From 3f6baa992d59da1c157fd502aa32d61299c65298 Mon Sep 17 00:00:00 2001
From: Nimisha Asthagiri <nasthagiri@edx.org>
Date: Wed, 28 Oct 2015 19:06:32 -0400
Subject: [PATCH] Transformer: VisibilityTransformer

---
 .../transformers/tests/__init__.py            |  0
 .../transformers/tests/test_visibility.py     | 43 ++++++++++
 .../course_blocks/transformers/visibility.py  | 80 +++++++++++++++++++
 3 files changed, 123 insertions(+)
 create mode 100644 lms/djangoapps/course_blocks/transformers/tests/__init__.py
 create mode 100644 lms/djangoapps/course_blocks/transformers/tests/test_visibility.py
 create mode 100644 lms/djangoapps/course_blocks/transformers/visibility.py

diff --git a/lms/djangoapps/course_blocks/transformers/tests/__init__.py b/lms/djangoapps/course_blocks/transformers/tests/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/lms/djangoapps/course_blocks/transformers/tests/test_visibility.py b/lms/djangoapps/course_blocks/transformers/tests/test_visibility.py
new file mode 100644
index 0000000000..c6841e707a
--- /dev/null
+++ b/lms/djangoapps/course_blocks/transformers/tests/test_visibility.py
@@ -0,0 +1,43 @@
+"""
+Tests for VisibilityTransformer.
+"""
+import ddt
+
+from ..visibility import VisibilityTransformer
+from .test_helpers import BlockParentsMapTestCase, update_block
+
+
+@ddt.ddt
+class VisibilityTransformerTestCase(BlockParentsMapTestCase):
+    """
+    VisibilityTransformer Test
+    """
+    # Following test cases are based on BlockParentsMapTestCase.parents_map
+    @ddt.data(
+        ({}, {0, 1, 2, 3, 4, 5, 6}, {}),
+        ({0}, {}, {1, 2, 3, 4, 5, 6}),
+        ({1}, {0, 2, 5, 6}, {3, 4}),
+        ({2}, {0, 1, 3, 4, 6}, {5}),
+        ({3}, {0, 1, 2, 4, 5, 6}, {}),
+        ({4}, {0, 1, 2, 3, 5, 6}, {}),
+        ({5}, {0, 1, 2, 3, 4, 6}, {}),
+        ({6}, {0, 1, 2, 3, 4, 5}, {}),
+        ({1, 2}, {0}, {3, 4, 5, 6}),
+        ({2, 4}, {0, 1, 3}, {5, 6}),
+        ({1, 2, 3, 4, 5, 6}, {0}, {}),
+    )
+    @ddt.unpack
+    def test_block_visibility(
+            self, staff_only_blocks, expected_visible_blocks, blocks_with_differing_access
+    ):
+        for idx, _ in enumerate(self.parents_map):
+            block = self.get_block(idx)
+            block.visible_to_staff_only = (idx in staff_only_blocks)
+            update_block(block)
+
+        self.assert_transform_results(
+            self.student,
+            expected_visible_blocks,
+            blocks_with_differing_access,
+            [VisibilityTransformer()],
+        )
diff --git a/lms/djangoapps/course_blocks/transformers/visibility.py b/lms/djangoapps/course_blocks/transformers/visibility.py
new file mode 100644
index 0000000000..cde91c1ad3
--- /dev/null
+++ b/lms/djangoapps/course_blocks/transformers/visibility.py
@@ -0,0 +1,80 @@
+"""
+Visibility Transformer implementation.
+"""
+from openedx.core.lib.block_cache.transformer import BlockStructureTransformer
+
+
+class VisibilityTransformer(BlockStructureTransformer):
+    """
+    A transformer that enforces the visible_to_staff_only field on
+    blocks by removing blocks from the block structure for which the
+    user does not have access. The visible_to_staff_only field on a
+    block is percolated down to its descendants, so that all blocks
+    enforce the visibility settings from their ancestors.
+
+    For a block with multiple parents, access is denied only if
+    visibility is denied for all its parents.
+
+    Staff users are exempted from visibility rules.
+    """
+    VERSION = 1
+
+    MERGED_VISIBLE_TO_STAFF_ONLY = 'merged_visible_to_staff_only'
+
+    @classmethod
+    def name(cls):
+        """
+        Unique identifier for the transformer's class;
+        same identifier used in setup.py.
+        """
+        return "visibility"
+
+    @classmethod
+    def get_visible_to_staff_only(cls, block_structure, block_key):
+        """
+        Returns whether the block with the given block_key in the
+        given block_structure should be visible to staff only per
+        computed value from ancestry chain.
+        """
+        return block_structure.get_transformer_block_field(
+            block_key, cls, cls.MERGED_VISIBLE_TO_STAFF_ONLY, False
+        )
+
+    @classmethod
+    def collect(cls, block_structure):
+        """
+        Collects any information that's necessary to execute this
+        transformer's transform method.
+        """
+        for block_key in block_structure.topological_traversal():
+
+            # compute merged value of visible_to_staff_only from all parents
+            parents = block_structure.get_parents(block_key)
+            all_parents_visible_to_staff_only = all(  # pylint: disable=invalid-name
+                cls.get_visible_to_staff_only(block_structure, parent_key)
+                for parent_key in parents
+            ) if parents else False
+
+            # set the merged value for this block
+            block_structure.set_transformer_block_field(
+                block_key,
+                cls,
+                cls.MERGED_VISIBLE_TO_STAFF_ONLY,
+                # merge visible_to_staff_only from all parents and this block
+                (
+                    all_parents_visible_to_staff_only or
+                    block_structure.get_xblock(block_key).visible_to_staff_only
+                )
+            )
+
+    def transform(self, usage_info, block_structure):
+        """
+        Mutates block_structure based on the given usage_info.
+        """
+        # Users with staff access bypass the Visibility check.
+        if usage_info.has_staff_access:
+            return
+
+        block_structure.remove_block_if(
+            lambda block_key: self.get_visible_to_staff_only(block_structure, block_key)
+        )