# encoding: ascii-8bit

require 'ffi'

# Wraps bitcoinconsensus.so (https://github.com/bitcoin/bitcoin)
# commit: 90c71548c795787b008bc337cb9332f75d1bccdb

module Bitcoin
  module BitcoinConsensus
    extend FFI::Library

    SCRIPT_VERIFY_NONE      = 0
    SCRIPT_VERIFY_P2SH      = (1 << 0)
    SCRIPT_VERIFY_STRICTENC = (1 << 1)
    SCRIPT_VERIFY_DERSIG    = (1 << 2)
    SCRIPT_VERIFY_LOW_S     = (1 << 3)
    SCRIPT_VERIFY_NULLDUMMY = (1 << 4)
    SCRIPT_VERIFY_SIGPUSHONLY = (1 << 5)
    SCRIPT_VERIFY_MINIMALDATA = (1 << 6)
    SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS = (1 << 7)
    SCRIPT_VERIFY_CLEANSTACK = (1 << 8)

    ERR_CODES = { 0 => :ok, 1 => :tx_index, 2 => :tx_size_mismatch, 3 => :tx_deserialize }

    def self.ffi_load_functions(file)
      class_eval <<-RUBY
        ffi_lib [ %[#{file}] ]
        attach_function :bitcoinconsensus_version, [], :uint

        # int bitcoinconsensus_verify_script(const unsigned char *scriptPubKey, unsigned int scriptPubKeyLen,
        #                                    const unsigned char *txTo        , unsigned int txToLen,
        #                                    unsigned int nIn, unsigned int flags, bitcoinconsensus_error* err);
        attach_function :bitcoinconsensus_verify_script, [:pointer, :uint, :pointer, :uint, :uint, :uint, :pointer], :int
      RUBY
    end

    def self.lib_available?
      @__lib_path ||= [ ENV['BITCOINCONSENSUS_LIB_PATH'], 'vendor/bitcoin/src/.libs/libbitcoinconsensus.so' ].find{|f| File.exists?(f.to_s) }
    end

    def self.init
      return if @bitcoin_consensus
      lib_path = lib_available?
      ffi_load_functions(lib_path)
      @bitcoin_consensus = true
    end

    # api version
    def self.version
      init
      bitcoinconsensus_version
    end

    def self.verify_script(input_index, script_pubkey, tx_payload, script_flags)
      init

      scriptPubKey = FFI::MemoryPointer.new(:uchar, script_pubkey.bytesize).put_bytes(0, script_pubkey)
      txTo = FFI::MemoryPointer.new(:uchar, tx_payload.bytesize).put_bytes(0, tx_payload)
      error_ret = FFI::MemoryPointer.new(:uint)

      ret = bitcoinconsensus_verify_script(scriptPubKey, scriptPubKey.size, txTo, txTo.size, input_index, script_flags, error_ret)

      case ret
      when 0
        false
      when 1
        (ERR_CODES[error_ret.read_int] == :ok) ? true : false
      else
        raise "error invalid result"
      end
    end

  end
end