class BitAuth

# File lib/bitauth.rb, line 8
def initialize(opts = {})
  if opts[:private_key]
    self.private_key = opts[:private_key]
    self.public_key = pubkey_from_privkey private_key
    self.sin = generate_sin public_key
  elsif opts[:public_key]
    self.public_key = opts[:public_key]
    self.sin = generate_sin public_key
  else
    generate_keys
  end
end

# File lib/bitauth.rb, line 21
def sign(data)
  fail(ArgumentError, 'Missing Private Key') if public_key.nil?

  hash = OpenSSL::Digest::SHA256.new.hexdigest data

  ecdsa = OpenSSL::PKey::EC.new('secp256k1')
  ecdsa.private_key = OpenSSL::BN.new private_key, 16

  ecdsa.dsa_sign_asn1([hash].pack('H*')).unpack('H*')[0]
end

# File lib/bitauth.rb, line 32
def verify(data, sig)
  hash = OpenSSL::Digest::SHA256.new.hexdigest data

  ecdsa = OpenSSL::PKey::EC.new('secp256k1')
  pub = OpenSSL::PKey::EC::Point.new(ecdsa.group, OpenSSL::BN.new(public_key, 16))

  ecdsa.public_key = pub
  ecdsa.dsa_verify_asn1([hash].pack('H*'), [sig].pack('H*'))
rescue
  false
end

# File lib/bitauth.rb, line 46
def base58(num)
  letters = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
  res = ''
  while num > 0
    num, r = num.divmod(58)
    res.prepend letters[r]
  end
  res
end

# File lib/bitauth.rb, line 83
def generate_keys
  ecdsa = OpenSSL::PKey::EC.new('secp256k1')
  keys = ecdsa.generate_key

  self.private_key = keys.private_key.to_s.to_i.to_s(16)
  self.public_key = pubkey_from_privkey private_key
  self.sin = generate_sin public_key
end

# File lib/bitauth.rb, line 56
def generate_sin(pubkey)
  sha = OpenSSL::Digest::SHA256.new
  ripe = OpenSSL::Digest::RIPEMD160.new

  hash = '0f02' + ripe.hexdigest(sha.digest([pubkey].pack('H*')))
  checksum = sha.hexdigest(sha.digest([hash].pack('H*')))[0...8]

  key = hash + checksum
  base58 key.hex
end

# File lib/bitauth.rb, line 67
def pubkey_from_privkey(privkey)
  ecdsa = OpenSSL::PKey::EC.new('secp256k1')
  priv = OpenSSL::BN.new(privkey, 16)

  pub = ecdsa.group.generator.mul([priv], []).to_bn.to_i.to_s(16).rjust(130, '0')

  x = [pub].pack('H*')[1..32].unpack('H*').first
  y = [pub].pack('H*')[33..64].unpack('H*').first.to_i(16)

  if y.odd?
    '03' + x
  else
    '02' + x
  end
end