captcha.js

const readline = require("readline");
const crypto = require("crypto");
const { FONT, FILL_CHARS, NOISE_CHARS } = require("./font");

const CHARS = Object.keys(FONT);
const CHAR_W = 5;
const CHAR_H = 7;
const SCALE_X = 2;
const PADDING = 3;

function makeLCG(seed) {
  let s = seed >>> 0;
  return () => {
    s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
    return s / 0xffffffff;
  };
}

function renderChar(ch, fill) {
  return FONT[ch].map((rowBits) => {
    let line = "";
    for (let bit = CHAR_W - 1; bit >= 0; bit--) {
      line += (rowBits >> bit) & 1 ? fill.repeat(SCALE_X) : " ".repeat(SCALE_X);
    }
    return line;
  });
}

function generateCaptcha(length = 5) {
  const seed = crypto.randomBytes(4).readUInt32BE(0);
  const rng = makeLCG(seed);

  const code = Array.from(
    { length },
    () => CHARS[Math.floor(rng() * CHARS.length)],
  ).join("");

  const charPxW = CHAR_W * SCALE_X;
  const totalW = length * charPxW + (length - 1) * PADDING + 8;
  const totalH = CHAR_H + 4;

  const canvas = Array.from({ length: totalH }, () => Array(totalW).fill(" "));

  let xCursor = 4;
  for (const ch of code) {
    const fill = FILL_CHARS[Math.floor(rng() * FILL_CHARS.length)];
    const vJit = Math.floor(rng() * 3) - 1;
    const rows = renderChar(ch, fill);
    rows.forEach((rowStr, rowIdx) => {
      const y = rowIdx + 1 + vJit;
      if (y < 0 || y >= totalH) return;
      for (let col = 0; col < rowStr.length; col++) {
        const x = xCursor + col;
        if (x >= 0 && x < totalW && rowStr[col] !== " ") {
          canvas[y][x] = rowStr[col];
        }
      }
    });
    xCursor += charPxW + PADDING;
  }

  const noiseDensity = 0.045;
  const noiseCount = Math.floor(totalW * totalH * noiseDensity);
  for (let i = 0; i < noiseCount; i++) {
    const y = Math.floor(rng() * totalH);
    const x = Math.floor(rng() * totalW);
    if (canvas[y][x] === " ") {
      canvas[y][x] = NOISE_CHARS[Math.floor(rng() * NOISE_CHARS.length)];
    }
  }

  for (let l = 0; l < 2; l++) {
    const y = 1 + Math.floor(rng() * (totalH - 2));
    const start = Math.floor(rng() * (totalW / 3));
    const end = Math.floor(totalW / 2 + rng() * (totalW / 2));
    const lch = ["─", "~", "=", "-"][Math.floor(rng() * 4)];
    for (let x = start; x < end; x++) {
      if (canvas[y][x] === " ") canvas[y][x] = lch;
    }
  }

  const artLines = canvas.map((row) => row.join(""));
  return { code, artLines, width: totalW };
}

function printBanner() {
  const inner = " .less X gitCaptcha ";
  const bar = "─".repeat(inner.length);
  console.log();
  console.log(`┌${bar}┐`);
  console.log(`│${inner}│`);
  console.log(`└${bar}┘`);
  console.log();
}

function printCaptcha({ artLines, width }) {
  const bar = "─".repeat(width + 2);
  console.log(`┌${bar}┐`);
  for (const line of artLines) {
    console.log(`│ ${line} │`);
  }
  console.log(`└${bar}┘`);
}

async function main() {
  const CODE_LEN = 5;

  printBanner();
  console.log(`Type the characters shown.`);
  console.log();

  let inputStream = process.stdin;
  let outputStream = process.stdout;
  if (process.platform !== "win32") {
    try {
      const fs = require("fs");
      const ttyFd = fs.openSync("/dev/tty", "r+");
      inputStream = fs.createReadStream(null, { fd: ttyFd, autoClose: false });
      outputStream = fs.createWriteStream(null, {
        fd: ttyFd,
        autoClose: false,
      });
    } catch {
    }
  }

  const rl = readline.createInterface({
    input: inputStream,
    output: outputStream,
    terminal: true,
  });

  const ask = (prompt) =>
    new Promise((resolve, reject) => {
      rl.question(prompt, resolve);
      rl.once("close", () => reject(new Error("closed")));
    });

  const captcha = generateCaptcha(CODE_LEN);
  printCaptcha(captcha);

  let answer;
  try {
    answer = await ask(`  » `);
  } catch {
    console.log(`\n\n Aborted. Commit blocked.\n`);
    rl.close();
    process.exit(1);
  }

  answer = answer.trim().toUpperCase();

  if (answer === captcha.code) {
    console.log();
    console.log(`\n\n Correct! Proceeding with commit…`);
    console.log();
    rl.close();
    process.exit(0);
  }

  console.log(`\n\n Commit blocked.`);
  console.log();
  rl.close();
  process.exit(1);
}

main().catch((err) => {
  console.error(err);
  process.exit(1);
});