package transcode

import (
	flatbuffers "github.com/google/flatbuffers/go"

	"scrabble/gateway/internal/backendclient"
	fb "scrabble/pkg/fbs/scrabblefb"
	"scrabble/pkg/wire"
)

// The encoders build the FlatBuffers response payloads from the backend's typed
// responses. FlatBuffers is built bottom-up: every string and child vector is
// created before the table that references it, and no two tables/vectors are
// under construction at once.

// buildSupportedLanguagesVector creates the Session.supported_languages [string]
// vector from langs. FlatBuffers is built bottom-up, so the caller must invoke this
// (which itself creates the element strings) before SessionStart and with no table
// under construction.
func buildSupportedLanguagesVector(b *flatbuffers.Builder, langs []string) flatbuffers.UOffsetT {
	offsets := make([]flatbuffers.UOffsetT, len(langs))
	for i, lang := range langs {
		offsets[i] = b.CreateString(lang)
	}
	fb.SessionStartSupportedLanguagesVector(b, len(langs))
	for i := len(offsets) - 1; i >= 0; i-- {
		b.PrependUOffsetT(offsets[i])
	}
	return b.EndVector(len(langs))
}

// encodeSession builds a Session payload. supportedLangs is the service's set of
// offered game languages, which the UI gates the New Game variant choice by.
func encodeSession(s backendclient.SessionResp, supportedLangs []string) []byte {
	b := flatbuffers.NewBuilder(128)
	token := b.CreateString(s.Token)
	uid := b.CreateString(s.UserID)
	name := b.CreateString(s.DisplayName)
	langs := buildSupportedLanguagesVector(b, supportedLangs)
	fb.SessionStart(b)
	fb.SessionAddToken(b, token)
	fb.SessionAddUserId(b, uid)
	fb.SessionAddIsGuest(b, s.IsGuest)
	fb.SessionAddDisplayName(b, name)
	fb.SessionAddSupportedLanguages(b, langs)
	b.Finish(fb.SessionEnd(b))
	return b.FinishedBytes()
}

// encodeAck builds an Ack payload.
func encodeAck(ok bool) []byte {
	b := flatbuffers.NewBuilder(16)
	fb.AckStart(b)
	fb.AckAddOk(b, ok)
	b.Finish(fb.AckEnd(b))
	return b.FinishedBytes()
}

// encodeProfile builds a Profile payload.
func encodeProfile(p backendclient.ProfileResp) []byte {
	b := flatbuffers.NewBuilder(192)
	uid := b.CreateString(p.UserID)
	name := b.CreateString(p.DisplayName)
	lang := b.CreateString(p.PreferredLanguage)
	tz := b.CreateString(p.TimeZone)
	awayStart := b.CreateString(p.AwayStart)
	awayEnd := b.CreateString(p.AwayEnd)
	fb.ProfileStart(b)
	fb.ProfileAddUserId(b, uid)
	fb.ProfileAddDisplayName(b, name)
	fb.ProfileAddPreferredLanguage(b, lang)
	fb.ProfileAddTimeZone(b, tz)
	fb.ProfileAddHintBalance(b, int32(p.HintBalance))
	fb.ProfileAddBlockChat(b, p.BlockChat)
	fb.ProfileAddBlockFriendRequests(b, p.BlockFriendRequests)
	fb.ProfileAddIsGuest(b, p.IsGuest)
	fb.ProfileAddAwayStart(b, awayStart)
	fb.ProfileAddAwayEnd(b, awayEnd)
	fb.ProfileAddNotificationsInAppOnly(b, p.NotificationsInAppOnly)
	b.Finish(fb.ProfileEnd(b))
	return b.FinishedBytes()
}

// encodeLinkResult builds a LinkResult payload. A switched-session token
// (a guest initiator whose durable counterpart won) is carried as a nested Session
// for the client to adopt; it is omitted otherwise. supportedLangs is the variant
// gating set for that switched session — the link flows run on the web, so it is the
// gateway's default (non-platform) set.
func encodeLinkResult(r backendclient.LinkResultResp, supportedLangs []string) []byte {
	b := flatbuffers.NewBuilder(256)
	status := b.CreateString(r.Status)
	secID := b.CreateString(r.SecondaryUserID)
	secName := b.CreateString(r.SecondaryName)
	hasSession := r.Token != "" && r.Profile != nil
	var sess flatbuffers.UOffsetT
	if hasSession {
		token := b.CreateString(r.Token)
		uid := b.CreateString(r.Profile.UserID)
		name := b.CreateString(r.Profile.DisplayName)
		langs := buildSupportedLanguagesVector(b, supportedLangs)
		fb.SessionStart(b)
		fb.SessionAddToken(b, token)
		fb.SessionAddUserId(b, uid)
		fb.SessionAddIsGuest(b, r.Profile.IsGuest)
		fb.SessionAddDisplayName(b, name)
		fb.SessionAddSupportedLanguages(b, langs)
		sess = fb.SessionEnd(b)
	}
	fb.LinkResultStart(b)
	fb.LinkResultAddStatus(b, status)
	fb.LinkResultAddSecondaryUserId(b, secID)
	fb.LinkResultAddSecondaryDisplayName(b, secName)
	fb.LinkResultAddSecondaryGames(b, int32(r.SecondaryGames))
	fb.LinkResultAddSecondaryFriends(b, int32(r.SecondaryFriends))
	if hasSession {
		fb.LinkResultAddSession(b, sess)
	}
	b.Finish(fb.LinkResultEnd(b))
	return b.FinishedBytes()
}

// encodeMoveResult builds a MoveResult payload.
func encodeMoveResult(r backendclient.MoveResultResp) []byte {
	b := flatbuffers.NewBuilder(512)
	move := buildMoveRecord(b, r.Move)
	game := buildGameView(b, r.Game)
	rackBytes := make([]byte, len(r.Rack))
	for i, v := range r.Rack {
		rackBytes[i] = byte(v)
	}
	rack := b.CreateByteVector(rackBytes)
	fb.MoveResultStart(b)
	fb.MoveResultAddMove(b, move)
	fb.MoveResultAddGame(b, game)
	fb.MoveResultAddRack(b, rack)
	fb.MoveResultAddBagLen(b, int32(r.BagLen))
	b.Finish(fb.MoveResultEnd(b))
	return b.FinishedBytes()
}

// encodeState builds a StateView payload. The rack is a vector of alphabet indices and the
// alphabet display table is included only when the backend returned it (the
// client requests it on a per-variant cache miss).
func encodeState(s backendclient.StateResp) []byte {
	b := flatbuffers.NewBuilder(512)
	b.Finish(wire.BuildStateView(b, toWireState(s)))
	return b.FinishedBytes()
}

// toWireState maps a StateResp to the shared wire.StateView.
func toWireState(s backendclient.StateResp) wire.StateView {
	alphabet := make([]wire.AlphabetEntry, len(s.Alphabet))
	for i, e := range s.Alphabet {
		alphabet[i] = wire.AlphabetEntry{Index: e.Index, Letter: e.Letter, Value: e.Value}
	}
	return wire.StateView{
		Game:           toWireGame(s.Game),
		Seat:           s.Seat,
		Rack:           s.Rack,
		BagLen:         s.BagLen,
		HintsRemaining: s.HintsRemaining,
		Alphabet:       alphabet,
	}
}

// encodeMatch builds a MatchResult payload.
func encodeMatch(m backendclient.MatchResp) []byte {
	b := flatbuffers.NewBuilder(512)
	matched := m.Matched && m.Game != nil
	var game flatbuffers.UOffsetT
	if matched {
		game = buildGameView(b, *m.Game)
	}
	fb.MatchResultStart(b)
	fb.MatchResultAddMatched(b, matched)
	if matched {
		fb.MatchResultAddGame(b, game)
	}
	b.Finish(fb.MatchResultEnd(b))
	return b.FinishedBytes()
}

// buildChatMessage builds a ChatMessage table and returns its offset.
func buildChatMessage(b *flatbuffers.Builder, c backendclient.ChatResp) flatbuffers.UOffsetT {
	id := b.CreateString(c.ID)
	gid := b.CreateString(c.GameID)
	sid := b.CreateString(c.SenderID)
	kind := b.CreateString(c.Kind)
	body := b.CreateString(c.Body)
	fb.ChatMessageStart(b)
	fb.ChatMessageAddId(b, id)
	fb.ChatMessageAddGameId(b, gid)
	fb.ChatMessageAddSenderId(b, sid)
	fb.ChatMessageAddKind(b, kind)
	fb.ChatMessageAddBody(b, body)
	fb.ChatMessageAddCreatedAtUnix(b, c.CreatedAtUnix)
	return fb.ChatMessageEnd(b)
}

// encodeChat builds a ChatMessage payload.
func encodeChat(c backendclient.ChatResp) []byte {
	b := flatbuffers.NewBuilder(192)
	b.Finish(buildChatMessage(b, c))
	return b.FinishedBytes()
}

// encodeHintResult builds a HintResult payload.
func encodeHintResult(r backendclient.HintResultResp) []byte {
	b := flatbuffers.NewBuilder(512)
	move := buildMoveRecord(b, r.Move)
	fb.HintResultStart(b)
	fb.HintResultAddMove(b, move)
	fb.HintResultAddHintsRemaining(b, int32(r.HintsRemaining))
	b.Finish(fb.HintResultEnd(b))
	return b.FinishedBytes()
}

// encodeEvalResult builds an EvalResult payload.
func encodeEvalResult(r backendclient.EvalResultResp) []byte {
	b := flatbuffers.NewBuilder(256)
	words := buildStringVector(b, r.Words, fb.EvalResultStartWordsVector)
	fb.EvalResultStart(b)
	fb.EvalResultAddLegal(b, r.Legal)
	fb.EvalResultAddScore(b, int32(r.Score))
	fb.EvalResultAddWords(b, words)
	b.Finish(fb.EvalResultEnd(b))
	return b.FinishedBytes()
}

// encodeWordCheck builds a WordCheckResult payload.
func encodeWordCheck(r backendclient.WordCheckResp) []byte {
	b := flatbuffers.NewBuilder(64)
	word := b.CreateString(r.Word)
	fb.WordCheckResultStart(b)
	fb.WordCheckResultAddWord(b, word)
	fb.WordCheckResultAddLegal(b, r.Legal)
	b.Finish(fb.WordCheckResultEnd(b))
	return b.FinishedBytes()
}

// encodeDraftView builds a DraftView payload wrapping the player's composition JSON. The
// string is empty for the save acknowledgement (the client ignores that payload).
func encodeDraftView(jsonStr string) []byte {
	b := flatbuffers.NewBuilder(256)
	j := b.CreateString(jsonStr)
	fb.DraftViewStart(b)
	fb.DraftViewAddJson(b, j)
	b.Finish(fb.DraftViewEnd(b))
	return b.FinishedBytes()
}

// encodeHistory builds a History payload (the decoded move journal).
func encodeHistory(r backendclient.HistoryResp) []byte {
	b := flatbuffers.NewBuilder(1024)
	moveOffs := make([]flatbuffers.UOffsetT, len(r.Moves))
	for i, m := range r.Moves {
		moveOffs[i] = buildMoveRecord(b, m)
	}
	fb.HistoryStartMovesVector(b, len(moveOffs))
	for i := len(moveOffs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(moveOffs[i])
	}
	moves := b.EndVector(len(moveOffs))
	gid := b.CreateString(r.GameID)
	fb.HistoryStart(b)
	fb.HistoryAddGameId(b, gid)
	fb.HistoryAddMoves(b, moves)
	b.Finish(fb.HistoryEnd(b))
	return b.FinishedBytes()
}

// encodeGameList builds a GameList payload (the caller's games).
func encodeGameList(r backendclient.GameListResp) []byte {
	b := flatbuffers.NewBuilder(1024)
	gameOffs := make([]flatbuffers.UOffsetT, len(r.Games))
	for i, g := range r.Games {
		gameOffs[i] = buildGameView(b, g)
	}
	fb.GameListStartGamesVector(b, len(gameOffs))
	for i := len(gameOffs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(gameOffs[i])
	}
	games := b.EndVector(len(gameOffs))
	fb.GameListStart(b)
	fb.GameListAddGames(b, games)
	b.Finish(fb.GameListEnd(b))
	return b.FinishedBytes()
}

// encodeChatList builds a ChatList payload (a game's chat history).
func encodeChatList(r backendclient.ChatListResp) []byte {
	b := flatbuffers.NewBuilder(512)
	msgOffs := make([]flatbuffers.UOffsetT, len(r.Messages))
	for i, m := range r.Messages {
		msgOffs[i] = buildChatMessage(b, m)
	}
	fb.ChatListStartMessagesVector(b, len(msgOffs))
	for i := len(msgOffs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(msgOffs[i])
	}
	msgs := b.EndVector(len(msgOffs))
	fb.ChatListStart(b)
	fb.ChatListAddMessages(b, msgs)
	b.Finish(fb.ChatListEnd(b))
	return b.FinishedBytes()
}

// buildGameView builds a GameView table and returns its offset.
func buildGameView(b *flatbuffers.Builder, g backendclient.GameResp) flatbuffers.UOffsetT {
	return wire.BuildGameView(b, toWireGame(g))
}

// toWireGame maps a GameResp to the shared wire.GameView.
func toWireGame(g backendclient.GameResp) wire.GameView {
	seats := make([]wire.SeatView, len(g.Seats))
	for i, s := range g.Seats {
		seats[i] = wire.SeatView{
			Seat:        s.Seat,
			AccountID:   s.AccountID,
			Score:       s.Score,
			HintsUsed:   s.HintsUsed,
			IsWinner:    s.IsWinner,
			DisplayName: s.DisplayName,
		}
	}
	return wire.GameView{
		ID:               g.ID,
		Variant:          g.Variant,
		DictVersion:      g.DictVersion,
		Status:           g.Status,
		Players:          g.Players,
		ToMove:           g.ToMove,
		TurnTimeoutSecs:  g.TurnTimeoutSecs,
		MoveCount:        g.MoveCount,
		EndReason:        g.EndReason,
		Seats:            seats,
		LastActivityUnix: g.LastActivityUnix,
	}
}

// buildMoveRecord builds a MoveRecord table and returns its offset.
func buildMoveRecord(b *flatbuffers.Builder, m backendclient.MoveRecordResp) flatbuffers.UOffsetT {
	tiles := make([]wire.TileRecord, len(m.Tiles))
	for i, t := range m.Tiles {
		tiles[i] = wire.TileRecord{Row: t.Row, Col: t.Col, Letter: t.Letter, Blank: t.Blank}
	}
	return wire.BuildMoveRecord(b, wire.MoveRecord{
		Player:  m.Player,
		Action:  m.Action,
		Dir:     m.Dir,
		MainRow: m.MainRow,
		MainCol: m.MainCol,
		Tiles:   tiles,
		Words:   m.Words,
		Count:   m.Count,
		Score:   m.Score,
		Total:   m.Total,
	})
}

// buildStringVector builds a vector of strings using the table-specific
// StartXVector function and returns the vector offset.
func buildStringVector(b *flatbuffers.Builder, items []string, start func(*flatbuffers.Builder, int) flatbuffers.UOffsetT) flatbuffers.UOffsetT {
	offs := make([]flatbuffers.UOffsetT, len(items))
	for i, s := range items {
		offs[i] = b.CreateString(s)
	}
	start(b, len(offs))
	for i := len(offs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(offs[i])
	}
	return b.EndVector(len(offs))
}