class Battle::AI
  #=============================================================================
  # Decide whether the opponent should switch Pokémon
  #=============================================================================
  def pbEnemyShouldWithdraw?
    return pbEnemyShouldWithdrawEx?(false)
  end

  def pbEnemyShouldWithdrawEx?(forceSwitch)
    return false if @wildBattler
    shouldSwitch = forceSwitch
    batonPass = -1
    moveType = nil
    # If Pokémon is within 6 levels of the foe, and foe's last move was
    # super-effective and powerful
    if !shouldSwitch && @user.turnCount > 0 && skill_check(AILevel.high)
      target = @user.pbDirectOpposing(true)
      if !target.fainted? && target.lastMoveUsed &&
         (target.level - @user.level).abs <= 6
        moveData = GameData::Move.get(target.lastMoveUsed)
        moveType = moveData.type
        typeMod = pbCalcTypeMod(moveType, target, @user)
        if Effectiveness.super_effective?(typeMod) && moveData.base_damage > 50
          switchChance = (moveData.base_damage > 70) ? 30 : 20
          shouldSwitch = (pbAIRandom(100) < switchChance)
        end
      end
    end
    # Pokémon can't do anything (must have been in battle for at least 5 rounds)
    if !@battle.pbCanChooseAnyMove?(@user.index) &&
       @user.turnCount && @user.turnCount >= 5
      shouldSwitch = true
    end
    # Pokémon is Perish Songed and has Baton Pass
    if skill_check(AILevel.high) && @user.effects[PBEffects::PerishSong] == 1
      @user.eachMoveWithIndex do |m, i|
        next if m.function != "SwitchOutUserPassOnEffects"   # Baton Pass
        next if !@battle.pbCanChooseMove?(@user.index, i, false)
        batonPass = i
        break
      end
    end
    # Pokémon will faint because of bad poisoning at the end of this round, but
    # would survive at least one more round if it were regular poisoning instead
    if @user.status == :POISON && @user.statusCount > 0 && skill_check(AILevel.high)
      toxicHP = @user.totalhp / 16
      nextToxicHP = toxicHP * (@user.effects[PBEffects::Toxic] + 1)
      if @user.hp <= nextToxicHP && @user.hp > toxicHP * 2
        shouldSwitch = true if pbAIRandom(100) < 80
      end
    end
    # Pokémon is Encored into an unfavourable move
    if @user.effects[PBEffects::Encore] > 0 && skill_check(AILevel.medium)
      idxEncoredMove = @user.pbEncoredMoveIndex
      if idxEncoredMove >= 0
        scoreSum   = 0
        scoreCount = 0
        @user.allOpposing.each do |b|
          scoreSum += pbGetMoveScore(@user.moves[idxEncoredMove], b)
          scoreCount += 1
        end
        if scoreCount > 0 && scoreSum / scoreCount <= 20
          shouldSwitch = true if pbAIRandom(100) < 80
        end
      end
    end
    # If there is a single foe and it is resting after Hyper Beam or is
    # Truanting (i.e. free turn)
    if @battle.pbSideSize(@user.index + 1) == 1 &&
       !@user.pbDirectOpposing.fainted? && skill_check(AILevel.high)
      opp = @user.pbDirectOpposing
      if (opp.effects[PBEffects::HyperBeam] > 0 ||
         (opp.hasActiveAbility?(:TRUANT) && opp.effects[PBEffects::Truant]))
        shouldSwitch = false if pbAIRandom(100) < 80
      end
    end
    # Sudden Death rule - I'm not sure what this means
    if @battle.rules["suddendeath"] && @user.turnCount > 0
      if @user.hp <= @user.totalhp / 4 && pbAIRandom(100) < 30
        shouldSwitch = true
      elsif @user.hp <= @user.totalhp / 2 && pbAIRandom(100) < 80
        shouldSwitch = true
      end
    end
    # Pokémon is about to faint because of Perish Song
    if @user.effects[PBEffects::PerishSong] == 1
      shouldSwitch = true
    end
    if shouldSwitch
      list = []
      idxPartyStart, idxPartyEnd = @battle.pbTeamIndexRangeFromBattlerIndex(@user.index)
      @battle.pbParty(@user.index).each_with_index do |pkmn, i|
        next if i == idxPartyEnd - 1   # Don't choose to switch in ace
        next if !@battle.pbCanSwitch?(@user.index, i)
        # If perish count is 1, it may be worth it to switch
        # even with Spikes, since Perish Song's effect will end
        if @user.effects[PBEffects::PerishSong] != 1
          # Will contain effects that recommend against switching
          spikes = @user.pbOwnSide.effects[PBEffects::Spikes]
          # Don't switch to this if too little HP
          if spikes > 0
            spikesDmg = [8, 6, 4][spikes - 1]
            next if pkmn.hp <= pkmn.totalhp / spikesDmg &&
                    !pkmn.hasType?(:FLYING) && !pkmn.hasActiveAbility?(:LEVITATE)
          end
        end
        # moveType is the type of the target's last used move
        if moveType && Effectiveness.ineffective?(pbCalcTypeMod(moveType, @user, @user))
          weight = 65
          typeMod = pbCalcTypeModPokemon(pkmn, @user.pbDirectOpposing(true))
          if Effectiveness.super_effective?(typeMod)
            # Greater weight if new Pokemon's type is effective against target
            weight = 85
          end
          list.unshift(i) if pbAIRandom(100) < weight   # Put this Pokemon first
        elsif moveType && Effectiveness.resistant?(pbCalcTypeMod(moveType, @user, @user))
          weight = 40
          typeMod = pbCalcTypeModPokemon(pkmn, @user.pbDirectOpposing(true))
          if Effectiveness.super_effective?(typeMod)
            # Greater weight if new Pokemon's type is effective against target
            weight = 60
          end
          list.unshift(i) if pbAIRandom(100) < weight   # Put this Pokemon first
        else
          list.push(i)   # put this Pokemon last
        end
      end
      if list.length > 0
        if batonPass >= 0 && @battle.pbRegisterMove(@user.index, batonPass, false)
          PBDebug.log("[AI] #{@user.pbThis} (#{@user.index}) will use Baton Pass to avoid Perish Song")
          return true
        end
        if @battle.pbRegisterSwitch(@user.index, list[0])
          PBDebug.log("[AI] #{@user.pbThis} (#{@user.index}) will switch with " +
                      @battle.pbParty(@user.index)[list[0]].name)
          return true
        end
      end
    end
    return false
  end

  # Choose a replacement Pokémon (called directly from @battle, not part of
  # action choosing).
  def pbDefaultChooseNewEnemy(idxBattler, party)
    set_up(idxBattler)
    enemies = []
    idxPartyStart, idxPartyEnd = @battle.pbTeamIndexRangeFromBattlerIndex(idxBattler)
    party.each_with_index do |_p, i|
      next if i == idxPartyEnd - 1 && enemies.length > 0   # Ignore ace if possible
      enemies.push(i) if @battle.pbCanSwitchLax?(idxBattler, i)
    end
    return -1 if enemies.length == 0
    return pbChooseBestNewEnemy(idxBattler, party, enemies)
  end

  def pbChooseBestNewEnemy(idxBattler, party, enemies)
    return -1 if !enemies || enemies.length == 0
    best    = -1
    bestSum = 0
    enemies.each do |i|
      pkmn = party[i]
      sum  = 0
      pkmn.moves.each do |m|
        next if m.base_damage == 0
        @battle.battlers[idxBattler].allOpposing.each do |b|
          bTypes = b.pbTypes(true)
          sum += Effectiveness.calculate(m.type, bTypes[0], bTypes[1], bTypes[2])
        end
      end
      if best == -1 || sum > bestSum
        best = i
        bestSum = sum
      end
    end
    return best
  end
end