pkg/app/http.go

package app

import (
	"bytes"
	"context"
	"crypto/sha1"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"text/template"
	"time"

	"github.com/maxence-charriere/go-app/v10/pkg/errors"
)

const (
	defaultThemeColor = "#2d2c2c"
)

// Handler configures an HTTP handler to serve HTML pages that initialize a
// Go WebAssembly (WASM) application along with its resources. It includes
// configurations for PWA features, offline support, auto-update, and more.
type Handler struct {
	// Name specifies the display name of the web app, used where space permits.
	Name string

	// ShortName is an abbreviated app name for limited display areas.
	ShortName string

	// Icon represents the app icon used for PWA, favicon, and the default
	// "not found" component. Attributes like crossorigin can be appended after
	// a space.
	Icon Icon

	// BackgroundColor sets a placeholder background color for the app page
	// before stylesheets load. Defaults to "#2d2c2c".
	BackgroundColor string

	// ThemeColor specifies the app's theme color, affecting OS-level UI elements
	// like the PWA title bar. Defaults to "#2d2c2c".
	ThemeColor string

	// LoadingLabel shows text during page load, with "{progress}" for progress.
	// Defaults to "{progress}%".
	LoadingLabel string

	// Lang defines the primary language of the app page. Defaults to "en".
	Lang string

	// Libraries are custom libraries to load with the page.
	Libraries []Library

	// Title sets the title of the app page.
	Title string

	// Description provides a summary of the page's content, used as default
	// meta description and og:description.
	Description string

	// Domain specifies the domain name for resolving page metadata like
	// 'og:url'.
	Domain string

	// Author lists the authors of the page.
	Author string

	// Keywords are words or phrases associated with the page.
	Keywords []string

	// Image specifies the default image path used by social networks.
	// Attributes like crossorigin can be appended after a space.
	Image string

	// Styles lists CSS files for the page, supporting local and external
	// resources. Attributes like crossorigin can be appended after a space.
	Styles []string

	// Fonts lists font files to preload, improving performance and visual
	// readiness. Attributes like crossorigin can be appended after a space.
	Fonts []string

	// Scripts lists JavaScript files for the page. Attributes like crossorigin,
	// async, and defer can be appended, separated with a space.
	Scripts []string

	// CacheableResources specifies extra static resources to cache for offline
	// access. Icon, Styles and Scripts are already cached by default.
	// Attributes like crossorigin can be appended after a space.
	CacheableResources []string

	// RawHeaders contains extra HTML headers for the page's <head> section.
	RawHeaders []string

	// HTML returns the page's HTML element. Defaults to app.Html().
	HTML func() HTMLHtml

	// Body returns the page's body element. Defaults to app.Body().
	Body func() HTMLBody

	// Env passes environment variables to the PWA. Note: Reserved keys
	// (GOAPP_VERSION, GOAPP_GOAPP_STATIC_RESOURCES_URL) cannot be
	// overridden and are used for internal configuration.
	Env map[string]string

	// InternalURLs lists URLs to open within the app, overriding default behavior
	// for external domains.
	InternalURLs []string

	// Preconnect specifies origins to preconnect to, speeding up future loads.
	// Attributes like crossorigin can be appended after a space.
	Preconnect []string

	// ProxyResources maps custom paths to static resources. /robots.txt,
	// /sitemap.xml, and /ads.txt, which are proxied by default.
	ProxyResources []ProxyResource

	// Resources resolves paths for static resources, specifically handling
	// paths prefixed with "/web/". Defaults to app.LocalDir("").
	Resources ResourceResolver

	// Version defines the app's version. It's crucial for determining if an
	// update is available. Must be set in live environments to avoid recurring
	// updates. Auto-generated by default for local development updates.
	Version string

	// WasmContentLength indicates the byte length of the WASM file for progress
	// calculation. Falls back to WasmContentLengthHeader if unset.
	WasmContentLength string

	// WasmContentLengthHeader specifies the HTTP header for the WASM file's
	// content length. Defaults to "Content-Length".
	WasmContentLengthHeader string

	// ServiceWorkerTemplate defines the app-worker.js template, defaulting
	// to DefaultAppWorkerJS. Modifications are discouraged to avoid potential
	// issues with go-app functionality.
	ServiceWorkerTemplate string

	once                 sync.Once
	etag                 string
	libraries            map[string][]byte
	proxyResources       map[string]ProxyResource
	cachedProxyResources *memoryCache
	cachedPWAResources   *memoryCache
}

func (h *Handler) init() {
	h.initVersion()
	h.initStaticResources()
	h.initLibraries()
	h.initLinks()
	h.initServiceWorker()
	h.initIcon()
	h.initPWA()
	h.initPageContent()
	h.initPWAResources()
	h.initProxyResources()
}

func (h *Handler) initVersion() {
	if h.Version == "" {
		t := time.Now().UTC().String()
		h.Version = fmt.Sprintf(`%x`, sha1.Sum([]byte(t)))
	}
	h.etag = `"` + h.Version + `"`
}

func (h *Handler) initStaticResources() {
	if h.Resources == nil {
		h.Resources = LocalDir("")
	}
}

func (h *Handler) initLibraries() {
	libs := make(map[string][]byte)
	for _, l := range h.Libraries {
		path, styles := l.Styles()
		if !strings.HasPrefix(path, "/") || len(styles) == 0 {
			continue
		}
		libs[path] = []byte(styles)
	}
	h.libraries = libs
}

func (h *Handler) initLinks() {
	styles := []string{"/app.css"}
	for path := range h.libraries {
		styles = append(styles, path)
	}
	h.Styles = append(styles, h.Styles...)
}

func (h *Handler) initServiceWorker() {
	if h.ServiceWorkerTemplate == "" {
		h.ServiceWorkerTemplate = DefaultAppWorkerJS
	}
}

func (h *Handler) initIcon() {
	if h.Icon.Default == "" {
		h.Icon.Default = "https://raw.githubusercontent.com/maxence-charriere/go-app/master/docs/web/icon.png"
		h.Icon.Large = "https://raw.githubusercontent.com/maxence-charriere/go-app/master/docs/web/icon.png"
	}

	if h.Icon.Maskable == "" {
		h.Icon.Maskable = h.Icon.Default
	}

	if h.Icon.SVG == "" {
		h.Icon.SVG = "https://raw.githubusercontent.com/maxence-charriere/go-app/master/docs/web/icon.svg"
	}
}

func (h *Handler) initPWA() {
	if h.Name == "" && h.ShortName == "" && h.Title == "" {
		h.Name = "App PWA"
	}
	if h.ShortName == "" {
		h.ShortName = h.Name
	}
	if h.Name == "" {
		h.Name = h.ShortName
	}

	if h.BackgroundColor == "" {
		h.BackgroundColor = defaultThemeColor
	}
	if h.ThemeColor == "" {
		h.ThemeColor = defaultThemeColor
	}

	if h.Lang == "" {
		h.Lang = "en"
	}

	if h.LoadingLabel == "" {
		h.LoadingLabel = "{progress}%"
	}
}

func (h *Handler) initPageContent() {
	if h.HTML == nil {
		h.HTML = Html
	}

	if h.Body == nil {
		h.Body = Body
	}

}

func (h *Handler) initPWAResources() {
	h.cachedPWAResources = newMemoryCache(5)

	h.cachedPWAResources.Set(cacheItem{
		Path:        "/wasm_exec.js",
		ContentType: "application/javascript",
		Body:        []byte(wasmExecJS()),
	})

	h.cachedPWAResources.Set(cacheItem{
		Path:        "/app.js",
		ContentType: "application/javascript",
		Body:        h.makeAppJS(),
	})

	h.cachedPWAResources.Set(cacheItem{
		Path:        "/app-worker.js",
		ContentType: "application/javascript",
		Body:        h.makeAppWorkerJS(),
	})

	h.cachedPWAResources.Set(cacheItem{
		Path:        "/manifest.webmanifest",
		ContentType: "application/manifest+json",
		Body:        h.makeManifestJSON(),
	})

	h.cachedPWAResources.Set(cacheItem{
		Path:        "/app.css",
		ContentType: "text/css",
		Body:        []byte(appCSS),
	})
}

func (h *Handler) makeAppJS() []byte {
	if h.Env == nil {
		h.Env = make(map[string]string)
	}
	internalURLs, _ := json.Marshal(h.InternalURLs)
	h.Env["GOAPP_INTERNAL_URLS"] = string(internalURLs)
	h.Env["GOAPP_VERSION"] = h.Version
	h.Env["GOAPP_STATIC_RESOURCES_URL"] = h.Resources.Resolve("/web")
	h.Env["GOAPP_ROOT_PREFIX"] = h.Resources.Resolve("/")

	for k, v := range h.Env {
		if err := os.Setenv(k, v); err != nil {
			Log(errors.New("setting app env variable failed").
				WithTag("name", k).
				WithTag("value", v).
				Wrap(err))
		}
	}

	var b bytes.Buffer
	if err := template.
		Must(template.New("app.js").Parse(appJS)).
		Execute(&b, struct {
			Env                     string
			LoadingLabel            string
			Wasm                    string
			WasmContentLength       string
			WasmContentLengthHeader string
			WorkerJS                string
		}{
			Env:                     jsonString(h.Env),
			LoadingLabel:            h.LoadingLabel,
			Wasm:                    h.Resources.Resolve("/web/app.wasm"),
			WasmContentLength:       h.WasmContentLength,
			WasmContentLengthHeader: h.WasmContentLengthHeader,
			WorkerJS:                h.Resources.Resolve("/app-worker.js"),
		}); err != nil {
		panic(errors.New("initializing app.js failed").Wrap(err))
	}
	return b.Bytes()
}

func (h *Handler) makeAppWorkerJS() []byte {
	resources := make(map[string]struct{})
	setResources := func(res ...string) {
		for _, r := range res {
			if resource := parseHTTPResource(r); resource.URL != "" {
				resources[resource.URL] = struct{}{}
			}
		}
	}
	setResources(
		"/app.css",
		"/app.js",
		"/manifest.webmanifest",
		"/wasm_exec.js",
		"/",
		"/web/app.wasm",
	)
	setResources(h.Icon.Default, h.Icon.Large, h.Icon.Maskable)
	setResources(h.Styles...)
	setResources(h.Fonts...)
	setResources(h.Scripts...)
	setResources(h.CacheableResources...)

	resourcesTocache := make([]string, 0, len(resources))
	for k := range resources {
		resourcesTocache = append(resourcesTocache, h.Resources.Resolve(k))
	}
	sort.Slice(resourcesTocache, func(a, b int) bool {
		return strings.Compare(resourcesTocache[a], resourcesTocache[b]) < 0
	})

	var b bytes.Buffer
	if err := template.
		Must(template.New("app-worker.js").Parse(h.ServiceWorkerTemplate)).
		Execute(&b, struct {
			Version          string
			ResourcesToCache string
		}{
			Version:          h.Version,
			ResourcesToCache: jsonString(resourcesTocache),
		}); err != nil {
		panic(errors.New("initializing app-worker.js failed").Wrap(err))
	}
	return b.Bytes()
}

func (h *Handler) makeManifestJSON() []byte {
	scope := h.Resources.Resolve("/")
	if scope != "/" && !strings.HasSuffix(scope, "/") {
		scope += "/"
	}

	var b bytes.Buffer
	if err := template.
		Must(template.New("manifest.webmanifest").Parse(manifestJSON)).
		Execute(&b, struct {
			ShortName       string
			Name            string
			Description     string
			DefaultIcon     string
			LargeIcon       string
			SVGIcon         string
			MaskableIcon    string
			BackgroundColor string
			ThemeColor      string
			Scope           string
			StartURL        string
		}{
			ShortName:       h.ShortName,
			Name:            h.Name,
			Description:     h.Description,
			DefaultIcon:     h.Resources.Resolve(h.Icon.Default),
			LargeIcon:       h.Resources.Resolve(h.Icon.Large),
			SVGIcon:         h.Resources.Resolve(h.Icon.SVG),
			MaskableIcon:    h.Resources.Resolve(h.Icon.Maskable),
			BackgroundColor: h.BackgroundColor,
			ThemeColor:      h.ThemeColor,
			Scope:           scope,
			StartURL:        h.Resources.Resolve("/"),
		}); err != nil {
		panic(errors.New("initializing manifest.webmanifest failed").Wrap(err))
	}
	return b.Bytes()
}

func (h *Handler) initProxyResources() {
	h.cachedProxyResources = newMemoryCache(len(h.ProxyResources))
	resources := make(map[string]ProxyResource)

	for _, r := range h.ProxyResources {
		switch r.Path {
		case "/wasm_exec.js",
			"/goapp.js",
			"/app.js",
			"/app-worker.js",
			"/manifest.json",
			"/manifest.webmanifest",
			"/app.css",
			"/app.wasm",
			"/goapp.wasm",
			"/":
			continue

		default:
			if strings.HasPrefix(r.Path, "/") && strings.HasPrefix(r.ResourcePath, "/web/") {
				resources[r.Path] = r
			}
		}
	}

	if _, ok := resources["/robots.txt"]; !ok {
		resources["/robots.txt"] = ProxyResource{
			Path:         "/robots.txt",
			ResourcePath: "/web/robots.txt",
		}
	}
	if _, ok := resources["/sitemap.xml"]; !ok {
		resources["/sitemap.xml"] = ProxyResource{
			Path:         "/sitemap.xml",
			ResourcePath: "/web/sitemap.xml",
		}
	}
	if _, ok := resources["/ads.txt"]; !ok {
		resources["/ads.txt"] = ProxyResource{
			Path:         "/ads.txt",
			ResourcePath: "/web/ads.txt",
		}
	}

	h.proxyResources = resources
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	h.once.Do(h.init)

	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("ETag", h.etag)

	etag := r.Header.Get("If-None-Match")
	if etag == h.etag {
		w.WriteHeader(http.StatusNotModified)
		return
	}

	path := r.URL.Path
	if strings.HasPrefix(path, "/"+h.Version+"/") {
		path = strings.TrimPrefix(path, "/"+h.Version)
	}

	fileHandler, isServingStaticResources := h.Resources.(http.Handler)
	if isServingStaticResources && strings.HasPrefix(path, "/web/") {
		fileHandler.ServeHTTP(w, r)
		return
	}

	switch path {
	case "/goapp.js":
		path = "/app.js"

	case "/manifest.json":
		path = "/manifest.webmanifest"

	case "/app.wasm", "/goapp.wasm":
		if isServingStaticResources {
			r2 := *r
			r2.URL.Path = h.Resources.Resolve("/web/app.wasm")
			fileHandler.ServeHTTP(w, &r2)
			return
		}
		w.WriteHeader(http.StatusNotFound)
		return

	}

	if res, ok := h.cachedPWAResources.Get(path); ok {
		h.serveCachedItem(w, res)
		return
	}

	if proxyResource, ok := h.proxyResources[path]; ok {
		h.serveProxyResource(proxyResource, w, r)
		return
	}

	if library, ok := h.libraries[path]; ok {
		h.serveLibrary(w, r, library)
		return
	}

	h.servePage(w, r)
}

func (h *Handler) serveCachedItem(w http.ResponseWriter, i cacheItem) {
	w.Header().Set("Content-Length", strconv.Itoa(i.Len()))
	w.Header().Set("Content-Type", i.ContentType)

	if i.ContentEncoding != "" {
		w.Header().Set("Content-Encoding", i.ContentEncoding)
	}

	w.WriteHeader(http.StatusOK)
	w.Write(i.Body)
}

func (h *Handler) serveProxyResource(resource ProxyResource, w http.ResponseWriter, r *http.Request) {
	var u string
	if _, ok := h.Resources.(http.Handler); ok {
		var protocol string
		if r.TLS != nil {
			protocol = "https://"
		} else {
			protocol = "http://"
		}
		u = protocol + r.Host + resource.ResourcePath
	} else {
		u = h.Resources.Resolve(resource.ResourcePath)
	}

	if i, ok := h.cachedProxyResources.Get(resource.Path); ok {
		h.serveCachedItem(w, i)
		return
	}

	res, err := http.Get(u)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		Log(errors.New("getting proxy static resource failed").
			WithTag("url", u).
			WithTag("proxy-path", resource.Path).
			WithTag("static-resource-path", resource.ResourcePath).
			Wrap(err),
		)
		return
	}
	defer res.Body.Close()

	if res.StatusCode != http.StatusOK {
		w.WriteHeader(http.StatusNotFound)
		return
	}

	body, err := io.ReadAll(res.Body)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		Log(errors.New("reading proxy static resource failed").
			WithTag("url", u).
			WithTag("proxy-path", resource.Path).
			WithTag("static-resource-path", resource.ResourcePath).
			Wrap(err),
		)
		return
	}

	item := cacheItem{
		Path:            resource.Path,
		ContentType:     res.Header.Get("Content-Type"),
		ContentEncoding: res.Header.Get("Content-Encoding"),
		Body:            body,
	}
	h.cachedProxyResources.Set(item)
	h.serveCachedItem(w, item)
}

func (h *Handler) servePage(w http.ResponseWriter, r *http.Request) {
	if routed := routes.routed(r.URL.Path); !routed {
		http.NotFound(w, r)
		return
	}

	ctx := context.Background()

	origin := *r.URL
	origin.Scheme = "http"

	page := makeRequestPage(&origin, h.Resources.Resolve)
	page.SetTitle(h.Title)
	page.SetLang(h.Lang)
	page.SetDescription(h.Description)
	page.SetAuthor(h.Author)
	page.SetKeywords(h.Keywords...)
	page.SetLoadingLabel(strings.ReplaceAll(h.LoadingLabel, "{progress}", "0"))
	page.SetImage(h.Image)

	engine := newEngine(ctx,
		&routes,
		h.Resources.Resolve,
		&page,
		actionHandlers,
	)
	engine.Navigate(page.URL(), false)
	engine.ConsumeAll()

	icon := h.Icon.SVG
	if icon == "" {
		icon = h.Icon.Default
	}

	var b bytes.Buffer
	err := engine.Encode(&b, h.HTML().
		Lang(page.Lang()).
		privateBody(
			Head().Body(
				Meta().Charset("UTF-8"),
				Meta().
					Name("author").
					Content(page.Author()),
				Meta().
					Name("description").
					Content(page.Description()),
				If(page.Keywords() != "", func() UI {
					return Meta().
						Name("keywords").
						Content(page.Keywords())
				}),
				Meta().
					Name("theme-color").
					Content(h.ThemeColor),
				Meta().
					Name("viewport").
					Content("width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0, viewport-fit=cover"),
				Meta().
					Property("og:url").
					Content(resolveOGResource(h.Domain, h.Resources.Resolve(page.URL().Path))),
				Meta().
					Property("og:title").
					Content(page.Title()),
				Meta().
					Property("og:description").
					Content(page.Description()),
				Meta().
					Property("og:type").
					Content("website"),
				Meta().
					Property("og:image").
					Content(resolveOGResource(h.Domain, page.Image())),
				Range(page.twitterCardMap).Map(func(k string) UI {
					v := page.twitterCardMap[k]
					if v == "" {
						return nil
					}
					if k == "twitter:image" {
						v = resolveOGResource(h.Domain, v)
					}
					return Meta().
						Name(k).
						Content(v)
				}),
				Title().Text(page.Title()),
				Range(h.Preconnect).Slice(func(i int) UI {
					if resource := parseHTTPResource(h.Preconnect[i]); resource.URL != "" {
						return resource.toLink().Rel("preconnect")
					}
					return nil
				}),
				Range(h.Fonts).Slice(func(i int) UI {
					if resource := parseHTTPResource(h.Fonts[i]); resource.URL != "" {
						return resource.toLink().
							Type("font/" + strings.TrimPrefix(filepath.Ext(resource.URL), ".")).
							Rel("preload").
							As("font")
					}
					return nil
				}),
				Range(page.Preloads()).Slice(func(i int) UI {
					p := page.Preloads()[i]
					if p.Href == "" || p.As == "" {
						return nil
					}

					if resource := parseHTTPResource(p.Href); resource.URL != "" {
						return resource.toLink().
							Type(p.Type).
							Rel("preload").
							As(p.As).
							FetchPriority(p.FetchPriority)
					}
					return nil
				}),
				Range(h.Styles).Slice(func(i int) UI {
					if resource := parseHTTPResource(h.Styles[i]); resource.URL != "" {
						return resource.toLink().
							Type("text/css").
							Rel("preload").
							As("style")
					}
					return nil
				}),
				Link().
					Rel("icon").
					Href(icon),
				Link().
					Rel("apple-touch-icon").
					Href(h.Icon.Maskable),
				Link().
					Rel("manifest").
					Href("/manifest.webmanifest"),
				Range(h.Styles).Slice(func(i int) UI {
					if resource := parseHTTPResource(h.Styles[i]); resource.URL != "" {
						return resource.toLink().
							Type("text/css").
							Rel("stylesheet")
					}
					return nil
				}),
				Script().
					Defer(true).
					Src("/wasm_exec.js"),
				Script().
					Defer(true).
					Src("/app.js"),
				Range(h.Scripts).Slice(func(i int) UI {
					if resource := parseHTTPResource(h.Scripts[i]); resource.URL != "" {
						return resource.toScript()
					}
					return nil

				}),
				Range(h.RawHeaders).Slice(func(i int) UI {
					return Raw(h.RawHeaders[i])
				}),
			),
			h.Body().privateBody(
				Aside().
					ID("app-wasm-loader").
					Class("goapp-app-info").
					Body(
						Img().
							ID("app-wasm-loader-icon").
							Class("goapp-logo goapp-spin").
							Alt("wasm loader icon").
							Src(h.Icon.Default),
						P().
							ID("app-wasm-loader-label").
							Class("goapp-label").
							Text(page.loadingLabel),
					),
			),
		))
	if err != nil {
		Log(errors.New("encoding html document failed").Wrap(err))
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Length", strconv.Itoa(b.Len()))
	w.Header().Set("Content-Type", "text/html")
	w.Write(b.Bytes())
}

func (h *Handler) serveLibrary(w http.ResponseWriter, r *http.Request, library []byte) {
	w.Header().Set("Content-Length", strconv.Itoa(len(library)))
	w.Header().Set("Content-Type", "text/css")
	w.Write(library)
}

// Icon represents a square image utilized in various contexts, such as the
// application icon, favicon, and loading icon. Paths specified for icons
// are relative to the root directory unless stated otherwise.
type Icon struct {
	// Default specifies the path or URL to a square image/png file with a
	// dimension of 192x192 pixels. Represents the standard application icon.
	Default string

	// Large indicates the path or URL to a larger square image/png file,
	// required to be 512x512 pixels. Used for high-resolution displays.
	Large string

	// SVG specifies the path or URL to an SVG file, providing vector-based
	// imagery for scalable application icons. Ideal for responsive design.
	SVG string

	// Maskable specifies the path or URL to an adaptive icon designed for various
	// operating system shapes. This icon must be a PNG image with 192x192 pixels.
	//
	// Used in PWA manifests and as meta tags for Apple browsers, these icons adapt
	// to device or browser shape requirements, avoiding unsightly cropping.
	//
	// To convert existing icons to a maskable format, visit
	// https://maskable.app/editor. This tool simplifies creating icons that meet
	// maskable specifications.
	//
	// If not specified, Icon.Default is used as a fallback. Specifying a maskable
	// icon enhances user experience on platforms supporting adaptive icons.
	Maskable string
}

func isRemoteLocation(path string) bool {
	return strings.HasPrefix(path, "https://") ||
		strings.HasPrefix(path, "http://")
}

func isStaticResourcePath(path string) bool {
	return strings.HasPrefix(path, "/web/") ||
		strings.HasPrefix(path, "web/")
}

type httpResource struct {
	URL         string
	LoadingMode string
	CrossOrigin string
}

func (r httpResource) toLink() HTMLLink {
	link := Link().Href(r.URL)
	if r.CrossOrigin != "" {
		link = link.CrossOrigin(strings.Trim(r.CrossOrigin, "true"))
	}
	return link
}

func (r httpResource) toScript() HTMLScript {
	script := Script().Src(r.URL)
	if r.CrossOrigin != "" {
		script = script.CrossOrigin(strings.Trim(r.CrossOrigin, "true"))
	}

	switch r.LoadingMode {
	case "defer":
		script = script.Defer(true)

	case "async":
		script = script.Async(true)
	}
	return script
}

func parseHTTPResource(v string) httpResource {
	var res httpResource
	for _, elem := range strings.Split(v, " ") {
		if elem = strings.TrimSpace(elem); elem == "" {
			continue
		}
		elem = strings.ToLower(elem)

		switch {
		case elem == "crossorigin":
			res.CrossOrigin = "true"

		case strings.HasPrefix(elem, "crossorigin="):
			res.CrossOrigin = strings.TrimPrefix(elem, "crossorigin=")

		case elem == "defer":
			res.LoadingMode = "defer"

		case elem == "async":
			res.LoadingMode = "async"

		default:
			res.URL = elem
		}
	}
	return res
}