configtree: T4235: implementation of config tree diff

2 files changed, 178 insertions, 0 deletions

diff --git a/src/config_diff.ml b/src/config_diff.ml
new file mode 100644
index 0000000..75d12dd
--- /dev/null
+++ b/src/config_diff.ml
@@ -0,0 +1,157 @@
+type change = Unchanged | Added | Deleted | Updated of string list
+
+type diff_func = ?with_children:bool -> string list -> change -> unit
+
+type diff_trees = {
+    left: Config_tree.t;
+    right: Config_tree.t;
+    add: Config_tree.t ref;
+    del: Config_tree.t ref;
+    inter: Config_tree.t ref;
+}
+
+exception Incommensurable
+exception Empty_comparison
+
+module ValueS = Set.Make(struct type t = string let compare = compare end)
+
+let make_diff_tree l r = { left = l; right = r;
+                           add = ref (Config_tree.make "root");
+                           del = ref (Config_tree.make "root");
+                           inter = ref (Config_tree.make "root");
+}
+
+let name_of n = Vytree.name_of_node n
+let data_of n = Vytree.data_of_node n
+let children_of n = Vytree.children_of_node n
+let make data name children = Vytree.make_full data name children
+
+let (^~) (node : Config_tree.t) (node' : Config_tree.t) =
+  name_of node = name_of node' &&
+  (data_of node).values <> (data_of node').values
+
+let left_opt_pairs n m =
+    (children_of n) |> List.map (fun x ->
+        let maybe_node =
+            (children_of m) |> List.find_opt (fun y ->
+                name_of y = name_of x) in
+        (Some x, maybe_node))
+
+let right_opt_pairs n m =
+    (children_of m) |> List.map (fun y ->
+        let maybe_node =
+            (children_of n) |> List.find_opt (fun x ->
+                name_of x = name_of y) in
+        (maybe_node, Some y))
+
+let opt_zip n m =
+    left_opt_pairs n m @ right_opt_pairs n m |> List.sort_uniq compare
+
+let get_opt_name left_opt right_opt =
+    match left_opt, right_opt with
+    | Some left_node, None -> name_of left_node
+    | None, Some right_node -> name_of right_node
+    | Some left_node, Some _ -> name_of left_node
+    | None, None -> raise Empty_comparison
+
+let update_path path left_opt right_opt =
+    let name = get_opt_name left_opt right_opt in
+    if name = "root" then path
+    else path @ [name]
+
+(* tree diff algorithm: walk the tree pair, calling a function of type
+   diff_func at bifurcation points; f acts as a form of continuation.
+   The idea of matching on pairs of (node opt) is from
+   https://github.com/LukeBurgessYeo/tree-diff
+*)
+let rec diff (path : string list) (f : diff_func) (l : (Config_tree.t option * Config_tree.t option) list) =
+    match l with
+    | [] -> ()
+    | (left_node_opt, right_node_opt) :: ls ->
+        (let path = update_path path left_node_opt right_node_opt in
+        match left_node_opt, right_node_opt with
+        | Some _, None -> f path Deleted
+        | None, Some _ -> f path Added
+        | Some left_node, Some right_node when left_node = right_node ->
+                f path Unchanged
+        | Some left_node, Some right_node when left_node ^~ right_node ->
+                let values = (data_of right_node).values in
+                f path (Updated values)
+        | Some left_node, Some right_node ->
+                (f ~with_children:false path Unchanged;
+                diff path f (opt_zip left_node right_node))
+        | None, None -> raise Empty_comparison)
+        ; diff path f ls
+
+(* copy node paths between trees *)
+let rec clone_path ?(with_children=true) ?(set_values=[]) old_root new_root path_done path_remaining =
+    match path_remaining with
+    | [] | [_] ->
+        let path_total = path_done @ path_remaining in
+        let old_node = Vytree.get old_root path_total in
+        let data = if not (set_values = []) then
+            { (data_of old_node) with Config_tree.values = set_values } else (data_of old_node) in
+        if with_children then
+            Vytree.insert ~children:(children_of old_node) new_root path_total data
+        else
+            Vytree.insert new_root path_total data
+    | name :: names ->
+        let path_done = path_done @ [name] in
+        let old_node = Vytree.get old_root path_done in
+        let new_root = Vytree.insert new_root path_done (data_of old_node) in
+        clone_path ~with_children:with_children ~set_values:set_values old_root new_root path_done names
+
+let clone ?(with_children=true) ?(set_values=[]) old_root new_root path =
+    match path with
+    | [] -> if with_children then old_root else new_root
+    | _ ->
+            let path_existing = Vytree.get_existent_path new_root path in
+            let path_remaining = Vylist.complement path path_existing in
+            clone_path ~with_children:with_children ~set_values:set_values old_root new_root path_existing path_remaining
+
+(* define the diff_func; in this instance, we imperatively build the difference trees *)
+let decorate_trees (trees : diff_trees) ?(with_children=true) (path : string list) (m : change) =
+    match m with
+    | Added -> trees.add := clone trees.right !(trees.add) path
+    | Deleted -> trees.del := clone ~with_children:false trees.left !(trees.del) path
+    | Unchanged -> trees.inter := clone ~with_children:with_children trees.left !(trees.inter) path
+    | Updated v ->
+            (* if in this case, node at path is guaranteed to exist *)
+            let ov = Config_tree.get_values trees.left path in
+            match ov, v with
+            | [_], [_] -> trees.del := clone trees.left !(trees.del) path;
+                          trees.add := clone trees.right !(trees.add) path
+            | _, _ -> let ovs = ValueS.of_list ov in
+                      let vs = ValueS.of_list v in
+                      let set_ov = ValueS.elements (ValueS.diff ovs vs) in
+                      let set_v = ValueS.elements (ValueS.diff vs ovs) in
+                      let set_inter = ValueS.elements (ValueS.inter ovs vs) in
+                      if not (set_ov = []) then
+                          trees.del := clone ~set_values:set_ov trees.left !(trees.del) path;
+                      if not (set_v = []) then
+                          trees.add := clone ~set_values:set_v trees.right !(trees.add) path;
+                      if not (set_inter = []) then
+                          trees.inter := clone ~set_values:set_inter trees.left !(trees.inter) path
+
+(* get sub trees for path-relative comparison *)
+let tree_at_path path node =
+    try
+        let node = Vytree.get node path in
+        make Config_tree.default_data "root" [node]
+    with Vytree.Nonexistent_path -> raise Empty_comparison
+
+(* call recursive diff on config_trees with decorate_trees as the diff_func *)
+let compare path left right =
+    if (name_of left) <> (name_of right) then
+        raise Incommensurable
+    else
+        let (left, right) = if not (path = []) then
+            (tree_at_path path left, tree_at_path path right) else (left, right) in
+        let trees = make_diff_tree left right in
+        diff [] (decorate_trees trees) [(Option.some left, Option.some right)];
+        trees
+
+(* wrapper to return diff trees *)
+let diffs path left right =
+    let trees = compare path left right in
+    (!(trees.add), !(trees.del), !(trees.inter))
diff --git a/src/config_diff.mli b/src/config_diff.mli
new file mode 100644
index 0000000..623c6ef
--- /dev/null
+++ b/src/config_diff.mli
@@ -0,0 +1,21 @@
+type change = Unchanged | Added | Deleted | Updated of string list
+
+type diff_func = ?with_children:bool -> string list -> change -> unit
+
+type diff_trees = {
+    left: Config_tree.t;
+    right: Config_tree.t;
+    add: Config_tree.t ref;
+    del: Config_tree.t ref;
+    inter: Config_tree.t ref;
+}
+
+exception Incommensurable
+exception Empty_comparison
+
+val make_diff_tree : Config_tree.t -> Config_tree.t -> diff_trees
+val clone : ?with_children:bool -> ?set_values:string list -> Config_tree.t -> Config_tree.t -> string list -> Config_tree.t
+val decorate_trees : diff_trees -> ?with_children:bool -> string list -> change -> unit
+val compare : string list -> Config_tree.t -> Config_tree.t -> diff_trees
+val diffs : string list -> Config_tree.t -> Config_tree.t -> Config_tree.t * Config_tree.t * Config_tree.t
+