Updated slow indexing to maintain its old schedule if re-enabled

lib/pinchflat/slow_indexing/slow_indexing_helpers.ex

@@ -28,10 +28,12 @@ defmodule Pinchflat.SlowIndexing.SlowIndexingHelpers do
   Returns {:ok, %Task{}}
   """
   def kickoff_indexing_task(%Source{} = source, job_args \\ %{}, job_opts \\ []) do
+    job_offset_seconds = calculate_job_offset_seconds(source)
+
     Tasks.delete_pending_tasks_for(source, "FastIndexingWorker")
     Tasks.delete_pending_tasks_for(source, "MediaCollectionIndexingWorker", include_executing: true)
 
-    MediaCollectionIndexingWorker.kickoff_with_task(source, job_args, job_opts)
+    MediaCollectionIndexingWorker.kickoff_with_task(source, job_args, job_opts ++ [schedule_in: job_offset_seconds])
   end
 
   @doc """
@@ -154,4 +156,14 @@ defmodule Pinchflat.SlowIndexing.SlowIndexingHelpers do
         changeset
     end
   end
+
+  # Find the difference between the current time and the last time the source was indexed
+  defp calculate_job_offset_seconds(%Source{last_indexed_at: nil}), do: 0
+
+  defp calculate_job_offset_seconds(source) do
+    offset_seconds = DateTime.diff(DateTime.utc_now(), source.last_indexed_at, :second)
+    index_frequency_seconds = source.index_frequency_minutes * 60
+
+    max(0, index_frequency_seconds - offset_seconds)
+  end
 end

lib/pinchflat/sources/sources.ex

@@ -328,8 +328,6 @@ defmodule Pinchflat.Sources do
 
     case {current_changes, applied_changes} do
       {%{index_frequency_minutes: mins}, %{enabled: true}} when mins > 0 ->
-        # TODO: consider scheduling the task for the future based on the index_frequency_minutes
-        # compared to `last_indexed_at`
         SlowIndexingHelpers.kickoff_indexing_task(source)
 
       {%{enabled: true}, %{index_frequency_minutes: mins}} when mins > 0 ->

test/pinchflat/slow_indexing/slow_indexing_helpers_test.exs

@@ -23,6 +23,36 @@ defmodule Pinchflat.SlowIndexing.SlowIndexingHelpersTest do
       assert_enqueued(worker: MediaCollectionIndexingWorker, args: %{"id" => source.id})
     end
 
+    test "schedules a job for the future based on when the source was last indexed" do
+      source = source_fixture(index_frequency_minutes: 30, last_indexed_at: now_minus(5, :minutes))
+
+      assert {:ok, _} = SlowIndexingHelpers.kickoff_indexing_task(source)
+
+      [job] = all_enqueued(worker: MediaCollectionIndexingWorker, args: %{"id" => source.id})
+
+      assert_in_delta DateTime.diff(job.scheduled_at, DateTime.utc_now(), :minute), 25, 1
+    end
+
+    test "schedules a job immediately if the source was indexed far in the past" do
+      source = source_fixture(index_frequency_minutes: 30, last_indexed_at: now_minus(60, :minutes))
+
+      assert {:ok, _} = SlowIndexingHelpers.kickoff_indexing_task(source)
+
+      [job] = all_enqueued(worker: MediaCollectionIndexingWorker, args: %{"id" => source.id})
+
+      assert_in_delta DateTime.diff(job.scheduled_at, DateTime.utc_now(), :second), 0, 1
+    end
+
+    test "schedules a job immediately if the source has never been indexed" do
+      source = source_fixture(index_frequency_minutes: 30, last_indexed_at: nil)
+
+      assert {:ok, _} = SlowIndexingHelpers.kickoff_indexing_task(source)
+
+      [job] = all_enqueued(worker: MediaCollectionIndexingWorker, args: %{"id" => source.id})
+
+      assert_in_delta DateTime.diff(job.scheduled_at, DateTime.utc_now(), :second), 0, 1
+    end
+
     test "creates and attaches a task" do
       source = source_fixture(index_frequency_minutes: 1)