export type SpyOf<T> = { [R in keyof T]: Partial<jest.Mock<T[R]>> } & T;

/**
 * The idea behind the autospy is to pass it a function constructor(a class) and it will
 * return an object that can be used instead of the initial one in constructors etc.
 *
 * If you pass in the wantedReturnValues it will return those /use the functions in there
 */
export function autoSpy<T extends Object>(obj: new (...args: any[]) => T, returnValues?: Partial<T>): SpyOf<T> {
    returnValues = returnValues || {};
    // tslint:disable-next-line:prefer-const
    let res: SpyOf<T> = {} as any;
    Object.keys(obj.prototype).forEach(key => {
        if (returnValues.hasOwnProperty(key)) {
            const valueToReturn = returnValues[key as any];
            if (typeof valueToReturn === 'function') {
                res[key] = jest.fn(valueToReturn);
            } else {
                res[key] = jest.fn(() => valueToReturn);
            }
        } else {
            res[key] = jest.fn();
        }
    });

    return res;
}