Fix DI-navigation support and FallbackStateForm handling for state machines

[Severnbli]

Text by me

Preface

In the Telegram group discussion I raised a question regarding the lack of support for DI-based navigation when using a state machine. A community member replied that he had also encountered this issue long before I did.

The Problems

There are two separate issues:

1. DI navigation when loading state
2. No way to specify a fallback form type for the IgnoreState case (FallbackStateForm) in standard state machines — the UseJSON(), UseXML(), and similar methods simply don’t have such a parameter and therefore cannot pass FallbackStateForm to the state machine.

My Solutions

Problem 1

I added an optional parameter fallbackForm to all serialization setup methods.

Problem 2

First, I modified the form factories. Previously, they could only create the start forms. Now, they can accept a desired form type and instantiate it directly.

Next, I changed the behavior of the SessionManager.LoadSessionStates method so that forms are now created via the factory.

This resolves the DI navigation issue, since the factory that integrates with the ServiceProvider now assigns it to the form. It also removes the need for parameterless constructors in forms when using DI-based navigation.

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Text by Copilot

This pull request refactors the form creation infrastructure in the codebase, generalizing the "StartForm" concept into a more flexible "FormFactory" approach. It replaces the previous IStartFormFactory and related implementations with a new IFormFactory interface and updates all usages throughout the builder and factory classes. Additionally, it enhances session serialization methods to accept a fallback form type.

Form Factory Refactoring:

• Introduced a new IFormFactory interface with methods to create forms by type or generic, and replaced all usages of IStartFormFactory with IFormFactory across the codebase. (TelegramBotBase/Interfaces/IFormFactory.cs, TelegramBotBase/Builder/BotBaseBuilder.cs, TelegramBotBase/BotBase.cs, TelegramBotBase/Builder/Interfaces/IAPIKeySelectionStage.cs, TelegramBotBase/Builder/Interfaces/IStartFormSelectionStage.cs) [1] [2] [3] [4] [5] [6]
• Replaced DefaultStartFormFactory and LambdaStartFormFactory with new implementations: DefaultFormFactory and LambdaFormFactory, providing more general form creation capabilities. (TelegramBotBase/Factories/DefaultFormFactory.cs, TelegramBotBase/Factories/LambdaFormFactory.cs, removed TelegramBotBase/Factories/DefaultStartFormFactory.cs, removed TelegramBotBase/Factories/LambdaStartFormFactory.cs) [1] [2] [3] [4]
• Refactored and renamed ServiceProviderStartFormFactory to ServiceProviderFormFactory, updating it to implement IFormFactory and support creation of arbitrary form types, not just the start form. (TelegramBotBase/Factories/ServiceProviderFormFactory.cs) [1] [2] [3]

Builder and API Changes:

• Updated builder methods and interfaces to use IFormFactory instead of IStartFormFactory, including method renames such as WithStartFormFactory → WithFormFactory and parameter updates in QuickStart and service provider methods. (TelegramBotBase/Builder/BotBaseBuilder.cs, TelegramBotBase/Builder/Interfaces/IAPIKeySelectionStage.cs, TelegramBotBase/Builder/Interfaces/IStartFormSelectionStage.cs) [1] [2] [3] [4] [5] [6]

Session Serialization Enhancements:

• Extended session serialization methods (UseJSON, UseSimpleJSON, UseXML) to accept an optional fallbackForm parameter, allowing for more robust deserialization and fallback behavior. Updated both implementation and interface documentation. (TelegramBotBase/Builder/BotBaseBuilder.cs, TelegramBotBase/Builder/Interfaces/ISessionSerializationStage.cs) [1] [2] [3] [4]

These changes modernize and unify the form creation pattern, making it easier to extend and maintain, while also improving the flexibility of session state handling.