redux-most-middleware2.ts

import { MiddlewareAPI, Middleware, Dispatch } from 'redux';
import { async } from 'most-subject';
import { mergeArray, Stream } from 'most';
import enhance, { EnhancedStore } from './make-typed-dispatch';

export interface Action<T = any, K extends keyof T = any> {
    type: K;
    payload: T[K];
}

export interface MergedCtx<S, A> {
    store: EnhancedStore<MiddlewareAPI<S>, A>;
}

export interface Epic<S, A, C = any> {
    (action$: Stream<Action<A>>, context: C & MergedCtx<S, A>): Stream<any>;
}

export default function createEpicMiddleware<S, A, C>(epics: Epic<S, A, C>[], context: C) {

    const middleware = (api: MiddlewareAPI<S>) => (next: Dispatch<S>) => {
        const store = enhance(api);
        const actionIn$ = async<any>();
        const ctx = Object.assign(context, { store });
        const epicArray$ = epics.map(ep => ep(actionIn$, ctx));
        const epic$ = mergeArray(epicArray$);

        epic$.drain();

        return (action: any) => actionIn$.next(next(action));
    };

    return middleware as Middleware;
}


export function select<T, K extends keyof T>(type: K, action$: Stream<Action<T>>): Stream<T[K]> {
    return (action$ as Stream<Action<T, K>>)
        .filter(x => x.type === type)
        .map(x => x.payload);
}