// Content hashing and constant-time comparison.

const crypto = require("crypto");


// SHA-256 of a Buffer or string (utf8) as lowercase hex; null/undefined hash as "".
const sha256Hex = (data) => {
    const buf = Buffer.isBuffer(data) ? data : Buffer.from(data || "");
    return crypto.createHash("sha256").update(buf).digest("hex");
};


// Timing-safe equality of two Buffers or strings (utf8): the comparison time
// does not depend on where they first differ (only on the length).
const constantTimeEqual = (a, b) => {
    const ba = Buffer.isBuffer(a) ? a : Buffer.from(String(a));
    const bb = Buffer.isBuffer(b) ? b : Buffer.from(String(b));
    if (ba.length !== bb.length) {
        return false;
    }
    return crypto.timingSafeEqual(ba, bb);
};


module.exports = {
    sha256Hex,
    constantTimeEqual
};