1 files changed, 152 insertions, 0 deletions
diff --git a/lib/kernel/Scope.ml b/lib/kernel/Scope.ml
new file mode 100644
index 0000000..23698ba
--- /dev/null
+++ b/lib/kernel/Scope.ml
@@ -0,0 +1,152 @@
+type home = {multigroup: string; schema: string}
+
+class type implementation = object
+  method branch : Protocols.Handle.t
+  method home : home
+  method previous : (Protocols.Handle.t option, Concepts.Condition.condition) result
+  method catalog : (string list, Concepts.Condition.condition) result
+end
+
+type Protocols.Handle.protocol += Scope of implementation
+
+let require handle =
+  Protocols.Handle.into handle (function Scope i -> Some i | _ -> None)
+  |> Option.to_result
+       ~none:
+         Concepts.Condition.(
+           condition "not-a-scope" "A handle was expected to be a branch state read from a home"
+             empty )
+
+let relations {multigroup; schema} =
+  Path.("multigroup" @/ multigroup @/ "schema" @/ schema @/ "relation" @/ this)
+
+let path home relation = Path.(of_list (to_list (relations home) @ [relation]))
+let denial multigroup = Path.("multigroup" @/ multigroup @/ "denial" @/ this)
+
+(* A name leaves out, from the left, what it shares with its home. *)
+let resolve home text =
+  match String.split_on_char ':' text with
+  | names when List.mem "" names -> None
+  | [r] -> Some (home, r)
+  | [s; r] -> Some ({home with schema= s}, r)
+  | [m; s; r] -> Some ({multigroup= m; schema= s}, r)
+  | _ -> None
+
+let locate home text = Option.map (fun (h, r) -> path h r) (resolve home text)
+
+let attribute home relation text =
+  match List.rev (String.split_on_char ':' text) with
+  | [a] -> Some a
+  | a :: rest when resolve home (String.concat ":" (List.rev rest)) = resolve home relation ->
+      Some a
+  | _ -> None
+
+(* every relation of a branch state, as multigroup:schema:relation *)
+let catalog_of branch =
+  let open Utilities.Result in
+  let name prefix last = String.concat ":" (List.rev (last :: prefix)) in
+  let rec down prefix handle properties =
+    let* level = Path.find handle Path.(List.hd properties @/ this) in
+    match level, List.tl properties with
+    | None, _ -> Ok []
+    | Some level, [] ->
+        let* listing = Protocols.Handle.require Protocols.Directory.from level in
+        let* names = Protocols.Directory.list listing in
+        Ok (List.map (name prefix) (BatFingerTree.to_list names))
+    | Some level, rest ->
+        let* named = Prototype.Directory.children level in
+        List.map (fun (n, child) -> down (n :: prefix) child rest) named
+        |> Utilities.List.sequence
+        |> Result.map List.concat
+  in
+  down [] branch ["multigroup"; "schema"; "relation"]
+
+let rec make branch home =
+  Prototype.mixture
+    [ Protocols.Directory.make
+        object
+          method list =
+            let open Utilities.Result in
+            let* found = Path.find branch (relations home) in
+            match found with
+            | None -> Ok BatFingerTree.empty
+            | Some found ->
+                let* listing = Protocols.Handle.require Protocols.Directory.from found in
+                Protocols.Directory.list listing
+
+          (* what is not a relation's name names no relation here *)
+          method find text =
+            match resolve home text with
+            | None -> Ok None
+            | Some (h, r) -> Path.find branch (path h r)
+        end;
+      Scope
+        object
+          method branch = branch
+          method home = home
+
+          method previous =
+            let open Utilities.Result in
+            let* previous = Path.find branch Path.("previous" @/ this) in
+            Ok (Option.map (fun p -> make p home) previous)
+
+          method catalog = catalog_of branch
+        end ]
+
+let heads = Path.("system" @/ "branch" @/ this)
+
+let of_root root ~branch home =
+  let open Utilities.Result in
+  let* state = Path.lookup root Path.("system" @/ "branch" @/ branch @/ this) in
+  Ok (make state home)
+
+let branch i = Protocols.Handle.invoke i (fun o -> o#branch)
+let home i = Protocols.Handle.invoke i (fun o -> o#home)
+let previous i = Protocols.Handle.invoke i (fun o -> o#previous)
+let catalog i = Protocols.Handle.invoke i (fun o -> o#catalog)
+
+module Error = struct
+  open Concepts.Condition
+
+  let malformed name =
+    condition "malformed-name"
+      "A relation is named relation, schema:relation or multigroup:schema:relation"
+      ("name" |=| Concepts.Value.String name)
+
+  let malformed_denial name =
+    condition "malformed-name" "A denial is named denial or multigroup:denial"
+      ("name" |=| Concepts.Value.String name)
+
+  let moved branch =
+    condition "serialization-conflict" "The branch moved on while this commit was made; retry it"
+      ("branch" |=| Concepts.Value.String branch)
+end
+
+let publish ?(denials = []) root ~branch ~home bindings =
+  let open Utilities.Result in
+  let* changes =
+    List.map
+      (fun (name, v) ->
+        match resolve home name with
+        | Some (h, r) -> Ok (relations h, r, v)
+        | None -> Error (Error.malformed name) )
+      bindings
+    |> Utilities.List.sequence
+  in
+  let* denied =
+    List.map
+      (fun (name, v) ->
+        match String.split_on_char ':' name with
+        | [d] when d <> "" -> Ok (denial home.multigroup, d, v)
+        | [m; d] when m <> "" && d <> "" -> Ok (denial m, d, v)
+        | _ -> Error (Error.malformed_denial name) )
+      denials
+    |> Utilities.List.sequence
+  in
+  let changes = changes @ denied in
+  if List.is_empty changes then Ok ()
+  else
+    let* state = Path.lookup root Path.("system" @/ "branch" @/ branch @/ this) in
+    let* next = Path.assoc_all state changes in
+    let* landed = Path.update root heads branch (Some state) (Some next) in
+    if landed then Ok () else Error (Error.moved branch)