Add ModDB download helper

This helper facility will seamlessly swap a "File" url (e.g. "https://www.moddb.com/games/tribes/downloads/starsiege-tribes-retro-version") into a mirror download link.

This enables installer authors to specify files to be downloaded directly from ModDB, e.g.

```
files:
    - t1_setup:
        url: https://www.moddb.com/games/tribes/downloads/starsiege-tribes-retro-version
        filename: t1retro.exe
        referer: https://www.moddb.com/games/tribes/downloads
```

Signed-off-by: Antoine Mazeas <antoine@karthanis.net>

lutris/gui/dialogs/__init__.py

@@ -4,6 +4,7 @@ from gettext import gettext as _
 
 import gi
 
+gi.require_version('Gdk', '3.0')
 gi.require_version('Gtk', '3.0')
 
 from gi.repository import Gdk, GLib, GObject, Gtk

lutris/installer/installer.py

@@ -15,6 +15,7 @@ from lutris.services import SERVICES
 from lutris.util.game_finder import find_linux_game_executable, find_windows_game_executable
 from lutris.util.gog import convert_gog_config_to_lutris, get_gog_config_from_path, get_gog_game_path
 from lutris.util.log import logger
+from lutris.util.moddb import downloadhelper as moddbhelper
 
 
 class LutrisInstaller:  # pylint: disable=too-many-instance-attributes
@@ -158,6 +159,8 @@ class LutrisInstaller:  # pylint: disable=too-many-instance-attributes
         # Run variable substitution on the URLs from the script
         for file in self.files:
             file.set_url(self.interpreter._substitute(file.url))
+            if moddbhelper.is_moddb_url(file.url):
+                file.set_url(moddbhelper.get_moddb_download_url(file.url))
 
         if installer_file_id and self.service:
             logger.info("Getting files for %s", installer_file_id)

lutris/util/moddb/downloadhelper.py

@@ -0,0 +1,27 @@
+"""Helper functions to assist downloading files from ModDB"""
+import moddb
+import re
+
+MODDB_FQDN = 'https://www.moddb.com'
+MODDB_URL_MATCHER = '^https://(www\.)?moddb\.com'
+
+def is_moddb_url(url):
+    return re.match(MODDB_URL_MATCHER, url.lower()) is not None
+
+def get_moddb_download_url(moddb_permalink_url):
+    return MODDB_FQDN + __autoselect_moddb_mirror(__get_html_and_resolve_mirrors_list(moddb_permalink_url))._url
+
+def __autoselect_moddb_mirror(mirrors_list):
+    # dumb autoselect for now: rank mirrors by capacity (lower is better), pick first (lowest load)
+    return sorted(mirrors_list, key=lambda m: m.capacity)[0]
+
+def __get_html_and_resolve_mirrors_list(moddb_permalink_url):
+    moddb_obj = moddb.parse_page(moddb_permalink_url)
+    if not isinstance(moddb_obj, moddb.File):
+        raise RuntimeError("supplied url does not point to the page of a file hosted on moddb.com")
+
+    mirrors_list = moddb_obj.get_mirrors()
+    if not any(mirrors_list):
+        raise RuntimeError("no available mirror for the file hosted on moddb.com")
+
+    return mirrors_list

lutris/util/test_config.py

@@ -2,6 +2,7 @@ import os
 
 import gi
 
+gi.require_version('Gdk', '3.0')
 gi.require_version('Gtk', '3.0')
 
 from lutris import startup

setup.py

@@ -45,6 +45,7 @@ setup(
         'lutris.util.egs',
         'lutris.util.graphics',
         'lutris.util.mame',
+        'lutris.util.moddb',
         'lutris.util.steam',
         'lutris.util.steam.vdf',
         'lutris.util.retroarch',
@@ -65,7 +66,8 @@ setup(
         'pypresence',
         'PyYAML',
         'requests',
-        'pypresence'
+        'pypresence',
+        'moddb'
     ],
     url='https://lutris.net',
     description='Video game preservation platform',

tests/test_moddb_helper.py

@@ -0,0 +1,37 @@
+import unittest
+from lutris.util.moddb import downloadhelper as moddb
+
+
+class ModDBHelperTests(unittest.TestCase):
+  def test_is_moddb_url_has_www_success(self):
+    url = 'https://www.moddb.com/something'
+    self.assertTrue(moddb.is_moddb_url(url))
+  
+  def test_is_moddb_url_no_slug_has_www_success(self):
+    url = 'https://www.moddb.com'
+    self.assertTrue(moddb.is_moddb_url(url))
+
+  def test_is_moddb_url_no_www_success(self):
+    url = 'https://moddb.com/something'
+    self.assertTrue(moddb.is_moddb_url(url))
+  
+  def test_is_moddb_url_no_slug_no_www_success(self):
+    url = 'https://moddb.com'
+    self.assertTrue(moddb.is_moddb_url(url))
+
+  def test_is_moddb_url_other_subdomain_failure(self):
+    url = 'https://subdomain.moddb.com/something'
+    self.assertFalse(moddb.is_moddb_url(url))
+  
+  def test_is_moddb_url_no_slug_other_subdomain_failure(self):
+    url = 'https://subdomain.moddb.com'
+    self.assertFalse(moddb.is_moddb_url(url))
+
+  def test_is_moddb_url_random_domain_failure(self):
+    url = 'https://somedomain.com/something'
+    self.assertFalse(moddb.is_moddb_url(url))
+  
+  def test_is_moddb_url_no_slug_random_domain_failure(self):
+    url = 'https://somedomain.com'
+    self.assertFalse(moddb.is_moddb_url(url))
+