Generate event to handlers and handler to events mappings.

The script generates two classes: `EventToHandlers` and HandlerToEvents
in the Rails `lib` directory so it's easier to see the big picture of
all subscriptions. It also helps to navigate between subscriptions and
events.

Execute the script using following command:
bin/rails r script/big_picture.rb

rails_application/.gitignore

@@ -31,3 +31,7 @@ yarn-debug.log*
 .ruby-version
 /app/assets/builds/*
 !/app/assets/builds/.keep
+
+# Event to handlers and handler to events mappings generated by big_picture.rb script
+/lib/event_to_handlers.rb
+/lib/handler_to_events.rb

rails_application/script/big_picture.rb

@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+class GenerateFiles
+  EVENT_TO_HANDLERS_FILE = "lib/event_to_handlers.rb"
+  HANDLER_TO_EVENTS_FILE = "lib/handler_to_events.rb"
+
+  def generate_event_to_handlers
+    File.open(EVENT_TO_HANDLERS_FILE, "w") do |f|
+      f.puts event_to_handlers_header
+
+      all_event_types.sort.each do |event_type|
+        f.puts indent("#{event_type} => [", 6)
+
+        event_store
+          .subscribers_for(event_type)
+          .each { |subscription| f.puts indent("#{handler_name(subscription)}, # #{handler_type(subscription)}", 8) }
+        f.puts indent("],", 6)
+      end
+
+      f.print footer
+    end
+  end
+
+  def generate_handler_to_events
+    handler_to_events =
+      all_event_types.each_with_object({}) do |event_type, acc|
+        event_store
+          .subscribers_for(event_type)
+          .each do |subscription|
+          acc[subscription] ||= []
+          acc[subscription] << event_type
+        end
+      end
+
+    File.open("lib/handler_to_events.rb", "w") do |f|
+      f.puts handler_to_events_header
+
+      handler_to_events
+        .keys
+        .sort_by { |h| handler_name(h) }
+        .each do |handler|
+        f.puts indent("#{handler_name(handler)} => [", 6)
+        handler_to_events[handler].sort.each { |event_type| f.puts indent("#{event_type},", 8) }
+        f.puts indent("],", 6)
+      end
+
+      f.print footer
+    end
+  end
+
+  def handler_name(handler)
+    case handler
+    when Class
+      handler.name
+    when Method
+      "#{handler.receiver}.method(:#{handler.original_name})"
+    else
+      handler.class.name
+    end
+  end
+
+  def all_event_types
+    ::Infra::Event.descendants.map(&:name)
+  end
+
+  def handler_type(subscription)
+    subscription.respond_to?(:perform_async) ? "async" : "SYNC"
+  end
+
+  def event_store
+    Rails.configuration.event_store
+  end
+
+  def handler_to_events_header
+    <<~EOF
+      class HandlerToEvents
+        # File autogenerated with script/big_picture.rb
+        def events
+          {
+    EOF
+  end
+
+  def event_to_handlers_header
+    <<~EOF
+      class EventToHandlers
+        # File autogenerated with script/big_picture.rb
+        def handlers
+          {
+    EOF
+  end
+
+  def footer
+    <<~EOF
+          }
+        end
+      end
+    EOF
+  end
+
+  def indent(str, spaces)
+    (" " * spaces) + str
+  end
+end
+
+script = GenerateFiles.new
+script.generate_event_to_handlers
+script.generate_handler_to_events