/*
 * Helpers for testing Redux.
 */

const FINISHED = "@@test/SPYSHOULDBEFINISHED";

/**
 * Creates the middleware that checks if specified actions are dispatched.
 * Use it like `const spy = spyInTheMiddle(fn1, fn2, ...), store = applyMiddleware(..., spy)(reducer);`.
 * The fn1, ... get action in the parameter and should return truthy value if it is the expected one,
 * in which case the expectation will be removed; and shoudl return falsy value if it can be ignored.
 * For the moment, only first expectation in the list is checked until it returns true, then it is removed and the next one will be used,
 * In case the action is invalid (like, it has right type but wrong payload), the expectation fn can (and should) throw,
 * for example using the test assertion (in chai/expect, assertions are truthy, so your expectation fn can look like below)
 *
 *     ({type, payload: {foo}}) => type == "FOOIFY" && expect(foo).to.equal("bar")
 *
 * All actions are passed downstream, unless you threw.
 *
 * @param expectations
 */
export const spyInTheMiddle = (...expectations) => store => next => action => {
    if (action.type == FINISHED && expectations.length > 0) throw new Error(`Expectations left unfulfilled: ${expectations.length}`);
    if (expectations[0] && expectations[0](action)) {
        expectations.shift();
    }
    return next(action);
};

/**
 * Call `store.dispatch(SPY_VERIFY)` at the end of the test.
 * It will pass if all expectations were fulfilled and fail if there are still some hanging there.
 * @type {{type: string}}
 */
export const SPY_VERIFY = {type: FINISHED};

/**
 * Reducer that always returns unchanged state.
 * @param state
 * @param action
 */
export const dumbReducer = (state, action) => state;