require 'grape/middleware/base'

module Grape
  module Middleware
    module Versioner
      # This middleware sets various version related rack environment variables
      # based on the HTTP Accept header with the pattern:
      # application/vnd.:vendor-:version+:format
      #
      # Example: For request header
      #    Accept: application/vnd.mycompany-v1+json
      #
      # The following rack env variables are set:
      #
      #    env['api.type']    => 'application'
      #    env['api.subtype'] => 'vnd.mycompany-v1+json'
      #    env['api.vendor]   => 'mycompany'
      #    env['api.version]  => 'v1'
      #    env['api.format]   => 'format'
      #
      # If version does not match this route, then a 406 is raised with
      # X-Cascade header to alert Rack::Mount to attempt the next matched
      # route.
      class Header < Base

        def before
          header = Rack::Accept::MediaType.new env['HTTP_ACCEPT']

          if strict?
            # If no Accept header:
            if header.qvalues.empty?
              throw :error, status: 406, headers: error_headers, message: 'Accept header must be set.'
            end
            # Remove any acceptable content types with ranges.
            header.qvalues.reject! do |media_type, _|
              Rack::Accept::Header.parse_media_type(media_type).find { |s| s == '*' }
            end
            # If all Accept headers included a range:
            if header.qvalues.empty?
              throw :error, status: 406, headers: error_headers, message: 'Accept header must not contain ranges ("*").'
            end
          end

          media_type = header.best_of available_media_types

          if media_type
            type, subtype = Rack::Accept::Header.parse_media_type media_type
            env['api.type']    = type
            env['api.subtype'] = subtype

            if /\Avnd\.([a-z0-9*.]+)(?:-([a-z0-9*\-.]+))?(?:\+([a-z0-9*\-.+]+))?\z/ =~ subtype
              env['api.vendor']  = $1
              env['api.version'] = $2
              env['api.format']  = $3  # weird that Grape::Middleware::Formatter also does this
            end
          # If none of the available content types are acceptable:
          elsif strict?
            throw :error, status: 406, headers: error_headers, message: '406 Not Acceptable'
          # If all acceptable content types specify a vendor or version that doesn't exist:
          elsif header.values.all? { |header_value| has_vendor?(header_value) || has_version?(header_value) }
            throw :error, status: 406, headers: error_headers, message: 'API vendor or version not found.'
          end
        end

        private

        def available_media_types
          available_media_types = []

          content_types.each do |extension, media_type|
            versions.reverse.each do |version|
              available_media_types += ["application/vnd.#{vendor}-#{version}+#{extension}", "application/vnd.#{vendor}-#{version}"]
            end
            available_media_types << "application/vnd.#{vendor}+#{extension}"
          end

          available_media_types << "application/vnd.#{vendor}"

          content_types.each do |_, media_type|
            available_media_types << media_type
          end

          available_media_types = available_media_types.flatten
        end

        def versions
          options[:versions] || []
        end

        def vendor
          options[:version_options] && options[:version_options][:vendor]
        end

        def strict?
          options[:version_options] && options[:version_options][:strict]
        end

        # By default those errors contain an `X-Cascade` header set to `pass`, which allows nesting and stacking
        # of routes (see [Rack::Mount](https://github.com/josh/rack-mount) for more information). To prevent
        # this behavior, and not add the `X-Cascade` header, one can set the `:cascade` option to `false`.
        def cascade?
          if options[:version_options] && options[:version_options].has_key?(:cascade)
            !!options[:version_options][:cascade]
          else
            true
          end
        end

        def error_headers
          cascade? ? { 'X-Cascade' => 'pass' } : {}
        end

        # @param [String] media_type a content type
        # @return [Boolean] whether the content type sets a vendor
        def has_vendor?(media_type)
          _, subtype = Rack::Accept::Header.parse_media_type media_type
          subtype[/\Avnd\.[a-z0-9*.]+/]
        end

        # @param [String] media_type a content type
        # @return [Boolean] whether the content type sets an API version
        def has_version?(media_type)
          _, subtype = Rack::Accept::Header.parse_media_type media_type
          subtype[/\Avnd\.[a-z0-9*.]+-[a-z0-9*\-.]+/]
        end

      end
    end
  end
end