module Discourse
  class SingleSignOn
    #
    # Conveniently cargo culted from https://github.com/discourse/discourse/blob/master/lib/single_sign_on.rb
    # with some very small changes to #parse since we're passing data in via json and not query params

    ACCESSORS = [:nonce, :name, :username, :email, :avatar_url, :avatar_force_update, :require_activation,
                 :bio, :external_id, :return_sso_url, :admin, :moderator, :suppress_welcome_message, :title,
                 :add_groups, :remove_groups]
    FIXNUMS = []
    BOOLS = [:avatar_force_update, :admin, :moderator, :require_activation, :suppress_welcome_message]
    NONCE_EXPIRY_TIME = 10.minutes

    SECRET = 'fake_secret'

    attr_accessor(*ACCESSORS)
    attr_accessor :sso_secret, :sso_url

    def self.sso_secret
      raise RuntimeError, 'sso_secret not implemented on class, be sure to set it on instance'
    end

    def self.sso_url
      raise RuntimeError, 'sso_url not implemented on class, be sure to set it on instance'
    end

    def self.parse(payload, sso_secret = nil)
      sso = new
      sso.sso_secret = sso_secret if sso_secret

      if sso.sign(payload[:sso]) != payload[:sig]
        diags = "\n\nsso: #{payload[:sso]}\n\nsig: #{payload[:sig]}\n\nexpected sig: #{sso.sign(payload[:sso])}"
        if payload[:sso] =~ /[^a-zA-Z0-9=\r\n\/+]/m
          raise RuntimeError, "The SSO field should be Base64 encoded, using only A-Z, a-z, 0-9, +, /, and = characters. Your input contains characters we don't understand as Base64, see http://en.wikipedia.org/wiki/Base64 #{diags}"
        else
          raise RuntimeError, "Bad signature for payload #{diags}"
        end
      end

      decoded = Base64.decode64(payload[:sso])
      decoded_hash = Rack::Utils.parse_query(decoded)

      ACCESSORS.each do |k|
        val = decoded_hash[k.to_s]
        val = val.to_i if FIXNUMS.include? k
        if BOOLS.include? k
          val = ['true', 'false'].include?(val) ? val == 'true' : nil
        end
        sso.send("#{k}=", val)
      end

      decoded_hash.each do |k,v|
        if field = k[/^custom\.(.+)$/, 1]
          sso.custom_fields[field] = v
        end
      end

      sso
    end

    def diagnostics
      SingleSignOn::ACCESSORS.map { |a| "#{a}: #{send(a)}" }.join("\n")
    end

    def sso_secret
      @sso_secret || self.class.sso_secret
    end

    def sso_url
      @sso_url || self.class.sso_url
    end

    def custom_fields
      @custom_fields ||= {}
    end

    def sign(payload)
      OpenSSL::HMAC.hexdigest('sha256', sso_secret, payload)
    end

    def to_url(base_url=nil)
      base = "#{base_url || sso_url}"
      "#{base}#{base.include?('?') ? '&' : '?'}#{payload}"
    end

    def payload
      payload = Base64.encode64(unsigned_payload)
      "sso=#{CGI::escape(payload)}&sig=#{sign(payload)}"
    end

    def unsigned_payload
      payload = {}

      ACCESSORS.each do |k|
       next if (val = send k) == nil
       payload[k] = val
      end

      @custom_fields&.each do |k, v|
        payload["custom.#{k}"] = v.to_s
      end

      Rack::Utils.build_query(payload)
    end
  end
end
