Add error dialog when opening a non-text document (#28)

* Add error dialog when opening a non-text document

* remove errant line

* clean up indentation

* clean whitespace

Author: wpkelso

src/Application.vala

@@ -141,8 +141,23 @@ public class Application : Gtk.Application {
     }
 
     public bool open_window_with_file (File file) {
-        if (file.query_file_type (FileQueryInfoFlags.NONE) != FileType.REGULAR) {
-            warning ("Couldn't open, not a regular file.");
+
+        if (!Utils.check_if_valid_text_file (file)) {
+            var window = get_windows ().first ().data;
+            var error_dialog = new
+                Granite.MessageDialog.with_image_from_icon_name (
+                        "Couldn't open file",
+                        "The specified file is not a valid text file",
+                        "dialog-error"
+                        ) {
+                    transient_for = window
+                };
+
+            error_dialog.response.connect ((response_id) => {
+                    error_dialog.destroy ();
+                    });
+
+            error_dialog.show ();
             return false;
         }
 

src/Utils.vala

@@ -33,4 +33,23 @@
             warning ("Failed to prepare target data directory %s\n", err.message);
         }
     }
+
+    public static bool check_if_valid_text_file (File file) {
+        try {
+            FileInfo info = file.query_info ("*", NOFOLLOW_SYMLINKS);
+
+            var content_type = info.get_content_type ();
+            if (info.get_file_type () == FileType.REGULAR &&
+                    ContentType.is_a (content_type, "text/*") ||
+                    ContentType.is_a (content_type, "application/x-zerosize")
+               ) {
+                return true;
+            }
+
+        } catch (Error err) {
+            warning ("Failed to get file information: %s", err.message);
+        }
+
+        return false;
+    }
  }