number-munchers/reducers/board/muncher.reducer.js

import * as MuncherActions from '../../actions/board/muncher.actions';
import { SETTINGS } from '../../App';

const initial = { x: 0, y: 0 };

const reducer = (state = initial, action) => {
    if (action.type !== MuncherActions.MUNCHER_ACTION) {
        return state;
    }

    switch (action.action) {
        case MuncherActions.LEFT:
            if (state.x === 0) {
                return state;
            }
            return { x: state.x - 1, y: state.y };

        case MuncherActions.RIGHT:
            if (state.x === SETTINGS.GRID_WIDTH - 1) {
                return state;
            }
            return { x: state.x + 1, y: state.y };

        case MuncherActions.UP:
            if (state.y === 0) {
                return state;
            }
            return { x: state.x, y: state.y - 1 };

        case MuncherActions.DOWN:
            if (state.y === SETTINGS.GRID_HEIGHT - 1) {
                return state;
            }
            return { x: state.x, y: state.y + 1 };

        case MuncherActions.MUNCH:
            return state;
    }

    return state;
};

export default reducer;