Limited Summon

//*****************************************************************
//*  spell template - LimitedSummon
//*
//*  written by: Anitarf
//*  requires: -Table
//*            -LinkedList
//*
//*            -a unit summoning ability
//*            -a unit summoned by the above ability
//*
//*  description: Limits the number of summoned units of one type
//*               that a single caster may summon. If the caster
//*               summons more than that many the oldest summoned
//*               unit belonging to that caster is removed.
//*
//*  technical: The spell may malfunction if the summoned units
//*             can be removed by triggers before they die. To
//*             avoid this, always kill your units before removing
//*             them, not just because of this spell but because
//*             removing units in general is a lame thing to do.
//*
//*****************************************************************

scope LimitedSummon initializer Init

    globals
        private constant integer SUMMON_UNIT_ID = 'h000' //the type of the summoned unit
        private constant integer SUMMON_ABILITY_ID = 'A000' //the ability used to summon the unit

        //the special effect to be used when an old summoned unit is killed to make room for the new:
        private constant string KILL_EFFECT_PATH = "Abilities\\Spells\\Other\\Charm\\CharmTarget.mdl"
        private constant string KILL_EFFECT_POINT = "origin"
    endglobals

    private function SummonLimit takes unit u returns integer
        //this determines how many units of the chosen type a caster can control
        return 2*GetUnitAbilityLevel(u, SUMMON_ABILITY_ID)
    endfunction

// END OF CALIBRATION SECTION    
// ================================================================


    globals
        private HandleTable gc
    endglobals

    private struct summoner
        unit u
        List l

        static method create takes unit u returns summoner
            local summoner s = summoner.allocate()
            set gc[u] = integer(s)
            set s.l = List.create()
            set s.u = u
            return s
        endmethod
        static method get takes unit u returns summoner
            local summoner s = summoner(gc[u])
            if s==0 then
                return summoner.create(u)
            endif
            return s
        endmethod

        method onDestroy takes nothing returns nothing
            call gc.flush(.u)
            call .l.destroy()
        endmethod
    endstruct

// ================================================================

    private struct summoned
        unit u
        Link l
        summoner parent

        static method get takes unit u returns summoned
            return summoned(gc[u])
        endmethod
        static method create takes unit u, unit summoning returns summoned
            local summoned s = summoned.allocate()
            local summoner sum = summoner.get(summoning)
            local unit k
            set s.u = u
            set s.parent = sum
            set s.l = Link.create(sum.l, integer(s))
            set gc[u] = integer(s)

            loop
                if s.parent.l.size > SummonLimit(s.parent.u) then
                    set k = summoned(s.parent.l.last.data).u
                    call DestroyEffect(AddSpecialEffectTarget(KILL_EFFECT_PATH, k, KILL_EFFECT_POINT))
                    call KillUnit(k)
                    set k = null
                else
                    exitwhen true
                endif
            endloop

            return s
        endmethod

        method onDestroy takes nothing returns nothing
            call gc.flush(.u)
            call .l.destroy()
            if .parent.l.size==0 then
                call .parent.destroy()
            endif
        endmethod
    endstruct

// ================================================================

    private function Summoning takes nothing returns boolean
        if GetUnitTypeId(GetSummonedUnit())==SUMMON_UNIT_ID then
            call summoned.create(GetSummonedUnit(), GetSummoningUnit())
        endif
        return false
    endfunction

    private function SummonDeath takes nothing returns boolean
        local summoned s
        if GetUnitTypeId(GetTriggerUnit())==SUMMON_UNIT_ID then
            set s = summoned.get(GetTriggerUnit())
            if s != 0 then
                call s.destroy()
            endif
        endif
        return false
    endfunction

// ================================================================

    private function Init takes nothing returns nothing
        local trigger t = CreateTrigger()
        call TriggerRegisterAnyUnitEventBJ(t, EVENT_PLAYER_UNIT_SUMMON)
        call TriggerAddCondition(t, Condition(function Summoning))

        set t = CreateTrigger()
        call TriggerRegisterAnyUnitEventBJ(t, EVENT_PLAYER_UNIT_DEATH)
        call TriggerAddCondition(t, Condition(function SummonDeath))

        set gc = HandleTable.create()
    endfunction
endscope