simple reducer decomposition

reducer-decomposition.js

const todos(state=[] , action){
	switch(action.type){
		case 'add_todo':
		case 'remove_todo':
		case 'toggle_todo':
			return todo(state , action)
		default : 
			return state
	}
}

const todo = function(state = {} , action){
	switch(action.type){
		case 'add_todo':
			return [...state , {
				action.id , 
				action.text , 
				completed : false
			}]
		case 'remove_todo':
			return [...state.slice(0 , action.id) , ...state( action.id + 1)]
		case 'toggle_todo':
			return [
					...state.slice(0 , action.id) , 
					{...state[action.id] , completed : !state[action.id].completed },
					...state.slice(action.id + 1)
				]	
	}
}


// visibility_filter -> (show_completed , show_active , show_all);


const visibility_filter(state = "show_all" , action){
	switch(action.type){
		case "show_all":
			return "show_all"
		case "show_completed":
			return "show_completed"
		case "show_active":
			return "show_active"
		default : 
			return state ; 
	}
}


// simple reducer decompossion . 
// {
// 	todos : [] , 
// 	visibility_filter : "show_all"
// }

// main reducer : could use combineReducer function . 
const reducer = (state = {} , action){
	return {
		todos : todos(state.todos , action) , 
		visibility_filter : visibility_filter(state.visibility_filter , action) 
	}
}
// combineReducers 

const {combineReducers} = Redux

const reducer2 = combineReducers({
	todos, 
	visibility_filter
})