module Contracthashtool

# File lib/contracthashtool.rb, line 35
def self.claim(private_key_wif, payee_address_or_ascii, nonce_hex)
  key = Bitcoin::Key.from_base58(private_key_wif)
  data = compute_data(payee_address_or_ascii, nonce_hex)[1]

  pubkey = [key.pub].pack("H*")
  tweak = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new("SHA256"), pubkey, data).to_i(16)
  group = OpenSSL::PKey::EC::Group.new("secp256k1")
  raise "order exceeded, verify parameters" if tweak >= group.order

  derived_key = (tweak + key.priv.to_i(16)) % group.order
  Bitcoin::Key.new(derived_key.to_s(16))
end

# File lib/contracthashtool.rb, line 49
def self.compute_data(address_or_ascii, nonce_hex)
  nonce = nonce_hex ? [nonce_hex].pack("H32") : SecureRandom.random_bytes(16)
  if Bitcoin.valid_address?(address_or_ascii)
    address_type = Bitcoin.address_type(address_or_ascii)
    case address_type
    when :hash160
      address_type = "P2PH"
    when :p2sh
      address_type = "P2SH"
    else
      raise "unsupported address type #{address_type}"
    end
    contract_bytes = [Bitcoin.hash160_from_address(address_or_ascii)].pack("H*")
  else
    address_type = "TEXT"
    contract_bytes = address_or_ascii
  end
  [ nonce.unpack("H*")[0], address_type + nonce + contract_bytes ]
end

# File lib/contracthashtool.rb, line 9
def self.generate(redeem_script_hex, payee_address_or_ascii, nonce_hex=nil)
  redeem_script = Bitcoin::Script.new([redeem_script_hex].pack("H*"))
  raise "only multisig redeem scripts are currently supported" unless redeem_script.is_multisig?
  nonce_hex, data = compute_data(payee_address_or_ascii, nonce_hex)

  derived_keys = []
  group = OpenSSL::PKey::EC::Group.new("secp256k1")
  redeem_script.get_multisig_pubkeys.each do |pubkey|
    tweak = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new("SHA256"), pubkey, data).to_i(16)
    raise "order exceeded, pick a new nonce" if tweak >= group.order
    tweak = OpenSSL::BN.new(tweak.to_s)
    key = Bitcoin::Key.new(nil, pubkey.unpack("H*")[0])
    key = key.instance_variable_get(:@key)
    point = group.generator.mul(tweak).add(key.public_key).to_bn.to_i
    key = Bitcoin::Key.new(nil, point.to_s(16))
    key.instance_eval{ @pubkey_compressed = true }
    derived_keys << key.pub
  end

  m = redeem_script.get_signatures_required
  p2sh_script, redeem_script = Bitcoin::Script.to_p2sh_multisig_script(m, *derived_keys)

  [ nonce_hex, redeem_script.unpack("H*")[0], Bitcoin::Script.new(p2sh_script).get_p2sh_address ]
end