import { identity } from "./composition.ts";

type cmpArgs = Readonly<{ key: (item: any) => any; reverse: boolean }>;
const cmpDefaults: cmpArgs = { key: identity, reverse: false };
/**
 * Compare operator, that can be used in sort() calls.
 */
export function cmp(args?: Partial<cmpArgs>): (a: any, b: any) => number {
  const fargs = { ...cmpDefaults, ...args };
  return (a, b) => {
    const ka = fargs.key(a);
    const kb = fargs.key(b);
    if (ka > kb) {
      return fargs.reverse ? -1 : 1;
    } else if (ka < kb) {
      return fargs.reverse ? 1 : -1;
    } else {
      return 0;
    }
  };
}

/**
 * Get a function to check the strict equality with a reference
 */
export function is<T, S extends T>(
  ref: T,
): (input: S) => input is Extract<T, S> {
  return (x): x is Extract<T, S> => x === ref;
}

/**
 * Convert a value to a boolean (are considered falsy: 0, false, "", {}, [], null, undefined)
 */
export function bool<T>(value: T | null | undefined): value is T;
export function bool(value: any): boolean {
  if (!value) {
    return false;
  } else if (value instanceof Set) {
    return value.size > 0;
  } else if (typeof value == "object") {
    return Object.keys(value).length > 0;
  } else {
    return true;
  }
}