mancala/apps/backend/src/game/GameSerialization.ts

import { EndReason, GameRecord, GameResult, MoveRecord } from "@mancala/core";
import { CommonMancalaGame, GameState, GameStep } from "mancala.js";
import { BackendGame, PlayerInfo } from "../models/Game";
import { publicUserId } from "./publicIds";
import { startClock } from "./GameClock";

type HistoryEntry = { playerId: string, moveIndex: number, boardSnapshot: number[], gameSteps: GameStep[] };

// What is kept in Valkey for a live game; enough to rebuild it after a restart.
export interface LiveGameSnapshot {
    version: 1;
    id: string;
    player1Id: string;
    player2Id: string;
    turnPlayerId: string;
    state: GameState;
    board: number[];
    history: HistoryEntry[];
    players: Record<string, PlayerInfo>;
    startedAt: number;
    moveTimes: number[];
    peakSpectators: number;
    allSpectatorIds: string[];
}

export interface GameEnding {
    endReason: EndReason;
    // Undefined when the game ends without a winner.
    winnerId?: string;
    leftUserId?: string;
}

export function toSnapshot(game: BackendGame): LiveGameSnapshot {
    const { mancalaGame } = game;
    return {
        version: 1,
        id: game.id,
        player1Id: mancalaGame.player1Id,
        player2Id: mancalaGame.player2Id,
        turnPlayerId: mancalaGame.turnPlayerId,
        state: mancalaGame.state,
        board: mancalaGame.board.getStoneArray(),
        history: mancalaGame.history as unknown as HistoryEntry[],
        players: game.players,
        startedAt: game.startedAt,
        moveTimes: game.moveTimes,
        peakSpectators: game.peakSpectators,
        allSpectatorIds: game.allSpectatorIds,
    };
}

export function isLiveGameSnapshot(value: unknown): value is LiveGameSnapshot {
    const snapshot = value as LiveGameSnapshot;
    return typeof snapshot === "object" && snapshot !== null && snapshot.version === 1
        && typeof snapshot.id === "string" && Array.isArray(snapshot.board) && snapshot.board.length === 14
        && Array.isArray(snapshot.history) && typeof snapshot.players === "object";
}

// Rebuilds a live game with real engine objects (rules, pits), so it can be played on.
export function fromSnapshot(snapshot: LiveGameSnapshot, params: { now: number, gameClockMs: number }): BackendGame {
    const mancalaGame = new CommonMancalaGame(snapshot.id, snapshot.player1Id, snapshot.player2Id);
    snapshot.board.forEach((stoneCount, index) => (mancalaGame.board.pits[index].stoneCount = stoneCount));
    mancalaGame.turnPlayerId = snapshot.turnPlayerId;
    mancalaGame.state = snapshot.state;
    mancalaGame.history.push(...snapshot.history);
    const player = (id: string): PlayerInfo => snapshot.players[id] ?? { userId: id, isGuest: true };
    return {
        id: snapshot.id,
        mancalaGame,
        gameUsersConnectionInfo: {
            user1ConnectionInfo: { ...player(snapshot.player1Id), isOnline: false },
            user2ConnectionInfo: { ...player(snapshot.player2Id), isOnline: false },
        },
        spectatorIds: [],
        allSpectatorIds: snapshot.allSpectatorIds,
        peakSpectators: snapshot.peakSpectators,
        players: snapshot.players,
        startedAt: snapshot.startedAt,
        moveTimes: snapshot.moveTimes,
        clock: startClock(params.gameClockMs, params.now),
        moveRemainingMs: [],
    };
}

export function getResult(game: BackendGame, ending: GameEnding): GameResult | null {
    const { player1Id, player2Id } = game.mancalaGame;
    if (ending.winnerId === player1Id) return "player1";
    if (ending.winnerId === player2Id) return "player2";
    return ending.endReason === "completed" ? "draw" : null;
}

// The record saved for a finished game; every id in it is a public id.
export function toGameRecord(game: BackendGame, ending: GameEnding, endedAt: number): GameRecord {
    const { mancalaGame } = game;
    const history = mancalaGame.history as unknown as HistoryEntry[];
    const playerSummary = (id: string) => {
        const player = game.players[id];
        const summary = { userId: publicUserId(id), isGuest: player?.isGuest ?? true };
        return player?.name === undefined ? summary : { ...summary, name: player.name };
    };
    const moves: MoveRecord[] = history.map((entry, i) => ({
        playerId: publicUserId(entry.playerId),
        moveIndex: entry.moveIndex,
        boardSnapshot: entry.boardSnapshot,
        gameSteps: entry.gameSteps,
        at: game.moveTimes[i] ?? endedAt,
    }));
    const record: GameRecord = {
        id: game.id,
        player1: playerSummary(mancalaGame.player1Id),
        player2: playerSummary(mancalaGame.player2Id),
        board: mancalaGame.board.getStoneArray(),
        result: getResult(game, ending),
        endReason: ending.endReason,
        startedAt: game.startedAt,
        endedAt,
        moveCount: moves.length,
        peakSpectators: game.peakSpectators,
        totalSpectators: game.allSpectatorIds.length,
        moves,
    };
    if (ending.leftUserId !== undefined) record.leftUserId = publicUserId(ending.leftUserId);
    return record;
}