package core

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

// errorTmpl is compiled from a literal, not from the theme's template
// files -- a broken view template is exactly the situation this page has
// to survive, so it cannot depend on LoadTemplates succeeding.
var errorTmpl = template.Must(template.New("error").Parse(`<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>{{.Code}} {{.Status}} &middot; {{.Site}}</title>
<link rel="stylesheet" href="/static/css/base.css">
</head>
<body>
<main class="wrap error-page">
  <p class="error-code">{{.Code}}</p>
  <h1 class="page-title">{{.Status}}</h1>
  <p class="page-subtitle">{{.Message}}</p>
  <p><a href="/">&larr; back to {{.Site}}</a></p>
</main>
</body>
</html>
`))

// renderErrorPage never returns an error: if the template somehow fails to
// execute, it falls back to a plain-text body rather than propagating.
func renderErrorPage(code int, site string) (body []byte, contentType string) {
	data := struct {
		Code                  int
		Status, Message, Site string
	}{
		Code:    code,
		Status:  http.StatusText(code),
		Message: friendlyMessage(code),
		Site:    site,
	}
	var buf bytes.Buffer
	if err := errorTmpl.Execute(&buf, data); err != nil {
		return []byte(fmt.Sprintf("%d %s\n", code, http.StatusText(code))), "text/plain; charset=utf-8"
	}
	return buf.Bytes(), "text/html; charset=utf-8"
}

// friendlyMessage keeps the diagnostic detail out of the response body --
// that stays in the server log -- while still telling a human what class
// of problem they hit.
func friendlyMessage(code int) string {
	switch code {
	case http.StatusNotFound:
		return "We couldn't find that repository, ref, or path."
	case http.StatusBadRequest:
		return "That request doesn't look right."
	case http.StatusRequestEntityTooLarge:
		return "That response is too large to display in full."
	default:
		return "Something went wrong rendering this page. The details were logged."
	}
}