api function to add conditions to canPlayerAddArea

api.lua

@@ -1,9 +1,14 @@
 local hudHandlers = {}
 
+areas.registered_protection_conditions = {}
 areas.registered_on_adds = {}
 areas.registered_on_removes = {}
 areas.registered_on_moves = {}
 
+function areas:registerProtectionCondition(func)
+	table.insert(areas.registered_protection_conditions, func)
+end
+
 function areas:registerOnAdd(func)
 	table.insert(areas.registered_on_adds, func)
 end

api.md

@@ -5,11 +5,26 @@ API list
 ---
 
  * `areas:registerHudHandler(handler)` - Registers a handler to add items to the Areas HUD.  See [HUD](#hud).
+ * `areas:registerProtectionCondition(func(pos1, pos2, name))` - 
+See [Protection Conditions](#Protection-Conditions)
  * `areas:registerOnAdd(func(id, area))`
  * `areas:registerOnRemove(func(id))`
  * `areas:registerOnMove(func(id, area, pos1, pos2))`
 
 
+Protection Conditions
+---
+
+With `areas:registerProtectionCondition(func(pos1, pos2, name))`
+you can register rules to control whether to allow or prohibit the creation of an area.
+
+Return values:
+* `true` Always create the area, no matter of other conditions. 
+Note that this includes the conditions set by this mod.
+* `false, errMsg` Disable the creation of the area and return an error message.
+* `nil` Enable the creation of the area, if all other callbacks return `nil` too.
+
+
 HUD
 ---
 

internal.lua

@@ -211,6 +211,8 @@ end
 -- if the area intersects other areas that they do not own.
 -- Also checks the size of the area and if the user already
 -- has more than max_areas.
+-- checks all possible restrictions registered with
+-- areas:registerProtectionCondition
 function areas:canPlayerAddArea(pos1, pos2, name)
 	local privs = minetest.get_player_privs(name)
 	if privs.areas then
@@ -258,7 +260,22 @@ function areas:canPlayerAddArea(pos1, pos2, name)
 				area.name, id, area.owner)
 	end
 
-	return true
+	local allowed = true
+	local errMsg
+	for i=1, #areas.registered_protection_conditions do
+		local res, msg = areas.registered_protection_conditions[i](pos1, pos2, name)
+		if res == true then
+			-- always allow to protect, no matter of other conditions
+			return true
+		elseif res == false then
+			-- there might be another callback that returns true, so we can't break here
+			allowed = false
+			-- save the first error that occurred
+			errMsg = errMsg or msg
+		end
+	end
+
+	return allowed, errMsg
 end
 
 -- Given a id returns a string in the format: