vcmi/lib/SpellMechanics.cpp

/*
 * SpellMechanics.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 "SpellMechanics.h"

#include "CObstacleInstance.h"
#include "mapObjects/CGHeroInstance.h"
#include "BattleState.h"
#include "CRandomGenerator.h"

#include "NetPacks.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;
	}
}

struct SpellCastContext
{
	SpellCastContext(std::vector<const CStack*> & attackedCres, BattleSpellCast & sc, StacksInjured & si):
		attackedCres(attackedCres), sc(sc), si(si){}; 
	std::vector<const CStack*> & attackedCres;
	BattleSpellCast & sc;
	StacksInjured & si;
};

class DefaultSpellMechanics: public ISpellMechanics
{
public:
	DefaultSpellMechanics(CSpell * s): ISpellMechanics(s){};
	
	std::vector<BattleHex> rangeInHexes(BattleHex centralHex, ui8 schoolLvl, ui8 side, bool *outDroppedHexes = nullptr) const override;
	std::set<const CStack *> getAffectedStacks(SpellTargetingContext & ctx) const override;
	
	ESpellCastProblem::ESpellCastProblem isImmuneByStack(const CGHeroInstance * caster, const CStack * obj) const override;
	
	//bool adventureCast(const SpellCastContext & context) const override; 
	void battleCast(const SpellCastEnvironment * env, BattleSpellCastParameters & parameters) const override;
protected:
	
	virtual void applyBattleEffects(const SpellCastEnvironment * env, BattleSpellCastParameters & parameters, SpellCastContext & ctx) const;
	
	virtual int calculateDuration(const CGHeroInstance * caster, int usedSpellPower) const;
};

class ObstacleMechanics: public DefaultSpellMechanics
{
public:
	ObstacleMechanics(CSpell * s): DefaultSpellMechanics(s){};		

protected:
	void applyBattleEffects(const SpellCastEnvironment * env, BattleSpellCastParameters & parameters, SpellCastContext & ctx) const override;	
};

class WallMechanics: public ObstacleMechanics
{
public:
	WallMechanics(CSpell * s): ObstacleMechanics(s){};	
	std::vector<BattleHex> rangeInHexes(BattleHex centralHex, ui8 schoolLvl, ui8 side, bool *outDroppedHexes = nullptr) const override;	
	
};

class ChainLightningMechanics: public DefaultSpellMechanics
{
public:
	ChainLightningMechanics(CSpell * s): DefaultSpellMechanics(s){};	
	std::set<const CStack *> getAffectedStacks(SpellTargetingContext & ctx) const override;
};

class CloneMechanics: public DefaultSpellMechanics
{
public:
	CloneMechanics(CSpell * s): DefaultSpellMechanics(s){};
	ESpellCastProblem::ESpellCastProblem isImmuneByStack(const CGHeroInstance * caster, const CStack * obj) const override;
};

class DispellHelpfulMechanics: public DefaultSpellMechanics
{
public:
	DispellHelpfulMechanics(CSpell * s): DefaultSpellMechanics(s){};
	ESpellCastProblem::ESpellCastProblem isImmuneByStack(const CGHeroInstance * caster, const CStack * obj) const override;	
};

class HypnotizeMechanics: public DefaultSpellMechanics
{
public:
	HypnotizeMechanics(CSpell * s): DefaultSpellMechanics(s){};	
	ESpellCastProblem::ESpellCastProblem isImmuneByStack(const CGHeroInstance * caster, const CStack * obj) const override;	
}; 

///all rising spells
class RisingSpellMechanics: public DefaultSpellMechanics
{
public:
	RisingSpellMechanics(CSpell * s): DefaultSpellMechanics(s){};		
	
};

///all rising spells but SACRIFICE
class SpecialRisingSpellMechanics: public RisingSpellMechanics
{
public:
	SpecialRisingSpellMechanics(CSpell * s): RisingSpellMechanics(s){};
	ESpellCastProblem::ESpellCastProblem isImmuneByStack(const CGHeroInstance * caster, const CStack * obj) const override;						
};

class SacrificeMechanics: public RisingSpellMechanics
{
public:
	SacrificeMechanics(CSpell * s): RisingSpellMechanics(s){};		
};

///ISpellMechanics
ISpellMechanics::ISpellMechanics(CSpell * s):
	owner(s)
{
	
}

ISpellMechanics * ISpellMechanics::createMechanics(CSpell* s)
{
	switch (s->id)
	{
	case SpellID::CLONE:
		return new CloneMechanics(s);
	case SpellID::DISPEL_HELPFUL_SPELLS:
		return new DispellHelpfulMechanics(s);
	case SpellID::SACRIFICE:
		return new SacrificeMechanics(s);
	case SpellID::CHAIN_LIGHTNING:
		return new ChainLightningMechanics(s);		
	case SpellID::FIRE_WALL:
	case SpellID::FORCE_FIELD:
		return new WallMechanics(s);		
	case SpellID::LAND_MINE:
	case SpellID::QUICKSAND:
		return new ObstacleMechanics(s);
	default:		
		if(s->isRisingSpell())
			return new SpecialRisingSpellMechanics(s);
		else	
			return new DefaultSpellMechanics(s);		
	}	
}


///DefaultSpellMechanics

//bool DefaultSpellMechanics::adventureCast(const SpellCastContext& context) const
//{
//	return false; //there is no general algorithm for casting adventure spells
//}

void DefaultSpellMechanics::battleCast(const SpellCastEnvironment * env, BattleSpellCastParameters & parameters) const
{
	BattleSpellCast sc;
	sc.side = parameters.casterSide;
	sc.id = owner->id;
	sc.skill = parameters.spellLvl;
	sc.tile = parameters.destination;
	sc.dmgToDisplay = 0;
	sc.castedByHero = nullptr != parameters.caster;
	sc.attackerType = (parameters.casterStack ? parameters.casterStack->type->idNumber : CreatureID(CreatureID::NONE));
	sc.manaGained = 0;
	sc.spellCost = 0;	
	
	//calculate spell cost
	if (parameters.caster) 
	{
		sc.spellCost = parameters.cb->battleGetSpellCost(owner, parameters.caster);

		if (parameters.secHero && parameters.mode == ECastingMode::HERO_CASTING) //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 == parameters.secHero->tempOwner)
				{
					vstd::amax(manaChannel, stack->valOfBonuses(Bonus::MANA_CHANNELING));
				}
			}
			sc.manaGained = (manaChannel * sc.spellCost) / 100;
		}
	}	
	
	
	//calculating affected creatures for all spells
	//must be vector, as in Chain Lightning order matters
	std::vector<const CStack*> attackedCres; //CStack vector is somewhat more suitable than ID vector

	auto creatures = owner->getAffectedStacks(parameters.cb, parameters.mode, parameters.casterColor, parameters.spellLvl, parameters.destination, parameters.caster);
	std::copy(creatures.begin(), creatures.end(), std::back_inserter(attackedCres));
	
	for (auto cre : attackedCres)
	{
		sc.affectedCres.insert (cre->ID);
	}
	
	//checking if creatures resist
	//resistance is applied only to negative spells
	if(owner->isNegative())
	{
		for(auto s : attackedCres)
		{
			const int prob = std::min((s)->magicResistance(), 100); //probability of resistance in %
			
			if(env->getRandomGenerator().nextInt(99) < prob)
			{
				sc.resisted.push_back(s->ID);
			}
		}
	}
	
	//TODO: extract dmg to display calculation	
	//calculating dmg to display
	if (owner->id == SpellID::DEATH_STARE || owner->id == SpellID::ACID_BREATH_DAMAGE)
	{
		sc.dmgToDisplay = parameters.usedSpellPower;
		if (owner->id == SpellID::DEATH_STARE)
			vstd::amin(sc.dmgToDisplay, (*attackedCres.begin())->count); //stack is already reduced after attack
	}	
		
	StacksInjured si;
	
	SpellCastContext ctx(attackedCres, sc, si);
	
	applyBattleEffects(env, parameters, ctx);
	
	env->sendAndApply(&sc);
	if(!si.stacks.empty()) //after spellcast info shows
		env->sendAndApply(&si);
	
	//reduce number of casts remaining
	//TODO: this should be part of BattleSpellCast apply
	if (parameters.mode == ECastingMode::CREATURE_ACTIVE_CASTING || parameters.mode == ECastingMode::ENCHANTER_CASTING) 
	{
		assert(parameters.casterStack);
		
		BattleSetStackProperty ssp;
		ssp.stackID = parameters.casterStack->ID;
		ssp.which = BattleSetStackProperty::CASTS;
		ssp.val = -1;
		ssp.absolute = false;
		env->sendAndApply(&ssp);
	}

	//Magic Mirror effect
	if (owner->isNegative() && parameters.mode != ECastingMode::MAGIC_MIRROR && owner->level && owner->getLevelInfo(0).range == "0") //it is actual spell and can be reflected to single target, no recurrence
	{
		for(auto & attackedCre : attackedCres)
		{
			int mirrorChance = (attackedCre)->valOfBonuses(Bonus::MAGIC_MIRROR);
			if(mirrorChance > env->getRandomGenerator().nextInt(99))
			{
				std::vector<const CStack *> mirrorTargets;
				auto battleStacks = parameters.cb->battleGetAllStacks(true);
				for (auto & battleStack : battleStacks)
				{
					if(battleStack->owner == parameters.casterColor) //get enemy stacks which can be affected by this spell
					{
						if (ESpellCastProblem::OK == owner->isImmuneByStack(nullptr, battleStack))
							mirrorTargets.push_back(battleStack);
					}
				}
				if (!mirrorTargets.empty())
				{
					int targetHex = (*RandomGeneratorUtil::nextItem(mirrorTargets, env->getRandomGenerator()))->position;
					
					BattleSpellCastParameters mirrorParameters = parameters;
					mirrorParameters.spellLvl = 0;
					mirrorParameters.casterSide = 1-parameters.casterSide;
					mirrorParameters.casterColor = (attackedCre)->owner;
					mirrorParameters.caster = nullptr;
					mirrorParameters.destination = targetHex;
					mirrorParameters.secHero = parameters.caster;
					mirrorParameters.mode = ECastingMode::MAGIC_MIRROR;
					mirrorParameters.casterStack = (attackedCre);
					mirrorParameters.selectedStack = nullptr;
					
					battleCast(env, mirrorParameters);					
				}
			}
		}
	}	
}

int DefaultSpellMechanics::calculateDuration(const CGHeroInstance* caster, int usedSpellPower) const
{
	if(!caster)
	{
		if (!usedSpellPower)
			return 3; //default duration of all creature spells
		else
			return usedSpellPower; //use creature spell power
	}
	switch(owner->id)
	{
	case SpellID::FRENZY:
		return 1;
	default: //other spells
		return caster->getPrimSkillLevel(PrimarySkill::SPELL_POWER) + caster->valOfBonuses(Bonus::SPELL_DURATION);
	}	
}


void DefaultSpellMechanics::applyBattleEffects(const SpellCastEnvironment* env, BattleSpellCastParameters& parameters, SpellCastContext & ctx) const
{
	//TODO:applying effects
	
	//applying effects
	if (owner->isOffensiveSpell())
	{
		int spellDamage = 0;
		if (parameters.casterStack && parameters.mode != ECastingMode::MAGIC_MIRROR)
		{
			int unitSpellPower = parameters.casterStack->valOfBonuses(Bonus::SPECIFIC_SPELL_POWER, owner->id.toEnum());
			if (unitSpellPower)
				ctx.sc.dmgToDisplay = spellDamage = parameters.casterStack->count * unitSpellPower; //TODO: handle immunities
			else //Faerie Dragon
			{
				parameters.usedSpellPower = parameters.casterStack->valOfBonuses(Bonus::CREATURE_SPELL_POWER) * parameters.casterStack->count / 100;
				ctx.sc.dmgToDisplay = 0;
			}
		}
		int chainLightningModifier = 0;
		for(auto & attackedCre : ctx.attackedCres)
		{
			if(vstd::contains(ctx.sc.resisted, (attackedCre)->ID)) //this creature resisted the spell
				continue;

			BattleStackAttacked bsa;
			if ((parameters.destination > -1 && (attackedCre)->coversPos(parameters.destination)) || (owner->getLevelInfo(parameters.spellLvl).range == "X" || parameters.mode == ECastingMode::ENCHANTER_CASTING))
				//display effect only upon primary target of area spell
				//FIXME: if no stack is attacked, there is no animation and interface freezes
			{
				bsa.flags |= BattleStackAttacked::EFFECT;
				bsa.effect = owner->mainEffectAnim;
			}
			if (spellDamage)
				bsa.damageAmount = spellDamage >> chainLightningModifier;
			else
				bsa.damageAmount =  owner->calculateDamage(parameters.caster, attackedCre, parameters.spellLvl, parameters.usedSpellPower) >> chainLightningModifier;

			ctx.sc.dmgToDisplay += 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;
		}
	}
	
	if (owner->hasEffects())
	{
		int stackSpellPower = 0;
		if (parameters.casterStack && parameters.mode != ECastingMode::MAGIC_MIRROR)
		{
			stackSpellPower =  parameters.casterStack->valOfBonuses(Bonus::CREATURE_ENCHANT_POWER);
		}
		SetStackEffect sse;
		Bonus pseudoBonus;
		pseudoBonus.sid = owner->id;
		pseudoBonus.val = parameters.spellLvl;
		pseudoBonus.turnsRemain = calculateDuration(parameters.caster, stackSpellPower ? stackSpellPower : parameters.usedSpellPower);
		CStack::stackEffectToFeature(sse.effect, pseudoBonus);
		if (owner->id == SpellID::SHIELD || owner->id == SpellID::AIR_SHIELD)
		{
			sse.effect.back().val = (100 - sse.effect.back().val); //fix to original config: shield should display damage reduction
		}
		if (owner->id == SpellID::BIND &&  parameters.casterStack)//bind
		{
			sse.effect.back().additionalInfo =  parameters.casterStack->ID; //we need to know who casted Bind
		}
		const Bonus * bonus = nullptr;
		if (parameters.caster)
			bonus = parameters.caster->getBonusLocalFirst(Selector::typeSubtype(Bonus::SPECIAL_PECULIAR_ENCHANT, owner->id));
		//TODO does hero specialty should affects his stack casting spells?

		si32 power = 0;
		for(const CStack * affected : ctx.attackedCres)
		{
			if(vstd::contains(ctx.sc.resisted, affected->ID)) //this creature resisted the spell
				continue;
			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;
						}
						Bonus specialBonus(sse.effect.back());
						specialBonus.val = power; //it doesn't necessarily make sense for some spells, use it wisely
						sse.uniqueBonuses.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 = CStack::featureGenerator(Bonus::PRIMARY_SKILL, PrimarySkill::ATTACK, power, pseudoBonus.turnsRemain);
						specialBonus.sid = owner->id;
						sse.uniqueBonuses.push_back (std::pair<ui32,Bonus> (affected->ID, specialBonus)); //additional attack to Slayer effect
					}
					break;
				}
			}
			if (parameters.caster && parameters.caster->hasBonusOfType(Bonus::SPECIAL_BLESS_DAMAGE, owner->id)) //TODO: better handling of bonus percentages
			{
				int damagePercent = parameters.caster->level * parameters.caster->valOfBonuses(Bonus::SPECIAL_BLESS_DAMAGE, owner->id.toEnum()) / tier;
				Bonus specialBonus = CStack::featureGenerator(Bonus::CREATURE_DAMAGE, 0, damagePercent, pseudoBonus.turnsRemain);
				specialBonus.valType = Bonus::PERCENT_TO_ALL;
				specialBonus.sid = owner->id;
				sse.uniqueBonuses.push_back (std::pair<ui32,Bonus> (affected->ID, specialBonus));
			}
		}

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

	}
	
	if(owner->isHealingSpell())
	{
		int hpGained = 0;
		if (parameters.casterStack)
		{
			int unitSpellPower = parameters.casterStack->valOfBonuses(Bonus::SPECIFIC_SPELL_POWER, owner->id.toEnum());
			if (unitSpellPower)
				hpGained = parameters.casterStack->count * unitSpellPower; //Archangel
			else //Faerie Dragon-like effect - unused so far
				parameters.usedSpellPower = parameters.casterStack->valOfBonuses(Bonus::CREATURE_SPELL_POWER) * parameters.casterStack->count / 100;
		}
		StacksHealedOrResurrected shr;
		shr.lifeDrain = false;
		shr.tentHealing = false;
		for(auto & attackedCre : ctx.attackedCres)
		{
			StacksHealedOrResurrected::HealInfo hi;
			hi.stackID = (attackedCre)->ID;
			if (parameters.casterStack) //casted by creature
			{
				if (hpGained)
				{
					hi.healedHP = parameters.cb->calculateHealedHP(hpGained, owner, attackedCre); //archangel
				}
				else
					hi.healedHP = parameters.cb->calculateHealedHP(owner, parameters.usedSpellPower, parameters.spellLvl, attackedCre); //any typical spell (commander's cure or animate dead)
			}
			else
				hi.healedHP = owner->calculateHealedHP(parameters.caster, attackedCre, parameters.selectedStack); //Casted by hero
			hi.lowLevelResurrection = parameters.spellLvl <= 1;
			shr.healedStacks.push_back(hi);
		}
		if(!shr.healedStacks.empty())
			env->sendAndApply(&shr);
		if(owner->id == SpellID::SACRIFICE) //remove victim
		{
			if(parameters.selectedStack == parameters.cb->battleActiveStack())
			//set another active stack than the one removed, or bad things will happen
			//TODO: make that part of BattleStacksRemoved? what about client update?
			{
				//makeStackDoNothing(gs->curB->getStack (selectedStack));

				BattleSetActiveStack sas;

				//std::vector<const CStack *> hlp;
				//battleGetStackQueue(hlp, 1, selectedStack); //next after this one

				//if(hlp.size())
				//{
				//	sas.stack = hlp[0]->ID;
				//}
				//else
				//	complain ("No new stack to activate!");
				sas.stack = parameters.cb->getNextStack()->ID; //why the hell next stack has same ID as current?
				env->sendAndApply(&sas);

			}
			BattleStacksRemoved bsr;
			bsr.stackIDs.insert(parameters.selectedStack->ID); //somehow it works for teleport?
			env->sendAndApply(&bsr);
		}
	}		
}


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 lest 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::set<const CStack *> DefaultSpellMechanics::getAffectedStacks(SpellTargetingContext & ctx) const
{
	std::set<const CStack* > attackedCres;//std::set to exclude multiple occurrences of two hex creatures
	
	const ui8 attackerSide = ctx.cb->playerToSide(ctx.casterColor) == 1;
	const auto attackedHexes = rangeInHexes(ctx.destination, ctx.schoolLvl, attackerSide);

	const CSpell::TargetInfo ti(owner, ctx.schoolLvl, ctx.mode);
	
	//TODO: more generic solution for mass spells
	if (owner->getLevelInfo(ctx.schoolLvl).range.size() > 1) //custom many-hex range
	{
		for(BattleHex hex : attackedHexes)
		{
			if(const CStack * st = ctx.cb->battleGetStackByPos(hex, ti.onlyAlive))
			{
				attackedCres.insert(st);
			}
		}
	}
	else if(ti.type == CSpell::CREATURE)
	{
		auto predicate = [=](const CStack * s){
			const bool positiveToAlly = owner->isPositive() && s->owner == ctx.casterColor;
			const bool negativeToEnemy = owner->isNegative() && s->owner != ctx.casterColor;
			const bool validTarget = s->isValidTarget(!ti.onlyAlive); //todo: this should be handled by spell class
	
			//for single target spells select stacks covering destination tile
			const bool rangeCovers = ti.massive || s->coversPos(ctx.destination);
			//handle smart targeting
			const bool positivenessFlag = !ti.smart || owner->isNeutral() || positiveToAlly || negativeToEnemy;
			
			return rangeCovers && positivenessFlag && validTarget;		
		};
		
		TStacks stacks = ctx.cb->battleGetStacksIf(predicate);
		
		if (ti.massive)
		{
			//for massive spells add all targets
			for (auto stack : stacks)
				attackedCres.insert(stack);

		}
		else
		{
			//for single target spells we must select one target. Alive stack is preferred (issue #1763)
			for(auto stack : stacks)
			{
				if(stack->alive())
				{
					attackedCres.insert(stack);
					break;
				}				
			}	
			
			if(attackedCres.empty() && !stacks.empty())
			{
				attackedCres.insert(stacks.front());
			}						
		}
	}
	else //custom range from attackedHexes
	{
		for(BattleHex hex : attackedHexes)
		{
			if(const CStack * st = ctx.cb->battleGetStackByPos(hex, ti.onlyAlive))
				attackedCres.insert(st);
		}
	}	
	
	return attackedCres;
}


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

///ObstacleMechanics
void ObstacleMechanics::applyBattleEffects(const SpellCastEnvironment* env, BattleSpellCastParameters& parameters, SpellCastContext& ctx) const
{
	auto placeObstacle = [&, this](BattleHex pos)
	{
		static int obstacleIdToGive =  parameters.cb->obstacles.size()
									? (parameters.cb->obstacles.back()->uniqueID+1)
									: 0;

		auto obstacle = make_shared<SpellCreatedObstacle>();
		switch(owner->id) // :/
		{
		case SpellID::QUICKSAND:
			obstacle->obstacleType = CObstacleInstance::QUICKSAND;
			obstacle->turnsRemaining = -1;
			obstacle->visibleForAnotherSide = false;
			break;
		case SpellID::LAND_MINE:
			obstacle->obstacleType = CObstacleInstance::LAND_MINE;
			obstacle->turnsRemaining = -1;
			obstacle->visibleForAnotherSide = false;
			break;
		case SpellID::FIRE_WALL:
			obstacle->obstacleType = CObstacleInstance::FIRE_WALL;
			obstacle->turnsRemaining = 2;
			obstacle->visibleForAnotherSide = true;
			break;
		case SpellID::FORCE_FIELD:
			obstacle->obstacleType = CObstacleInstance::FORCE_FIELD;
			obstacle->turnsRemaining = 2;
			obstacle->visibleForAnotherSide = true;
			break;
		default:
			//this function cannot be used with spells that do not create obstacles
			assert(0);
		}

		obstacle->pos = pos;
		obstacle->casterSide = parameters.casterSide;
		obstacle->ID = owner->id;
		obstacle->spellLevel = parameters.spellLvl;
		obstacle->casterSpellPower = parameters.usedSpellPower;
		obstacle->uniqueID = obstacleIdToGive++;

		BattleObstaclePlaced bop;
		bop.obstacle = obstacle;
		env->sendAndApply(&bop);
	};	
	
	switch (owner->id)
	{
	case SpellID::QUICKSAND:
	case SpellID::LAND_MINE:
		{
			std::vector<BattleHex> availableTiles;
			for(int i = 0; i < GameConstants::BFIELD_SIZE; i += 1)
			{
				BattleHex hex = i;
				if(hex.getX() > 2 && hex.getX() < 14 && !(parameters.cb->battleGetStackByPos(hex, false)) && !(parameters.cb->battleGetObstacleOnPos(hex, false)))
					availableTiles.push_back(hex);
			}
			boost::range::random_shuffle(availableTiles);

			const int patchesForSkill[] = {4, 4, 6, 8};
			const int patchesToPut = std::min<int>(patchesForSkill[parameters.spellLvl], availableTiles.size());

			//land mines or quicksand patches are handled as spell created obstacles
			for (int i = 0; i < patchesToPut; i++)
				placeObstacle(availableTiles.at(i));
		}

		break;
	case SpellID::FORCE_FIELD:
		placeObstacle(parameters.destination);
		break;
	case SpellID::FIRE_WALL:
		{
			//fire wall is build from multiple obstacles - one fire piece for each affected hex
			auto affectedHexes = owner->rangeInHexes(parameters.destination, parameters.spellLvl, parameters.casterSide);
			for(BattleHex hex : affectedHexes)
				placeObstacle(hex);
		}
		break;
	default:		
		assert(0);
	}			
}


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

	std::vector<BattleHex> ret;	
	
	//Special case - shape of obstacle depends on caster's side
	//TODO make it possible through spell_info config

	BattleHex::EDir firstStep, secondStep;
	if(side)
	{
		firstStep = BattleHex::TOP_LEFT;
		secondStep = BattleHex::TOP_RIGHT;
	}
	else
	{
		firstStep = BattleHex::TOP_RIGHT;
		secondStep = BattleHex::TOP_LEFT;
	}

	//Adds hex to the ret if it's valid. Otherwise sets output arg flag if given.
	auto addIfValid = [&](BattleHex hex)
	{
		if(hex.isValid())
			ret.push_back(hex);
		else if(outDroppedHexes)
			*outDroppedHexes = true;
	};

	ret.push_back(centralHex);
	addIfValid(centralHex.moveInDir(firstStep, false));
	if(schoolLvl >= 2) //advanced versions of fire wall / force field cotnains of 3 hexes
		addIfValid(centralHex.moveInDir(secondStep, false)); //moveInDir function modifies subject hex

	return ret;	
}

///ChainLightningMechanics
std::set<const CStack *> ChainLightningMechanics::getAffectedStacks(SpellTargetingContext & ctx) const
{
	std::set<const CStack* > attackedCres;
	
	std::set<BattleHex> possibleHexes;
	for(auto stack : ctx.cb->battleGetAllStacks())
	{
		if(stack->isValidTarget())
		{
			for(auto hex : stack->getHexes())
			{
				possibleHexes.insert (hex);
			}
		}
	}
	int targetsOnLevel[4] = {4, 4, 5, 5};

	BattleHex lightningHex = ctx.destination;
	for(int i = 0; i < targetsOnLevel[ctx.schoolLvl]; ++i)
	{
		auto stack = ctx.cb->battleGetStackByPos(lightningHex, true);
		if(!stack)
			break;
		attackedCres.insert (stack);
		for(auto hex : stack->getHexes())
		{
			possibleHexes.erase(hex); //can't hit same place twice
		}
		if(possibleHexes.empty()) //not enough targets
			break;
		lightningHex = BattleHex::getClosestTile(stack->attackerOwned, ctx.destination, possibleHexes);
	}	
		
	return attackedCres;
}

///CloneMechanics
ESpellCastProblem::ESpellCastProblem CloneMechanics::isImmuneByStack(const CGHeroInstance* caster, const CStack * obj) const
{
	//can't clone already cloned creature
	if (vstd::contains(obj->state, EBattleStackState::CLONED))
		return ESpellCastProblem::STACK_IMMUNE_TO_SPELL;
	//TODO: how about stacks casting Clone?
	//currently Clone casted by stack is assumed Expert level
	ui8 schoolLevel;
	if (caster)
	{
		schoolLevel = caster->getSpellSchoolLevel(owner);
	}
	else
	{
		schoolLevel = 3;
	}

	if (schoolLevel < 3)
	{
		int maxLevel = (std::max(schoolLevel, (ui8)1) + 4);
		int creLevel = obj->getCreature()->level;
		if (maxLevel < creLevel) //tier 1-5 for basic, 1-6 for advanced, any level for expert
			return ESpellCastProblem::STACK_IMMUNE_TO_SPELL;
	}
	//use default algorithm only if there is no mechanics-related problem		
	return DefaultSpellMechanics::isImmuneByStack(caster,obj);	
}

///DispellHelpfulMechanics
ESpellCastProblem::ESpellCastProblem DispellHelpfulMechanics::isImmuneByStack(const CGHeroInstance* caster,  const CStack* obj) const
{
	TBonusListPtr spellBon = obj->getSpellBonuses();
	bool hasPositiveSpell = false;
	for(const Bonus * b : *spellBon)
	{
		if(SpellID(b->sid).toSpell()->isPositive())
		{
			hasPositiveSpell = true;
			break;
		}
	}
	if(!hasPositiveSpell)
	{
		return ESpellCastProblem::NO_SPELLS_TO_DISPEL;
	}
	
	//use default algorithm only if there is no mechanics-related problem		
	return DefaultSpellMechanics::isImmuneByStack(caster,obj);	
}

///HypnotizeMechanics
ESpellCastProblem::ESpellCastProblem HypnotizeMechanics::isImmuneByStack(const CGHeroInstance* caster, const CStack* obj) const
{
	if(nullptr != caster) //do not resist hypnotize casted after attack, for example
	{
		//TODO: what with other creatures casting hypnotize, Faerie Dragons style?
		ui64 subjectHealth = (obj->count - 1) * obj->MaxHealth() + obj->firstHPleft;
		//apply 'damage' bonus for hypnotize, including hero specialty
		ui64 maxHealth = owner->calculateBonus(caster->getPrimSkillLevel(PrimarySkill::SPELL_POWER)
			* owner->power + owner->getPower(caster->getSpellSchoolLevel(owner)), caster, obj);
		if (subjectHealth > maxHealth)
			return ESpellCastProblem::STACK_IMMUNE_TO_SPELL;
	}			
	return DefaultSpellMechanics::isImmuneByStack(caster,obj);
}


///SpecialRisingSpellMechanics
ESpellCastProblem::ESpellCastProblem SpecialRisingSpellMechanics::isImmuneByStack(const CGHeroInstance* caster, const CStack* obj) const
{
	// following does apply to resurrect and animate dead(?) only
	// for sacrifice health calculation and health limit check don't matter

	if(obj->count >= obj->baseAmount)
		return ESpellCastProblem::STACK_IMMUNE_TO_SPELL;
	
	if (caster) //FIXME: Archangels can cast immune stack
	{
		auto maxHealth = owner->calculateHealedHP (caster, obj);
		if (maxHealth < obj->MaxHealth()) //must be able to rise at least one full creature
			return ESpellCastProblem::STACK_IMMUNE_TO_SPELL;
	}	
	
	return DefaultSpellMechanics::isImmuneByStack(caster,obj);	
}