1 files changed, 42 insertions, 0 deletions
diff --git a/gn2/wqflask/startup.py b/gn2/wqflask/startup.py
new file mode 100644
index 00000000..069755fe
--- /dev/null
+++ b/gn2/wqflask/startup.py
@@ -0,0 +1,42 @@
+"""Checks to do before the application is started."""
+from typing import Tuple
+
+from flask import Blueprint, current_app, render_template
+
+class StartupError(Exception):
+    """Base class for Application Check Errors."""
+
+class MissingConfigurationError(StartupError):
+    """Raised in case of a missing required setting."""
+
+    def __init__(self, missing=Tuple[str, ...]):
+        """Initialise the MissingConfigurationError object."""
+        super().__init__("At least one required configuration is missing.")
+        self.missing = missing
+
+startup_errors = Blueprint("app_check_errors", __name__)
+__MANDATORY_CONFIGURATIONS__ = (
+    "REDIS_URL", # URI to Redis server
+    "SQL_URI", # URI to MariaDB server
+    "GN_SERVER_URL", # REST API Server
+    "AUTH_SERVER_URL" # Auth(entic/oris)ation Server
+)
+
+def check_mandatory_configs(app):
+    """Check that all mandatory configuration settings are defined."""
+    missing = tuple(
+        setting for setting in __MANDATORY_CONFIGURATIONS__
+        if (setting not in app.config
+            or app.config.get(setting) is None
+            or app.config.get(setting).strip() == ""))
+    if len(missing) > 0:
+        print(missing)
+        raise MissingConfigurationError(missing)
+
+@startup_errors.route("/")
+def error_index():
+    """Display errors experienced at application startup"""
+    return render_template(
+        "startup_errors.html",
+        error_type = type(current_app.startup_error).__name__,
+        error_value = current_app.startup_error)