package notify

import (
	"time"

	flatbuffers "github.com/google/flatbuffers/go"
	"github.com/google/uuid"

	"scrabble/backend/internal/engine"
	fb "scrabble/pkg/fbs/scrabblefb"
)

// The constructors below build one Intent per live event, FlatBuffers-encoding
// the payload with the shared scrabblefb schema. Keeping the encoding here lets
// the game/social/lobby services emit events without importing the wire schema.

// YourTurn announces to userID that it is their turn in game gameID, with the turn's nominal
// deadline. opponentName, lastAction, lastWord and scoreLine enrich the out-of-app push (Stage
// 17): the player who just moved, their move kind, the main word of a scoring play (empty
// otherwise) and the recipient-first running score line. Empty strings render the plain "your
// turn" text. moveCount is the post-move count, which the client compares against its cached
// game to detect a missed in-app move and fall back to a refetch (R4).
func YourTurn(userID, gameID uuid.UUID, deadline time.Time, opponentName, lastAction, lastWord, scoreLine string, moveCount int) Intent {
	b := flatbuffers.NewBuilder(128)
	gid := b.CreateString(gameID.String())
	name := b.CreateString(opponentName)
	action := b.CreateString(lastAction)
	word := b.CreateString(lastWord)
	score := b.CreateString(scoreLine)
	fb.YourTurnEventStart(b)
	fb.YourTurnEventAddGameId(b, gid)
	fb.YourTurnEventAddDeadlineUnix(b, deadline.Unix())
	fb.YourTurnEventAddOpponentName(b, name)
	fb.YourTurnEventAddLastAction(b, action)
	fb.YourTurnEventAddLastWord(b, word)
	fb.YourTurnEventAddScoreLine(b, score)
	fb.YourTurnEventAddMoveCount(b, int32(moveCount))
	b.Finish(fb.YourTurnEventEnd(b))
	return Intent{UserID: userID, Kind: KindYourTurn, Payload: b.FinishedBytes(), EventID: eventID()}
}

// GameOver announces to userID that game gameID finished. result is the outcome from userID's
// own perspective ("won"/"lost"/"draw") and scoreLine is the recipient-first final score; both
// feed the out-of-app "game over" push (Stage 17). game is the final post-game summary (the
// adjusted scores after rack penalties and the winner flag), so an in-app client settles the
// finished game from the event without a refetch (R4).
func GameOver(userID, gameID uuid.UUID, result, scoreLine string, game GameSummary) Intent {
	b := flatbuffers.NewBuilder(512)
	gid := b.CreateString(gameID.String())
	res := b.CreateString(result)
	score := b.CreateString(scoreLine)
	gameOff := buildGameView(b, game)
	fb.GameOverEventStart(b)
	fb.GameOverEventAddGameId(b, gid)
	fb.GameOverEventAddResult(b, res)
	fb.GameOverEventAddScoreLine(b, score)
	fb.GameOverEventAddGame(b, gameOff)
	b.Finish(fb.GameOverEventEnd(b))
	return Intent{UserID: userID, Kind: KindGameOver, Payload: b.FinishedBytes(), EventID: eventID()}
}

// OpponentMoved tells userID that move was just committed in game gameID, carrying it as a delta
// the client applies to its cached game without a refetch (R4): move is the decoded play/pass/
// exchange, game is the post-move summary (per-seat scores, to_move, move_count, status) and
// bagLen is the bag size after the draw. The seat/action/score/total scalars repeat the move's
// summary for pre-R4 wire back-compat.
func OpponentMoved(userID, gameID uuid.UUID, move engine.MoveRecord, game GameSummary, bagLen int) Intent {
	b := flatbuffers.NewBuilder(512)
	gid := b.CreateString(gameID.String())
	act := b.CreateString(move.Action.String())
	moveOff := buildMoveRecord(b, move)
	gameOff := buildGameView(b, game)
	fb.OpponentMovedEventStart(b)
	fb.OpponentMovedEventAddGameId(b, gid)
	fb.OpponentMovedEventAddSeat(b, int32(move.Player))
	fb.OpponentMovedEventAddAction(b, act)
	fb.OpponentMovedEventAddScore(b, int32(move.Score))
	fb.OpponentMovedEventAddTotal(b, int32(move.Total))
	fb.OpponentMovedEventAddMove(b, moveOff)
	fb.OpponentMovedEventAddGame(b, gameOff)
	fb.OpponentMovedEventAddBagLen(b, int32(bagLen))
	b.Finish(fb.OpponentMovedEventEnd(b))
	return Intent{UserID: userID, Kind: KindOpponentMoved, Payload: b.FinishedBytes(), EventID: eventID()}
}

// ChatMessage delivers a stored chat message (or nudge) to userID.
func ChatMessage(userID, gameID, senderID uuid.UUID, id, kind, body string, createdAt time.Time) Intent {
	b := flatbuffers.NewBuilder(128)
	idOff := b.CreateString(id)
	gid := b.CreateString(gameID.String())
	sid := b.CreateString(senderID.String())
	kindOff := b.CreateString(kind)
	bodyOff := b.CreateString(body)
	fb.ChatMessageStart(b)
	fb.ChatMessageAddId(b, idOff)
	fb.ChatMessageAddGameId(b, gid)
	fb.ChatMessageAddSenderId(b, sid)
	fb.ChatMessageAddKind(b, kindOff)
	fb.ChatMessageAddBody(b, bodyOff)
	fb.ChatMessageAddCreatedAtUnix(b, createdAt.Unix())
	b.Finish(fb.ChatMessageEnd(b))
	return Intent{UserID: userID, Kind: KindChatMessage, Payload: b.FinishedBytes(), EventID: eventID()}
}

// Nudge tells userID that fromUserID nudged them in game gameID.
func Nudge(userID, gameID, fromUserID uuid.UUID) Intent {
	b := flatbuffers.NewBuilder(64)
	gid := b.CreateString(gameID.String())
	from := b.CreateString(fromUserID.String())
	fb.NudgeEventStart(b)
	fb.NudgeEventAddGameId(b, gid)
	fb.NudgeEventAddFromUserId(b, from)
	b.Finish(fb.NudgeEventEnd(b))
	return Intent{UserID: userID, Kind: KindNudge, Payload: b.FinishedBytes(), EventID: eventID()}
}

// MatchFound tells userID that game gameID, which they are seated in, has started (an auto-match
// pairing or a robot substitution). state is the recipient's full initial view of the new game,
// so the client navigates straight in from the event with no follow-up fetch (R4).
func MatchFound(userID, gameID uuid.UUID, state PlayerState) Intent {
	b := flatbuffers.NewBuilder(512)
	gid := b.CreateString(gameID.String())
	stateOff := buildStateView(b, state)
	fb.MatchFoundEventStart(b)
	fb.MatchFoundEventAddGameId(b, gid)
	fb.MatchFoundEventAddState(b, stateOff)
	b.Finish(fb.MatchFoundEventEnd(b))
	return Intent{UserID: userID, Kind: KindMatchFound, Payload: b.FinishedBytes(), EventID: eventID()}
}

// Notification is a lightweight "re-poll" signal to userID that something in their lobby
// changed. kind is a sub-discriminator (NotifyFriendRequest, NotifyFriendAdded,
// NotifyFriendDeclined, NotifyInvitation, NotifyGameStarted). It carries no payload; prefer the
// enriched constructors below, which let the client update its lobby without a refetch (R4).
func Notification(userID uuid.UUID, kind string) Intent {
	b := flatbuffers.NewBuilder(32)
	k := b.CreateString(kind)
	fb.NotificationEventStart(b)
	fb.NotificationEventAddKind(b, k)
	b.Finish(fb.NotificationEventEnd(b))
	return Intent{UserID: userID, Kind: KindNotification, Payload: b.FinishedBytes(), EventID: eventID()}
}

// NotificationAccount builds a lobby notification of one of the friend_* kinds carrying the
// account it concerns (the requester, the new friend or the decliner), so the client updates its
// requests/friends lists and the in-game "add friend" state without a refetch (R4).
func NotificationAccount(userID uuid.UUID, kind string, acc AccountRef) Intent {
	b := flatbuffers.NewBuilder(128)
	k := b.CreateString(kind)
	accOff := buildAccountRef(b, acc)
	fb.NotificationEventStart(b)
	fb.NotificationEventAddKind(b, k)
	fb.NotificationEventAddAccount(b, accOff)
	b.Finish(fb.NotificationEventEnd(b))
	return Intent{UserID: userID, Kind: KindNotification, Payload: b.FinishedBytes(), EventID: eventID()}
}

// NotificationGameStarted builds the NotifyGameStarted notification carrying the recipient's
// initial view of the just-started invited game, so the client seeds its game cache and the
// lobby list without a refetch (R4).
func NotificationGameStarted(userID uuid.UUID, state PlayerState) Intent {
	b := flatbuffers.NewBuilder(512)
	k := b.CreateString(NotifyGameStarted)
	stateOff := buildStateView(b, state)
	fb.NotificationEventStart(b)
	fb.NotificationEventAddKind(b, k)
	fb.NotificationEventAddState(b, stateOff)
	b.Finish(fb.NotificationEventEnd(b))
	return Intent{UserID: userID, Kind: KindNotification, Payload: b.FinishedBytes(), EventID: eventID()}
}

// NotificationInvitation builds the NotifyInvitation notification carrying the new invitation,
// so the client adds it to its lobby invitations list without a refetch (R4).
func NotificationInvitation(userID uuid.UUID, inv InvitationSummary) Intent {
	b := flatbuffers.NewBuilder(512)
	k := b.CreateString(NotifyInvitation)
	invOff := buildInvitation(b, inv)
	fb.NotificationEventStart(b)
	fb.NotificationEventAddKind(b, k)
	fb.NotificationEventAddInvitation(b, invOff)
	b.Finish(fb.NotificationEventEnd(b))
	return Intent{UserID: userID, Kind: KindNotification, Payload: b.FinishedBytes(), EventID: eventID()}
}

// eventID returns a best-effort correlation id for one emitted event.
func eventID() string {
	if id, err := uuid.NewV7(); err == nil {
		return id.String()
	}
	return ""
}