module React
  class State

    ALWAYS_UPDATE_STATE_AFTER_RENDER = Hyperloop.on_client? # if on server then we don't wait to update the state
    @rendering_level = 0

    class << self
      attr_reader :current_observer

      def has_observers?(object, name)
        !observers_by_name[object][name].empty?
      end

      def bulk_update
        saved_bulk_update_flag = @bulk_update_flag
        @bulk_update_flag = true
        yield
      ensure
        @bulk_update_flag = saved_bulk_update_flag
      end

      # React already will batch together updates inside of event handlers
      # so we don't have to, and having Hyperstack batch them outside of the
      # event handler causes INPUT/TEXT/SELECT s not to work properly.
      # This method is called by the Component event wrapper.
      def ignore_bulk_updates(*args)
        saved_ignore_bulk_update_flag = @ignore_bulk_update_flag
        @ignore_bulk_update_flag = true
        yield(*args)
      ensure
        @ignore_bulk_update_flag = saved_ignore_bulk_update_flag
      end

      def set_state2(object, name, value, updates, exclusions = nil)
        # set object's name state to value, tell all observers it has changed.
        # Observers must implement update_react_js_state
        object_needs_notification = object.respond_to?(:update_react_js_state)
        observers_by_name[object][name].dup.each do |observer|
          next if exclusions && exclusions.include?(observer)
          updates[observer] += [object, name, value]
          object_needs_notification = false if object == observer
        end
        updates[object] += [nil, name, value] if object_needs_notification
      end

      def initialize_states(object, initial_values) # initialize objects' name/value pairs
        states[object].merge!(initial_values || {})
      end

      def get_state(object, name, current_observer = @current_observer)
        # get current value of name for object, remember that the current object depends on this state,
        # current observer can be overriden with last param
        if current_observer && !new_observers[current_observer][object].include?(name)
          new_observers[current_observer][object] << name
        end
        if @delayed_updates && @delayed_updates[object][name]
          @delayed_updates[object][name][1] << current_observer
        end
        states[object][name]
      end

      # ReactDOM.unstable_batchedUpdates does not seem to improve things here, ill leave it here commented for reference
      # and later investigation
      #if `ReactDOM.unstable_batchedUpdates !== undefined`
      #  %x{
      #    ReactDOM.unstable_batchedUpdates(function(){
      #      #{updates.each { |observer, args| observer.update_react_js_state(*args) }}
      #    });
      #  }
      #else # run the other one
      def set_state(object, name, value, delay=ALWAYS_UPDATE_STATE_AFTER_RENDER)
        states[object][name] = value
        delay = false if object.respond_to?(:set_state_synchronously?) && object.set_state_synchronously?
        if !@ignore_bulk_update_flag && (delay || @bulk_update_flag)
          @delayed_updates ||= Hash.new { |h, k| h[k] = {} }
          @delayed_updates[object][name] = [value, Set.new]
          @delayed_updater ||= after(0.001) do
            delayed_updates = @delayed_updates
            @delayed_updates = Hash.new { |h, k| h[k] = {} } # could this be nil???
            @delayed_updater = nil
            updates = Hash.new { |hash, key| hash[key] = Array.new }
            delayed_updates.each do |object, name_hash|
              name_hash.each do |name, value_and_set|
                set_state2(object, name, value_and_set[0], updates, value_and_set[1])
              end
            end
            updates.each { |observer, args| observer.update_react_js_state(*args) }
          end
        elsif @rendering_level == 0
          updates = Hash.new { |hash, key| hash[key] = Array.new }
          set_state2(object, name, value, updates)
          updates.each { |observer, args| observer.update_react_js_state(*args) }
        end
        value
      ensure
        'Disabling JIT for Safari bug'
      end

      def will_be_observing?(object, name, current_observer)
        current_observer && new_observers[current_observer][object].include?(name)
      end

      def is_observing?(object, name, current_observer)
        current_observer && observers_by_name[object][name].include?(current_observer)
      end

      def update_states_to_observe(current_observer = @current_observer)  # should be called after the last after_render callback, currently called after components render method
        raise "update_states_to_observer called outside of watch block" unless current_observer
        current_observers[current_observer].each do |object, names|
          names.each do |name|
            observers_by_name[object][name].delete(current_observer)
          end
        end
        observers = current_observers[current_observer] = new_observers[current_observer]
        new_observers.delete(current_observer)
        observers.each do |object, names|
          names.each do |name|
            observers_by_name[object][name] << current_observer
          end
        end
      end

      def remove # call after component is unmounted
        raise "remove called outside of watch block" unless @current_observer
        current_observers[@current_observer].each do |object, names|
          names.each do |name|
            observers_by_name[object][name].delete(@current_observer)
          end
        end
        current_observers.delete(@current_observer)
      end

      def set_state_context_to(observer, rendering = nil) # wrap all execution that may set or get states in a block so we know which observer is executing
        saved_current_observer = @current_observer
        @current_observer = observer
        @rendering_level += 1 if rendering
        return_value = yield
        return_value
      ensure
        @current_observer = saved_current_observer
        @rendering_level -= 1 if rendering
        return_value
      end

      def states
        @states ||= Hash.new { |h, k| h[k] = {} }
      end

      [:new_observers, :current_observers, :observers_by_name].each do |method_name|
        define_method(method_name) do
          instance_variable_get("@#{method_name}") ||
          instance_variable_set("@#{method_name}", Hash.new { |h, k| h[k] = Hash.new { |h, k| h[k] = [] } })
        end
      end
    end
  end
end