Display link for Pay button (#2017)

fixes #635

BTCPayServer/Views/Stores/PayButton.cshtml

@@ -153,6 +153,9 @@
         <div class="col-lg-5">
             <h4>Preview</h4>
             <div id="preview"></div>
+            <h4 class="mt-2">Link</h4>
+            <span>Alternatively, you can share this link or encode it in a QR code</span>
+            <div id="preview-link"></div>
         </div>
     </div>
     <hr />

BTCPayServer/wwwroot/paybutton/paybutton.js

@@ -188,7 +188,17 @@ function inputChanges(event, buttonSize) {
 
     $("#mainCode").text(html).html();
     $("#preview").html(html);
-
+    var form = document.querySelector("#preview form");
+    var url =  new URL(form.getAttribute("action"));
+    var formData =   new FormData(form);
+    formData.forEach((value, key) => {
+        if(key !== "jsonResponse"){
+            url.searchParams.append(key, value);
+        }
+    });
+    url = url.href;
+    $("#preview-link").append(`<a href="${url}">${url}</a>`)
+    
     $('pre code').each(function (i, block) {
         hljs.highlightBlock(block);
     });