server.js

var http = require('http');
var fs = require('fs');
var path = require('path');

// model constants
var NUM_VALUES = 15;
var TABLE_SIZE = Math.pow(NUM_VALUES, 6);
var NUM_PATTERNS = 8;

var PATTERNS = [
    [[0, 0], [1, 0], [2, 0], [3, 0], [0, 1], [1, 1]],
    [[0, 0], [1, 0], [0, 1], [1, 1], [0, 2], [1, 2]],
    [[0, 0], [1, 0], [2, 0], [0, 1], [1, 1], [2, 1]],
    [[0, 0], [1, 0], [0, 1], [1, 1], [2, 1], [3, 1]],
    [[0, 0], [1, 0], [2, 0], [3, 0], [2, 1], [3, 1]],
    [[0, 0], [1, 0], [2, 0], [1, 1], [2, 1], [3, 1]],
    [[0, 0], [1, 0], [0, 1], [1, 1], [2, 1], [2, 2]],
    [[0, 0], [1, 0], [2, 0], [0, 1], [1, 1], [1, 2]],
];

var SYMMETRY_FNS = [
    function (x, y) { return [x, y] },
    function (x, y) { return [3 - x, y] },
    function (x, y) { return [x, 3 - y] },
    function (x, y) { return [3 - x, 3 - y] },
    function (x, y) { return [y, x] },
    function (x, y) { return [3 - y, x] },
    function (x, y) { return [y, 3 - x] },
    function (x, y) { return [3 - y, 3 - x] },
];

// precompute tuple lookups
var NUM_TUPLES = NUM_PATTERNS * 8;
var tupleCoords = new Int32Array(NUM_TUPLES * 6);
var tupleTable = new Int32Array(NUM_TUPLES);

var ti = 0;
for (var p = 0; p < NUM_PATTERNS; p++) {
    for (var s = 0; s < 8; s++) {
        tupleTable[ti] = p;
        for (var i = 0; i < 6; i++) {
            var c = SYMMETRY_FNS[s](PATTERNS[p][i][0], PATTERNS[p][i][1]);
            tupleCoords[ti * 6 + i] = c[0] * 4 + c[1];
        }
        ti++;
    }
}

// tile index mapping
var TILE_TO_IDX = new Uint8Array(65536);
TILE_TO_IDX[0] = 0;
for (var i = 1; i <= 16; i++) {
    TILE_TO_IDX[Math.min(1 << i, 65535)] = Math.min(i, NUM_VALUES - 1);
}

// allocate + load weights
console.log('Loading model weights...');
var weights = [];
for (var i = 0; i < NUM_PATTERNS; i++) {
    weights.push(new Float32Array(TABLE_SIZE));
}

// check local dir first, then parent (works both standalone and in-tree)
var WEIGHTS_FILE = fs.existsSync(path.join(__dirname, 'model_weights.bin'))
    ? path.join(__dirname, 'model_weights.bin')
    : path.join(__dirname, '..', 'model_weights.bin');
var META_FILE = fs.existsSync(path.join(__dirname, 'model_meta.json'))
    ? path.join(__dirname, 'model_meta.json')
    : path.join(__dirname, '..', 'model_meta.json');

if (!fs.existsSync(WEIGHTS_FILE)) {
    console.error('model_weights.bin not found. Train the model first.');
    process.exit(1);
}

var meta = JSON.parse(fs.readFileSync(META_FILE, 'utf8'));
var buf = fs.readFileSync(WEIGHTS_FILE);
var off = 0;
for (var i = 0; i < NUM_PATTERNS; i++) {
    var src = new Float32Array(buf.buffer, buf.byteOffset + off, TABLE_SIZE);
    weights[i].set(src);
    off += TABLE_SIZE * 4;
}
console.log('Model loaded (' + meta.gamesPlayed.toLocaleString() + ' games, max tile ' + meta.maxTile + ')');


function evaluate(board) {
    var score = 0;
    var ci = 0;
    for (var t = 0; t < NUM_TUPLES; t++) {
        var idx = board[tupleCoords[ci]];
        idx = idx * NUM_VALUES + board[tupleCoords[ci + 1]];
        idx = idx * NUM_VALUES + board[tupleCoords[ci + 2]];
        idx = idx * NUM_VALUES + board[tupleCoords[ci + 3]];
        idx = idx * NUM_VALUES + board[tupleCoords[ci + 4]];
        idx = idx * NUM_VALUES + board[tupleCoords[ci + 5]];
        score += weights[tupleTable[t]][idx];
        ci += 6;
    }
    return score;
}

var _merged = new Uint8Array(16);
var _tempBoards = [new Uint8Array(16), new Uint8Array(16),
new Uint8Array(16), new Uint8Array(16)];

var VECTORS_X = [0, 1, 0, -1];
var VECTORS_Y = [-1, 0, 1, 0];

function simulateMove(board, dir, out) {
    out.set(board);
    _merged.fill(0);
    var reward = 0, moved = false;
    var vx = VECTORS_X[dir], vy = VECTORS_Y[dir];
    var tx = vx === 1 ? [3, 2, 1, 0] : [0, 1, 2, 3];
    var ty = vy === 1 ? [3, 2, 1, 0] : [0, 1, 2, 3];

    for (var i = 0; i < 4; i++) {
        for (var j = 0; j < 4; j++) {
            var cx = tx[i], cy = ty[j];
            var ci = cx * 4 + cy;
            var val = out[ci];
            if (val === 0) continue;
            var px = cx, py = cy;
            var nx = cx + vx, ny = cy + vy;
            while (nx >= 0 && nx < 4 && ny >= 0 && ny < 4 && out[nx * 4 + ny] === 0) {
                px = nx; py = ny; nx += vx; ny += vy;
            }
            var ni = nx * 4 + ny, pi = px * 4 + py;
            if (nx >= 0 && nx < 4 && ny >= 0 && ny < 4 && out[ni] === val && !_merged[ni]) {
                out[ci] = 0;
                var nv = val + 1;
                out[ni] = nv;
                _merged[ni] = 1;
                reward += (nv < NUM_VALUES) ? (1 << nv) : (1 << (NUM_VALUES - 1));
                moved = true;
            } else if (pi !== ci) {
                out[ci] = 0;
                out[pi] = val;
                moved = true;
            }
        }
    }
    return { reward: reward, moved: moved };
}

function getBestMove(board) {
    var bestScore = -Infinity;
    var bestDir = -1;
    for (var d = 0; d < 4; d++) {
        var r = simulateMove(board, d, _tempBoards[d]);
        if (!r.moved) continue;
        var sc = r.reward + evaluate(_tempBoards[d]);
        if (sc > bestScore) { bestScore = sc; bestDir = d; }
    }
    return bestDir;
}

// convert browser cell format to internal indices
function boardFromCells(cells) {
    var board = new Uint8Array(16);
    for (var x = 0; x < 4; x++)
        for (var y = 0; y < 4; y++) {
            var v = cells[x][y];
            board[x * 4 + y] = v === 0 ? 0 : (TILE_TO_IDX[v] || 0);
        }
    return board;
}


// static file server
var MIME = {
    '.html': 'text/html', '.css': 'text/css',
    '.js': 'application/javascript', '.json': 'application/json',
    '.ico': 'image/x-icon', '.png': 'image/png',
    '.jpg': 'image/jpeg', '.woff': 'font/woff',
    '.woff2': 'font/woff2', '.ttf': 'font/ttf',
    '.svg': 'image/svg+xml',
};

var RUNNER_DIR = path.resolve(__dirname);
var PROJECT_DIR = path.resolve(__dirname, '..');

// HF Spaces uses port 7860
var PORT = parseInt(process.env.PORT, 10) || 3000;

function serveStatic(reqPath, res) {
    var safePath = reqPath === '/' ? '/index.html' : reqPath;
    safePath = decodeURIComponent(safePath);

    // try runner dir first (overrides), then project root
    var runnerFile = path.resolve(RUNNER_DIR, '.' + safePath);
    var projectFile = path.resolve(PROJECT_DIR, '.' + safePath);

    var filePath;
    if (runnerFile.startsWith(RUNNER_DIR) && fs.existsSync(runnerFile) &&
        fs.statSync(runnerFile).isFile()) {
        filePath = runnerFile;
    } else if (projectFile.startsWith(PROJECT_DIR)) {
        filePath = projectFile;
    } else {
        res.writeHead(403); res.end('Forbidden');
        return;
    }

    fs.readFile(filePath, function (err, data) {
        if (err) {
            res.writeHead(404); res.end('Not found');
            return;
        }
        var ext = path.extname(filePath).toLowerCase();
        res.writeHead(200, { 'Content-Type': MIME[ext] || 'application/octet-stream' });
        res.end(data);
    });
}

function readBody(req) {
    return new Promise(function (resolve, reject) {
        var chunks = [];
        var size = 0;
        req.on('data', function (chunk) {
            size += chunk.length;
            if (size > 102400) { reject(new Error('too big')); req.destroy(); return; }
            chunks.push(chunk);
        });
        req.on('end', function () { resolve(Buffer.concat(chunks).toString()); });
        req.on('error', reject);
    });
}


var server = http.createServer(function (req, res) {
    var url = new (require('url').URL)(req.url, 'http://localhost');
    var pathname = url.pathname;

    // single API endpoint - get best move for a board state
    if (pathname === '/api/move' && req.method === 'POST') {
        readBody(req).then(function (raw) {
            var body = JSON.parse(raw);
            var board = boardFromCells(body.cells);
            var dir = getBestMove(board);

            res.writeHead(200, {
                'Content-Type': 'application/json',
                'Access-Control-Allow-Origin': '*'
            });
            res.end(JSON.stringify({ direction: dir }));
        }).catch(function (e) {
            res.writeHead(400, { 'Content-Type': 'application/json' });
            res.end(JSON.stringify({ error: e.message }));
        });
        return;
    }

    if (req.method === 'OPTIONS') {
        res.writeHead(204, {
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Methods': 'GET, POST, OPTIONS',
            'Access-Control-Allow-Headers': 'Content-Type'
        });
        res.end();
        return;
    }

    serveStatic(pathname, res);
});

server.listen(PORT, function () {
    console.log('2048 running at http://localhost:' + PORT);
});