WIP

withDefaults.ts

type AnyFunction = (...args: any) => any
type FunctionWithOneArg<T extends AnyFunction> = (args: Record<string, any>) => ReturnType<T>
type Without<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>
type Arguments<T> = [T] extends [(...args: infer U) => any]
  ? U
  : [T] extends [void] ? [] : [T]

type PartialArg<T> = Partial<Arguments<T>[0]>

function withDefaults<T extends FunctionWithOneArg<T>>(fn: T, defaults: PartialArg<T>)  {
    type FunctionOpts = Arguments<typeof myFunction>[0]
    type DefaultKeys = keyof typeof defaults

    type FunctionDefaults = Pick<Partial<FunctionOpts>, DefaultKeys>

    type NewOpts 
    return (args:) => {

    }
}


function myFunction(args: {
    foo: string;
    bar: string;
}) {
    return {foo, bar}
}

type myFunctionArgs = Arguments<typeof myFunction>[0]


const myFunctionWithDefaults = withDefaults(myFunction, {
    foo: '1',
})


console.log(myFunctionWithDefaults({
    bar: '2',
}))

console.log(myFunctionWithDefaults({
    bar: '2',
}))