thi-ng/umbrella

/**
 * Class behavior mixin based on:
 * - http://raganwald.com/2015/06/26/decorators-in-es7.html
 *
 * Additionally only injects/overwrites properties in target, which are NOT
 * marked with
 * [`@nomixin`](https://docs.thi.ng/umbrella/api/functions/nomixin.html) (i.e.
 * those which haven't set their `configurable` property descriptor flag to
 * `false`)
 *
 * @param behaviour - to mixin
 * @param sharedBehaviour -
 * @returns decorator function
 */
export const mixin = (behaviour: any, sharedBehaviour: any = {}) => {
    const instanceKeys = Reflect.ownKeys(behaviour);
    const sharedKeys = Reflect.ownKeys(sharedBehaviour);
    const typeTag = Symbol("isa");

    function _mixin(clazz: any) {
        for (let key of instanceKeys) {
            const existing = Object.getOwnPropertyDescriptor(
                clazz.prototype,
                key
            );
            if (!existing || existing.configurable) {
                Object.defineProperty(clazz.prototype, key, {
                    value: behaviour[key],
                    writable: true,
                });
            } else {
                // console.log(`not patching: ${clazz.name}.${key.toString()}`);
            }
        }
        Object.defineProperty(clazz.prototype, typeTag, { value: true });
        return clazz;
    }

    for (let key of sharedKeys) {
        Object.defineProperty(_mixin, key, {
            value: sharedBehaviour[key],
            enumerable: sharedBehaviour.propertyIsEnumerable(key),
        });
    }

    Object.defineProperty(_mixin, Symbol.hasInstance, {
        value: (x: any) => !!x[typeTag],
    });

    return _mixin;
};