updux/src/reducer.ts

import { Action } from '@reduxjs/toolkit';
import * as R from 'remeda';
import { DuxConfig } from './types.js';
import { Mutation } from './Updux.js';
import u from '@yanick/updeep-remeda';

export type MutationCase = {
    matcher: (action: Action) => boolean;
    mutation: Mutation;
    terminal: boolean;
};

export function buildReducer(
    initialStateState: unknown,
    mutations: MutationCase[] = [],
    defaultMutation?: Omit<MutationCase, 'matcher'>,
    subduxes: Record<string, DuxConfig> = {},
) {
    const subReducers = R.mapValues(subduxes, R.prop('reducer'));

    // TODO matcherMutation
    // TODO defaultMutation
    //
    const reducer = (state = initialStateState, action: Action) => {
        if (!action?.type) throw new Error('reducer called with a bad action');

        let active = mutations.filter(({ matcher }) => matcher(action));

        if (active.length === 0 && defaultMutation)
            active.push(defaultMutation as any);

        if (
            !active.some(R.prop<any, any>('terminal')) &&
            Object.values(subReducers).length > 0
        ) {
            active.push({
                mutation: (payload, action) => (state) => {
                    return u(
                        state,
                        R.mapValues(
                            subReducers,
                            (reducer, slice) => (state) => {
                                return (reducer as any)(state, action);
                            },
                        ),
                    );
                },
            } as any);
        }

        // frozen objects don't play well with immer
        // if (Object.isFrozen(state)) {
        //     state = { ...(state as any) };
        // }
        return active.reduce(
            (state, { mutation }) =>
                mutation((action as any).payload, action)(state),
            state,
        );
    };

    return reducer;
}