Use smallest area at given position (#79)

When checking for permission to interact, currently the smallest id takes precedence in a situation where areas enclose other areas. This makes it complicated to set up private areas within faction areas and vice versa. Same applies for open areas within a bigger private area.

When multiple areas have the same volume, players seem to agree that the most recently protected area should also take precedence.
Since we can't guarantee that the largest id is the most recent, we still use that info as we have no other way to determine age.

api.lua

@@ -95,14 +95,36 @@ function areas:getAreasIntersectingArea(pos1, pos2)
 	return res
 end
 
--- Checks if the area is unprotected or owned by you
+-- Returns smallest area at position and its id or nil.
+-- If multiple areas have the same volume, larger id takes precedence.
+function areas:getSmallestAreaAtPos(pos)
+	local smallest_area, smallest_id, volume
+	local smallest_volume = math.huge
+	for id, area in pairs(self:getAreasAtPos(pos)) do
+		volume =	(area.pos2.x - area.pos1.x + 1)
+					* (area.pos2.y - area.pos1.y + 1)
+					* (area.pos2.z - area.pos1.z + 1)
+		if smallest_volume >= volume then
+			smallest_area = area
+			smallest_id = id
+			smallest_volume = volume
+		end
+	end
+	return smallest_area, smallest_id
+end
+
+-- Checks if the area is unprotected, open, owned by player
+-- or player is part of faction of smallest area at position.
 function areas:canInteract(pos, name)
 	if minetest.check_player_privs(name, self.adminPrivs) then
 		return true
 	end
-	local owned = false
+	local area = self:getSmallestAreaAtPos(pos)
-	for _, area in pairs(self:getAreasAtPos(pos)) do
+	-- No area, player owns it or area is open
-		if area.owner == name or area.open then
+	if not area
+		or area.owner == name
+		or area.open
+	then
 		return true
 	elseif areas.factions_available and area.faction_open then
 		if (factions.version or 0) < 2 then
@@ -122,9 +144,7 @@ function areas:canInteract(pos, name)
 			end
 		end
 	end
-		owned = true
+	return false
-	end
-	return not owned
 end
 
 -- Returns a table (list) of all players that own an area