class Aws::S3::Presigner

def build_signer(cfg)
  Aws::Sigv4::Signer.new(
    service: 's3',
    region: cfg.region,
    credentials_provider: cfg.credentials,
    unsigned_headers: [
      'cache-control',
      'content-length', # due to a ELB bug
      'expect',
      'max-forwards',
      'pragma',
      'te',
      'if-match',
      'if-none-match',
      'if-modified-since',
      'if-unmodified-since',
      'if-range',
      'accept',
      'proxy-authorization',
      'from',
      'referer',
      'user-agent',
      'x-amzn-trace-id'
    ],
    uri_escape_path: false
  )
end

def expires_in(params)
  if expires_in = params.delete(:expires_in)
    if expires_in > ONE_WEEK
      msg = "expires_in value of #{expires_in} exceeds one-week maximum"
      raise ArgumentError, msg
    end
    expires_in
  else
    FIFTEEN_MINUTES
  end
end

def http_scheme(params, virtual_host)
  if params.delete(:secure) == false || virtual_host
    'http'
  else
    @client.config.endpoint.scheme
  end
end

def initialize(options = {})
  @client = options[:client] || Aws::S3::Client.new
end

def presigned_url(method, params = {})
  if params[:key].nil? or params[:key] == ''
    raise ArgumentError, ":key must not be blank"
  end
  virtual_host = !!params.delete(:virtual_host)
  scheme = http_scheme(params, virtual_host)
  req = @client.build_request(method, params)
  use_bucket_as_hostname(req) if virtual_host
  sign_but_dont_send(req, expires_in(params), scheme)
  req.send_request.data
end

def sign_but_dont_send(req, expires_in, scheme)
  http_req = req.context.http_request
  req.handlers.remove(Aws::S3::Plugins::S3Signer::LegacyHandler)
  req.handlers.remove(Aws::S3::Plugins::S3Signer::V4Handler)
  req.handlers.remove(Seahorse::Client::Plugins::ContentLength::Handler)
  signer = build_signer(req.context.config)
  req.handle(step: :send) do |context|
    if scheme != http_req.endpoint.scheme
      endpoint = http_req.endpoint.dup
      endpoint.scheme = scheme
      endpoint.port = (scheme == 'http' ? 80 : 443)
      http_req.endpoint = URI.parse(endpoint.to_s)
    end
    # hoist x-amz-* headers to the querystring
    query = http_req.endpoint.query ? http_req.endpoint.query.split('&') : []
    http_req.headers.keys.each do |key|
      if key.match(/^x-amz/i)
        value = Aws::Sigv4::Signer.uri_escape(http_req.headers.delete(key))
        key = Aws::Sigv4::Signer.uri_escape(key)
        query << "#{key}=#{value}"
      end
    end
    http_req.endpoint.query = query.join('&') unless query.empty?
    url = signer.presign_url(
      http_method: http_req.http_method,
      url: http_req.endpoint,
      headers: http_req.headers,
      body_digest: 'UNSIGNED-PAYLOAD',
      expires_in: expires_in
    ).to_s
    Seahorse::Client::Response.new(context: context, data: url)
  end
end

def use_bucket_as_hostname(req)
  req.handlers.remove(Plugins::BucketDns::Handler)
  req.handle do |context|
    uri = context.http_request.endpoint
    uri.host = context.params[:bucket]
    uri.path.sub!("/#{context.params[:bucket]}", '')
    uri.scheme = 'http'
    uri.port = 80
    @handler.call(context)
  end
end