WebUI: handle drag and drop events

This allows user to drag and drop .torrent files and URL links onto the
main window and will open the respective dialog.
Dropping folders are not supported due to technical reasons.

Closes #6038.

src/webui/www/private/scripts/client.js

@@ -128,7 +128,6 @@ const qbtVersion = function() {
 };
 
 window.addEvent('load', function() {
-
     const saveColumnSizes = function() {
         const filters_width = $('Filters').getSize().x;
         const properties_height_rel = $('propertiesPanel').getSize().y / Window.getSize().y;
@@ -1187,6 +1186,98 @@ window.addEvent('load', function() {
     $('searchTabLink').addEvent('click', showSearchTab);
     $('rssTabLink').addEvent('click', showRssTab);
     updateTabDisplay();
+
+    const registerDragAndDrop = () => {
+        $('desktop').addEventListener('dragover', (ev) => {
+            if (ev.preventDefault)
+                ev.preventDefault();
+        });
+
+        $('desktop').addEventListener('dragenter', (ev) => {
+            if (ev.preventDefault)
+                ev.preventDefault();
+        });
+
+        $('desktop').addEventListener("drop", (ev) => {
+            if (ev.preventDefault)
+                ev.preventDefault();
+
+            const droppedFiles = ev.dataTransfer.files;
+
+            if (droppedFiles.length > 0) {
+                // dropped files or folders
+
+                // can't handle folder due to cannot put the filelist (from dropped folder)
+                // to <input> `files` field
+                for (const item of ev.dataTransfer.items) {
+                    if (item.webkitGetAsEntry().isDirectory)
+                        return;
+                }
+
+                const id = 'uploadPage';
+                new MochaUI.Window({
+                    id: id,
+                    title: "QBT_TR(Upload local torrent)QBT_TR[CONTEXT=HttpServer]",
+                    loadMethod: 'iframe',
+                    contentURL: new URI("upload.html").toString(),
+                    addClass: 'windowFrame', // fixes iframe scrolling on iOS Safari
+                    scrollbars: true,
+                    maximizable: false,
+                    paddingVertical: 0,
+                    paddingHorizontal: 0,
+                    width: loadWindowWidth(id, 500),
+                    height: loadWindowHeight(id, 460),
+                    onResize: () => {
+                        saveWindowSize(id);
+                    },
+                    onContentLoaded: () => {
+                        const fileInput = $(`${id}_iframe`).contentDocument.getElementById('fileselect');
+                        fileInput.files = droppedFiles;
+                    }
+                });
+            }
+
+            const droppedText = ev.dataTransfer.getData("text");
+            if (droppedText.length > 0) {
+                // dropped text
+
+                const urls = droppedText.split('\n')
+                    .map((str) => str.trim())
+                    .filter((str) => {
+                        const lowercaseStr = str.toLowerCase();
+                        return lowercaseStr.startsWith("http:")
+                            || lowercaseStr.startsWith("https:")
+                            || lowercaseStr.startsWith("magnet:")
+                            || ((str.length === 40) && !(/[^0-9A-Fa-f]/.test(str))) // v1 hex-encoded SHA-1 info-hash
+                            || ((str.length === 32) && !(/[^2-7A-Za-z]/.test(str))); // v1 Base32 encoded SHA-1 info-hash
+                    });
+
+                if (urls.length <= 0)
+                    return;
+
+                const id = 'downloadPage';
+                const contentURI = new URI('download.html').setData("urls", urls.map(encodeURIComponent).join("|"));
+                new MochaUI.Window({
+                    id: id,
+                    title: "QBT_TR(Download from URLs)QBT_TR[CONTEXT=downloadFromURL]",
+                    loadMethod: 'iframe',
+                    contentURL: contentURI.toString(),
+                    addClass: 'windowFrame', // fixes iframe scrolling on iOS Safari
+                    scrollbars: true,
+                    maximizable: false,
+                    closable: true,
+                    paddingVertical: 0,
+                    paddingHorizontal: 0,
+                    width: loadWindowWidth(id, 500),
+                    height: loadWindowHeight(id, 600),
+                    onResize: () => {
+                        saveWindowSize(id);
+                    }
+                });
+            }
+        });
+    };
+    registerDragAndDrop();
 });
 
 function registerMagnetHandler() {