// Chapter 35 example: notes in a slice, protected by a mutex. The notes are gone
// when the server stops.
// Run with: go run exercises/35/02-notes-in-memory.go

package main

import (
	"bytes"
	"fmt"
	"html/template"
	"net/http"
	"slices"
	"strings"
	"sync"
	"unicode/utf8"
)

const maxNoteLength = 200

type note struct {
	Text string
}

// mu protects notes. Any code that reads or changes notes must hold mu.
var mu sync.Mutex
var notes = []note{}

// allNotes returns a copy, so that the caller does not need mu to read it.
func allNotes() []note {
	mu.Lock()
	defer mu.Unlock()

	return slices.Clone(notes)
}

func addNote(n note) {
	mu.Lock()
	defer mu.Unlock()

	notes = append(notes, n)
}

const notesText = `<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Notes</title>
</head>
<body>
<h1>Notes</h1>
<ul>
{{range .}}
<li>{{.Text}}</li>
{{else}}
<li>No notes yet.</li>
{{end}}
</ul>
<form action="/notes" method="post">
<p><label>New note: <input type="text" name="text"></label></p>
<p><button type="submit">Add</button></p>
</form>
</body>
</html>
`

var notesTemplate = template.Must(template.New("notes").Parse(notesText))

func handleHome(w http.ResponseWriter, r *http.Request) {
	var page bytes.Buffer
	err := notesTemplate.Execute(&page, allNotes())
	if err != nil {
		fmt.Println("Template error:", err)
		http.Error(w, "The page could not be built.", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	page.WriteTo(w)
}

func handleAdd(w http.ResponseWriter, r *http.Request) {
	text := strings.TrimSpace(r.FormValue("text"))
	if text == "" {
		http.Error(w, "The note is empty.", http.StatusBadRequest)
		return
	}
	if utf8.RuneCountInString(text) > maxNoteLength {
		http.Error(w, "The note is too long.", http.StatusBadRequest)
		return
	}

	addNote(note{Text: text})

	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func main() {
	http.HandleFunc("GET /{$}", handleHome)
	http.HandleFunc("POST /notes", handleAdd)

	fmt.Println("Server running at http://localhost:8080")
	fmt.Println("Press Ctrl+C to stop it.")

	err := http.ListenAndServe("localhost:8080", nil)
	if err != nil {
		fmt.Println("Server stopped:", err)
	}
}