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Event store using PostgreSQL for persistence.
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Files
lib/event_store/publisher.ex
defmodule EventStore.Publisher do
@moduledoc """
Publish events appended to all streams to subscriptions process, ordered by event id
"""
use GenServer
require Logger
alias EventStore.{Publisher,PendingEvents}
alias EventStore.Subscriptions
defmodule PendingEvents do
defstruct initial_event_id: nil, last_event_id: nil, stream_uuid: nil, events: []
end
defstruct last_published_event_id: 0, pending_events: %{}
def start_link do
GenServer.start_link(__MODULE__, %Publisher{}, name: __MODULE__)
end
def notify_events(stream_uuid, events) do
GenServer.cast(__MODULE__, {:notify_events, stream_uuid, events})
end
def init(%Publisher{} = state) do
{:ok, state}
end
def handle_cast({:notify_events, stream_uuid, events}, %Publisher{last_published_event_id: last_published_event_id, pending_events: pending_events} = state) do
expected_event_id = last_published_event_id + 1
initial_event_id = first_event_id(events)
last_event_id = last_event_id(events)
state = case initial_event_id do
^expected_event_id ->
# events are in expected order, immediately notify subscribers
Subscriptions.notify_events(stream_uuid, events)
%Publisher{state | last_published_event_id: last_event_id }
initial_event_id ->
# events are out of order
pending = %PendingEvents{
initial_event_id: initial_event_id,
last_event_id: last_event_id,
stream_uuid: stream_uuid,
events: events
}
# attempt to publish pending events
GenServer.cast(self, {:notify_pending_events})
%Publisher{state | pending_events: Map.put(pending_events, initial_event_id, pending) }
end
{:noreply, state}
end
def handle_cast({:notify_pending_events}, %Publisher{last_published_event_id: last_published_event_id, pending_events: pending_events} = state) do
next_event_id = last_published_event_id + 1
state = case Map.get(pending_events, next_event_id) do
%PendingEvents{stream_uuid: stream_uuid, events: events, last_event_id: last_event_id} ->
Subscriptions.notify_events(stream_uuid, events)
%Publisher{state | last_published_event_id: last_event_id, pending_events: Map.delete(pending_events, next_event_id) }
nil -> state
end
{:noreply, state}
end
defp first_event_id([first|_]), do: first.event_id
defp last_event_id(events), do: List.last(events).event_id
end