vcmi/lib/spells/CDefaultSpellMechanics.cpp

/*
 * CDefaultSpellMechanics.cpp, part of VCMI engine
 *
 * Authors: listed in file AUTHORS in main folder
 *
 * License: GNU General Public License v2.0 or later
 * Full text of license available in license.txt file, in main folder
 *
 */

#include "StdInc.h"

#include "CDefaultSpellMechanics.h"

#include "../CStack.h"
#include "../battle/BattleInfo.h"

#include "../CGeneralTextHandler.h"

namespace SRSLPraserHelpers
{
	static int XYToHex(int x, int y)
	{
		return x + GameConstants::BFIELD_WIDTH * y;
	}

	static int XYToHex(std::pair<int, int> xy)
	{
		return XYToHex(xy.first, xy.second);
	}

	static int hexToY(int battleFieldPosition)
	{
		return battleFieldPosition/GameConstants::BFIELD_WIDTH;
	}

	static int hexToX(int battleFieldPosition)
	{
		int pos = battleFieldPosition - hexToY(battleFieldPosition) * GameConstants::BFIELD_WIDTH;
		return pos;
	}

	static std::pair<int, int> hexToPair(int battleFieldPosition)
	{
		return std::make_pair(hexToX(battleFieldPosition), hexToY(battleFieldPosition));
	}

	//moves hex by one hex in given direction
	//0 - left top, 1 - right top, 2 - right, 3 - right bottom, 4 - left bottom, 5 - left
	static std::pair<int, int> gotoDir(int x, int y, int direction)
	{
		switch(direction)
		{
		case 0: //top left
			return std::make_pair((y%2) ? x-1 : x, y-1);
		case 1: //top right
			return std::make_pair((y%2) ? x : x+1, y-1);
		case 2:  //right
			return std::make_pair(x+1, y);
		case 3: //right bottom
			return std::make_pair((y%2) ? x : x+1, y+1);
		case 4: //left bottom
			return std::make_pair((y%2) ? x-1 : x, y+1);
		case 5: //left
			return std::make_pair(x-1, y);
		default:
			throw std::runtime_error("Disaster: wrong direction in SRSLPraserHelpers::gotoDir!\n");
		}
	}

	static std::pair<int, int> gotoDir(std::pair<int, int> xy, int direction)
	{
		return gotoDir(xy.first, xy.second, direction);
	}

	static bool isGoodHex(std::pair<int, int> xy)
	{
		return xy.first >=0 && xy.first < GameConstants::BFIELD_WIDTH && xy.second >= 0 && xy.second < GameConstants::BFIELD_HEIGHT;
	}

	//helper function for rangeInHexes
	static std::set<ui16> getInRange(unsigned int center, int low, int high)
	{
		std::set<ui16> ret;
		if(low == 0)
		{
			ret.insert(center);
		}

		std::pair<int, int> mainPointForLayer[6]; //A, B, C, D, E, F points
		for(auto & elem : mainPointForLayer)
			elem = hexToPair(center);

		for(int it=1; it<=high; ++it) //it - distance to the center
		{
			for(int b=0; b<6; ++b)
				mainPointForLayer[b] = gotoDir(mainPointForLayer[b], b);

			if(it>=low)
			{
				std::pair<int, int> curHex;

				//adding lines (A-b, B-c, C-d, etc)
				for(int v=0; v<6; ++v)
				{
					curHex = mainPointForLayer[v];
					for(int h=0; h<it; ++h)
					{
						if(isGoodHex(curHex))
							ret.insert(XYToHex(curHex));
						curHex = gotoDir(curHex, (v+2)%6);
					}
				}

			} //if(it>=low)
		}

		return ret;
	}
}

SpellCastContext::SpellCastContext(const DefaultSpellMechanics * mechanics_, const SpellCastEnvironment * env_, const BattleSpellCastParameters & parameters_):
	mechanics(mechanics_), env(env_), attackedCres(), sc(), si(), parameters(parameters_), otherHero(nullptr), spellCost(0), damageToDisplay(0)
{
	sc.side = parameters.casterSide;
	sc.id = mechanics->owner->id;
	sc.skill = parameters.spellLvl;
	sc.tile = parameters.getFirstDestinationHex();
	sc.castByHero = parameters.mode == ECastingMode::HERO_CASTING;
	sc.casterStack = (parameters.casterStack ? parameters.casterStack->ID : -1);
	sc.manaGained = 0;

	//check it there is opponent hero
	const ui8 otherSide = 1-parameters.casterSide;

	if(parameters.cb->battleHasHero(otherSide))
		otherHero = parameters.cb->battleGetFightingHero(otherSide);

	logGlobal->debugStream() << "Started spell cast. Spell: " << mechanics->owner->name << "; mode:" << parameters.mode;
}

SpellCastContext::~SpellCastContext()
{
	logGlobal->debugStream() << "Finished spell cast. Spell: " << mechanics->owner->name << "; mode:" << parameters.mode;
}

void SpellCastContext::addDamageToDisplay(const si32 value)
{
	damageToDisplay += value;
}

void SpellCastContext::setDamageToDisplay(const si32 value)
{
	damageToDisplay = value;
}

void SpellCastContext::prepareBattleLog()
{
	bool displayDamage = true;

	mechanics->battleLog(sc.battleLog, parameters, attackedCres, damageToDisplay, displayDamage);

	displayDamage = displayDamage && damageToDisplay > 0;

	if(displayDamage)
	{
        MetaString line;

        line.addTxt(MetaString::GENERAL_TXT, 376);
        line.addReplacement(MetaString::SPELL_NAME, mechanics->owner->id.toEnum());
        line.addReplacement(damageToDisplay);

        sc.battleLog.push_back(line);
	}
}

void SpellCastContext::beforeCast()
{
	//calculate spell cost
	if(parameters.mode == ECastingMode::HERO_CASTING)
	{
		spellCost = parameters.cb->battleGetSpellCost(mechanics->owner, parameters.casterHero);

		if(nullptr != otherHero) //handle mana channel
		{
			int manaChannel = 0;
			for(const CStack * stack : parameters.cb->battleGetAllStacks(true)) //TODO: shouldn't bonus system handle it somehow?
			{
				if(stack->owner == otherHero->tempOwner)
				{
					vstd::amax(manaChannel, stack->valOfBonuses(Bonus::MANA_CHANNELING));
				}
			}
			sc.manaGained = (manaChannel * spellCost) / 100;
		}

		logGlobal->debugStream() << "spellCost: " << spellCost;
	}
}

void SpellCastContext::afterCast()
{
	for(auto sta : attackedCres)
	{
		sc.affectedCres.insert(sta->ID);
	}

	prepareBattleLog();

	env->sendAndApply(&sc);

	if(parameters.mode == ECastingMode::HERO_CASTING)
	{
		//spend mana
		SetMana sm;
		sm.absolute = false;

		sm.hid = parameters.casterHero->id;
		sm.val = -spellCost;

		env->sendAndApply(&sm);

		if(sc.manaGained > 0)
		{
			assert(otherHero);

			sm.hid = otherHero->id;
			sm.val = sc.manaGained;
			env->sendAndApply(&sm);
		}
	}
	else if (parameters.mode == ECastingMode::CREATURE_ACTIVE_CASTING || parameters.mode == ECastingMode::ENCHANTER_CASTING)
	{
		//reduce number of casts remaining
		assert(parameters.casterStack);

		BattleSetStackProperty ssp;
		ssp.stackID = parameters.casterStack->ID;
		ssp.which = BattleSetStackProperty::CASTS;
		ssp.val = -1;
		ssp.absolute = false;
		env->sendAndApply(&ssp);
	}
	if(!si.stacks.empty()) //after spellcast info shows
		env->sendAndApply(&si);
}

///DefaultSpellMechanics
void DefaultSpellMechanics::applyBattle(BattleInfo * battle, const BattleSpellCast * packet) const
{
	if (packet->castByHero)
	{
		if (packet->side < 2)
		{
			battle->sides[packet->side].castSpellsCount++;
		}
	}

	//handle countering spells
	for(auto stackID : packet->affectedCres)
	{
		CStack * s = battle->getStack(stackID);
		s->popBonuses([&](const Bonus * b) -> bool
		{
			//check for each bonus if it should be removed
			const bool isSpellEffect = Selector::sourceType(Bonus::SPELL_EFFECT)(b);
			const int spellID = isSpellEffect ? b->sid : -1;
			//No exceptions, ANY spell can be countered, even if it can`t be dispelled.
			return isSpellEffect && vstd::contains(owner->counteredSpells, spellID);
		});
	}
}

void DefaultSpellMechanics::battleCast(const SpellCastEnvironment * env, const BattleSpellCastParameters & parameters) const
{
	if(nullptr == parameters.caster)
	{
		env->complain("No spell-caster provided.");
		return;
	}

	std::vector <const CStack*> reflected;//for magic mirror

	cast(env, parameters, reflected);

	//Magic Mirror effect
	for(auto & attackedCre : reflected)
	{
		if(parameters.mode == ECastingMode::MAGIC_MIRROR)
		{
			logGlobal->error("Magic mirror recurrence!");
			return;
		}

		TStacks mirrorTargets = parameters.cb->battleGetStacksIf([this, parameters](const CStack * battleStack)
		{
			//Get all enemy stacks. Magic mirror can reflect to immune creature (with no effect)
			return battleStack->owner == parameters.casterColor && battleStack->isValidTarget(false);
		});

		if(!mirrorTargets.empty())
		{
			int targetHex = (*RandomGeneratorUtil::nextItem(mirrorTargets, env->getRandomGenerator()))->position;

			BattleSpellCastParameters mirrorParameters(parameters, attackedCre);
			mirrorParameters.aimToHex(targetHex);
			mirrorParameters.cast(env);
		}
	}
}

void DefaultSpellMechanics::cast(const SpellCastEnvironment * env, const BattleSpellCastParameters & parameters, std::vector <const CStack*> & reflected) const
{
	SpellCastContext ctx(this, env, parameters);

	ctx.beforeCast();

	ctx.attackedCres = owner->getAffectedStacks(parameters.cb, parameters.mode, parameters.caster, parameters.spellLvl, parameters.getFirstDestinationHex());

	logGlobal->debugStream() << "will affect " << ctx.attackedCres.size() << " stacks";

	handleResistance(env, ctx);

	if(parameters.mode != ECastingMode::MAGIC_MIRROR)
		handleMagicMirror(env, ctx, reflected);

	applyBattleEffects(env, parameters, ctx);

	ctx.afterCast();
}

void DefaultSpellMechanics::battleLog(std::vector<MetaString> & logLines, const BattleSpellCastParameters & parameters,
	const std::vector<const CStack *> & attacked, const si32 damageToDisplay, bool & displayDamage) const
{
	if(attacked.size() != 1)
	{
		displayDamage = true;
		battleLogDefault(logLines, parameters, attacked);
		return;
	}

	auto attackedStack = attacked.at(0);

	auto getPluralFormat = [attackedStack](const int baseTextID) -> si32
	{
		return attackedStack->count > 1 ? baseTextID + 1 : baseTextID;
	};

	auto logSimple = [attackedStack, &logLines, getPluralFormat](const int baseTextID)
	{
		MetaString line;
		line.addTxt(MetaString::GENERAL_TXT, getPluralFormat(baseTextID));
		line.addReplacement(*attackedStack);
		logLines.push_back(line);
	};

	auto logPlural = [attackedStack, &logLines, getPluralFormat](const int baseTextID)
	{
		MetaString line;
		line.addTxt(MetaString::GENERAL_TXT, baseTextID);
		line.addReplacement(MetaString::CRE_PL_NAMES, attackedStack->getCreature()->idNumber.num);
		logLines.push_back(line);
	};

	displayDamage = false; //in most following cases damage info text is custom

	switch(owner->id)
	{
	case SpellID::STONE_GAZE:
		logSimple(558);
		break;
	case SpellID::POISON:
		logSimple(561);
		break;
	case SpellID::BIND:
		logPlural(560);//Roots and vines bind the %s to the ground!
		break;
	case SpellID::DISEASE:
		logSimple(553);
		break;
	case SpellID::PARALYZE:
		logSimple(563);
		break;
	case SpellID::AGE:
		{
			//The %s shrivel with age, and lose %d hit points."
			MetaString line;
			line.addTxt(MetaString::GENERAL_TXT, getPluralFormat(551));
			line.addReplacement(MetaString::CRE_PL_NAMES, attackedStack->getCreature()->idNumber.num);

			//todo: display effect from only this cast
			TBonusListPtr bl = attackedStack->getBonuses(Selector::type(Bonus::STACK_HEALTH));
			const int fullHP = bl->totalValue();
			bl->remove_if(Selector::source(Bonus::SPELL_EFFECT, SpellID::AGE));
			line.addReplacement(fullHP - bl->totalValue());
			logLines.push_back(line);
		}
		break;
	case SpellID::THUNDERBOLT:
		{
			logPlural(367);
			MetaString line;
			//todo: handle newlines in metastring
			std::string text = VLC->generaltexth->allTexts[343].substr(1, VLC->generaltexth->allTexts[343].size() - 1); //Does %d points of damage.
			line << text;
			line.addReplacement(damageToDisplay); //no more text afterwards
			logLines.push_back(line);
		}
		break;
	case SpellID::DISPEL_HELPFUL_SPELLS:
		logPlural(555);
		break;
	case SpellID::DEATH_STARE:
		if (damageToDisplay > 0)
		{
			MetaString line;
			if (damageToDisplay > 1)
			{
				line.addTxt(MetaString::GENERAL_TXT, 119); //%d %s die under the terrible gaze of the %s.
				line.addReplacement(damageToDisplay);
				line.addReplacement(MetaString::CRE_PL_NAMES, attackedStack->getCreature()->idNumber.num);
			}
			else
			{
				line.addTxt(MetaString::GENERAL_TXT, 118); //One %s dies under the terrible gaze of the %s.
				line.addReplacement(MetaString::CRE_SING_NAMES, attackedStack->getCreature()->idNumber.num);
			}
			parameters.caster->getCasterName(line);
			logLines.push_back(line);
		}
		break;
	default:
		displayDamage = true;
		battleLogDefault(logLines, parameters, attacked);
		break;
	}
}

void DefaultSpellMechanics::battleLogDefault(std::vector<MetaString> & logLines, const BattleSpellCastParameters & parameters, const std::vector<const CStack*> & attacked) const
{
	MetaString line;
	parameters.caster->getCastDescription(owner, attacked, line);
	logLines.push_back(line);
}

void DefaultSpellMechanics::applyBattleEffects(const SpellCastEnvironment * env, const BattleSpellCastParameters & parameters, SpellCastContext & ctx) const
{
	if(owner->isOffensiveSpell())
		defaultDamageEffect(env, parameters, ctx);

	if(owner->hasEffects())
		defaultTimedEffect(env, parameters, ctx);
}

void DefaultSpellMechanics::defaultDamageEffect(const SpellCastEnvironment * env, const BattleSpellCastParameters & parameters, SpellCastContext & ctx) const
{
	const int rawDamage = parameters.getEffectValue();
	int chainLightningModifier = 0;
	for(auto & attackedCre : ctx.attackedCres)
	{
		BattleStackAttacked bsa;
		bsa.damageAmount = owner->adjustRawDamage(parameters.caster, attackedCre, rawDamage) >> chainLightningModifier;
		ctx.addDamageToDisplay(bsa.damageAmount);

		bsa.stackAttacked = (attackedCre)->ID;
		if(parameters.mode == ECastingMode::ENCHANTER_CASTING) //multiple damage spells cast
			bsa.attackerID = parameters.casterStack->ID;
		else
			bsa.attackerID = -1;
		(attackedCre)->prepareAttacked(bsa, env->getRandomGenerator());
		ctx.si.stacks.push_back(bsa);

		if(owner->id == SpellID::CHAIN_LIGHTNING)
			++chainLightningModifier;
	}
}

void DefaultSpellMechanics::defaultTimedEffect(const SpellCastEnvironment * env, const BattleSpellCastParameters & parameters, SpellCastContext & ctx) const
{
	SetStackEffect sse;
	//get default spell duration (spell power with bonuses for heroes)
	int duration = parameters.enchantPower;
	//generate actual stack bonuses
	{
		si32 maxDuration = 0;

		owner->getEffects(sse.effect, parameters.effectLevel, false, duration, &maxDuration);
		owner->getEffects(sse.cumulativeEffects, parameters.effectLevel, true, duration, &maxDuration);

		//if all spell effects have special duration, use it later for special bonuses
		duration = maxDuration;
	}
	//fix to original config: shield should display damage reduction
	if(owner->id == SpellID::SHIELD || owner->id == SpellID::AIR_SHIELD)
	{
		sse.effect.at(sse.effect.size() - 1).val = (100 - sse.effect.back().val);
	}
	//we need to know who cast Bind
	else if(owner->id == SpellID::BIND && parameters.casterStack)
	{
		sse.effect.at(sse.effect.size() - 1).additionalInfo = parameters.casterStack->ID;
	}
	std::shared_ptr<Bonus> bonus = nullptr;
	if(parameters.casterHero)
		bonus = parameters.casterHero->getBonusLocalFirst(Selector::typeSubtype(Bonus::SPECIAL_PECULIAR_ENCHANT, owner->id));
	//TODO does hero specialty should affects his stack casting spells?

	for(const CStack * affected : ctx.attackedCres)
	{
		si32 power = 0;
		sse.stacks.push_back(affected->ID);

		//Apply hero specials - peculiar enchants
		const ui8 tier = std::max((ui8)1, affected->getCreature()->level); //don't divide by 0 for certain creatures (commanders, war machines)
		if(bonus)
		{
			switch(bonus->additionalInfo)
			{
			case 0: //normal
				{
					switch(tier)
					{
					case 1:
					case 2:
						power = 3;
						break;
					case 3:
					case 4:
						power = 2;
						break;
					case 5:
					case 6:
						power = 1;
						break;
					}
					for(const Bonus & b : sse.effect)
					{
						Bonus specialBonus(b);
						specialBonus.val = power; //it doesn't necessarily make sense for some spells, use it wisely
						specialBonus.turnsRemain = duration;
						sse.uniqueBonuses.push_back(std::pair<ui32, Bonus>(affected->ID, specialBonus)); //additional premy to given effect
					}
					for(const Bonus & b : sse.cumulativeEffects)
					{
						Bonus specialBonus(b);
						specialBonus.val = power; //it doesn't necessarily make sense for some spells, use it wisely
						specialBonus.turnsRemain = duration;
						sse.cumulativeUniqueBonuses.push_back(std::pair<ui32, Bonus>(affected->ID, specialBonus)); //additional premy to given effect
					}
				}
				break;
			case 1: //only Coronius as yet
				{
					power = std::max(5 - tier, 0);
					Bonus specialBonus(Bonus::N_TURNS, Bonus::PRIMARY_SKILL, Bonus::SPELL_EFFECT, power, owner->id, PrimarySkill::ATTACK);
					specialBonus.turnsRemain = duration;
					sse.uniqueBonuses.push_back(std::pair<ui32,Bonus>(affected->ID, specialBonus)); //additional attack to Slayer effect
				}
				break;
			}
		}
		if(parameters.casterHero && parameters.casterHero->hasBonusOfType(Bonus::SPECIAL_BLESS_DAMAGE, owner->id)) //TODO: better handling of bonus percentages
		{
			int damagePercent = parameters.casterHero->level * parameters.casterHero->valOfBonuses(Bonus::SPECIAL_BLESS_DAMAGE, owner->id.toEnum()) / tier;
			Bonus specialBonus(Bonus::N_TURNS, Bonus::CREATURE_DAMAGE, Bonus::SPELL_EFFECT, damagePercent, owner->id, 0, Bonus::PERCENT_TO_ALL);
			specialBonus.turnsRemain = duration;
			sse.uniqueBonuses.push_back(std::pair<ui32,Bonus>(affected->ID, specialBonus));
		}
	}

	if(!sse.stacks.empty())
		env->sendAndApply(&sse);
}

std::vector<BattleHex> DefaultSpellMechanics::rangeInHexes(BattleHex centralHex, ui8 schoolLvl, ui8 side, bool *outDroppedHexes) const
{
	using namespace SRSLPraserHelpers;

	std::vector<BattleHex> ret;
	std::string rng = owner->getLevelInfo(schoolLvl).range + ','; //copy + artificial comma for easier handling

	if(rng.size() >= 2 && rng[0] != 'X') //there is at least one hex in range (+artificial comma)
	{
		std::string number1, number2;
		int beg, end;
		bool readingFirst = true;
		for(auto & elem : rng)
		{
			if(std::isdigit(elem) ) //reading number
			{
				if(readingFirst)
					number1 += elem;
				else
					number2 += elem;
			}
			else if(elem == ',') //comma
			{
				//calculating variables
				if(readingFirst)
				{
					beg = atoi(number1.c_str());
					number1 = "";
				}
				else
				{
					end = atoi(number2.c_str());
					number2 = "";
				}
				//obtaining new hexes
				std::set<ui16> curLayer;
				if(readingFirst)
				{
					curLayer = getInRange(centralHex, beg, beg);
				}
				else
				{
					curLayer = getInRange(centralHex, beg, end);
					readingFirst = true;
				}
				//adding abtained hexes
				for(auto & curLayer_it : curLayer)
				{
					ret.push_back(curLayer_it);
				}

			}
			else if(elem == '-') //dash
			{
				beg = atoi(number1.c_str());
				number1 = "";
				readingFirst = false;
			}
		}
	}

	//remove duplicates (TODO check if actually needed)
	range::unique(ret);
	return ret;
}

std::vector<const CStack *> DefaultSpellMechanics::getAffectedStacks(const CBattleInfoCallback * cb, const SpellTargetingContext & ctx) const
{
	std::vector<const CStack *> attackedCres = calculateAffectedStacks(cb, ctx);
	handleImmunities(cb, ctx, attackedCres);
	return attackedCres;
}

std::vector<const CStack *> DefaultSpellMechanics::calculateAffectedStacks(const CBattleInfoCallback* cb, const SpellTargetingContext& ctx) const
{
	std::set<const CStack* > attackedCres;//std::set to exclude multiple occurrences of two hex creatures

	const si8 playerSide = cb->playerToSide(ctx.caster->getOwner());
	if(playerSide < 0)
		return std::vector<const CStack *>();
	auto attackedHexes = rangeInHexes(ctx.destination, ctx.schoolLvl, playerSide);

	//hackfix for banned creature massive spells
	if(!ctx.ti.massive && owner->getLevelInfo(ctx.schoolLvl).range == "X")
		attackedHexes.push_back(ctx.destination);

	auto mainFilter = [=](const CStack * s)
	{
		const bool positiveToAlly = owner->isPositive() && s->owner == ctx.caster->getOwner();
		const bool negativeToEnemy = owner->isNegative() && s->owner != ctx.caster->getOwner();
		const bool validTarget = s->isValidTarget(!ctx.ti.onlyAlive); //todo: this should be handled by spell class
		const bool positivenessFlag = !ctx.ti.smart || owner->isNeutral() || positiveToAlly || negativeToEnemy;

		return positivenessFlag && validTarget;
	};

	if(ctx.ti.type == CSpell::CREATURE && attackedHexes.size() == 1)
	{
		//for single target spells we must select one target. Alive stack is preferred (issue #1763)

		auto predicate = [&](const CStack * s)
		{
			return s->coversPos(attackedHexes.at(0)) && mainFilter(s);
		};

		TStacks stacks = cb->battleGetStacksIf(predicate);

		for(auto stack : stacks)
		{
			if(stack->alive())
			{
				attackedCres.insert(stack);
				break;
			}
		}

		if(attackedCres.empty() && !stacks.empty())
		{
			attackedCres.insert(stacks.front());
		}
	}
	else if(ctx.ti.massive)
	{
		TStacks stacks = cb->battleGetStacksIf(mainFilter);
		for (auto stack : stacks)
			attackedCres.insert(stack);
	}
	else //custom range from attackedHexes
	{
		for(BattleHex hex : attackedHexes)
		{
			if(const CStack * st = cb->battleGetStackByPos(hex, ctx.ti.onlyAlive))
				if(mainFilter(st))
					attackedCres.insert(st);;
		}
	}

	std::vector<const CStack *> res;
	std::copy(attackedCres.begin(), attackedCres.end(), std::back_inserter(res));

	return res;
}

ESpellCastProblem::ESpellCastProblem DefaultSpellMechanics::canBeCast(const CBattleInfoCallback * cb, const ECastingMode::ECastingMode mode, const ISpellCaster * caster) const
{
	//no problems by default, this method is for spell-specific problems
	return ESpellCastProblem::OK;
}

ESpellCastProblem::ESpellCastProblem DefaultSpellMechanics::canBeCast(const CBattleInfoCallback * cb, const SpellTargetingContext & ctx) const
{
	if(ctx.mode == ECastingMode::CREATURE_ACTIVE_CASTING || ctx.mode == ECastingMode::HERO_CASTING)
	{
		std::vector<const CStack *> affected = getAffectedStacks(cb, ctx);

		//allow to cast spell if affects is at least one smart target
		bool targetExists = false;

		for(const CStack * stack : affected)
		{
			bool casterStack = stack->owner == ctx.caster->getOwner();

			switch (owner->positiveness)
			{
			case CSpell::POSITIVE:
				if(casterStack)
					targetExists = true;
				break;
			case CSpell::NEUTRAL:
				targetExists = true;
				break;
			case CSpell::NEGATIVE:
				if(!casterStack)
					targetExists = true;
				break;
			}

			if(targetExists)
				break;
		}

		if(!targetExists)
			return ESpellCastProblem::NO_APPROPRIATE_TARGET;
	}

	return ESpellCastProblem::OK;
}

ESpellCastProblem::ESpellCastProblem DefaultSpellMechanics::isImmuneByStack(const ISpellCaster * caster, const CStack * obj) const
{
	//by default use general algorithm
	return owner->internalIsImmune(caster, obj);
}

bool DefaultSpellMechanics::dispellSelector(const Bonus * bonus)
{
	if(bonus->source == Bonus::SPELL_EFFECT)
	{
		const CSpell * sourceSpell = SpellID(bonus->sid).toSpell();
		if(!sourceSpell)
			return false;//error
		//Special case: DISRUPTING_RAY is "immune" to dispell
		//Other even PERMANENT effects can be removed (f.e. BIND)
		if(sourceSpell->id == SpellID::DISRUPTING_RAY)
			return false;
		//Special case:do not remove lifetime marker
		if(sourceSpell->id == SpellID::CLONE)
			return false;
		//stack may have inherited effects
		if(sourceSpell->isAdventureSpell())
			return false;
		return true;
	}
	//not spell effect
	return false;
}

void DefaultSpellMechanics::doDispell(BattleInfo * battle, const BattleSpellCast * packet, const CSelector & selector) const
{
	for(auto stackID : packet->affectedCres)
	{
		CStack *s = battle->getStack(stackID);
		s->popBonuses(selector.And(dispellSelector));
	}
}

bool DefaultSpellMechanics::canDispell(const IBonusBearer * obj, const CSelector & selector, const std::string & cachingStr/* = "" */) const
{
	return obj->hasBonus(selector.And(dispellSelector), Selector::all, cachingStr);
}

void DefaultSpellMechanics::handleImmunities(const CBattleInfoCallback * cb, const SpellTargetingContext & ctx, std::vector<const CStack*> & stacks) const
{
	auto predicate = [&, this](const CStack * s)->bool
	{
		bool hitDirectly = ctx.ti.alwaysHitDirectly && s->coversPos(ctx.destination);
		bool notImmune = (ESpellCastProblem::OK == owner->isImmuneByStack(ctx.caster, s));

		return !(hitDirectly || notImmune);
	};
	vstd::erase_if(stacks, predicate);
}

void DefaultSpellMechanics::handleMagicMirror(const SpellCastEnvironment * env, SpellCastContext & ctx, std::vector <const CStack*> & reflected) const
{
	//reflection is applied only to negative spells
	//if it is actual spell and can be reflected to single target, no recurrence
	const bool tryMagicMirror = owner->isNegative() && owner->level && owner->getLevelInfo(0).range == "0";
	if(tryMagicMirror)
	{
		for(auto s : ctx.attackedCres)
		{
			const int mirrorChance = (s)->valOfBonuses(Bonus::MAGIC_MIRROR);
			if(env->getRandomGenerator().nextInt(99) < mirrorChance)
				reflected.push_back(s);
		}

		vstd::erase_if(ctx.attackedCres, [&reflected](const CStack * s)
		{
			return vstd::contains(reflected, s);
		});

		for(auto s : reflected)
		{
			BattleSpellCast::CustomEffect effect;
			effect.effect = 3;
			effect.stack = s->ID;
			ctx.sc.customEffects.push_back(effect);
		}
	}
}

void DefaultSpellMechanics::handleResistance(const SpellCastEnvironment * env, SpellCastContext & ctx) const
{
	//checking if creatures resist
	//resistance is applied only to negative spells
	if(owner->isNegative())
	{
		std::vector <const CStack*> resisted;
		for(auto s : ctx.attackedCres)
		{
			//magic resistance
			const int prob = std::min((s)->magicResistance(), 100); //probability of resistance in %

			if(env->getRandomGenerator().nextInt(99) < prob)
			{
				resisted.push_back(s);
			}
		}

		vstd::erase_if(ctx.attackedCres, [&resisted](const CStack * s)
		{
			return vstd::contains(resisted, s);
		});

		for(auto s : resisted)
		{
			BattleSpellCast::CustomEffect effect;
			effect.effect = 78;
			effect.stack = s->ID;
			ctx.sc.customEffects.push_back(effect);
		}
	}
}

bool DefaultSpellMechanics::requiresCreatureTarget() const
{
	//most spells affects creatures somehow regardless of Target Type
	//for few exceptions see overrides
	return true;
}

ESpellCastProblem::ESpellCastProblem SpecialSpellMechanics::canBeCast(const CBattleInfoCallback * cb, const SpellTargetingContext & ctx) const
{
	//no problems by default
	//common problems handled by CSpell
	return ESpellCastProblem::OK;
}

std::vector<const CStack *> SpecialSpellMechanics::calculateAffectedStacks(const CBattleInfoCallback * cb, const SpellTargetingContext & ctx) const
{
	return std::vector<const CStack *>();
}