OpenSSH randomart

openssh.randomart.js

const defaultSymbols = 'ES .o+=*BOX@%&#/^'.split('');

const defaultBounds = {
    width: 17,
    height: 9
};

const generateBoard = (data, bounds) => {
    /* create board */
    const board = [];

    for (var i = 0; i < bounds.width; i++) {
        board[i] = [];
        for (var j = 0; j < bounds.height; j++) {
            board[i][j] = 2 /* empty */;
        }
    }

    let x = bounds.width >> 1;
    let y = bounds.height >> 1;

    board[x][y] = 1 /* start */;

    for (let i = 0; i < data.length; ++i) {
        const b = data[i];

        for (let s = 0; s < 8; s += 2) {
            const d = (b >> s) & 3;

            switch (d) {
                case 0: // up
                case 1:
                    if (y > 0) {
                        y--;
                    }

                    break;

                case 2: // down
                case 3:
                    if (y < (bounds.height - 1)) {
                        y++;
                    }

                    break;
            }

            switch (d) {
                case 0: // left
                case 2:
                    if (x > 0) {
                        x--;
                    }

                    break;

                case 1: // right
                case 3:
                    if (x < (bounds.width - 1)) {
                        x++;
                    }

                    break;
            }

            if (board[x][y] >= 2 /* empty */) {
                board[x][y]++;
            }
        }
    }

    board[x][y] = 0 /* end */;

    return {
        board,
        bounds
    };
}

const randomart = (data, opts) => {
    const options = opts || {};

    const bounds = options.bounds || defaultBounds;
    const symbols = options.symbols || defaultSymbols;

    const board = generateBoard(data, bounds);

    const width = board.bounds.width;
    const height = board.bounds.height;

    const result = [];

    for (let i = 0; i < height; i++) {
        result[i] = [];

        for (let j = 0; j < width; j++) {
            result[i][j] = symbols[board.board[j][i]] || symbols[2 /* empty */];
        }

        result[i] = result[i].join('');
    }

    return result.join('\n');
}

setInterval(() => {
    const width = 17 * 2;
    const height = 9 * 2;

    let rart = randomart(
        require('crypto').randomBytes(32),
        {
            bounds: {
                width,
                height
            },
            symbols: 'ES .o+=*BOX@%&#/^'.split('')
        }
    );

    // +--[ RSA 2048 ]---+
    const title = 'RSA 2048';

    const titleBounds = title.length + 4;
    const signBounds = 2;
    const boundsOfMidchars = (width + 2) - titleBounds - signBounds;

    const bOMH1 = boundsOfMidchars / 2;
    const bOMH2 = boundsOfMidchars >> 1;
    const isOdd = (boundsOfMidchars / 2) !== (boundsOfMidchars >> 1);

    const leadingPad = '-'.repeat(bOMH2);
    const trailingPad = '-'.repeat(isOdd ? (bOMH1 + 1) : bOMH2);

    const titleChars = `+${leadingPad}[ ${title} ]${trailingPad}+`
    const postambleChars = `+${'-'.repeat(width)}+`
    const rartChars = rart.split('\n').map(line => `|${line}|`).join('\n');

    process.stdout.write(
        `\x1b[1;1H\r\x1b[0J\x1b[1G\x1b[1;1H\r${titleChars}\n${rartChars}\n${postambleChars}`
    );
}, 100);