-- object_singleton - Make an object into a singleton
--    (system_utils_a component)
-- Template attachment: any
-- Created by: Patrick Ferland
-- Created on: 06/23/2008
 
-- Revision History
    -- 06/23/2008 P.Ferland - New script
    -- 07/02/2008 P.Ferland - Destroyed() no longer removes singleton reference if self is not world singleton
    
--[[
How to use the Singleton script

1.  Attach object_singleton[11661:4] to the desired template
2.  Attach world_singleton[11661:5] to the world object
3.  Object creation is now only allowed in a singleton fashion

NOTE:
The world must be saved (manually, by a world builder) whenever a singleton is added or removed, if the
reference must be maintained -- persistent world properties cannot be saved via script!  (Not that it doesn't try.)

]]--

-- Constants
    -- no constants

-- Script Properties
    -- no properties

-- Commands
    -- no commands

-- Triggers

Trigger attach()

    Debug('Created singleton of ' .. self.type .. ' : ' .. self.id)

    local w = GetWorld()
    
    if (w.singleton_tracker ~= nil) then
        local singleton = w.singleton_tracker[self.type]
        if (singleton ~= nil) then
            if (GetObjectById(singleton.id).id ~= self.id) then
                 Debug('Existing ' .. self.type .. ' singleton : ' .. singleton.id)
                
                DestroyObject(self)
                return
            end
        end
        w.singleton_tracker[self.type] = self
    else
         Debug('World singleton tracker could not be accessed.  Allowing default creation.') 
    end
    
    SaveToDb(w)

end

Trigger destroyed(place_id)

    Debug('Destroying singleton of ' .. self.type .. ' : ' .. self.id)

    local w = GetWorld()
    
    if (w.singleton_tracker ~= nil) then
        local singleton = w.singleton_tracker[self.type]
        if (singleton ~= nil) then
            if (singleton.id == self.id) then
                w.singleton_tracker[self.type] = nil
            end
        end
    else
         Debug('World singleton tracker could not be accessed.  Cannot remove singleton reference.') 
    end
    
    SaveToDb(w)
    
end

-- Local functions
    -- no functions