Strong typed endpoint

endpoint.ts

type Split<S extends string, D extends string> = S extends `${infer T}${D}${infer U}` ? [T, ...Split<U, D>] : [S];
type Cast<S extends string> = S extends 'string' ? string : S extends 'number' ? number : never;
type Urlify<S extends string> = S extends `{${infer TKey}:${infer TType}}` ? [TKey, Cast<TType>] : S extends `{${infer TKey}}` ? [TKey, string | number] : S

type UrlifyEach<V, L extends string[] = []> = 
    V extends [] 
        ? L 
        : V extends [string] 
            ? [...L, Urlify<V[0]>]
            : V extends [string, ...infer R]
                ? UrlifyEach<R, [...L, Urlify<V[0]>]>
                : []

type ConvertTuple<TValue, TResult extends Record<string, unknown>> = TValue extends [infer TKey, infer TType] ? TKey extends string ? {[Key in keyof TResult]: TResult[Key]} & {[R in TKey]: TType} : TResult : TResult

type GetParams<TValue extends Array<any>, TResult extends Record<string, unknown> = {}>  = 
    TValue extends []
        ? TResult
        : TValue extends [infer R]
            ? R extends string
                ? TResult
                : ConvertTuple<R, TResult>
                : TValue extends [infer T, ...infer R]
                    ? GetParams<R, ConvertTuple<T, TResult>>
                    : TResult


type Params<T extends string> = GetParams<UrlifyEach<Split<T, '/'>>>

function endpoint<TUrl extends string>(url: TUrl): keyof Params<TUrl> extends [] ? () => string : (params: Params<TUrl>) => string {
    return (params?: Params<TUrl>) => {
        const toParse = params ?? {}
        const keys = Object.keys(toParse)
        
        return ''
    }
}

const r1 = endpoint('/')()
const r2 = endpoint('/foo/bar')()
const r3 = endpoint('/foo/{id}')({id: ''})
const r4 = endpoint('/foo/{id:number}')({id: 1})