require "sinbotra"
require "sinatra"
require "json"

module Sinbotra
  class Server < Sinatra::Base
    configure do
      raise ArgumentError, "You need to set a FACEBOOK_PAGE_TOKEN environmental variable to run the server!" unless ENV["FACEBOOK_PAGE_TOKEN"]
      raise ArgumentError, "You need to set a FACEBOOK_APP_SECRET environmental variable to run the server!" unless ENV["FACEBOOK_APP_SECRET"]
      raise ArgumentError, "You need to set a FACEBOOK_CHALLENGE environmental variable to run the server!"  unless ENV["FACEBOOK_CHALLENGE"]
    end

    helpers do
      def verify_facebook_signature!(payload_body)
        digest = OpenSSL::HMAC.hexdigest(
          OpenSSL::Digest.new("sha1"),
          ENV["FACEBOOK_APP_SECRET"],
          payload_body
        )
        signature = "sha1=" + digest
        return halt 403, "Signatures didn't match!" unless Rack::Utils.secure_compare(signature, request.env["HTTP_X_HUB_SIGNATURE"])
      end

      def match_facebook_challenge(params)
        matching = params["hub.mode"] == "subscribe" &&
                   params["hub.verify_token"] == ENV.fetch("FACEBOOK_CHALLENGE")
        matching ? params["hub.challenge"] : nil
      end
    end

    get "/facebook/webhook" do
      if challenge = match_facebook_challenge(params)
        challenge
      else
        status 403
      end
    end

    post "/facebook/webhook" do
      payload = request.body.read
      verify_facebook_signature!(payload)
      begin
        msg = JSON.load(payload)
        Sinbotra::Bot.handle(:facebook, msg)
        "OK"
      rescue Exception => e
        STDERR.puts e.message
        STDERR.puts e.backtrace
        status 500
        "ERROR"
      end
    end
  end
end