From f98a23418fb7986ac3948e0966b15a2857350e43 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Milo=C5=A1=20Jovanovi=C4=87?= <mrjovanovic@posteo.eu>
Date: Thu, 24 Sep 2026 20:01:01 -0700
Subject: [PATCH] add delta sync before each reconcile, have it not repeat if
 it's been done in the last minute

---
 reconcile.go |  3 +++
 server.go    |  2 ++
 sync.go      | 17 +++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/reconcile.go b/reconcile.go
index 34492c1..9eb22fc 100644
--- a/reconcile.go
+++ b/reconcile.go
@@ -6,6 +6,9 @@ import (
 )
 
 func (s *Server) reconcile(ctx context.Context, runID int64, rep *User, dept string) error {
+	if err := s.syncIfStale(ctx, time.Minute); err != nil {
+		log.Printf("run %d: pre-run sync failed, using cached roster: %v", runID, err)
+	}
 	reps, err := s.store.RepsFor(rep.ChapterID, dept)
 	if err != nil {
 		return err
diff --git a/server.go b/server.go
index cebbb4a..a8ab49f 100644
--- a/server.go
+++ b/server.go
@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"sync"
 )
 
 // User is the subset of an ST user record this worker cares about.
@@ -53,6 +54,7 @@ type Server struct {
 	eligible map[string]bool
 	// runTimeout caps a single reconcile.
 	runTimeout time.Duration
+	syncMu     sync.Mutex
 }
 
 func NewServer(st STClient, store Store, secret string, eligible map[string]bool) *Server {
diff --git a/sync.go b/sync.go
index 678ca40..843817f 100644
--- a/sync.go
+++ b/sync.go
@@ -44,3 +44,20 @@ func (s *Server) SyncRoster(ctx context.Context) error {
 	log.Printf("synced %d users (since=%d)", len(users), since)
 	return s.store.SetLastSync(started)
 }
+
+// syncIfStale runs a delta sync unless one completed within maxAge (1 min)
+// Serialized so a burst of runs triggers one sync, not one each.
+func (s *Server) syncIfStale(ctx context.Context, maxAge time.Duration) error {
+	s.syncMu.Lock()
+	defer s.syncMu.Unlock()
+
+	last, err := s.store.LastSync()
+	if err != nil {
+		return err
+	}
+	if time.Since(time.Unix(last, 0)) < maxAge {
+		return nil
+	}
+	return s.SyncRoster(ctx)
+}
+