require "json"
require "ipaddr"

module BetterErrors
  # Better Errors' error handling middleware. Including this in your middleware
  # stack will show a Better Errors error page for exceptions raised below this
  # middleware.
  # 
  # If you are using Ruby on Rails, you do not need to manually insert this 
  # middleware into your middleware stack.
  # 
  # @example Sinatra
  #   require "better_errors"
  # 
  #   if development?
  #     use BetterErrors::Middleware
  #   end
  #
  # @example Rack
  #   require "better_errors"
  #   if ENV["RACK_ENV"] == "development"
  #     use BetterErrors::Middleware
  #   end
  # 
  class Middleware
    # A new instance of BetterErrors::Middleware
    # 
    # @param app      The Rack app/middleware to wrap with Better Errors
    # @param handler  The error handler to use.
    def initialize(app, handler = ErrorPage)
      @app      = app
      @handler  = handler
    end
    
    # Calls the Better Errors middleware
    # 
    # @param [Hash] env
    # @return [Array]
    def call(env)
      if local_request? env
        better_errors_call env
      else
        @app.call env
      end
    end
    
  private
    IPV4_LOCAL = IPAddr.new("127.0.0.0/8")
    IPV6_LOCAL = IPAddr.new("::1/128")

    def local_request?(env)
      # REMOTE_ADDR is not in the rack spec, so some application servers do
      # not provide it.
      return true unless env["REMOTE_ADDR"]
      ip = IPAddr.new env["REMOTE_ADDR"]
      IPV4_LOCAL.include? ip or IPV6_LOCAL.include? ip
    end

    def better_errors_call(env)
      case env["PATH_INFO"]
      when %r{\A/__better_errors/(?<oid>-?\d+)/(?<method>\w+)\z}
        internal_call env, $~
      when %r{\A/__better_errors/?\z}
        show_error_page env
      else
        protected_app_call env
      end
    end

    def protected_app_call(env)
      @app.call env
    rescue Exception => ex
      @error_page = @handler.new ex, env
      log_exception
      show_error_page(env)
    end

    def show_error_page(env)
      type, content = if @error_page
        if text?(env)
          [ 'plain', @error_page.render('text') ]
        else
          [ 'html', @error_page.render ]
        end
      else
        [ 'html', no_errors_page ]
      end

      [500, { "Content-Type" => "text/#{type}; charset=utf-8" }, [content]]
    end

    def text?(env)
      env["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest" ||
      !env["HTTP_ACCEPT"].to_s.include?('html')
    end
    
    def log_exception
      return unless BetterErrors.logger
      
      message = "\n#{@error_page.exception.class} - #{@error_page.exception.message}:\n"
      @error_page.backtrace_frames.each do |frame|
        message << "  #{frame}\n"
      end
      
      BetterErrors.logger.fatal message
    end
  
    def internal_call(env, opts)
      if opts[:oid].to_i != @error_page.object_id
        return [200, { "Content-Type" => "text/plain; charset=utf-8" }, [JSON.dump(error: "Session expired")]]
      end

      env["rack.input"].rewind
      response = @error_page.send("do_#{opts[:method]}", JSON.parse(env["rack.input"].read))
      [200, { "Content-Type" => "text/plain; charset=utf-8" }, [JSON.dump(response)]]
    end

    def no_errors_page
      "<h1>No errors</h1><p>No errors have been recorded yet.</p><hr>" +
      "<code>Better Errors v#{BetterErrors::VERSION}</code>"
    end
  end
end