tools.js

import deepFreeze from "deep-freeze";
import isPlainObject from "lodash/fp/isPlainObject";

export function wrapSanityChecks(reducer) {
    if (process.env.NODE_ENV === "production") return reducer;

    return (state, action) => {

        if (!isPlainObject(action)) {
            const msg = `Bad action object of type ${typeof action}`;
            console.log(msg, action);
            throw new Error(msg);
        }

        // Actions should be serializable so that they can be replayed using
        // Redux Devtools. Serializable actions also would allow sending them
        // over network etc.
        try {
            JSON.stringify(action);
        } catch (error) {
            const msg = "Invalid action! Actions must be serializable";
            console.log(msg, action);
            throw new Error(msg);
        }


        // Ensure immutable state and actions. Reducers should never mutate
        // those.
        state = reducer(deepFreeze(state), deepFreeze(action));

        if (!isPlainObject(state)) {
            const msg = `State screwed by action ${action.type}. Store state is now '${typeof state}'`;
            console.log(msg, action);
            throw new Error(msg);
        }

        return state;
    };
}