<?php

declare(strict_types=1);

namespace CodeHydrater\services\paragon_crypto;

/**
 * @copyright Paragon Initiative Enterprises
 * @license Creative Commons Attribution 4.0 International / ISC
 * @link https://github.com/paragonie/pecl-libsodium-doc/blob/master/chapters/09-recipes.md
 */

class password_storage {
    
    const SALT_SIZE_IN_BYTES = 16;
    private $random_engine;
    
    public function __construct() {
        $this->random_engine = new \tts\random_engine();
    }
    
    public function generate_a_key(): string {
        return sodium_bin2hex($this->random_engine->get_bytes(SODIUM_CRYPTO_SECRETBOX_KEYBYTES));
    }

    /**
     * Hash then encrypt a password
     * 
     * @param string $password   - The user's password
     * @param string $secret_key - The main_magic key for all passwords
     * @return string
     */
    public function hash(#[\SensitiveParameter] string $password, #[\SensitiveParameter] string $secret_key): string {
        // First, let's calculate the hash
        $hashed = sodium_crypto_pwhash_scryptsalsa208sha256_str(
                $password,
                SODIUM_CRYPTO_PWHASH_SCRYPTSALSA208SHA256_OPSLIMIT_INTERACTIVE,
                SODIUM_CRYPTO_PWHASH_SCRYPTSALSA208SHA256_MEMLIMIT_INTERACTIVE
        );
        $salt = $this->random_engine->get_bytes(self::SALT_SIZE_IN_BYTES);
        list ($enc_key, $auth_key) = $this->split_keys($secret_key, sodium_bin2hex($salt));
        sodium_memzero($secret_key);
        sodium_memzero($password);
        $nonce = $this->random_engine->get_bytes(
                SODIUM_CRYPTO_STREAM_NONCEBYTES
        );
        $cipher_text = sodium_crypto_stream_xor(
                $hashed,
                $nonce,
                $enc_key
        );

        $mac = sodium_crypto_auth($nonce . $cipher_text, $auth_key);
        sodium_memzero($enc_key);
        sodium_memzero($auth_key);
        
        return sodium_bin2hex($mac . $nonce . $salt . $cipher_text);
    }

    /**
     * Decrypt then verify a password
     * 
     * @param string $password   - The user-provided password
     * @param string $stored     - The encrypted password hash
     * @param string $secret_key - The main_magic key for all passwords
     */
    public function verify(#[\SensitiveParameter] string $password, string $stored, #[\SensitiveParameter] string $secret_key): bool {
        $data = sodium_hex2bin($stored);
        $mac = mb_substr(
                $data,
                0,
                SODIUM_CRYPTO_AUTH_BYTES,
                '8bit'
        );
        $nonce = mb_substr(
                $data,
                SODIUM_CRYPTO_AUTH_BYTES,
                SODIUM_CRYPTO_STREAM_NONCEBYTES,
                '8bit'
        );
        $salt = mb_substr(
                $data,
                SODIUM_CRYPTO_AUTH_BYTES + SODIUM_CRYPTO_STREAM_NONCEBYTES,
                self::SALT_SIZE_IN_BYTES,
                '8bit'
        );
        $cipher_text = mb_substr(
                $data,
                SODIUM_CRYPTO_AUTH_BYTES + SODIUM_CRYPTO_STREAM_NONCEBYTES + self::SALT_SIZE_IN_BYTES,
                null,
                '8bit'
        );
        list ($enc_key, $auth_key) = $this->split_keys($secret_key, sodium_bin2hex($salt));
        
        if (sodium_crypto_auth_verify($mac, $nonce . $cipher_text, $auth_key)) {
            sodium_memzero($auth_key);
            $hash_str = sodium_crypto_stream_xor($cipher_text, $nonce, $enc_key);
            sodium_memzero($enc_key);
            if ($hash_str !== false) {
                $ret = sodium_crypto_pwhash_scryptsalsa208sha256_str_verify($hash_str, $password);
                sodium_memzero($password);
                return $ret;
            }
        } else {
            sodium_memzero($auth_key);
            sodium_memzero($enc_key);
        }
        throw new \Exception('Decryption failed.');
    }

    /**
     * @return array(2) [encryption key, authentication key]
     */
    private function split_keys(#[\SensitiveParameter] string $secret_key, #[\SensitiveParameter] string $salt): array {
        $enc_key  = hash_hkdf('sha256', $secret_key, SODIUM_CRYPTO_STREAM_KEYBYTES, 'encryption', $salt);
        $auth_key = hash_hkdf('sha256', $secret_key, SODIUM_CRYPTO_AUTH_KEYBYTES, 'authentication', $salt);
        return [$enc_key, $auth_key];
    }

}

/*
$c = new \tts\services\paragon_crypto\password_storage();
$k = $c->generate_a_key();
$h = $c->hash("HelpMe", $k);
var_dump( $c->verify("HelpMe", $h, $k) );
 */