[Scripting Question] Strength Sap not taking stat stages into account

[Tommaniacal]

Hello, using the following script will successfully heal based on the opponent's attack, and then lower it 1 stage.

class PokeBattle_Move_CF13 < PokeBattle_Move
  def pbEffect(attacker,opponent,hitnum=0,alltargets=nil,showanimation=true)
    if attacker.effects[PBEffects::HealBlock]>0
      bob="heal"
      bob=_INTL("use {1}",name) if !opponent.pbCanReduceStatStage?(PBStats::ATTACK,true,false,attacker)
      @battle.pbDisplay(_INTL("{1} can't {2} because of Heal Block!",attacker.pbThis,bob))
      return -1 if !opponent.pbCanReduceStatStage?(PBStats::ATTACK,true,false,attacker)
    elsif attacker.hp==attacker.totalhp
      @battle.pbDisplay(_INTL("{1}'s HP is full!",attacker.pbThis))
      return -1 if !opponent.pbCanReduceStatStage?(PBStats::ATTACK,true,false,attacker)
    else
      oatk=opponent.attack
      attacker.pbRecoverHP(oatk,true)
      @battle.pbDisplay(_INTL("{1}'s HP was restored.",attacker.pbThis))
    end
    if opponent.pbCanReduceStatStage?(PBStats::ATTACK,true,false,attacker)
      opponent.pbReduceStat(PBStats::ATTACK,1,true,true,false,attacker)
    end
    return 0
  end
end

However, it doesn't appear to take stat changes into account, so using Strength Sap repeatedly doesn't decrease the amount of HP it heals. How do I go about fixing this?