[Spell] JASS fireball

[Roflan]

I am learning JASS and I've made a basic fireball spell. The fireball moves fine but I can't make it deal damage yet. I struggle with the GroupEnumUnitsInRange() function. How to make it work? Here's my code:

globals
    group FGroup = CreateGroup()
    location array Point
    unit array temp
endglobals
 
function Trigger_SpellFireball_Actions takes nothing returns nothing
    local unit u = GetTriggerUnit() 
    local location point1 = GetUnitLoc(u)
    local location point2 = GetSpellTargetLoc()
    local unit fireball = CreateUnitAtLoc(GetTriggerPlayer(), 'h021', point1, 0)
    local integer cv = GetUnitUserData(fireball) // I use Unit Indexer system
 
    call SetUnitAnimationByIndex(u, 3)
    set Point[cv] = point2
    set temp[cv] = fireball
    call GroupAddUnit(FGroup, fireball)
 
    set u = null
    set point1 = null
    set point2 = null
    set fireball = null
endfunction

function Trigger_SpellFireball_Conditions takes nothing returns boolean
    return GetSpellAbilityId() == 'A02P'
endfunction
//===========================================================================
function InitTrig_SpellFireball takes nothing returns nothing
    set gg_trg_SpellFireball = CreateTrigger(  )
    call TriggerRegisterAnyUnitEventBJ( gg_trg_SpellFireball, EVENT_PLAYER_UNIT_SPELL_EFFECT )
    call TriggerAddCondition( gg_trg_SpellFireball , Condition(function Trigger_SpellFireball_Conditions))
    call TriggerAddAction( gg_trg_SpellFireball, function Trigger_SpellFireball_Actions )
endfunction

function F_damager takes nothing returns nothing

//call UnitDamageTarget(??, GetFilterUnit(), 50, false, false, ATTACK_TYPE_NORMAL, DAMAGE_TYPE_NORMAL, WEAPON_TYPE_WHOKNOWS)

// how do I pass the caster in here? how not to damage myself and my allies?

endfunction

function F_Callback takes nothing returns nothing
    local integer cv = GetUnitUserData(GetEnumUnit())
    local group damagegroup = CreateGroup()
    local location point1 = GetUnitLoc(GetEnumUnit())
    local location point2 = Point[cv]
    local real facing = AngleBetweenPoints(point1, point2)
    local real x = GetLocationX(point1) + 20 * Cos(facing * bj_DEGTORAD)
    local real y = GetLocationY(point1) + 20 * Sin(facing * bj_DEGTORAD)
 
 
 
    if DistanceBetweenPoints(point1, point2) > 20 then
    call SetUnitPosition(GetEnumUnit(), x, y)
    call DestroyEffect(AddSpecialEffectLoc("Abilities\\Spells\\Other\\Doom\\DoomDeath.mdl",point1))
    call GroupEnumUnitsInRange(damagegroup, x,y, 250, Filter(function F_damager))
    call GroupClear(damagegroup)
    else
    call KillUnit(GetEnumUnit())
    call GroupRemoveUnit(FGroup, GetEnumUnit())
    call GroupClear(damagegroup)
    endif
 
endfunction

function Trig_SpellFireballMover_Actions takes nothing returns nothing
    call ForGroup(FGroup, function F_Callback)
endfunction

//===========================================================================
function InitTrig_SpellFireballMover takes nothing returns nothing
    set gg_trg_SpellFireballMover = CreateTrigger(  )
    call TriggerRegisterTimerEventPeriodic( gg_trg_SpellFireballMover, 0.03 )
    call TriggerAddAction( gg_trg_SpellFireballMover, function Trig_SpellFireballMover_Actions )
endfunction

Is there any convenient way to pass variables between functions besides hashtables? Would structs be helpful here? (if yes, how would it look like?) Could you show how to make this trigger better?

p.s. Do I need to constantly clear groups to avoid leaks or even turn off the periodic trigger when idle?