require 'stringio'
require 'time'
require 'webmachine/streaming'
require 'webmachine/media_type'
require 'webmachine/quoted_string'
require 'webmachine/etags'
require 'webmachine/header_negotiation'
require 'webmachine/constants'

module Webmachine
  module Decision
    # Methods that assist the Decision {Flow}.
    module Helpers
      include QuotedString
      include Streaming
      include HeaderNegotiation

      # Determines if the response has a body/entity set.
      def has_response_body?
        !response.body.nil? && !response.body.empty?
      end

      # If the response body exists, encode it.
      # @see #encode_body
      def encode_body_if_set
        encode_body if has_response_body?
      end

      # Encodes the body in the selected charset and encoding.
      def encode_body
        body = response.body
        chosen_charset = metadata[CHARSET]
        chosen_encoding = metadata[CONTENT_ENCODING]
        charsetter = resource.charsets_provided&.find { |c, _| c == chosen_charset }&.last || :charset_nop
        encoder = resource.encodings_provided[chosen_encoding]
        response.body = case body
        when String # 1.8 treats Strings as Enumerable
          resource.send(encoder, resource.send(charsetter, body))
        when IO, StringIO
          IOEncoder.new(resource, encoder, charsetter, body)
        when Fiber
          FiberEncoder.new(resource, encoder, charsetter, body)
        when Enumerable
          EnumerableEncoder.new(resource, encoder, charsetter, body)
        else
          if body.respond_to?(:call)
            CallableEncoder.new(resource, encoder, charsetter, body)
          else
            resource.send(encoder, resource.send(charsetter, body))
          end
        end
        if body_is_fixed_length?
          ensure_content_length(response)
        else
          response.headers.delete CONTENT_LENGTH
          response.headers[TRANSFER_ENCODING] = 'chunked'
        end
      end

      # Assists in receiving request bodies
      def accept_helper
        content_type = MediaType.parse(request.content_type || 'application/octet-stream')
        acceptable = resource.content_types_accepted.find { |ct, _| content_type.match?(ct) }
        if acceptable
          resource.send(acceptable.last)
        else
          415
        end
      end

      # Computes the entries for the 'Vary' response header
      def variances
        resource.variances.tap do |v|
          v.unshift 'Accept-Language' if resource.languages_provided.size > 1
          v.unshift 'Accept-Charset' if resource.charsets_provided && resource.charsets_provided.size > 1
          v.unshift 'Accept-Encoding' if resource.encodings_provided.size > 1
          v.unshift 'Accept' if resource.content_types_provided.size > 1
        end
      end

      # Adds caching-related headers to the response.
      def add_caching_headers
        if etag = resource.generate_etag
          response.headers['ETag'] = ETag.new(etag).to_s
        end
        if expires = resource.expires
          response.headers['Expires'] = expires.httpdate
        end
        if modified = resource.last_modified
          response.headers['Last-Modified'] = modified.httpdate
        end
      end

      # Determines whether the response is of a fixed lenghth, i.e. it
      # is a String or IO with known size.
      def body_is_fixed_length?
        response.body.respond_to?(:bytesize) &&
          Integer === response.body.bytesize
      end
    end # module Helpers
  end # module Decision
end # module Webmachine