () => void;
};

type TypedFlags<Flags extends AnyFlags> = {
    [F in keyof Flags]: Flags[F] extends { isMultiple: true }
        ? PossiblyOptionalFlag<Flags[F], Array<TypedFlag<Flags[F]>>>
        : PossiblyOptionalFlag<Flags[F], TypedFlag<Flags[F]>>;
};