#331 Proposition for a new search app arch (#332)

* #331  Draft for the search arch

* #331  Subtask new search arch implementation

* #331  Drop contexts in favor of results processing

* #331  Minor imports fix

* #331  Review#1 fixes. Approve docs

pages/context/base.py

@@ -7,7 +7,7 @@
 class Context(abc.ABC):
 
     @abc.abstractmethod
-    def context(self) -> typing.Dict[str, typing.Any]:
+    def context(self) -> typing.ContextDict:
         ...
 
 

search/arch_draft.py

@@ -0,0 +1,93 @@
+"""
+This is temporary module with the arch concept for the search.
+
+@todo #331:60m  Implement the new arch at the search app.
+ All you need is to implement ContextsStack class
+ and place the other classes to the relevant places.
+ `search.search` module will be fully rewritten.
+ You also can drop away starting_by_term functionality.
+ See "is_name_start_by_term" aggregation parameter
+ inside search.search.search function.
+"""
+
+import abc
+import typing
+from itertools import chain
+
+from django.db.models import QuerySet
+from django.http import JsonResponse
+
+from images.models import Image
+
+
+class Representable(abc.ABC):
+    """Contract for objects that come as search results by different QuerySets."""
+
+    @property
+    def name(self):
+        raise NotImplemented()
+
+    @property
+    def url(self):
+        raise NotImplemented()
+
+
+class Result:
+    """
+    One item in a search results list.
+
+    Casts given object to common and clear result interface.
+    In case of the search module object is model instance.
+    Different objects can have very different interfaces.
+    That's why the class unifies it.
+    """
+    def __init__(self, obj: Representable):
+        self.name: str = obj.name
+        self.url: str = obj.url
+        self.image: Image = getattr(obj, 'image', None)
+        self.price: float = getattr(obj, 'price', 0.0)
+
+
+class Results:
+    def __init__(self, results_qs: QuerySet):
+        """`results_qs` is QuerySet with already searched and sorted entities."""
+        isinstance(results_qs.model, Representable)
+        self.qs = results_qs
+
+    def list(self) -> typing.List[Result]:
+        return [Result(o) for o in self.qs]
+
+
+class ResultsStack:
+    """Stack results with different merge strategies."""
+
+    def __init__(self, result_sets: typing.Iterable[Results]):
+        self.sets = result_sets
+
+    def chain(self) -> typing.Iterator[Result]:
+        return chain(*self.sets)
+
+
+# it's some client code:
+class CategoryQuerySet(QuerySet):
+    pass
+
+
+class ProductQuerySet(QuerySet):
+    pass
+
+
+def autocomplete(request, query):
+    # we'll use django orm search based on postgresql.
+    # Query sets will already contain searched entities.
+    # https://docs.djangoproject.com/en/1.11/topics/db/search/
+    return JsonResponse(list(
+        ResultsStack([
+            Results(
+                CategoryQuerySet().filter(name__search=query),
+            ),
+            Results(
+                ProductQuerySet().filter(name__search=query),
+            ),
+        ]).chain()
+    ))