class Update {
    constructor (state) {
        this.newState = state;
        this.effects = [];
    }

    state (update) {
        this.newState = { ...this.newState, update };
    }

    effect (fn) {
        this.effects.push(fn);
    }
}

function assertHasUpdateMethod (component) {
    utils.assert(
        utils.isFunction(component.update),
        `withUpdates requires ${component.displayName} to implement an 'update' method`
    );
}

function assertIsThenable (thenable, componentName) {
    utils.assert(
        thenable.then && utils.isFunction(thenable.then),
        `Scheduled effects must return thenables. Check the 'update' method of ${componentName}`
    );
}

function effectsMixinForChannel (channel) {
    return {
        componentWillMount () {
            this.schedule(this.props, null, false);
        },
        
        componentWillReceiveProps (nextProps) {
            this.schedule(this.props, nextProps, true);
        },
        
        schedule (props, nextProps, isMounted) {
            assertHasUpdateMethod(this);
            const update = this.update(this.props, nextProps, new Update(this, channel), true);

            // Syncronously handle state updates
            this.setState(update.newState);

            // Schedule eventual updates
            this.effects.forEach((effect) => {
                const thenable = effect();
                assertIsThenable(thenable, component.displayName);
                thenable.then(this.applyEffect, this.applyEffect);
            });
        },

        applyEffect (actionOrUpdate, ...additionalData) {
            // Promise returns either a string constant Action...
            if (utils.isString(actionOrUpdate)) {
                channel.publish(actionOrUpdate, { additionalData });
            }

            // ...or an object to merge into component state
            if (utils.isObject(actionOrUpdate)) {
                this.setState(actionOrUpdate);
            }
        }
    };
}

export { effectsMixinForChannel };

// default effects mixin publishes on default channel
export default effectsMixinForChannel();