✨(back) allow theme customnization using a configuration file

We want to customize the theme by using a configuration file. This
configuration file path can be defined using the settings
THEME_CUSTOMIZATION_FILE_PATH. If this file does not exists or is an
invalid json, an empty json object will be added in the config endpoint.

src/backend/core/tests/test_api_config.py

@@ -2,6 +2,8 @@
 Test config API endpoints in the Impress core app.
 """
 
+import json
+
 from django.test import override_settings
 
 import pytest
@@ -24,6 +26,7 @@ pytestmark = pytest.mark.django_db
     MEDIA_BASE_URL="http://testserver/",
     POSTHOG_KEY={"id": "132456", "host": "https://eu.i.posthog-test.com"},
     SENTRY_DSN="https://sentry.test/123",
+    THEME_CUSTOMIZATION_FILE_PATH="",
 )
 @pytest.mark.parametrize("is_authenticated", [False, True])
 def test_api_config(is_authenticated):
@@ -56,4 +59,98 @@ def test_api_config(is_authenticated):
         "POSTHOG_KEY": {"id": "132456", "host": "https://eu.i.posthog-test.com"},
         "SENTRY_DSN": "https://sentry.test/123",
         "AI_FEATURE_ENABLED": False,
+        "theme_customization": {},
     }
+
+
+@override_settings(
+    THEME_CUSTOMIZATION_FILE_PATH="/not/existing/file.json",
+)
+@pytest.mark.parametrize("is_authenticated", [False, True])
+def test_api_config_with_invalid_theme_customization_file(is_authenticated):
+    """Anonymous users should be allowed to get the configuration."""
+    client = APIClient()
+
+    if is_authenticated:
+        user = factories.UserFactory()
+        client.force_login(user)
+
+    response = client.get("/api/v1.0/config/")
+    assert response.status_code == HTTP_200_OK
+    content = response.json()
+    assert content["theme_customization"] == {}
+
+
+@override_settings(
+    THEME_CUSTOMIZATION_FILE_PATH="/configuration/theme/invalid.json",
+)
+@pytest.mark.parametrize("is_authenticated", [False, True])
+def test_api_config_with_invalid_json_theme_customization_file(is_authenticated, fs):
+    """Anonymous users should be allowed to get the configuration."""
+    fs.create_file(
+        "/configuration/theme/invalid.json",
+        contents="invalid json",
+    )
+    client = APIClient()
+
+    if is_authenticated:
+        user = factories.UserFactory()
+        client.force_login(user)
+
+    response = client.get("/api/v1.0/config/")
+    assert response.status_code == HTTP_200_OK
+    content = response.json()
+    assert content["theme_customization"] == {}
+
+
+@override_settings(
+    THEME_CUSTOMIZATION_FILE_PATH="/configuration/theme/default.json",
+)
+@pytest.mark.parametrize("is_authenticated", [False, True])
+def test_api_config_with_theme_customization(is_authenticated, fs):
+    """Anonymous users should be allowed to get the configuration."""
+    fs.create_file(
+        "/configuration/theme/default.json",
+        contents=json.dumps(
+            {
+                "colors": {
+                    "primary": "#000000",
+                    "secondary": "#000000",
+                },
+            }
+        ),
+    )
+    client = APIClient()
+
+    if is_authenticated:
+        user = factories.UserFactory()
+        client.force_login(user)
+
+    response = client.get("/api/v1.0/config/")
+    assert response.status_code == HTTP_200_OK
+    content = response.json()
+    assert content["theme_customization"] == {
+        "colors": {
+            "primary": "#000000",
+            "secondary": "#000000",
+        },
+    }
+
+
+@pytest.mark.parametrize("is_authenticated", [False, True])
+def test_api_config_with_original_theme_customization(is_authenticated, settings):
+    """Anonymous users should be allowed to get the configuration."""
+    client = APIClient()
+
+    if is_authenticated:
+        user = factories.UserFactory()
+        client.force_login(user)
+
+    response = client.get("/api/v1.0/config/")
+    assert response.status_code == HTTP_200_OK
+    content = response.json()
+
+    with open(settings.THEME_CUSTOMIZATION_FILE_PATH, "r", encoding="utf-8") as f:
+        theme_customization = json.load(f)
+
+    assert content["theme_customization"] == theme_customization