From b1e38bc6973a3b856e611dcb747f780ac99fe198 Mon Sep 17 00:00:00 2001
From: Marcin Czenko <marcin.czenko@pm.me>
Date: Thu, 23 Oct 2025 02:01:49 +0200
Subject: [PATCH] adds a callback called before download starts (helps testing
 the sorting of the archives)

---
 communities/codex_archive_downloader.go      | 17 +++++++++++++++--
 communities/codex_archive_downloader_test.go | 14 +++++++++++++-
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/communities/codex_archive_downloader.go b/communities/codex_archive_downloader.go
index ecf81a1..b8a593f 100644
--- a/communities/codex_archive_downloader.go
+++ b/communities/codex_archive_downloader.go
@@ -43,8 +43,9 @@ type CodexArchiveDownloader struct {
 	cancelled        bool
 	pollingInterval  time.Duration // configurable polling interval for HasCid checks
 
-	// Callback for signaling archive download completion
-	onArchiveDownloaded func(hash string, from, to uint64)
+	// Callbacks
+	onArchiveDownloaded       func(hash string, from, to uint64)
+	onStartingArchiveDownload func(hash string, from, to uint64)
 }
 
 // NewCodexArchiveDownloader creates a new archive downloader
@@ -75,6 +76,13 @@ func (d *CodexArchiveDownloader) SetOnArchiveDownloaded(callback func(hash strin
 	d.onArchiveDownloaded = callback
 }
 
+// SetOnStartingArchiveDownload sets a callback function to be called before starting an archive download
+// This callback is called on the main thread before launching goroutines, making it useful for testing
+// the deterministic order in which archives are processed (sorted newest first)
+func (d *CodexArchiveDownloader) SetOnStartingArchiveDownload(callback func(hash string, from, to uint64)) {
+	d.onStartingArchiveDownload = callback
+}
+
 // GetTotalArchivesCount returns the total number of archives to download
 func (d *CodexArchiveDownloader) GetTotalArchivesCount() int {
 	return d.totalArchivesCount
@@ -205,6 +213,11 @@ func (d *CodexArchiveDownloader) downloadAllArchives() {
 		d.archiveDownloadCancel[archive.hash] = archiveCancelChan
 		d.mu.Unlock()
 
+		// Call callback before starting
+		if d.onStartingArchiveDownload != nil {
+			d.onStartingArchiveDownload(archive.hash, archive.from, archive.to)
+		}
+
 		// Trigger archive download and track progress in a goroutine
 		go func(archiveHash, archiveCid string, archiveFrom, archiveTo uint64, archiveCancel chan struct{}) {
 			err := d.triggerSingleArchiveDownload(archiveHash, archiveCid, archiveCancel)
diff --git a/communities/codex_archive_downloader_test.go b/communities/codex_archive_downloader_test.go
index 7d2e9e4..767938e 100644
--- a/communities/codex_archive_downloader_test.go
+++ b/communities/codex_archive_downloader_test.go
@@ -156,7 +156,13 @@ func (suite *CodexArchiveDownloaderTestifySuite) TestMultipleArchives() {
 	downloader := communities.NewCodexArchiveDownloader(suite.mockClient, index, communityID, existingArchiveIDs, cancelChan)
 	downloader.SetPollingInterval(10 * time.Millisecond)
 
-	// Track completed archives
+	// Track the order in which archives are started (deterministic)
+	var startOrder []string
+	downloader.SetOnStartingArchiveDownload(func(hash string, from, to uint64) {
+		startOrder = append(startOrder, hash)
+	})
+
+	// Track completed archives (non-deterministic due to concurrency)
 	completedArchives := make(map[string]bool)
 	downloader.SetOnArchiveDownloaded(func(hash string, from, to uint64) {
 		completedArchives[hash] = true
@@ -185,8 +191,14 @@ func (suite *CodexArchiveDownloaderTestifySuite) TestMultipleArchives() {
 	assert.Contains(suite.T(), completedArchives, "archive-2", "Should have completed archive-2")
 	assert.Contains(suite.T(), completedArchives, "archive-3", "Should have completed archive-3")
 
+	// Verify sorting: archives should be started in most-recent-first order (deterministic)
+	// This tests the internal sorting logic before concurrency begins
+	expectedStartOrder := []string{"archive-3", "archive-2", "archive-1"}
+	assert.Equal(suite.T(), expectedStartOrder, startOrder, "Archives should be started in most-recent-first order")
+
 	suite.T().Log("✅ Multiple archives test passed")
 	suite.T().Logf("   - Completed %d out of %d archives", len(completedArchives), 3)
+	suite.T().Logf("   - Start order (sorted): %v", startOrder)
 }
 
 // Run the test suite