Simple Event Handler

--[[
    #SimpleEventHandler 1.0.0.2
    Created in 2013 by Necro
    Licensed under CC0 1.0 Universal(CC0 1.0) (read below)
]]--

--[[
    CC0 1.0 Universal (CC0 1.0) - Public Domain Dedication:
    The person who associated a work with this deed has dedicated the work to the public domain
    by waiving all of his or her rights to the work worldwide under copyright law, including all
    related and neighboring rights, to the extent allowed by law.

    You can copy, modify, distribute and perform the work, even for commercial purposes,
    all without asking permission. See Other Information below.
]]--

SimpleEventHandler=SimpleEventHandler or {}
SimpleEventHandler.listenerTable=SimpleEventHandler.listenerTable or {}

function SimpleEventHandler.addEvent(e)
    if not SimpleEventHandler.listenerTable[e] then
        SimpleEventHandler.listenerTable[e]={}
        print("SEH:Added event "..tostring(e))
        return true
    else
        error("SEH exception:attempt to override an existing event")
    end
end

function SimpleEventHandler.removeEvent(e)
    if SimpleEventHandler.listenerTable[e] then
        SimpleEventHandler.listenerTable[e]=nil
        print("SEH:Removed event "..tostring(e))
        return true
    else
        error("SEH exception:attempt to remove a not existing event")
    end
end

--[[
    To be called by a script.
]]--

function SimpleEventHandler.addListener(e,f)
    if not SimpleEventHandler.listenerTable[e] then
        error("SEH exception:attempt to add listener to a not existing event")
    end
    f = (type(f)=="string" and _G[f]) or f
    table.insert(SimpleEventHandler.listenerTable[e],f)
    print("SEH:Added listener "..tostring(f).." to "..tostring(e))
    return true
end

function SimpleEventHandler.callEvent(e,...)
    if not SimpleEventHandler.listenerTable[e] then
        error("SEH exception:attempt to call a not existing event")
    end
    local ret=nil
    for i,j in pairs(SimpleEventHandler.listenerTable[e]) do
        local temp=j(...)
        if ret==nil then
            ret=temp
        end
    end
    --print("SEH:Called event "..tostring(e))
    return ret
end

function SimpleEventHandler.removeListener(e,f)
    local ret=false
    for i,j in pairs(SimpleEventHandler.listenerTable[e]) do
        if j==f then
            table.remove(SimpleEventHandler.listenerTable[e],i)
            print("SEH:Removed listener "..tostring(f).." from "..tostring(e))
            ret=true
        end
    end
    if not ret then
        error("SEH exception:attempt to remove listener from not existing event")
    end
    return ret
end