From b870b5a34e35de91a313ad57e6212b1e26ecde44 Mon Sep 17 00:00:00 2001
From: bakpakin <calsrose@gmail.com>
Date: Tue, 8 Sep 2015 13:36:27 -0400
Subject: [PATCH] Add onAddToWorld and onRemoveFromWorld callbacks to systems.
 Also, adding or removing systems to a world twice raises an error.

---
 spec/tiny_spec.lua |  9 +++++++--
 tiny.lua           | 30 ++++++++++++++++++------------
 2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/spec/tiny_spec.lua b/spec/tiny_spec.lua
index 83e62c1..b2ba9a6 100644
--- a/spec/tiny_spec.lua
+++ b/spec/tiny_spec.lua
@@ -120,6 +120,11 @@ describe('tiny-ecs:', function()
             timePassed = 0
         end)
 
+        after_each(function()
+            world:clearSystems()
+            world:refresh()
+        end)
+
         it("Create World", function()
             assert.equals(world:getEntityCount(), 3)
             assert.equals(world:getSystemCount(), 2)
@@ -196,7 +201,7 @@ describe('tiny-ecs:', function()
 
         it("Add Systems Multiple Times", function()
             world:update(1)
-            world:add(moveSystem, oneTimeSystem)
+            assert.has_error(function() world:add(moveSystem, oneTimeSystem) end, "System already belongs to a World.")
             world:update(2)
             assert.equals(2, world:getSystemCount())
             assert.equals(3, world:getEntityCount())
@@ -206,7 +211,7 @@ describe('tiny-ecs:', function()
             world:update(1)
             world:remove(moveSystem)
             world:update(2)
-            world:remove(moveSystem)
+            assert.has_error(function() world:remove(moveSystem) end, "System does not belong to this World.")
             world:update(2)
             assert.equals(1, world:getSystemCount())
             assert.equals(3, world:getEntityCount())
diff --git a/tiny.lua b/tiny.lua
index 972d7a0..fae5dbe 100644
--- a/tiny.lua
+++ b/tiny.lua
@@ -449,7 +449,7 @@ function tiny.remove(world, ...)
             if isSystem(obj) then
                 tiny_removeSystem(world, obj)
             else -- Assume obj is an Entity
-               tiny_removeEntity(world, obj)
+                tiny_removeEntity(world, obj)
             end
         end
     end
@@ -476,19 +476,21 @@ function tiny_manageSystems(world)
     for i = 1, #s2r do
         local system = s2r[i]
         local index = system.index
-        if system.world == world then
-            local onRemove = system.onRemove
-            if onRemove then
-                local entityList = system.entities
-                for j = 1, #entityList do
-                    onRemove(system, entityList[j])
-                end
-            end
-            tremove(systems, index)
-            for j = index, #systems do
-                systems[j].index = j
+        local onRemove = system.onRemove
+        if onRemove then
+            local entityList = system.entities
+            for j = 1, #entityList do
+                onRemove(system, entityList[j])
             end
         end
+        tremove(systems, index)
+        for j = index, #systems do
+            systems[j].index = j
+        end
+        local onRemoveFromWorld = system.onRemoveFromWorld
+        if onRemoveFromWorld then
+            onRemoveFromWorld(system, world)
+        end
         s2r[i] = nil
 
         -- Clean up System
@@ -514,6 +516,10 @@ function tiny_manageSystems(world)
             local index = #systems + 1
             system.index = index
             systems[index] = system
+            local onAddToWorld = system.onAddToWorld
+            if onAddToWorld then
+                onAddToWorld(system, world)
+            end
 
             -- Try to add Entities
             local onAdd = system.onAdd