package game

// BattleUnit is a pet in play with its attached foods applied. Power
// (attack) is unaffected by damage; a unit dies when Damage >= Power.
type BattleUnit struct {
	Card   Card   `json:"card"`
	Foods  []Card `json:"foods,omitempty"`
	Bonus  int    `json:"bonus"`  // total power added by foods (and eating)
	Damage int    `json:"damage"` // damage markers accumulated this battle
}

func (u *BattleUnit) Power() int  { return u.Card.Power + u.Bonus }
func (u *BattleUnit) Alive() bool { return u.Damage < u.Power() }

// activePerk returns the perk this unit benefits from: only the
// last-applied perk counts when several are attached.
func (u *BattleUnit) activePerk() *Card {
	for i := len(u.Foods) - 1; i >= 0; i-- {
		if u.Foods[i].Perk {
			return &u.Foods[i]
		}
	}
	return nil
}

// effects returns the unit's live effects: its own plus its active perk's.
func (u *BattleUnit) effects() []Effect {
	effs := u.Card.Effects
	if perk := u.activePerk(); perk != nil {
		effs = append(append([]Effect(nil), effs...), perk.Effects...)
	}
	return effs
}

// prevention totals the unit's passive per-attack damage reduction (Garlic).
func (u *BattleUnit) prevention() int {
	total := 0
	for _, e := range u.effects() {
		if e.Trigger == TriggerPassive && e.Action == ActionPreventDamage {
			total += e.count()
		}
	}
	return total
}

// takeHit applies one attack of the given strength and returns the damage
// actually dealt after prevention.
func (u *BattleUnit) takeHit(amount int) int {
	if amount <= 0 {
		return 0
	}
	dealt := max(0, amount-u.prevention())
	u.Damage += dealt
	return dealt
}

// isBee reports whether a card is a summoned Bee.
func isBee(c Card) bool { return c.IsPet() && c.Name == "Bee" }

// BattleEvent is one step of the battle, in order, for clients to animate.
type BattleEvent struct {
	// "reveal": Seat flipped Card off their stack (food or pet).
	// "summon": an effect put Card on top of Seat's stack.
	// "rock":   Seat's pet threw rocks at Target's pet in play.
	// "clash":  the pets in play traded blows.
	// "eat":    Seat's pet ate apples; Bonus is its new total.
	Type   string `json:"type"`
	Seat   int    `json:"seat,omitempty"`
	Target int    `json:"target,omitempty"`
	Card   *Card  `json:"card,omitempty"`
	// clash: per-seat damage totals / deaths after the exchange.
	Damage []int  `json:"damage,omitempty"`
	Died   []bool `json:"died,omitempty"`
	// rock: dice total rolled and the target pet's resulting state.
	Roll        int  `json:"roll"`
	DamageAfter int  `json:"damageAfter,omitempty"`
	TargetDied  bool `json:"targetDied,omitempty"`
	// eat: the pet's power bonus after eating.
	Bonus int `json:"bonus,omitempty"`
}

// BattleResult is the full, public record of one round's battle. Only what
// was revealed appears in Events; the rest of the winner's stack stays
// hidden.
type BattleResult struct {
	Round      int           `json:"round"`
	StackSizes []int         `json:"stackSizes"` // starting deck size per seat
	Events     []BattleEvent `json:"events"`
	WinnerSeat int           `json:"winnerSeat"` // -1 = draw
	Trophies   int           `json:"trophies"`   // awarded to the winner
}

// battleSide is one seat's live state during the simulation.
type battleSide struct {
	stack        []Card // remaining face-down cards, top first
	pending      []Card // foods revealed and waiting for a pet
	unit         *BattleUnit
	beesFainted  int   // friendly bees fainted so far (Dog)
	delayedRocks []int // set-aside Badgers: rocks to throw when the next pet plays
}

// queuedPlay is a play-time effect waiting to resolve after reveals.
type queuedPlay struct {
	seat   int
	unit   *BattleUnit // the pet whose play queued this (must still be in play for eats)
	effect Effect
	badger bool // delayedRocks payout: hits EVERY active pet, own included
}

// resolveBattle simulates the battle from the players' arranged decks,
// records the event log, awards trophies, and moves to PhaseBattle.
//
// The battle is a stack machine: each side reveals cards off the top of
// their deck until a pet is in play (foods along the way attach to it; only
// the last-applied perk counts). If anyone can no longer field a pet the
// battle ends. Otherwise play effects resolve — rocks roll dice (faces
// 0,0,1,1,2,2) and can faint a pet before the clash. Then the two pets deal
// their full Power to each other simultaneously as damage markers; a pet
// with Damage >= Power faints, firing Faint effects. Survivors that took
// damage fire Hurt effects. Garlic prevents 1 damage from every attack that
// hits its pet; a clash that deals no damage to anyone ends the battle as a
// stalemate.
func (g *Game) resolveBattle() {
	n := len(g.Players)
	res := &BattleResult{Round: g.Round, WinnerSeat: -1, StackSizes: make([]int, n)}
	sides := make([]*battleSide, n)
	for _, p := range g.Players {
		sides[p.Seat] = &battleSide{stack: append([]Card(nil), p.Deck...)}
		res.StackSizes[p.Seat] = len(p.Deck)
	}
	emit := func(ev BattleEvent) { res.Events = append(res.Events, ev) }

	summon := func(seat int, c Card) {
		s := sides[seat]
		s.stack = append([]Card{c}, s.stack...)
		emit(BattleEvent{Type: "summon", Seat: seat, Card: &c})
	}

	// faint fires the unit's faint effects (its own and its perk's) in
	// effect order, and tracks fainted bees.
	faint := func(seat int, u *BattleUnit) {
		if isBee(u.Card) {
			sides[seat].beesFainted++
		}
		for _, e := range u.effects() {
			if e.Trigger != TriggerFaint {
				continue
			}
			switch e.Action {
			case ActionSummonTop:
				target := seat
				if e.Target == "enemy" {
					target = (seat + 1) % n
				}
				for range e.count() {
					if e.Card == "bee" {
						summon(target, g.newBee())
					} else {
						summon(target, g.newApple())
					}
				}
			case ActionRecycleApples:
				recycled := 0
				for _, f := range u.Foods {
					if f.Food == FoodApple && recycled < e.count() {
						summon(seat, f)
						recycled++
					}
				}
			case ActionDelayedRocks:
				sides[seat].delayedRocks = append(sides[seat].delayedRocks, e.count())
			}
		}
	}

	// hurt fires Hurt effects on a pet that was damaged and survived.
	hurt := func(seat int, u *BattleUnit) {
		if !u.Alive() {
			return
		}
		for _, e := range u.effects() {
			if e.Trigger != TriggerHurt {
				continue
			}
			switch e.Action {
			case ActionEatApple:
				for range e.count() {
					u.Foods = append(u.Foods, g.newApple())
					u.Bonus++
				}
				emit(BattleEvent{Type: "eat", Seat: seat, Bonus: u.Bonus})
			case ActionSummonTop:
				for range e.count() {
					if e.Card == "bee" {
						summon(seat, g.newBee())
					} else {
						summon(seat, g.newApple())
					}
				}
			}
		}
	}

	// throwRocks rolls `dice` rock dice against one target's pet, handling
	// prevention, death (with faint), and hurt. Reports whether it killed.
	throwRocks := func(from, target, dice int) (killed bool) {
		tu := sides[target].unit
		if tu == nil {
			return false
		}
		roll := 0
		for range dice {
			roll += g.rollRockDie()
		}
		dealt := tu.takeHit(roll)
		died := !tu.Alive()
		emit(BattleEvent{
			Type: "rock", Seat: from, Target: target, Roll: roll,
			DamageAfter: tu.Damage, TargetDied: died,
		})
		if died {
			faint(target, tu)
			sides[target].unit = nil
			return true
		}
		if dealt > 0 {
			hurt(target, tu)
		}
		return false
	}

	// The exchange loop terminates: every clash kills at least one pet or
	// is a detected stalemate, and summons are finite. The guard is just
	// insurance as effects get richer.
	for range 10_000 {
		// Reveal until every side has a pet in play or runs out. Play
		// effects queue up and resolve after all reveals (simultaneous).
		var plays []queuedPlay
		for seat, s := range sides {
			for s.unit == nil && len(s.stack) > 0 {
				c := s.stack[0]
				s.stack = s.stack[1:]
				emit(BattleEvent{Type: "reveal", Seat: seat, Card: &c})
				if c.IsFood() {
					s.pending = append(s.pending, c)
					continue
				}
				u := &BattleUnit{Card: c, Foods: s.pending}
				for _, f := range s.pending {
					if f.Food == FoodApple {
						u.Bonus++
					}
				}
				s.pending = nil
				s.unit = u
				// Set-aside Badgers pay out when the next pet plays,
				// before that pet's own play effects.
				for _, dice := range s.delayedRocks {
					plays = append(plays, queuedPlay{seat: seat, unit: u, badger: true,
						effect: Effect{Action: ActionThrowRock, Count: dice}})
				}
				s.delayedRocks = nil
				for _, e := range u.effects() {
					if e.Trigger == TriggerPlay {
						plays = append(plays, queuedPlay{seat: seat, unit: u, effect: e})
					}
				}
			}
		}

		// Battle over? A side that couldn't field a pet is out; no further
		// effects resolve.
		anyOut := false
		for _, s := range sides {
			if s.unit == nil {
				anyOut = true
			}
		}
		if anyOut {
			break
		}

		// Resolve play effects. Rocks land before the clash and can faint
		// pets outright.
		rockDeath := false
		for _, q := range plays {
			switch q.effect.Action {
			case ActionThrowRock:
				if q.badger {
					// At EACH active pet, the owner's own included.
					for seat := range sides {
						if throwRocks(q.seat, seat, q.effect.count()) {
							rockDeath = true
						}
					}
				} else {
					target := -1
					for off := 1; off < n; off++ {
						cand := (q.seat + off) % n
						if sides[cand].unit != nil {
							target = cand
							break
						}
					}
					if target >= 0 && throwRocks(q.seat, target, q.effect.count()) {
						rockDeath = true
					}
				}
			case ActionEatApple:
				// Skip if the eater already died (e.g. to Badger rocks).
				if sides[q.seat].unit != q.unit {
					continue
				}
				count := q.effect.count()
				if q.effect.Per == PerFaintedBees {
					count *= sides[q.seat].beesFainted
				}
				if count > 0 {
					for range count {
						q.unit.Foods = append(q.unit.Foods, g.newApple())
						q.unit.Bonus++
					}
					emit(BattleEvent{Type: "eat", Seat: q.seat, Bonus: q.unit.Bonus})
				}
			}
		}
		if rockDeath {
			continue // refill before any clash
		}

		// Clash. Two-player for now; >2-player battle pairings come later
		// (the surrounding state is already per-seat).
		ua, ub := sides[0].unit, sides[1].unit
		dealtA := ua.takeHit(ub.Power())
		dealtB := ub.takeHit(ua.Power())
		emit(BattleEvent{
			Type:   "clash",
			Damage: []int{ua.Damage, ub.Damage},
			Died:   []bool{!ua.Alive(), !ub.Alive()},
		})
		if ua.Alive() && ub.Alive() && dealtA == 0 && dealtB == 0 {
			break // stalemate: nothing can ever change
		}
		dealt := []int{dealtA, dealtB}
		for seat, u := range []*BattleUnit{ua, ub} {
			if !u.Alive() {
				faint(seat, u)
				sides[seat].unit = nil
			} else if dealt[seat] > 0 {
				hurt(seat, u)
			}
		}
	}

	// A single side still holding a pet in play wins; anything else
	// (everyone out, or a stalemate with pets on both sides) is a draw.
	winner := -1
	for seat, s := range sides {
		if s.unit != nil {
			if winner >= 0 {
				winner = -1 // stalemate / >2-player safety
				break
			}
			winner = seat
		}
	}
	res.WinnerSeat = winner
	if winner >= 0 {
		res.Trophies = 1
		if g.Round == MaxRounds {
			res.Trophies = 2
		}
		g.Players[winner].Trophies += res.Trophies
	}

	g.Battle = res
	g.Phase = PhaseBattle
	for _, p := range g.Players {
		p.Ready = false
	}
}