helper: Show confirmation overlay before displaying any media.

Test amended.

Author: preetmishra

tests/helper/test_helper.py

@@ -322,9 +322,11 @@ def test_open_media(mocker, media_link, message_id, expected_path, platform,
     sys = mocker.patch('zulipterminal.helper.sys')
     sys.platform = platform
     open = mocker.patch('zulipterminal.helper.open')
+    partial = mocker.patch('zulipterminal.helper.partial')
 
     open_media(controller, media_link, message_id)
 
-    params = subprocess.run.call_args_list[0][0][0]
+    params = partial.call_args_list[0][0][1]
     assert params[0] == expected_command
     assert params[1] == expected_path
+    controller.show_confirmation_overlay.called

zulipterminal/helper.py

@@ -4,7 +4,7 @@
 import sys
 import time
 from collections import OrderedDict, defaultdict
-from functools import wraps
+from functools import partial, wraps
 from itertools import chain, combinations
 from re import ASCII, match
 from tempfile import gettempdir
@@ -16,6 +16,7 @@
 
 import lxml.html
 import requests
+import urwid
 from mypy_extensions import TypedDict
 
 
@@ -665,4 +666,7 @@ def open_media(controller: Any, media_link: str, message_id: int) -> None:
         'darwin': 'open',
     }
     command = image_viewers[sys.platform]
-    subprocess.run([command, img_path])
+    callback = partial(subprocess.run, [command, img_path])
+    question = urwid.Text("Your requested media has been downloaded."
+                          " Do you want to view it?")
+    controller.show_confirmation_overlay(question, callback)