require_relative '../data_conversion'

module Ccrypto
  module Ruby
    class HKDFEngine
      include DataConversion
      include TR::CondUtils

      def initialize(*args, &block)
        @config = args.first

        raise KDFEngineException, "KDF config is expected" if not @config.is_a?(Ccrypto::KDFConfig)
        raise KDFEngineException, "Output bit length (outBitLength) value is not given or not a positive value (#{@config.outBitLength})" if is_empty?(@config.outBitLength) or @config.outBitLength <= 0


        @config.salt = SecureRandom.random_bytes(16) if is_empty?(@config.salt)
      end

      def derive(input, output = :binary)

        digest = init_digest(@config.digest)

        @config.info = "" if @config.info.nil?

        res = OpenSSL::KDF.hkdf(input, salt: @config.salt, info: @config.info, length: @config.outBitLength/8, hash: digest)

        case output
        when :hex
          to_hex(res)
        when :b64
          to_b64(res)
        else
          res
        end
      end

      private
      def init_digest(algo)
        if DigestEngine.is_supported?(algo)
          conf = DigestEngine.engineKeys[algo]
          if not_empty?(conf)
            OpenSSL::Digest.new(conf.provider_config)
          else
            raise DigestEngineException, "Algo config '#{algo}' not found"
          end
        else
          raise DigestEngineException, "Digest algo '#{algo}' is not supported"
        end
      end

    end
  end
end