Macro for defining Chronicle event types.

Use Chronicle.Events.EventType in an event struct module to annotate it with a stable event type identifier and generation number. Chronicle uses these to register the event schema and route events to the correct observers.

You can also declare model-bound constraints directly on the event type through attributes:

defmodule MyApp.Events.UserRegistered do
  use Chronicle.Events.EventType, id: "user-registered-v1"
  defstruct [:email]

  @unique :email
  unique_event_type()
end

defmodule MyApp.Events.UserDeleted do
  use Chronicle.Events.EventType, id: "user-deleted-v1"
  defstruct [:email]

  @remove_constraint "email"
end

Usage

defmodule MyApp.Events.AccountOpened do
  use Chronicle.Events.EventType, id: "account-opened-v1"
  defstruct [:account_id, :owner_name, :initial_balance]
end

With an explicit generation:

defmodule MyApp.Events.FundsDeposited do
  use Chronicle.Events.EventType, id: "funds-deposited", generation: 2
  defstruct [:account_id, :amount, :currency]
end

Introspection

Modules that use Chronicle.Events.EventType expose metadata via __chronicle_event_type__/1:

MyApp.Events.AccountOpened.__chronicle_event_type__(:id)
#=> "account-opened-v1"

MyApp.Events.AccountOpened.__chronicle_event_type__(:generation)
#=> 1

Chronicle also generates a Jason.Encoder implementation automatically so events can be serialized to JSON for storage. Event fields are encoded using their atom keys as-is (snake_case).