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Event store using PostgreSQL for persistence.
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lib/event_store/notifications/reader.ex
defmodule EventStore.Notifications.Reader do
@moduledoc false
# Reads events from storage by each event number range received.
use GenStage
alias EventStore.RecordedEvent
alias EventStore.Storage
defmodule State do
defstruct [:conn, :serializer, :subscribe_to]
end
def start_link(opts \\ []) do
state = %State{
conn: Keyword.fetch!(opts, :conn),
serializer: Keyword.fetch!(opts, :serializer),
subscribe_to: Keyword.fetch!(opts, :subscribe_to)
}
start_opts = Keyword.take(opts, [:name, :timeout, :debug, :spawn_opt])
GenStage.start_link(__MODULE__, state, start_opts)
end
# Starts a permanent subscription to the listener producer stage which will
# automatically start requesting items.
def init(%State{} = state) do
%State{subscribe_to: subscribe_to} = state
{:producer_consumer, state,
[
dispatcher: GenStage.BroadcastDispatcher,
subscribe_to: [{subscribe_to, max_demand: 1}]
]}
end
# Fetch events from storage and pass onwards to subscibers
def handle_events(events, _from, state) do
stream_events = Enum.map(events, &read_events(&1, state))
{:noreply, stream_events, state}
end
defp read_events(event, %State{} = state) do
{stream_uuid, stream_id, from_stream_version, to_stream_version} = event
%State{conn: conn, serializer: serializer} = state
count = to_stream_version - from_stream_version + 1
with {:ok, events} <-
Storage.read_stream_forward(conn, stream_id, from_stream_version, count),
deserialized_events <- deserialize_recorded_events(events, serializer) do
{stream_uuid, deserialized_events}
end
end
defp deserialize_recorded_events(recorded_events, serializer) do
Enum.map(recorded_events, &RecordedEvent.deserialize(&1, serializer))
end
end