2 files changed, 73 insertions, 0 deletions
diff --git a/lib/backend/managers/Handle.ml b/lib/backend/managers/Handle.ml
new file mode 100644
index 0000000..ed2f220
--- /dev/null
+++ b/lib/backend/managers/Handle.ml
@@ -0,0 +1,51 @@
+module type HANDLER = sig
+  type t
+  type handle
+  type cursor
+
+  val open_ : t -> path:Concepts.Path.t -> (handle, Concepts.Condition.condition) result
+
+  val open_cursor :
+    handle ->
+    args:Concepts.Value.value BatFingerTree.t ->
+    (cursor, Concepts.Condition.condition) result
+
+  val next : cursor -> (Concepts.Tuple.t option, Concepts.Condition.condition) result
+  val close : cursor -> unit
+end
+
+let not_a_relation () : Concepts.Condition.condition =
+  Concepts.Condition.condition "not-a-relation"
+    "handle does not refer to a stored or ephemeral relation" Concepts.Condition.empty
+
+module Make (Store : Abstract.Storage.STORAGE) = struct
+  module Cur = Cursor.Make (Store)
+
+  type t = {objects: Object.rnt_object_tree; txn: Store.transaction}
+  type handle = {object_: Object.registry; txn: Store.transaction}
+  type cursor = Cur.cursor
+
+  let create objects txn = {objects; txn}
+
+  let open_ t ~path =
+    let object_ = Object.find path t.objects in
+    Ok {object_; txn= t.txn}
+
+  let relation_descriptor (object_ : Object.registry) :
+      (Cursor.descriptor, Concepts.Condition.condition) result =
+    let {Object.entry; _} = object_ in
+    match entry.Object.kind with
+    | Object.Relation {merkle_root} -> Ok (Cursor.Stored {merkle_root})
+    | Object.EphemeralRelation {merkle_root; dependencies} ->
+        Ok (Cursor.Ephemeral {merkle_root; dependencies})
+    | _ -> Error (not_a_relation ())
+
+  let open_cursor handle ~args =
+    let open Utilities.Result in
+    let* descriptor = relation_descriptor handle.object_ in
+    Cur.open_ handle.txn descriptor ~args
+
+  let next = Cur.next
+  let close = Cur.close
+  let object_ (handle : handle) = handle.object_
+end
diff --git a/lib/backend/managers/Handle.mli b/lib/backend/managers/Handle.mli
new file mode 100644
index 0000000..5fc82b8
--- /dev/null
+++ b/lib/backend/managers/Handle.mli
@@ -0,0 +1,22 @@
+module type HANDLER = sig
+  type t
+  type handle
+  type cursor
+
+  val open_ : t -> path:Concepts.Path.t -> (handle, Concepts.Condition.condition) result
+
+  val open_cursor :
+    handle ->
+    args:Concepts.Value.value BatFingerTree.t ->
+    (cursor, Concepts.Condition.condition) result
+
+  val next : cursor -> (Concepts.Tuple.t option, Concepts.Condition.condition) result
+  val close : cursor -> unit
+end
+
+module Make (Store : Abstract.Storage.STORAGE) : sig
+  include HANDLER
+
+  val create : Object.rnt_object_tree -> Store.transaction -> t
+  val object_ : handle -> Object.registry
+end