Provide a new @navtree REST API service

src/osha/oira/services/configure.zcml

@@ -12,4 +12,13 @@
       name="@tool-versions"
       />
 
+  <plone:service
+      method="GET"
+      factory=".navigation.NavigationService"
+      permission="zope2.View"
+      for="*"
+      layer="osha.oira.interfaces.IOSHAContentSkinLayer"
+      name="@navtree"
+      />
+
 </configure>

src/osha/oira/services/navigation.py

@@ -0,0 +1,67 @@
+from plone import api
+from plone.restapi.services import Service
+
+
+class NavigationService(Service):
+    """This JSON service reuses the navigation tile to serve through the
+    REST API the navigation tree of this context.
+
+    The nodes of the tree should be prepared to have a successful
+    JSON serialization.
+
+    This method removes the keys:
+
+    - brain (which is not serializable)
+    - parent (which will create a circular reference)
+
+    and renames some keys to match the plone.restapi standards:
+
+    - portal_type -> @type
+    - url -> @id
+
+    It also fixes the portal_type which is returned normalized
+    with a dash instead of a dot.
+    """
+
+    def fix_node(self, node):
+        """Prepare a node for serialization"""
+        banned_keys = [
+            "brain",  # not serializable
+            "parent",  # creates a circular reference
+        ]
+        for key in banned_keys:
+            if key in node:
+                del node[key]
+
+        # Rename keys to match plone.restapi standards
+        mapping = {
+            "portal_type": "@type",
+            "url": "@id",
+            "children": "items",
+        }
+        for old_key, new_key in mapping.items():
+            if old_key in node:
+                node[new_key] = node.pop(old_key)
+
+        # Fix the portal_type
+        if "@type" in node:
+            node["@type"] = node["@type"].replace("-", ".")
+
+        # Recurse into children
+        if "items" in node:
+            for child in node["items"]:
+                self.fix_node(child)
+
+        return node
+
+    def reply(self):
+        """We use the navtree tile to get the navigation tree,
+        but we have to fiddle with the nodes to have a proper serialization.
+        """
+        navtree_tile = api.content.get_view("navtree", self.context, self.request)
+        navtree_tile.update()
+        tree = [self.fix_node(node) for node in navtree_tile.tree]
+        return {
+            "@id": self.request.getURL(),
+            "items": tree,
+        }