add sources endpoint and improve datasource middleware

Author: ExpDev07

app/routes/__init__.py

@@ -1,12 +1,12 @@
-from flask import Blueprint, redirect, request, current_app as app
+from flask import Blueprint, redirect, request, abort, current_app as app
 from ..data import data_source
 
 # Follow the import order to avoid circular dependency
 api_v1 = Blueprint('api_v1', __name__, url_prefix='')
 api_v2 = Blueprint('api_v2', __name__, url_prefix='/v2')
 
 # API version 2.
-from .v2 import locations, latest
+from .v2 import locations, latest, sources
 
 # API version 1.
 from .v1 import confirmed, deaths, recovered, all
@@ -23,8 +23,12 @@ def datasource():
     Attaches the datasource to the request.
     """
     # Retrieve the datas ource from query param.
-    source = request.args.get('source', type=str, default='jhu')
+    source = data_source(request.args.get('source', type=str, default='jhu'))
+
+    # Abort with 404 if source cannot be found.
+    if not source:
+        return abort(404, description='The provided data-source was not found.')
 
     # Attach source to request and return it.
-    request.source = data_source(source)
+    request.source = source
     pass

app/routes/v2/sources.py

@@ -0,0 +1,12 @@
+from flask import jsonify
+from ...data import data_sources
+from ...routes import api_v2 as api
+
+@api.route('/sources')
+def sources():
+    """
+    Retrieves a list of data-sources that are availble to use.
+    """
+    return jsonify({
+        'sources': list(data_sources.keys())
+    })