package transcode

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

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

// 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.

// encodeSession builds a Session payload.
func encodeSession(s backendclient.SessionResp) []byte {
	b := flatbuffers.NewBuilder(128)
	token := b.CreateString(s.Token)
	uid := b.CreateString(s.UserID)
	name := b.CreateString(s.DisplayName)
	fb.SessionStart(b)
	fb.SessionAddToken(b, token)
	fb.SessionAddUserId(b, uid)
	fb.SessionAddIsGuest(b, s.IsGuest)
	fb.SessionAddDisplayName(b, name)
	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 (Stage 11). 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.
func encodeLinkResult(r backendclient.LinkResultResp) []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)
		fb.SessionStart(b)
		fb.SessionAddToken(b, token)
		fb.SessionAddUserId(b, uid)
		fb.SessionAddIsGuest(b, r.Profile.IsGuest)
		fb.SessionAddDisplayName(b, name)
		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)
	fb.MoveResultStart(b)
	fb.MoveResultAddMove(b, move)
	fb.MoveResultAddGame(b, game)
	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 (Stage 13: the
// client requests it on a per-variant cache miss).
func encodeState(s backendclient.StateResp) []byte {
	b := flatbuffers.NewBuilder(512)
	game := buildGameView(b, s.Game)
	rackBytes := make([]byte, len(s.Rack))
	for i, v := range s.Rack {
		rackBytes[i] = byte(v)
	}
	rack := b.CreateByteVector(rackBytes)
	hasAlphabet := len(s.Alphabet) > 0
	var alphabet flatbuffers.UOffsetT
	if hasAlphabet {
		alphabet = buildAlphabet(b, s.Alphabet)
	}
	fb.StateViewStart(b)
	fb.StateViewAddGame(b, game)
	fb.StateViewAddSeat(b, int32(s.Seat))
	fb.StateViewAddRack(b, rack)
	fb.StateViewAddBagLen(b, int32(s.BagLen))
	fb.StateViewAddHintsRemaining(b, int32(s.HintsRemaining))
	if hasAlphabet {
		fb.StateViewAddAlphabet(b, alphabet)
	}
	b.Finish(fb.StateViewEnd(b))
	return b.FinishedBytes()
}

// buildAlphabet builds the AlphabetEntry vector for a StateView and returns its offset.
func buildAlphabet(b *flatbuffers.Builder, entries []backendclient.AlphabetEntryJSON) flatbuffers.UOffsetT {
	offs := make([]flatbuffers.UOffsetT, len(entries))
	for i, e := range entries {
		letter := b.CreateString(e.Letter)
		fb.AlphabetEntryStart(b)
		fb.AlphabetEntryAddIndex(b, byte(e.Index))
		fb.AlphabetEntryAddLetter(b, letter)
		fb.AlphabetEntryAddValue(b, int32(e.Value))
		offs[i] = fb.AlphabetEntryEnd(b)
	}
	fb.StateViewStartAlphabetVector(b, len(offs))
	for i := len(offs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(offs[i])
	}
	return b.EndVector(len(offs))
}

// 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()
}

// 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 {
	seatOffs := make([]flatbuffers.UOffsetT, len(g.Seats))
	for i, s := range g.Seats {
		aid := b.CreateString(s.AccountID)
		dname := b.CreateString(s.DisplayName)
		fb.SeatViewStart(b)
		fb.SeatViewAddSeat(b, int32(s.Seat))
		fb.SeatViewAddAccountId(b, aid)
		fb.SeatViewAddScore(b, int32(s.Score))
		fb.SeatViewAddHintsUsed(b, int32(s.HintsUsed))
		fb.SeatViewAddIsWinner(b, s.IsWinner)
		fb.SeatViewAddDisplayName(b, dname)
		seatOffs[i] = fb.SeatViewEnd(b)
	}
	fb.GameViewStartSeatsVector(b, len(seatOffs))
	for i := len(seatOffs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(seatOffs[i])
	}
	seats := b.EndVector(len(seatOffs))

	id := b.CreateString(g.ID)
	variant := b.CreateString(g.Variant)
	dictVer := b.CreateString(g.DictVersion)
	status := b.CreateString(g.Status)
	endReason := b.CreateString(g.EndReason)

	fb.GameViewStart(b)
	fb.GameViewAddId(b, id)
	fb.GameViewAddVariant(b, variant)
	fb.GameViewAddDictVersion(b, dictVer)
	fb.GameViewAddStatus(b, status)
	fb.GameViewAddPlayers(b, int32(g.Players))
	fb.GameViewAddToMove(b, int32(g.ToMove))
	fb.GameViewAddTurnTimeoutSecs(b, int32(g.TurnTimeoutSecs))
	fb.GameViewAddMoveCount(b, int32(g.MoveCount))
	fb.GameViewAddEndReason(b, endReason)
	fb.GameViewAddSeats(b, seats)
	return fb.GameViewEnd(b)
}

// buildMoveRecord builds a MoveRecord table and returns its offset.
func buildMoveRecord(b *flatbuffers.Builder, m backendclient.MoveRecordResp) flatbuffers.UOffsetT {
	tileOffs := make([]flatbuffers.UOffsetT, len(m.Tiles))
	for i, t := range m.Tiles {
		letter := b.CreateString(t.Letter)
		fb.TileRecordStart(b)
		fb.TileRecordAddRow(b, int32(t.Row))
		fb.TileRecordAddCol(b, int32(t.Col))
		fb.TileRecordAddLetter(b, letter)
		fb.TileRecordAddBlank(b, t.Blank)
		tileOffs[i] = fb.TileRecordEnd(b)
	}
	fb.MoveRecordStartTilesVector(b, len(tileOffs))
	for i := len(tileOffs) - 1; i >= 0; i-- {
		b.PrependUOffsetT(tileOffs[i])
	}
	tiles := b.EndVector(len(tileOffs))

	words := buildStringVector(b, m.Words, fb.MoveRecordStartWordsVector)

	action := b.CreateString(m.Action)
	dir := b.CreateString(m.Dir)
	fb.MoveRecordStart(b)
	fb.MoveRecordAddPlayer(b, int32(m.Player))
	fb.MoveRecordAddAction(b, action)
	fb.MoveRecordAddDir(b, dir)
	fb.MoveRecordAddMainRow(b, int32(m.MainRow))
	fb.MoveRecordAddMainCol(b, int32(m.MainCol))
	fb.MoveRecordAddTiles(b, tiles)
	fb.MoveRecordAddWords(b, words)
	fb.MoveRecordAddCount(b, int32(m.Count))
	fb.MoveRecordAddScore(b, int32(m.Score))
	fb.MoveRecordAddTotal(b, int32(m.Total))
	return fb.MoveRecordEnd(b)
}

// 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))
}