Improve Markdown support

Close #259

app/src/main/java/com/topjohnwu/magisk/asyncs/MarkDownWindow.java

@@ -0,0 +1,50 @@
+package com.topjohnwu.magisk.asyncs;
+
+import android.app.Activity;
+import android.support.v7.app.AlertDialog;
+import android.webkit.WebView;
+
+import com.topjohnwu.magisk.R;
+import com.topjohnwu.magisk.utils.WebService;
+
+import org.commonmark.node.Node;
+import org.commonmark.parser.Parser;
+import org.commonmark.renderer.html.HtmlRenderer;
+
+public class MarkDownWindow extends ParallelTask<Void, Void, String> {
+
+    private String mTitle, mUrl;
+
+    public MarkDownWindow(Activity context, String title, String url) {
+        super(context);
+        mTitle = title;
+        mUrl = url;
+    }
+
+    @Override
+    protected String doInBackground(Void... voids) {
+        String md = WebService.getString(mUrl);
+        Parser parser = Parser.builder().build();
+        HtmlRenderer renderer = HtmlRenderer.builder().build();
+        Node doc = parser.parse(md);
+        return renderer.render(doc);
+    }
+
+    @Override
+    protected void onPostExecute(String html) {
+        AlertDialog.Builder alert = new AlertDialog.Builder(getActivity());
+        alert.setTitle(mTitle);
+
+        WebView wv = new WebView(getActivity());
+
+        html = String.format(
+                "<link rel='stylesheet' type='text/css' href='file:///android_asset/%s.css'/> %s",
+                getMagiskManager().isDarkTheme ? "dark" : "light", html);
+
+        wv.loadDataWithBaseURL("fake://", html, "text/html", "UTF-8", null);
+
+        alert.setView(wv);
+        alert.setNegativeButton(R.string.close, (dialog, id) -> dialog.dismiss());
+        alert.show();
+    }
+}