--!strict
local types = require(script.Parent.Parent.Parent.Parent:WaitForChild('es7-types'))
type Object = types.Object
type Array<T> = types.Array<T>

type mapFn<T, U> = (element: T, index: number) -> U
type mapFnWithThisArg<T, U> = (thisArg: any, element: T, index: number) -> U

return function<T, U>(
	value: string,
	mapFn: (mapFn<T, U> | mapFnWithThisArg<T, U>)?,
	thisArg: Object?
	-- FIXME Luau: need overloading so the return type on this is more sane and doesn't require manual casts
): Array<U> | Array<T> | Array<string>
	local array = {}

	local valueStringLength = #value
	array = table.create(valueStringLength)
	if mapFn then
		for i = 1, valueStringLength do
			if thisArg ~= nil then
				(array :: Array<U>)[i] = (mapFn :: mapFnWithThisArg<T, U>)(thisArg, string.sub(value, i, i) :: any, i)
			else
				(array :: Array<U>)[i] = (mapFn :: mapFn<T, U>)(string.sub(value, i, i) :: any, i)
			end
		end
	else
		for i = 1, valueStringLength do
			(array :: Array<string>)[i] = string.sub(value, i, i)
		end
	end

	return array
end
