Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/ui/static_javascript.go

@@ -0,0 +1,38 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package ui // import "miniflux.app/v2/internal/ui"
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"miniflux.app/v2/internal/http/request"
+	"miniflux.app/v2/internal/http/response"
+	"miniflux.app/v2/internal/http/response/html"
+	"miniflux.app/v2/internal/http/route"
+	"miniflux.app/v2/internal/ui/static"
+)
+
+func (h *handler) showJavascript(w http.ResponseWriter, r *http.Request) {
+	filename := request.RouteStringParam(r, "name")
+	etag, found := static.JavascriptBundleChecksums[filename]
+	if !found {
+		html.NotFound(w, r)
+		return
+	}
+
+	response.New(w, r).WithCaching(etag, 48*time.Hour, func(b *response.Builder) {
+		contents := static.JavascriptBundles[filename]
+
+		if filename == "service-worker" {
+			variables := fmt.Sprintf(`const OFFLINE_URL="%s";`, route.Path(h.router, "offline"))
+			contents = append([]byte(variables)[:], contents[:]...)
+		}
+
+		b.WithHeader("Content-Type", "text/javascript; charset=utf-8")
+		b.WithBody(contents)
+		b.Write()
+	})
+}