From be75413eaf4aef85274cc16c2283486799d99d73 Mon Sep 17 00:00:00 2001
From: John Estabrook <jestabro@vyos.io>
Date: Wed, 27 Mar 2024 13:20:47 -0500
Subject: T6180: add ability to apply mask to config tree

---
 src/config_diff.ml  | 29 +++++++++++++++++++++++++++++
 src/config_diff.mli |  1 +
 2 files changed, 30 insertions(+)

diff --git a/src/config_diff.ml b/src/config_diff.ml
index 35a5b55..3529a5d 100644
--- a/src/config_diff.ml
+++ b/src/config_diff.ml
@@ -390,6 +390,35 @@ let show_diff ?(cmds=false) path left right =
         in
         strs
 
+let is_terminal_path node path =
+    try
+        let n = Vytree.get node path in
+        match (Vytree.children_of_node n) with
+        | [] -> true
+        | _ -> false
+    with Vytree.Nonexistent_path -> false
+
+(* mask function; mask applied on right *)
+let mask_func ?recurse:_ (path : string list) (Diff_tree res) (m : change) =
+    match m with
+    | Added -> Diff_tree (res)
+    | Subtracted ->
+            (match path with
+            | [_] -> Diff_tree {res with left = Vytree.delete res.left path}
+            |  _  -> if not (is_terminal_path res.right (list_but_last path)) then
+                         Diff_tree {res with left = Vytree.delete res.left path}
+                     else Diff_tree (res))
+    | Unchanged -> Diff_tree (res)
+    | Updated _ -> Diff_tree (res)
+
+(* call recursive diff with mask_func; mask applied on right *)
+let mask_tree left right =
+    let trees = make_diff_trees left right in
+    let d = diff [] mask_func trees (Option.some left, Option.some right)
+    in
+    let res = eval_result d in
+    res.left
+
 let union_of_values (n : Config_tree.t) (m : Config_tree.t) =
     let set_n = ValueS.of_list (data_of n).values in
     let set_m = ValueS.of_list (data_of m).values in
diff --git a/src/config_diff.mli b/src/config_diff.mli
index c995ba3..6adf5a7 100644
--- a/src/config_diff.mli
+++ b/src/config_diff.mli
@@ -37,3 +37,4 @@ exception Nonexistent_child
 val diff_tree : string list -> Config_tree.t -> Config_tree.t -> Config_tree.t
 val show_diff : ?cmds:bool -> string list -> Config_tree.t -> Config_tree.t -> string
 val tree_union : Config_tree.t -> Config_tree.t -> Config_tree.t
+val mask_tree : Config_tree.t -> Config_tree.t -> Config_tree.t
-- 
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