import * as R from "./refinement.ts";
import { pipe } from "./fn.ts";

type Person = { name: string };
type Rec = Record<string, unknown>;

const nonnull = (u: unknown): u is Rec => u !== null && u !== undefined;
const hasKey =
  <K extends string>(key: K) => (u: Rec): u is Record<K, unknown> =>
    Object.hasOwn(u, key);
const person = (u: Record<"name", unknown>): u is Person =>
  typeof u.name ===
    "string";

const isPerson = pipe(nonnull, R.compose(hasKey("name")), R.compose(person));

const value1 = null;
const value2 = {};
const value3 = { name: 1 };
const value4 = { name: "Brandon" };

const result1 = isPerson(value1); // false
const result2 = isPerson(value2); // false
const result3 = isPerson(value3); // false
const result4 = isPerson(value4); // true, value4: Person