learn_golang/go-web-app/gowiki/wiki.go

package main

import (
	"html/template"
	"log"
	"net/http"
	"os"
	"regexp"
)

// Template caching
var templates = template.Must(template.ParseFiles("edit.html", "view.html"))

// Validation to prevent abitrary paths
var validPath = regexp.MustCompile("^/(edit|save|view)/([a-zA-Z0-9]+)$")

// A wiki consists of a series of interconnected pages, each of which has a title and a body
type Page struct {
	Title string
	//The Body element is a []byte rather than string because that is the type expected by the io libraries we will use
	Body []byte
}

// save Saves a page to disk.
func (p *Page) save() error {
	filename := p.Title + ".txt"
	return os.WriteFile(filename, p.Body, 0600)
}

// Not neccessary after makeHandler implemented this.

// func getTitle(w http.ResponseWriter, r *http.Request) (string, error) {
// 	m := validPath.FindStringSubmatch(r.URL.Path)
// 	if m == nil {
// 		http.NotFound(w, r)
// 		return "", errors.New("invalid Page Title")
// 	}
// 	return m[2], nil // The title is the second subexpression
// }

// loadPage loads a Page from disk.
// It takes the title of the page as an argument, reads the corresponding
// file, and returns a pointer to a Page struct containing the title and body.
// If an error occurs during reading, it returns the error.
func loadPage(title string) (*Page, error) {
	filename := title + ".txt"
	body, err := os.ReadFile(filename)

	if err != nil {
		return nil, err
	}
	return &Page{Title: title, Body: body}, nil
}

func renderTemplate(w http.ResponseWriter, tmpl string, p *Page) {
	// In efficient. No cacheing
	// t, err := template.ParseFiles(tmpl + ".html")
	// if err != nil {
	// 	http.Error(w, err.Error(), http.StatusInternalServerError)
	// 	return
	// }
	// err = t.Execute(w, p)

	//With caching
	err := templates.ExecuteTemplate(w, tmpl+".html", p)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

// Wraps a handler function, includes validation checks on titles
func makeHandler(fn func(http.ResponseWriter, *http.Request, string)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		m := validPath.FindStringSubmatch(r.URL.Path)
		if m == nil {
			http.NotFound(w, r)
			return
		}
		fn(w, r, m[2])
	}
}

func viewHandler(w http.ResponseWriter, r *http.Request, title string) {
	// html := "<h1>%s</h1><div>%s</div>"
	// title := r.URL.Path[len("/view/"):]
	// Not neccesary after makeHandler was implemented
	// title, err := getTitle(w, r)
	// if err != nil {
	// 	return
	// }
	page, err := loadPage(title)
	// fmt.Fprintf(w, html, page.Title, page.Body)
	// t, _ := template.ParseFiles("view.html")
	// t.Execute(w, page)

	// handle non-existant pages
	if err != nil {
		http.Redirect(w, r, "/edit/"+title, http.StatusFound)
		return
	}
	renderTemplate(w, "view", page)
}

func editHandler(w http.ResponseWriter, r *http.Request, title string) {
	// title := r.URL.Path[len("/edit/"):]
	// Not neccesary after makeHandler was implemented
	// title, err := getTitle(w, r)
	// if err != nil {
	// 	return
	// }
	page, err := loadPage(title)
	if err != nil {
		page = &Page{Title: title}
	}
	// First Take
	// fmt.Fprintf(w, "<h1>Editing %s</h1>"+
	// 	"<form action=\"/save/%s\" method=\"POST\">"+
	// 	"<textarea name=\"body\">%s</textarea><br>"+
	// 	"<input type=\"submit\" value=\"Save\">"+
	// 	"</form>",
	// 	page.Title, page.Title, page.Body)
	// Take Two
	// t, _ := template.ParseFiles("edit.html")
	// t.Execute(w, page)
	// Take Three
	renderTemplate(w, "edit", page)
}

func saveHandler(w http.ResponseWriter, r *http.Request, title string) {
	// title := r.URL.Path[len("/save/"):]
	// Not neccesary after makeHandler was implemented
	// title, err := getTitle(w, r)
	// if err != nil {
	// 	return
	// }
	body := r.FormValue("body")
	p := &Page{Title: title, Body: []byte(body)}
	err := p.save()

	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	http.Redirect(w, r, "/view/"+title, http.StatusFound)
}

func main() {
	log.Printf("%s\n", templates.DefinedTemplates())
	// Using function literal and closures to handle not found
	// http.HandleFunc("/view/", viewHandler)
	// http.HandleFunc("/edit/", editHandler)
	// http.HandleFunc("/save/", saveHandler)
	http.HandleFunc("/view/", makeHandler(viewHandler))
	http.HandleFunc("/edit/", makeHandler(editHandler))
	http.HandleFunc("/save/", makeHandler(saveHandler))

	log.Println("Serving on: http://0.0.0.0:5001")
	log.Fatal(http.ListenAndServe(":5001", nil))
}

// func main() {
// 	p1 := &Page{Title: "TestPage", Body: []byte("This is a test page.")}
// 	p1.save()
// 	p2, _ := loadPage("TestPage")
// 	fmt.Println(string(p2.Body))
// }