package ai

import (
	"math/rand/v2"
	"slices"

	"github.com/greyson/super-auto-pets-board-game/internal/game"
)

// applyTemplateShopEffects mirrors the engine's shop-time triggers on a
// hypothetical deck: buying an Otter really does come with an apple, and the
// bot should value that. Only deck-changing effects matter here (coin
// refunds don't alter the deck being scored).
func (cx *ctx) applyTemplateShopEffects(deck []game.Card, c game.Card, trigger game.EffectTrigger) []game.Card {
	for _, e := range c.Effects {
		if e.Trigger != trigger || cx.v.Round < e.MinRound {
			continue
		}
		switch e.Action {
		case game.ActionGainApple:
			for range max(e.Count, 1) {
				deck = append(deck, cx.simApple())
			}
		case game.ActionDoubleApples:
			apples := 0
			for _, dc := range deck {
				if dc.Food == game.FoodApple {
					apples++
				}
			}
			for range apples {
				deck = append(deck, cx.simApple())
			}
		}
	}
	return deck
}

func (cx *ctx) simApple() game.Card {
	return game.Card{
		ID:        cx.nextSimID(),
		Kind:      game.KindFood,
		Name:      "Apple",
		Food:      game.FoodApple,
		Temporary: true,
	}
}

// previewSellDown applies the sell-down a pass would eventually force onto a
// hypothetical deck: while over the pet limit, the lowest-value pet is sold
// for an apple. This lets the bot buy a sixth pet on purpose, knowing what
// it will cost.
func (cx *ctx) previewSellDown(deck []game.Card) []game.Card {
	for {
		pets := 0
		worst, worstVal := -1, 0.0
		for i, c := range deck {
			if !c.IsPet() {
				continue
			}
			pets++
			if v := keepValue(c); worst < 0 || v < worstVal {
				worst, worstVal = i, v
			}
		}
		if pets <= cx.v.MaxPets || worst < 0 {
			return deck
		}
		sold := deck[worst]
		deck = slices.Delete(deck, worst, worst+1)
		deck = append(deck, cx.simApple())
		deck = cx.applyTemplateShopEffects(deck, sold, game.TriggerSell)
	}
}

// score fills in every candidate's score: a weighted blend of the estimated
// next-battle win chance (deck arranged by the book ordering — the full
// ordering search happens later, at arrange time) and the deck's future
// value. All candidates face the same opponent guesses.
func (b *Bot) score(cx *ctx, cands []candidate) {
	oppSamples, simsPer := b.budget()
	oppDecks := cx.oppArrangements(oppSamples)
	alpha := immediateWeight(cx.v)
	for i := range cands {
		total := 0.0
		for _, deck := range cands[i].decks {
			imm := cx.winProb(heuristicOrder(deck, 0), oppDecks, simsPer)
			fut := normFuture(deckValue(deck, cx.v.Round, cx.v.MaxRounds))
			total += alpha*imm + (1-alpha)*fut
		}
		cands[i].score = total/float64(len(cands[i].decks)) + cands[i].bias
	}
}

// decideShop picks one shop action: buy a row card, sell some own cards,
// trade in a suit triple, or pass. Only buying costs gold; selling and
// trading are free, and passing (the only way to end the round's shopping)
// is legal only at or under the pet limit.
func (b *Bot) decideShop(v *game.View, mem *Memory) *Action {
	cx := newCtx(v, mem)
	deck := cx.me.Deck
	var cands []candidate

	// Passing ends the bot's shopping for the round; it is the baseline every
	// other option must beat, nudged down while unspent coins remain because
	// spending them is usually right. Illegal over the pet limit — the sell
	// and trade candidates below always exist then, so the bot works its way
	// back under.
	if cx.me.PetCount <= v.MaxPets {
		bias := 0.0
		if cx.me.Coins > 0 {
			bias = -0.02
		}
		cands = append(cands, candidate{
			act:   &Action{Type: "pass"},
			decks: [][]game.Card{slices.Clone(deck)},
			bias:  bias,
		})
	}

	if cx.me.Coins > 0 {
		for i, c := range v.ShopRow {
			if c.ID == "" {
				continue
			}
			nd := append(slices.Clone(deck), c)
			nd = cx.applyTemplateShopEffects(nd, c, game.TriggerBuy)
			nd = cx.previewSellDown(nd)
			cands = append(cands, candidate{
				act:   &Action{Type: "buy", Row: i},
				decks: [][]game.Card{nd},
			})
		}
	}

	// Sell candidates: the worst 1, 2, or 3 keepers. Selling is free and
	// takes any number of cards, so bulk-dumping junk before a battle is one
	// action. Temporary cards are excluded — selling an apple for an apple
	// does nothing.
	sellable := slices.Clone(deck)
	sellable = slices.DeleteFunc(sellable, func(c game.Card) bool { return c.Temporary })
	slices.SortStableFunc(sellable, func(a, b game.Card) int {
		av, bv := keepValue(a), keepValue(b)
		switch {
		case av < bv:
			return -1
		case av > bv:
			return 1
		}
		return 0
	})
	for k := 1; k <= min(3, len(sellable)); k++ {
		ids := make([]string, 0, k)
		nd := slices.Clone(deck)
		for _, s := range sellable[:k] {
			ids = append(ids, s.ID)
			idx := slices.IndexFunc(nd, func(c game.Card) bool { return c.ID == s.ID })
			nd = slices.Delete(nd, idx, idx+1)
			nd = append(nd, cx.simApple())
			nd = cx.applyTemplateShopEffects(nd, s, game.TriggerSell)
		}
		cands = append(cands, candidate{
			act:   &Action{Type: "sell", Cards: ids},
			decks: [][]game.Card{nd},
		})
	}

	// Trade candidates: for each suit with three or more pets, trade the
	// three lowest-value ones. The reward card is unknown (top two of the
	// next tier's deck), so each trade is scored across several sampled
	// rewards.
	if v.Round < v.MaxRounds && v.Round < len(v.DeckCounts) && v.DeckCounts[v.Round] >= 2 {
		bySuit := map[game.Suit][]game.Card{}
		for _, c := range deck {
			if c.IsPet() && c.Suit != "" {
				bySuit[c.Suit] = append(bySuit[c.Suit], c)
			}
		}
		for _, pets := range bySuit {
			if len(pets) < game.TradeInCount {
				continue
			}
			slices.SortStableFunc(pets, func(a, b game.Card) int {
				av, bv := keepValue(a), keepValue(b)
				switch {
				case av < bv:
					return -1
				case av > bv:
					return 1
				}
				return 0
			})
			trio := pets[:game.TradeInCount]
			base := slices.Clone(deck)
			ids := make([]string, 0, game.TradeInCount)
			for _, t := range trio {
				ids = append(ids, t.ID)
				idx := slices.IndexFunc(base, func(c game.Card) bool { return c.ID == t.ID })
				base = slices.Delete(base, idx, idx+1)
				base = cx.applyTemplateShopEffects(base, t, game.TriggerTriple)
			}
			pool := cx.unseenPool(v.Round + 1)
			if len(pool) == 0 {
				pool = game.TierContents(v.Round + 1)
			}
			var decks [][]game.Card
			for range 3 {
				reward := pool[rand.IntN(len(pool))]
				reward.ID = cx.nextSimID()
				nd := append(slices.Clone(base), reward)
				nd = cx.applyTemplateShopEffects(nd, reward, game.TriggerBuy)
				nd = cx.previewSellDown(nd)
				decks = append(decks, nd)
			}
			cands = append(cands, candidate{
				act:   &Action{Type: "trade", Cards: ids},
				decks: decks,
			})
		}
	}

	b.score(cx, cands)
	return b.pick(cands).act
}

// decideTradeChoose resolves the bot's own pending trade: score keeping
// either revealed card and pick.
func (b *Bot) decideTradeChoose(v *game.View, mem *Memory) *Action {
	cx := newCtx(v, mem)
	var cands []candidate
	for pick, c := range v.Pending.Options {
		nd := append(slices.Clone(cx.me.Deck), c)
		nd = cx.applyTemplateShopEffects(nd, c, game.TriggerBuy)
		nd = cx.previewSellDown(nd)
		cands = append(cands, candidate{
			act:   &Action{Type: "tradeChoose", Pick: pick},
			decks: [][]game.Card{nd},
		})
	}
	b.score(cx, cands)
	return b.pick(cands).act
}