// Chapter 34 example: what happens when Execute fails halfway. The template asks
// for a field that does not exist, so that Execute always fails here.
// Run with: go run exercises/34/02-execute-error.go

package main

import (
	"bytes"
	"fmt"
	"html/template"
	"net/http"
)

type pageData struct {
	Name string
}

const brokenText = `<h1>{{.Name}}</h1>
<p>{{.Missing}}</p>
`

var brokenTemplate = template.Must(template.New("broken").Parse(brokenText))

// handleDirect writes straight to the visitor, so the first half of the page
// has gone out by the time Execute fails.
func handleDirect(w http.ResponseWriter, r *http.Request) {
	data := pageData{Name: "Keiko"}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	err := brokenTemplate.Execute(w, data)
	if err != nil {
		fmt.Println("Template error:", err)
	}
}

// handleBuffered builds the whole page in memory first, so nothing has gone out
// when Execute fails, and it can still choose the status.
func handleBuffered(w http.ResponseWriter, r *http.Request) {
	data := pageData{Name: "Keiko"}

	var page bytes.Buffer
	err := brokenTemplate.Execute(&page, data)
	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 main() {
	http.HandleFunc("GET /direct", handleDirect)
	http.HandleFunc("GET /buffered", handleBuffered)

	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)
	}
}