class Aws::Signers::V2

def host(http_request)
  endpoint = http_request.endpoint
  host = endpoint.host.downcase
  if
    (endpoint.scheme == 'http' && endpoint.port != 80) ||
    (endpoint.scheme == 'https' && endpoint.port != 443)
  then
    host += ":#{endpoint.port}"
  end
  host
end

def sign(http_request)
  params = http_request.body.param_list
  params.set('AWSAccessKeyId', @credentials.access_key_id)
  params.set('SecurityToken', @credentials.session_token) if
    @credentials.session_token
  params.set('Timestamp', Time.now.utc.strftime('%Y-%m-%dT%H:%M:%SZ'))
  params.set('SignatureVersion', '2')
  params.set('SignatureMethod', 'HmacSHA256')
  params.delete('Signature')
  params.set('Signature', signature(http_request, params))
  http_request.body = params.to_io
end

def signature(http_request, params)
  sha256_hmac(string_to_sign(http_request, params))
end

def string_to_sign(http_request, params)
  [
    http_request.http_method,
    host(http_request),
    http_request.endpoint.path,
    params.to_s,
  ].join("\n")
end