From 89cb60e394a956d3800eb4577d747db7cc37a812 Mon Sep 17 00:00:00 2001
From: BuckarooBanzay <BuckarooBanzay@users.noreply.github.com>
Date: Tue, 14 Mar 2023 14:00:32 +0100
Subject: [PATCH] add `building_def.remove_conditions` support

---
 conditions.lua |  9 ++++++++-
 readme.md      |  5 +++++
 remove.lua     | 18 +++++++++++++++---
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/conditions.lua b/conditions.lua
index 208034d..5598caf 100644
--- a/conditions.lua
+++ b/conditions.lua
@@ -72,13 +72,20 @@ function building_lib.check_condition_group(mapblock_pos1, mapblock_pos2, condit
 		elseif selector == "base" then
 			-- match only base positions
 			it = mapblock_lib.pos_iterator(mapblock_pos1, {x=mapblock_pos2.x, y=mapblock_pos1.y, z=mapblock_pos2.z})
-		elseif selector == "underground" then
+		elseif selector == "underground" or selector == "below" then
 			-- match only underground positions
 			it = mapblock_lib.pos_iterator({
 				x=mapblock_pos1.x, y=mapblock_pos1.y-1, z=mapblock_pos1.z
 			},{
 				x=mapblock_pos2.x, y=mapblock_pos1.y-1, z=mapblock_pos2.z
 			})
+		elseif selector == "above" then
+			-- match only above positions
+			it = mapblock_lib.pos_iterator({
+				x=mapblock_pos1.x, y=mapblock_pos1.y+1, z=mapblock_pos1.z
+			},{
+				x=mapblock_pos2.x, y=mapblock_pos1.y+1, z=mapblock_pos2.z
+			})
 		else
 			-- try to parse a manual position
 			local rel_pos = minetest.string_to_pos(selector)
diff --git a/readme.md b/readme.md
index 6ec9b87..10ba9ec 100644
--- a/readme.md
+++ b/readme.md
@@ -20,8 +20,13 @@ local success, message = building_lib.remove(mapblock_pos)
 building_lib.register_building("buildings:my_building", {
 	placement = "mapblock_lib",
 	conditions = {
+		-- can only be placed if the whole area is empty
 		{["*"] = { empty = true }}
 	},
+	remove_conditions = {
+		-- can only be removed if nothing is built above
+		{["above"] = { empty = true }}
+	},
 	-- simple catalog
 	catalog = "my.zip",
 	-- more catalog options
diff --git a/remove.lua b/remove.lua
index 649ed6e..40277bf 100644
--- a/remove.lua
+++ b/remove.lua
@@ -1,15 +1,27 @@
 
 function building_lib.can_remove(mapblock_pos)
-    local mapblock_data = mapblock_lib.resolve_data_link(building_lib.store, mapblock_pos)
-    if not mapblock_data or not mapblock_data.building then
+    local building_info, origin = building_lib.get_placed_building_info(mapblock_pos)
+    if not building_info then
         return false, "no building found"
     end
 
-    local building_def = building_lib.get_building(mapblock_data.building.name)
+    local building_def = building_lib.get_building(building_info.name)
     if not building_def then
         return false, "unknown building"
     end
 
+    if building_def.remove_conditions then
+        -- check removal conditions
+        local size = building_info.size or {x=1, y=1, z=1}
+        local mapblock_pos2 = vector.add(origin, vector.subtract(size, 1))
+        local success, message = building_lib.check_condition_groups(
+            origin, mapblock_pos2, building_def.remove_conditions
+        )
+        if not success then
+            return false, message
+        end
+    end
+
     return true
 end