// Chapter 35 example: loading and saving a JSON file, with no server. Each run
// adds one note. It reads and writes notes.json in the folder you run it from.
// Run with: go run exercises/35/04-notes-file.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
)

const notesFile = "notes.json"

type note struct {
	Text string
}

// loadNotes reads the file. A file that does not exist yet means no notes, which
// is normal on the first run. Any other problem is an error.
func loadNotes() ([]note, error) {
	data, err := os.ReadFile(notesFile)
	if errors.Is(err, os.ErrNotExist) {
		return []note{}, nil
	}
	if err != nil {
		return nil, err
	}

	var loaded []note
	err = json.Unmarshal(data, &loaded)
	if err != nil {
		return nil, fmt.Errorf("%s is not valid: %v", notesFile, err)
	}
	return loaded, nil
}

// saveNotes writes a temporary file, then renames it over the real one.
func saveNotes(list []note) error {
	data, err := json.MarshalIndent(list, "", "  ")
	if err != nil {
		return err
	}

	temporary := notesFile + ".tmp"
	err = os.WriteFile(temporary, data, 0644)
	if err != nil {
		return err
	}
	return os.Rename(temporary, notesFile)
}

func main() {
	notes, err := loadNotes()
	if err != nil {
		fmt.Println("Error:", err)
		return
	}
	fmt.Println("Notes found:", len(notes))

	notes = append(notes, note{Text: "Another note"})

	err = saveNotes(notes)
	if err != nil {
		fmt.Println("Error:", err)
		return
	}
	fmt.Println("Notes saved:", len(notes))
}