updux/src/Updux.js

import R from 'remeda';

import { action } from './actions.js';

function isActionGen(action) {
    return typeof action === "function" && action.type;
}

export class Updux {
    #localInitial = {};
    #subduxes = {};
    #actions;
    #mutations = {};
    #config = {};

    constructor(config = {}) {
        this.#config = config;
        this.#localInitial = config.initial ?? {};
        this.#subduxes = config.subduxes ?? {};

        this.#actions = R.mapValues( config.actions ?? {},  (arg,name) =>
            isActionGen(arg) ? arg : action(name,arg)
        );
        Object.entries(this.#subduxes).forEach( ([slice,sub]) => this.#addSubduxActions(slice,sub) )
    }

    #addSubduxActions(_slice, subdux) {
        if( ! subdux.actions ) return;
        // TODO action 'blah' defined multiple times: <where>
        Object.entries( subdux.actions ).forEach( ([action,gen]) => {
            if( this.#actions[action] ) {
                if( this.#actions[action] === gen ) return;
                throw new Error(`action '${action}' already defined`);
            }

            this.#actions[action] = gen;
        });
    }

    get actions() {
        return this.#actions;
    }

    get initial() {
        if (Object.keys(this.#subduxes).length === 0) return this.#localInitial;

        return Object.assign(
            {},
            this.#localInitial,
            R.mapValues(this.#subduxes, ({ initial }) => initial),
        );
    }

    get reducer() {
        return (state, action) => this.upreducer(action)(state);
    }

    get upreducer() {
        return (action) => (state) => {
            const mutation = this.#mutations[action.type];

            if (mutation) {
                state = mutation(action.payload, action)(state);
            }

            return state;
        };
    }

    setMutation(action, mutation) {
        this.#mutations[action.type] = mutation;
    }
}