fetcher cash tag creator.

cash-tag-factory.ts

type KV = Record<string, any>;

type MyParameters<F> = F extends (...args: infer P) => unknown
  ? P extends [infer A]
    ? A extends KV
      ? KV
      : [A]
    : P
  : never;

function cashTagFactory<F extends (...params: any[]) => unknown>(
  fetcher: F,
): (params: MyParameters<F>) => string {
  return (params) => {
    let kv: Record<string, any> = params;
    if (Array.isArray(params)) {
      kv = Object.fromEntries(params.map((v, i) => [`p${i}`, `${v}`]));
    }
    return `${new URLSearchParams({ _fn: fetcher.name, ...kv })}`;
  };
}

const f1 = ({ name, age }: { name: string; age: number }) => `${name}:${age}`;
const f2 = (name: string, age: number) => `${name}:${age}`;
f1.getTag = cashTagFactory(f1);
f2.getTag = cashTagFactory(f2);
console.log(f1.getTag({ name: "matsuby", age: 32 })); // "_fn=f1&name=matsuby&age=32"
console.log(f2.getTag(["matsuby", 32])); // "_fn=f2&p0=matsuby&p1=32"

// TODO: getTag　can't accepet positional arguments😕
// console.log(f2.getTag("matsuby", 32)); // Expected 1 arguments, but got 2.