#!/usr/bin/env perl

##
## Author......: See docs/credits.txt
## License.....: MIT
##

use strict;
use warnings;

use Crypt::PBKDF2;
use Crypt::AuthEnc::GCM;
use MIME::Base64 qw (decode_base64 encode_base64);

sub module_constraints { [[8, 256], [64, 64], [-1, -1], [-1, -1], [-1, -1]] }

sub module_generate_hash
{
  my $word = shift;
  my $salt = shift;
  my $iv   = shift // random_hex_string (32);
  my $ct   = shift;

  my $kdf = Crypt::PBKDF2->new
  (
    hasher     => Crypt::PBKDF2->hasher_from_algorithm ('HMACSHA2', 256),
    iterations => 10000,
    output_len => 32
  );

  my $ct_len = 64;

  my $salt_bin = pack ("H*", $salt);

  my $key = $kdf->PBKDF2 ($salt_bin, $word);

  my $iv_bin = pack ("H*", $iv);

  my $pt = "";

  if (! defined ($ct))
  {
    $pt = "[{\"type\":\"HD Key Tree\",\"data\":{\"mnemonic\":[112,97,121,109,101,110,116,32,117,112,115,101,116,32,109,101,116,97,108,32,99,104,97,112,116,101,114,32,114,117,110,32,97,100,109,105,116,32,109,101,97,115,117,114,101,32,114,101,109,105,110,100,32,115,117,112,112,108,121,32,104,111,112,101,32,101,110,101,109,121,32,104,101,100,103,101,104,111,103],\"numberOfAccounts\":1,\"hdPath\":\"m/44'/60'/0'/0\"}}]";
  }
  else # verify / decrypt
  {
    my $ct_bin = pack ("H*", $ct);

    my $aes = Crypt::AuthEnc::GCM->new ("AES", $key, $iv_bin);

    $pt = $aes->decrypt_add ($ct_bin);

    if ($pt =~ m/^[ -~]*$/) # is_valid_printable_32 ()
    {
      # ok
    }
    else
    {
      $pt = ""; # fake
    }
  }

  $pt = substr ($pt, 0, $ct_len);

  my $aes = Crypt::AuthEnc::GCM->new ("AES", $key, $iv_bin);

  my $ct_bin = $aes->encrypt_add ($pt);

  my $hash = sprintf ('$metamask-short$%s$%s$%s', encode_base64 ($salt_bin, ""), encode_base64 ($iv_bin, ""), encode_base64 ($ct_bin, ""));

  return $hash;
}

sub module_verify_hash
{
  my $line = shift;

  my $idx = index ($line, ':');

  return unless $idx >= 0;

  my $hash = substr ($line, 0, $idx);
  my $word = substr ($line, $idx + 1);

  return unless substr ($hash, 0, 16) eq '$metamask-short$';

  my (undef, $signature, $salt, $iv, $ct) = split '\$', $hash;

  return unless defined $signature;
  return unless defined $salt;
  return unless defined $iv;
  return unless defined $ct;

  my $salt_bin = decode_base64 ($salt);
  my $iv_bin   = decode_base64 ($iv);
  my $ct_bin   = decode_base64 ($ct);

  return unless length $salt_bin == 32;
  return unless length $iv_bin   == 16;
  return unless length $ct_bin   == 64;

  my $word_packed = pack_if_HEX_notation ($word);

  my $new_hash = module_generate_hash ($word_packed, unpack ("H*", $salt_bin), unpack ("H*", $iv_bin), unpack ("H*", $ct_bin));

  return ($new_hash, $word);
}

1;