const std = @import("std");
const Allocator = std.mem.Allocator;

var argon2_params = std.crypto.pwhash.argon2.Params{
    .t = 4, // time cost
    .m = 256, // memory cost (in KiB)
    .p = 1, // parallelism (this doesnt do anything because we are targeting wasm, and we do multithreading differently anyways)
};

const dk_len: usize = 32; // 16 or 32 byte key
var derived: [dk_len]u8 = undefined;
var buffer_hash_hex: [64]u8 = undefined;

fn bytesToHex(bytes: []const u8, output: []u8) void {
    const hex_chars = "0123456789abcdef";
    var i: usize = 0;
    while (i < bytes.len) : (i += 1) {
        output[i * 2] = hex_chars[(bytes[i] >> 4)];
        output[i * 2 + 1] = hex_chars[bytes[i] & 0x0F];
    }
}

pub fn hash(allocator: Allocator, challenge: []const u8, nonce: []const u8) ![]u8 {
    try std.crypto.pwhash.argon2.kdf(allocator, &derived, nonce, challenge, argon2_params, .argon2id);

    var hash_bytes: [32]u8 = undefined;
    std.crypto.hash.sha2.Sha256.hash(&derived, @ptrCast(hash_bytes[0..].ptr), .{});

    bytesToHex(&hash_bytes, &buffer_hash_hex);
    return buffer_hash_hex[0..];
}