module Munson
  module Middleware
    class EncodeJsonApi < Faraday::Middleware
      CONTENT_TYPE = 'Content-Type'.freeze
      ACCEPT       = 'Accept'.freeze
      MIME_TYPE    = 'application/vnd.api+json'.freeze
      USER_AGENT   = 'User-Agent'.freeze

      def initialize(app, key_formatter = nil)
        super(app)
        @key_formatter = key_formatter
      end

      def call(env)
        env[:request_headers][USER_AGENT] = "Munson v#{Munson::VERSION}"
        env[:request_headers][ACCEPT] ||= MIME_TYPE
        match_content_type(env) do |data|
          env[:body] = encode data
        end
        @app.call env
      end

      def encode(data)
        json = @key_formatter ? @key_formatter.externalize(data) : data
        ::JSON.dump(json)
      end

      def match_content_type(env)
        if process_request?(env)
          env[:request_headers][CONTENT_TYPE] ||= MIME_TYPE
          yield env[:body] unless env[:body].respond_to?(:to_str)
        end
      end

      def process_request?(env)
        type = request_type(env)
        has_body?(env) and (type.empty? or type == MIME_TYPE)
      end

      def has_body?(env)
        body = env[:body] and !(body.respond_to?(:to_str) and body.empty?)
      end

      def request_type(env)
        type = env[:request_headers][CONTENT_TYPE].to_s
        type = type.split(';', 2).first if type.index(';')
        type
      end
    end
  end
end

Faraday::Request.register_middleware :"Munson::Middleware::EncodeJsonApi" => Munson::Middleware::EncodeJsonApi