From 76c34f2470d64608d2a3a5a468dfa6259c0017d0 Mon Sep 17 00:00:00 2001
From: Keenan Brock <keenan@thebrocks.net>
Date: Sat, 11 Mar 2023 00:44:35 -0500
Subject: [PATCH] update depth_cache_column using math

Use math to adjust the depth_cache instead of re-calculating the depth

Goal is to remove regular expression change
---
 lib/ancestry/materialized_path_pg.rb | 26 +++++++++++++++++++++-----
 test/concerns/depth_caching_test.rb  | 21 ++++++++++++++++++++-
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/lib/ancestry/materialized_path_pg.rb b/lib/ancestry/materialized_path_pg.rb
index 5374be7c..99c5f3df 100644
--- a/lib/ancestry/materialized_path_pg.rb
+++ b/lib/ancestry/materialized_path_pg.rb
@@ -7,17 +7,33 @@ def update_descendants_with_new_ancestry
         ancestry_column = ancestry_base_class.ancestry_column
         old_ancestry = self.class.generate_ancestry( path_ids_before_last_save )
         new_ancestry = self.class.generate_ancestry( path_ids )
-        update_clause = [
+        descendants_clause = [
           "#{ancestry_column} = replace(#{ancestry_column}, '#{old_ancestry}', '#{new_ancestry}')"
         ]
 
-        if ancestry_base_class.respond_to?(:depth_cache_column) && respond_to?(ancestry_base_class.depth_cache_column)
-          depth_cache_column = ancestry_base_class.depth_cache_column.to_s
-          update_clause << "#{depth_cache_column} = length(regexp_replace(regexp_replace(ancestry, '^#{Regexp.escape(old_ancestry)}', '#{new_ancestry}'), '[^#{ancestry_base_class.ancestry_delimiter}]', '', 'g')) #{ancestry_base_class.ancestry_format == :materialized_path2 ? '-' : '+'} 1"
-        end
+        update_descendants_hook(descendants_clause, old_ancestry, new_ancestry)
+        unscoped_descendants_before_save.update_all descendants_clause.join(', ')
 
         unscoped_descendants_before_save.update_all update_clause.join(', ')
       end
     end
+
+    # TODO: only install this if depth_cache is turned on (use chain_methods?)
+    def update_descendants_hook(descendants_clause, old_ancestry, new_ancestry)
+      if ancestry_base_class.respond_to?(:depth_cache_column) && respond_to?(ancestry_base_class.depth_cache_column)
+        depth_cache_column = ancestry_base_class.depth_cache_column.to_s
+        depth_change = ancestry_depth_change(old_ancestry, new_ancestry)
+        if depth_change != 0
+          descendants_clause << "#{depth_cache_column} = #{depth_cache_column} + #{depth_change}"
+        end
+      end
+        end
+      end
+    end
+
+    # pulled out to make testing easier
+    def ancestry_depth_change(old_value, new_value)
+      parse_ancestry_column(new_value).size - parse_ancestry_column(old_value).size
+    end
   end
 end
diff --git a/test/concerns/depth_caching_test.rb b/test/concerns/depth_caching_test.rb
index 6fae4cba..7f90d982 100644
--- a/test/concerns/depth_caching_test.rb
+++ b/test/concerns/depth_caching_test.rb
@@ -90,4 +90,23 @@ def test_exception_on_unknown_depth_column
       end
     end
   end
-end
\ No newline at end of file
+
+  def test_ancestry_depth_change
+    AncestryTestDatabase.with_model do |model|
+      # this lets us test ancestry_depth_change but leaves model in a strange state
+      # do not create objects
+      model.extend(Ancestry::MaterializedPathPg)
+      {
+        [[], [1]]        => +1,
+        [[1], []]        => -1,
+        [[1], [2]]       =>  0,
+        [[1], [1, 2, 3]] => +2,
+        [[1, 2, 3], [1]] => -2
+      }.each do |(before, after), diff|
+        a_before = model.generate_ancestry(before)
+        a_after = model.generate_ancestry(after)
+        assert_equal(diff, model.ancestry_depth_change(a_before, a_after))
+      end
+    end
+  end
+end