package ai

import (
	"encoding/json"
	"fmt"
	"slices"

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

// Memory is the bot's private notebook: everything it has legitimately
// learned from public information, carried between turns (and, serialized
// into the game state, across server restarts). It is the bot's substitute
// for a human player's attention — nothing in here is unavailable to a human
// watching the same screen.
type Memory struct {
	LastSeq         int         `json:"lastSeq"`         // last event-log entry processed
	LastBattleRound int         `json:"lastBattleRound"` // last battle lineup ingested
	PrevShopRow     []game.Card `json:"prevShopRow"`     // shop row at the previous observation
	// Opps models every other seat at the table, keyed by seat. A bot fights a
	// different opponent each round (see the rulebook's pairings), and every
	// battle is played in the open, so it tracks the whole field rather than
	// one rival.
	Opps map[int]*OppModel `json:"opps,omitempty"`
}

// OppModel is the bot's belief about one opponent's deck. Known holds cards
// it has actually seen there (battle lineups reveal entire decks each round;
// shop buys are public); Hidden counts cards it knows exist but has never
// seen — trade-in picks, whose tier is public but whose identity is not.
type OppModel struct {
	Seat   int          `json:"seat"`
	Known  []game.Card  `json:"known"`
	Hidden []HiddenCard `json:"hidden,omitempty"`
}

// opp returns the model for a seat, creating it on first sight.
func (m *Memory) opp(seat int) *OppModel {
	if m.Opps == nil {
		m.Opps = map[int]*OppModel{}
	}
	o, ok := m.Opps[seat]
	if !ok {
		o = &OppModel{Seat: seat}
		m.Opps[seat] = o
	}
	return o
}

// Opp returns the bot's model of one seat. A seat it has never seen comes back
// empty rather than nil, so callers can read it unconditionally.
func (m *Memory) Opp(seat int) *OppModel {
	if o, ok := m.Opps[seat]; ok {
		return o
	}
	return &OppModel{Seat: seat}
}

// HiddenCard is a card the opponent holds that the bot has not seen. Name is
// set when the card was later named publicly (e.g. a trade pick revealed by
// its buy ability) — the suit still isn't known, but the stats are.
type HiddenCard struct {
	Tier int    `json:"tier"`
	Name string `json:"name,omitempty"`
}

// LoadMemory decodes a bot's stored memory; a nil or corrupt blob yields a
// fresh one (the model self-heals from the next battle lineup anyway).
func LoadMemory(raw json.RawMessage) *Memory {
	m := &Memory{}
	if len(raw) > 0 {
		_ = json.Unmarshal(raw, m)
		// Notebooks written before the bot tracked a whole field held a single
		// "opp"; file it under its seat.
		var legacy struct {
			Opp *OppModel `json:"opp"`
		}
		if json.Unmarshal(raw, &legacy) == nil && legacy.Opp != nil && len(m.Opps) == 0 {
			m.Opps = map[int]*OppModel{legacy.Opp.Seat: legacy.Opp}
		}
	}
	return m
}

// Marshal encodes the memory for storage on the bot's Player.
func (m *Memory) Marshal() json.RawMessage {
	raw, err := json.Marshal(m)
	if err != nil {
		return nil
	}
	return raw
}

// Observe updates the memory from the bot's latest view. The server calls
// this on every state change, so consecutive observations are one action
// apart. It reads three public sources, in order:
//
//  1. new event-log entries, whose structured tags describe opponent shop
//     actions (buys name the card, sells name what left, trades list the
//     discarded trio, spawn entries count apples gained);
//  2. the round's battle lineups, which reveal every deck in full and reset
//     the models to ground truth every round (so any drift lasts one round);
//  3. each opponent's public deck size, as a reconciliation safety net.
//
// Every source is table-wide: the bot follows all its rivals, not only the one
// it happens to be paired against, because it will face each of them later.
func Observe(v *game.View, m *Memory) {
	if v.YouSeat < 0 {
		return
	}
	isOpponent := func(seat int) bool {
		return seat >= 0 && seat != v.YouSeat && v.PlayerView(seat) != nil
	}

	for _, e := range v.Log {
		if e.Seq <= m.LastSeq {
			continue
		}
		m.LastSeq = e.Seq
		if !isOpponent(e.Seat) {
			continue
		}
		opp := m.opp(e.Seat)
		switch {
		case e.Kind == game.LogBuy:
			if c, ok := cardByID(m.PrevShopRow, e.Source); ok {
				// An Avocado buy is set aside, not kept in the deck (Golden
				// pack): don't add it to the deck model.
				if c.Food != game.FoodAvocado {
					opp.Known = append(opp.Known, c)
				}
			} else if c, ok := templateByName(v.Packs, e.CardName); ok {
				if c.Food != game.FoodAvocado {
					opp.Known = append(opp.Known, c)
				}
			}
		case e.Kind == game.LogSell:
			opp.remove(e.Source, e.CardName)
			opp.Known = append(opp.Known, memApple(len(opp.Known)))
		case e.Kind == game.LogTrade:
			for _, id := range e.Cards {
				opp.remove(id, "")
			}
		case e.Kind == game.LogTradePick:
			opp.Hidden = append(opp.Hidden,
				HiddenCard{Tier: min(e.Round+1, game.MaxRounds), Name: e.CardName})
		case e.Spawn == "apple" && e.Kind == "":
			n := max(e.Count, 1)
			for range n {
				opp.Known = append(opp.Known, memApple(len(opp.Known)))
			}
		}
	}

	// Battle lineups are ground truth: rebuild each opponent's model from their
	// revealed deck, minus temporary cards (they expire with the battle). Every
	// table's battle is public, so one round refreshes the whole field.
	for _, b := range v.Battles {
		if b == nil || b.Round <= m.LastBattleRound {
			continue
		}
		for side, seat := range b.Seats {
			if !isOpponent(seat) || side >= len(b.Lineups) {
				continue
			}
			opp := m.opp(seat)
			opp.Known = opp.Known[:0]
			opp.Hidden = nil
			for _, c := range b.Lineups[side] {
				if !c.Temporary {
					opp.Known = append(opp.Known, c)
				}
			}
		}
	}
	for _, b := range v.Battles {
		if b != nil {
			m.LastBattleRound = max(m.LastBattleRound, b.Round)
		}
	}

	// Reconcile with the public deck sizes. Skipped during the battle phase,
	// where the live decks still hold temporaries the models exclude.
	if v.Phase == game.PhaseShop || v.Phase == game.PhaseArrange {
		for _, p := range v.Players {
			if !isOpponent(p.Seat) {
				continue
			}
			m.opp(p.Seat).reconcile(p.DeckSize, v.Round)
		}
	}

	m.PrevShopRow = append(m.PrevShopRow[:0], v.ShopRow...)
}

// remove drops one card from the model: by exact ID when we tracked it, by
// name as a fallback (model-minted apples have synthetic IDs), and failing
// both, one hidden card — something we didn't know they had, now gone.
func (o *OppModel) remove(id, name string) {
	if i := slices.IndexFunc(o.Known, func(c game.Card) bool { return c.ID == id }); i >= 0 {
		o.Known = slices.Delete(o.Known, i, i+1)
		return
	}
	if name != "" {
		if i := slices.IndexFunc(o.Known, func(c game.Card) bool { return c.Name == name }); i >= 0 {
			o.Known = slices.Delete(o.Known, i, i+1)
			return
		}
	}
	if len(o.Hidden) > 0 {
		o.Hidden = o.Hidden[:len(o.Hidden)-1]
	}
}

// reconcile forces the model to hold exactly size cards, the count everyone can
// see, padding with unknowns of the current tier or dropping the excess.
func (o *OppModel) reconcile(size, round int) {
	for len(o.Known)+len(o.Hidden) < size {
		o.Hidden = append(o.Hidden, HiddenCard{Tier: round})
	}
	for len(o.Known)+len(o.Hidden) > size {
		if len(o.Hidden) > 0 {
			o.Hidden = o.Hidden[:len(o.Hidden)-1]
		} else {
			o.Known = o.Known[:len(o.Known)-1]
		}
	}
}

func cardByID(cards []game.Card, id string) (game.Card, bool) {
	if id == "" {
		return game.Card{}, false
	}
	for _, c := range cards {
		if c.ID == id {
			return c, true
		}
	}
	return game.Card{}, false
}

// templateByName mints a reference copy of a named card from the printed tier
// contents of the packs in play. The suit is whatever the first printed copy
// has — callers only rely on stats and effects.
func templateByName(packs []string, name string) (game.Card, bool) {
	if name == "" {
		return game.Card{}, false
	}
	for tier := 1; tier <= game.MaxRounds; tier++ {
		for _, c := range game.TierContentsForPacks(packs, tier) {
			if c.Name == name {
				return c, true
			}
		}
	}
	return game.Card{}, false
}

// memApple mints an apple for the opponent model. The ID is synthetic — it
// only needs to not collide with real card IDs.
func memApple(n int) game.Card {
	return game.Card{
		ID:        fmt.Sprintf("mem-apple-%d", n),
		Kind:      game.KindFood,
		Name:      "Apple",
		Food:      game.FoodApple,
		Temporary: true,
	}
}