1 files changed, 60 insertions, 0 deletions
diff --git a/lib/kernel/Branch.ml b/lib/kernel/Branch.ml
new file mode 100644
index 0000000..2aaa9ca
--- /dev/null
+++ b/lib/kernel/Branch.ml
@@ -0,0 +1,60 @@
+module Multigroup = Merkle.StringKey (* FIXME *)
+
+module Make (S : Abstract.Storage.STORAGE) = struct
+  (* Branch has a name, a set of multigroups, and a backlink to the previous state
+     multigroup has a name and a set of schemas
+     schema has a name and a set of relations
+
+     /branch/master/multigroup/universe/schema/sky/relation/planet
+   *)
+
+  module SI = Storage.Make (S)
+
+  module MultigroupM = Merkle.Interface (S) (Merkle.StringKey) (Multigroup)
+
+  type t = {
+    multigroups : MultigroupM.address;
+    previous : t SI.Pointer.t option
+  }
+
+  module rec Representation : Concepts.Encoding.Record.S with type t = t = Concepts.Encoding.Record.Make (Body)
+  and Body : Concepts.Encoding.Record.BODY = struct
+    type nonrec t = t
+
+    let load tx addr =
+      SI.get_req tx addr
+      |> Utilities.Result.fmap Representation.of_blob
+
+    let tag = 'Y'
+    let malformed () =
+      Concepts.Condition.
+      (condition "malformed-branch" "The on-disk representation of a branch did not conform to what was expected. Is your database corrupted?"
+         empty)
+
+    let fields { multigroups; previous } =
+      let open Concepts.Encoding in
+      ["multigroups", Value.bencode_of_hash multigroups;
+       "previous", Value.bencode_of_option
+                     (fun v -> SI.Pointer.address_of v
+                               |> SI.as_hash
+                               |> Value.bencode_of_hash)
+                     previous]
+
+    let of_fields fields =
+      let open Utilities.Result in
+      let open Concepts.Encoding in
+      let* multigroups = Bencode.field "multigroups" fields |> fmap Value.hash_of_bencode in
+      let* previous = Bencode.field "previous" fields
+                      |> fmap (Value.option_of_bencode
+                                 (fun v -> Value.hash_of_bencode v
+                                           |> Result.map (fun hash -> S.Hash hash)
+                                           |> Result.map (Fun.flip (SI.Pointer.make) load))) in
+      Ok { multigroups; previous }
+  end
+
+  class branch = object
+    (* TODO *)
+  end
+
+  let load _tx _conn _name _addr = failwith "TODO"
+end