gotodo/internal/persist/persist.go

package persist

import (
	"encoding/json"
	"fmt"
	"io"
	"os"

	"snamellit.com/play/todo/internal/model"
)

var EMPTY_TODO = model.Todo{Id: 0, Title: "", Completed: false}

var maxId int = 0

var todos model.Todos

type eventType string
const (
	ADDED eventType = "ADDED"
	DELETED eventType = "DELETED"
	CHANGED eventType = "CHANGED"
)

type event struct {
	Kind eventType 
	Todo model.Todo
}

func readTodos() (model.Todos, error) {
	f, err := os.OpenFile("todo_events.txt", os.O_RDONLY|os.O_CREATE, 0644)
	defer f.Close()
	if err != nil {
		return nil, err
	}

	dec := json.NewDecoder(f)

	todos = make(model.Todos)
	for {
		var e event
		err = dec.Decode(&e)
		if err != nil {
			if err == io.EOF {
				break
			}
			return nil, err
		}
		fmt.Println("Read event", e)
		id := e.Todo.Id
		if id > maxId {
			maxId = id
		}
		applyEvent(e.Kind, e.Todo)
	}
	return todos, nil
}

func applyEvent(kind eventType, todo model.Todo) error {
	id := todo.Id
	switch t := kind; t {
	case ADDED:
		fmt.Println("apply add ", todo)
		todos[id] = todo
	case CHANGED:
		fmt.Println("apply change ", todo)
		todos[id] = todo
	case DELETED:
		fmt.Println("apply delete ", todo)
		delete(todos, id)
	default:
		return fmt.Errorf("Unknown event type %s", t)
	}
	return nil
}

func addEvent(kind eventType, todo model.Todo) error {
	err := applyEvent(kind, todo)
	if err != nil {
		return err
	}
	
	f, err := os.OpenFile("todo_events.txt", os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
	defer f.Close()
	if err != nil {
		return err
	}
	fmt.Println("Write todo", todo)
	enc := json.NewEncoder(f)
	e := event{Kind: kind, Todo: todo}
	fmt.Println("Write event", e)
	err = enc.Encode(e)
	if err != nil {
		return err
	}
	return nil
}

func GetTodos() (model.Todos, error) {
	if len(todos) == 0 {
		return readTodos()
	}
	return todos, nil
}


func GetTodoById(id int) (model.Todo, error) {
	todo, present := todos[id]
	if !present {
		return EMPTY_TODO, fmt.Errorf("Todo with id %d not found", id)
	}
	return todo, nil
}

func SetTodo(todo model.Todo) error {
	fmt.Println("SetTodo", todo)
	todos[todo.Id] = todo
	return addEvent(CHANGED, todo)
}

func AddTodo(title string) error {
	fmt.Println("AddTodo", title)
	maxId++;
	todo := model.Todo{Id: maxId, Title: title, Completed: false}
	return addEvent(ADDED, todo)
}

func DeleteTodoById(id int) error {
	delete(todos, id)
	return addEvent(DELETED, model.Todo{Id: id})
}