Paginate the job_tasks page.

This commit adds pagination to the /api/v1/jobs/{id}/job_tasks/ page,
which previously lacked it.

AC-1340

awx/api/utils/decorators.py

@@ -0,0 +1,66 @@
+# Copyright (c) 2014 Ansible, Inc.
+# All Rights Reserved.
+
+import collections
+import copy
+import functools
+
+from rest_framework.response import Response
+from rest_framework.settings import api_settings
+
+def paginated(method):
+    """Given an method with a Django REST Framework API method signature
+    (e.g. `def get(self, request, ...):`), abstract out boilerplate pagination
+    duties.
+
+    This causes the method to receive two additional keyword arguments:
+    `limit`, and `offset`. The method expects a two-tuple to be
+    returned, with a result list as the first item, and the total number
+    of results (across all pages) as the second item.
+    """
+    @functools.wraps(method)
+    def func(self, request, *args, **kwargs):
+        # Manually spin up pagination.
+        # How many results do we show?
+        limit = api_settings.PAGINATE_BY
+        if request.QUERY_PARAMS.get(api_settings.PAGINATE_BY_PARAM, False):
+            limit = request.QUERY_PARAMS[api_settings.PAGINATE_BY_PARAM]
+        if api_settings.MAX_PAGINATE_BY:
+            limit = min(api_settings.MAX_PAGINATE_BY, limit)
+        limit = int(limit)
+
+        # What page are we on?
+        page = int(request.QUERY_PARAMS.get('page', 1))
+        offset = (page - 1) * limit
+
+        # Add the limit, offset, and page variables to the keyword arguments
+        # being sent to the underlying method.
+        kwargs['limit'] = limit
+        kwargs['offset'] = offset
+
+        # Okay, call the underlying method.
+        results, count = method(self, request, *args, **kwargs)
+
+        # Determine the next and previous pages, if any.
+        prev, next_ = None, None
+        if page > 1:
+            get_copy = copy.copy(request.GET)
+            get_copy['page'] = page - 1
+            prev = '%s?%s' % (request.path, get_copy.urlencode())
+        if count > offset + limit:
+            get_copy = copy.copy(request.GET)
+            get_copy['page'] = page + 1
+            next_ = '%s?%s' % (request.path, get_copy.urlencode())
+
+        # Compile the results into a dictionary with pagination
+        # information.
+        answer = collections.OrderedDict((
+            ('count', count),
+            ('next', next_),
+            ('previous', prev),
+            ('results', results),
+        ))
+
+        # Okay, we're done; return response data.
+        return Response(answer)
+    return func