require 'json'

module Appsignal
  class Transaction
    HTTP_REQUEST   = 'http_request'.freeze
    BACKGROUND_JOB = 'background_job'.freeze
    FRONTEND       = 'frontend'.freeze
    BLANK          = ''.freeze

    # Based on what Rails uses + some variables we'd like to show
    ENV_METHODS = %w(CONTENT_LENGTH AUTH_TYPE GATEWAY_INTERFACE
    PATH_TRANSLATED REMOTE_HOST REMOTE_IDENT REMOTE_USER REMOTE_ADDR
    REQUEST_METHOD SERVER_NAME SERVER_PORT SERVER_PROTOCOL REQUEST_URI PATH_INFO

    HTTP_X_REQUEST_START HTTP_X_MIDDLEWARE_START HTTP_X_QUEUE_START
    HTTP_X_QUEUE_TIME HTTP_X_HEROKU_QUEUE_WAIT_TIME HTTP_X_APPLICATION_START
    HTTP_ACCEPT HTTP_ACCEPT_CHARSET HTTP_ACCEPT_ENCODING HTTP_ACCEPT_LANGUAGE
    HTTP_CACHE_CONTROL HTTP_CONNECTION HTTP_USER_AGENT HTTP_FROM HTTP_NEGOTIATE
    HTTP_PRAGMA HTTP_REFERER HTTP_X_FORWARDED_FOR HTTP_CLIENT_IP HTTP_RANGE
    HTTP_X_AUTH_TOKEN)

    class << self
      def create(id, namespace, request, options={})
        # Allow middleware to force a new transaction
        if options.include?(:force) && options[:force]
          Thread.current[:appsignal_transaction] = nil
        end

        # Check if we already have a running transaction
        if Thread.current[:appsignal_transaction] != nil
          # Log the issue and return the current transaction
          Appsignal.logger.debug("Trying to start new transaction #{id} but #{current.transaction_id} is already running. Using #{current.transaction_id}")

          # Return the current (running) transaction
          current
        else
          # Otherwise, start a new transaction
          Thread.current[:appsignal_transaction] = Appsignal::Transaction.new(id, namespace, request, options)
        end
      end

      def current
        Thread.current[:appsignal_transaction] || NilTransaction.new
      end

      def complete_current!
        current.complete
      rescue => e
        Appsignal.logger.error("Failed to complete transaction ##{current.transaction_id}. #{e.message}")
      ensure
        Thread.current[:appsignal_transaction] = nil
      end

      def garbage_collection_profiler
        @garbage_collection_profiler ||= Appsignal::GarbageCollectionProfiler.new
      end
    end

    attr_reader :ext, :transaction_id, :namespace, :request, :paused, :tags, :options, :discarded

    def initialize(transaction_id, namespace, request, options={})
      @transaction_id = transaction_id
      @namespace = namespace
      @request = request
      @paused = false
      @discarded = false
      @tags = {}
      @store = Hash.new({})
      @options = options
      @options[:params_method] ||= :params

      @ext = Appsignal::Extension.start_transaction(
        @transaction_id,
        @namespace,
        self.class.garbage_collection_profiler.total_time
      )
    end

    def nil_transaction?
      false
    end

    def complete
      if discarded?
        Appsignal.logger.debug('Skipping transaction because it was manually discarded.'.freeze)
        return
      end
      if @ext.finish(self.class.garbage_collection_profiler.total_time)
        sample_data
      end
      @ext.complete
    end

    def pause!
      @paused = true
    end

    def resume!
      @paused = false
    end

    def paused?
      @paused == true
    end

    def discard!
      @discarded = true
    end

    def restore!
      @discarded = false
    end

    def discarded?
      @discarded == true
    end

    def store(key)
      @store[key]
    end

    def set_tags(given_tags={})
      @tags.merge!(given_tags)
    end

    def set_action(action)
      return unless action
      @ext.set_action(action)
    end

    def set_http_or_background_action(from=request.params)
      return unless from
      group_and_action = [
        from[:controller] || from[:class],
        from[:action] || from[:method]
      ]
      set_action(group_and_action.compact.join('#'))
    end

    def set_queue_start(start)
      return unless start
      @ext.set_queue_start(start)
    rescue RangeError
      Appsignal.logger.warn("Queue start value #{start} is too big")
    end

    def set_http_or_background_queue_start
      if namespace == HTTP_REQUEST
        set_queue_start(http_queue_start)
      elsif namespace == BACKGROUND_JOB
        set_queue_start(background_queue_start)
      end
    end

    def set_metadata(key, value)
      return unless key && value
      @ext.set_metadata(key, value)
    end

    def set_sample_data(key, data)
      return unless key && data && (data.is_a?(Array) || data.is_a?(Hash))
      @ext.set_sample_data(
        key.to_s,
        Appsignal::Utils.data_generate(data)
      )
    rescue RuntimeError => e
      Appsignal.logger.error("Error generating data (#{e.class}: #{e.message}) for '#{data.inspect}'")
    end

    def sample_data
      {
        :params       => sanitized_params,
        :environment  => sanitized_environment,
        :session_data => sanitized_session_data,
        :metadata     => metadata,
        :tags         => sanitized_tags
      }.each do |key, data|
        set_sample_data(key, data)
      end
    end

    def set_error(error)
      return unless error
      return unless Appsignal.active?
      return if Appsignal.is_ignored_error?(error)

      backtrace = cleaned_backtrace(error.backtrace)
      @ext.set_error(
        error.class.name,
        error.message.to_s,
        backtrace ? Appsignal::Utils.data_generate(backtrace) : Appsignal::Extension.data_array_new
      )
    end
    alias_method :add_exception, :set_error

    def start_event
      @ext.start_event(self.class.garbage_collection_profiler.total_time)
    end

    def finish_event(name, title, body, body_format=Appsignal::EventFormatter::DEFAULT)
      @ext.finish_event(
        name,
        title || BLANK,
        body || BLANK,
        body_format || Appsignal::EventFormatter::DEFAULT,
        self.class.garbage_collection_profiler.total_time
      )
    end

    def record_event(name, title, body, duration, body_format=Appsignal::EventFormatter::DEFAULT)
      @ext.record_event(
        name,
        title || BLANK,
        body || BLANK,
        duration,
        body_format || Appsignal::EventFormatter::DEFAULT
      )
    end

    def instrument(name, title=nil, body=nil, body_format=Appsignal::EventFormatter::DEFAULT)
      start_event
      r = yield
      finish_event(name, title, body, body_format)
      r
    end

    class GenericRequest
      attr_reader :env

      def initialize(env)
        @env = env
      end

      def params
        env[:params]
      end
    end

    protected

    # Returns calculated background queue start time in milliseconds, based on
    # environment values.
    #
    # @return [nil] if no {#environment} is present.
    # @return [nil] if there is no `:queue_start` in the {#environment}.
    # @return [Integer]
    def background_queue_start
      env = environment
      return unless env
      queue_start = env[:queue_start]
      return unless queue_start

      (queue_start.to_f * 1000.0).to_i
    end

    # Returns HTTP queue start time in milliseconds.
    #
    # @return [nil] if no queue start time is found.
    # @return [nil] if begin time is too low to be plausible.
    # @return [Integer] queue start in milliseconds.
    def http_queue_start
      env = environment
      return unless env
      env_var = env["HTTP_X_QUEUE_START".freeze] || env["HTTP_X_REQUEST_START".freeze]
      return unless env_var
      cleaned_value = env_var.tr("^0-9".freeze, "".freeze)
      return if cleaned_value.empty?

      value = cleaned_value.to_i
      if value > 4_102_441_200_000
        # Value is in microseconds. Transform to milliseconds.
        value / 1_000
      elsif value < 946_681_200_000
        # Value is too low to be plausible
        nil
      else
        # Value is in milliseconds
        value
      end
    end

    def sanitized_params
      return unless Appsignal.config[:send_params]
      return unless request.respond_to?(options[:params_method])

      params =
        begin
          request.send options[:params_method]
        rescue => e
          # Getting params from the request has been know to fail.
          Appsignal.logger.debug "Exception while getting params: #{e}"
          nil
        end
      return unless params

      options = {}
      if Appsignal.config[:filter_parameters]
        options[:filter_parameters] = Appsignal.config[:filter_parameters]
      end
      Appsignal::Utils::ParamsSanitizer.sanitize params, options
    end

    # Returns sanitized environment for a transaction.
    #
    # The environment of a transaction can contain a lot of information, not
    # all of it useful for debugging.
    #
    # Only the values from the keys specified in `ENV_METHODS` are returned.
    #
    # @return [nil] if no environment is present.
    # @return [Hash<String, Object>]
    def sanitized_environment
      env = environment
      return if env.empty?

      {}.tap do |out|
        ENV_METHODS.each do |key|
          out[key] = env[key] if env[key]
        end
      end
    end

    # Returns sanitized session data.
    #
    # The session data is sanitized by the {Appsignal::Utils::ParamsSanitizer}.
    #
    # @return [nil] if `:skip_session_data` config is set to `true`.
    # @return [nil] if the {#request} object doesn't respond to `#session`.
    # @return [nil] if the {#request} session data is `nil`.
    # @return [Hash<String, Object>]
    def sanitized_session_data
      return if Appsignal.config[:skip_session_data] ||
          !request.respond_to?(:session)
      session = request.session
      return unless session

      Appsignal::Utils::ParamsSanitizer.sanitize(session.to_hash)
    end

    # Returns metadata from the environment.
    #
    # @return [nil] if no `:metadata` key is present in the {#environment}.
    # @return [Hash<String, Object>]
    def metadata
      environment[:metadata]
    end

    # Returns the environment for a transaction.
    #
    # Returns an empty Hash when the {#request} object doesn't listen to the
    # `#env` method or the `#env` is nil.
    #
    # @return [Hash<String, Object>]
    def environment
      return {} unless request.respond_to?(:env)
      return {} unless request.env

      request.env
    end

    # Only keep tags if they meet the following criteria:
    # * Key is a symbol or string with less then 100 chars
    # * Value is a symbol or string with less then 100 chars
    # * Value is an integer
    def sanitized_tags
      @tags.select do |k, v|
        (k.is_a?(Symbol) || k.is_a?(String) && k.length <= 100) &&
          (((v.is_a?(Symbol) || v.is_a?(String)) && v.length <= 100) || (v.is_a?(Integer)))
      end
    end

    def cleaned_backtrace(backtrace)
      if defined?(::Rails) && backtrace
        ::Rails.backtrace_cleaner.clean(backtrace, nil)
      else
        backtrace
      end
    end

    # Stub that is returned by `Transaction.current` if there is no current transaction, so
    # that it's still safe to call methods on it if there is none.
    class NilTransaction
      def method_missing(m, *args, &block)
      end

      # Instrument should still yield
      def instrument(*args)
        yield
      end

      def nil_transaction?
        true
      end
    end
  end
end