Implement search engine & service in backend

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/repo/migrations/20191022083446_add_eager_materialized_view_for_searching_events.exs

@@ -0,0 +1,65 @@
+defmodule Mobilizon.Storage.Repo.Migrations.AddEagerMaterializedViewForSearchingEvents do
+  use Ecto.Migration
+  import Ecto.Query
+
+  alias Mobilizon.Storage.Repo
+  alias Mobilizon.Service.Search
+  alias Mobilizon.Events.Event
+
+  require Logger
+
+  def up do
+    create table(:event_search, primary_key: false) do
+      add(:id, references(:events, on_delete: :delete_all, on_update: :update_all),
+        primary_key: true
+      )
+
+      add(:title, :text, null: false)
+      add(:document, :tsvector)
+    end
+
+    # to support full-text searches
+    create(index("event_search", [:document], using: :gin))
+
+    # to support substring title matches with ILIKE
+    execute(
+      "CREATE INDEX event_search_title_trgm_index ON event_search USING gin (title gin_trgm_ops)"
+    )
+
+    # to support updating CONCURRENTLY
+    create(unique_index("event_search", [:id]))
+
+    flush()
+
+    events =
+      Event
+      |> preload([e], :tags)
+      |> Repo.all()
+
+    nb_events = length(events)
+
+    IO.puts("\nStarting setting up search for #{nb_events} events, this can take a while…\n")
+    insert_search_event(events, nb_events)
+  end
+
+  defp insert_search_event([%Event{url: url} = event | events], nb_events) do
+    with {:ok, _} <- Search.insert_search_event(event) do
+      Logger.debug("Added event #{url} to the search")
+    else
+      {:error, res} ->
+        Logger.error("Error while adding event #{url} to the search: #{inspect(res)}")
+    end
+
+    ProgressBar.render(nb_events - length(events), nb_events)
+
+    insert_search_event(events, nb_events)
+  end
+
+  defp insert_search_event([], nb_events) do
+    IO.puts("\nFinished setting up search for #{nb_events} events!\n")
+  end
+
+  def down do
+    drop(table(:event_search))
+  end
+end