[Scheduler] Proposal - initial structure for Symfony Scheduler documentation

Author: alli83

scheduler.rst

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+Scheduler
+=========
+
+The Symfony Scheduler is a powerful and flexible component designed to manage the scheduling of tasks within your PHP application.
+
+Introduction to the case:
+-------------------------
+
+- Provide a case scenario of sending tasks as messages to different handlers.
+- Reference Symfony Messenger for the non recurring approach :doc:`Messenger component docs </components/messenger>`.
+- To emphasize that this doesn't cover every situation and that certain cases will require recurrence, we can provide a few examples.
+
+On the basis of a case study in the context of a full stack Symfony application, we will cover the following topics:
+
+Symfony Scheduler basics:
+-------------------------
+
+Exploring differences and parallels between Symfony Messenger and Symfony Scheduler.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+- Outline the key differences and similarities between Symfony Messenger and Symfony Scheduler.
+- Compare the different cycles.
+- Introduce the Scheduler Transport and its particularity: generate directly the different messages to handle
+
+The Concept of Recurring Message in Symfony Scheduler
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A message associated with a Trigger
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- The importance of setting the frequency for your messages: Introduce the concept of a Trigger in Symfony Scheduler encompassing all the different types.
+
+A dynamic vision for the messages generated
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Introduce the possibility to define your message via a callback: MessageCallbackProvider
+
+Clarifying the need to define and attach Recurring Messages to a Schedule.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Explain the necessity of returning a Schedule (Schedule provider) and attaching recurring messages and the importance of defining on which schedule the recurring messages will be attached.
+
+Exploring alternatives for crafting your Recurring Messages.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Explore alternative methods for creating recurring messages (via attributes).
+
+
+Managing Scheduled Messages:
+----------------------------
+
+Modifying Scheduled Messages in real time
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Emphasize the importance of dynamically modifying scheduled messages.
+
+Exploring Strategies for adding, removing, and modifying entries within the Schedule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Discuss approaches to add, remove, or modify messages within the schedule.
+- Explore actions within a handler and introduce the concept of events in Symfony.
+
+Managing Scheduled Messages via Events:
+---------------------------------------
+
+A strategic event handling
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Explain the different types of events in Symfony (PRE_RUN_EVENT / POST_RUN_EVENT / FAILURE_EVENT)
+- Mention the distinctive feature of the PRE_RUN_EVENT to prevent a message from being handled by its designated handler.
+
+Efficient management with Symfony Scheduler:
+--------------------------------------------
+
+- Detail the special considerations for efficient management, including caching, locking, and the use of multiple schedules (possibility to scale up your schedules).
+- Demonstrate the possibility of redispatching a message.
+