require 'digest/sha1'
require 'open-uri'

require 'rubygems'

require 'mongrel'
require 'filemagic/ext'

class SecureDownloadRedux < GemPlugin::Plugin '/handlers'

  # Our version ;-)
  VERSION = '0.0.4'

  include Mongrel::HttpHandlerPlugin

  URL_RE = %r{\A(?:ht|f)tps?://}io

  def initialize(options = {})
    super

    @base = File.expand_path(@options[:base] || '.')

    if @base == '/'
      raise ArgumentError, 'specifying a base path of / is way too dangerous!'
    end

    @secret = @options[:secret]

    if @secret.nil? || @secret.empty?
      raise ArgumentError, 'secret missing'
    end

    @url_method = @options[:url_method] || 'redirect2'

    if respond_to?(method = "send_url_#{@url_method}", true)
      self.class.send(:alias_method, :send_url, method)
    else
      raise ArgumentError, "unknown URL method #{@url_method}"
    end
  end

  def process(request, response)
    @query = Mongrel::HttpRequest.query_parse(request.params['QUERY_STRING'])

    if !required_params_given? || timeout? || !authorized?
      response.start(@status) {}
    else
      @status   = 200  # OK
      @response = response

      url? ? send_url : send_file
    end
  end

  private

  def required_params_given?
    @status = 500  # Internal Server Error

    @path      = @query['path']      and
    @timestamp = @query['timestamp'] and
    @token     = @query['token']
  end

  def timeout?
    @status = 408  # Request Timeout
    @timestamp.to_i < Time.now.to_i
  end

  def authorized?
    @status = 403  # Forbidden
    @token == compute_token
  end

  def compute_token
    Digest::SHA1.hexdigest(@secret + @path + @timestamp)
  end

  def url?
    @path =~ URL_RE
  end

  def send_url_read
    @response.body = open(@path) unless @header_only
    @response.send_body
  end

  def send_url_redirect1
    @status = 303  # See Other vs. Found (302) vs. Temporary Redirect (307)

    @response.start(@status, true) { |head, body|
      head['Location'] = @path
      #head['Content-type'] = ???

      body.write(%Q{See <a href="#{@path}">#{@path}</a>})
    }
  end

  def send_url_redirect2
    @response.socket.write(Mongrel::Const::REDIRECT % @path)
  end

  def send_file
    path = File.expand_path(File.join(@base, @path))

    # Prevent double-dot vulnerability!
    return unless path =~ %r{\A#{Regexp.escape(@base)}/}

    file = File.stat(path)
    size = file.size
    time = file.mtime

    @response.status = @status

    @response.header[Mongrel::Const::LAST_MODIFIED] = time.httpdate
    @response.header[Mongrel::Const::ETAG]          = Mongrel::Const::ETAG_FORMAT % [time.to_i, size, file.ino]
    @response.header[Mongrel::Const::CONTENT_TYPE]  = File.content_type(path) || @default_content_type
    @response.header['Content-Disposition']         = %Q{inline; filename="#{File.basename(path)}"}

    @response.send_status(size)
    @response.send_header

    @header_only ? @response.send_body : @response.send_file(@path)
  end

end