feat(scrobble): add backoffDelay schedule (1m, 5m, 30m, 2h, 6h, give up)

internal/scrobble/worker.go

@@ -0,0 +1,30 @@
+package scrobble
+
+import (
+	"time"
+)
+
+// backoffSchedule maps the failure count (1-indexed: 1 = first failure
+// just happened) to the delay before the next attempt. Per spec §M4a:
+// 1m → 5m → 30m → 2h → 6h, then give up.
+var backoffSchedule = []time.Duration{
+	1 * time.Minute,
+	5 * time.Minute,
+	30 * time.Minute,
+	2 * time.Hour,
+	6 * time.Hour,
+}
+
+const maxAttempts = 5
+
+// backoffDelay returns the delay before the next attempt given the value
+// of the `attempts` column AFTER the failure has been recorded (1-indexed:
+// attempts=1 means the first failure just happened, the next retry should
+// wait 1 minute). Returns (_, false) when attempts > maxAttempts (the
+// caller should mark the row failed).
+func backoffDelay(attempts int) (time.Duration, bool) {
+	if attempts < 1 || attempts > maxAttempts {
+		return 0, false
+	}
+	return backoffSchedule[attempts-1], true
+}

internal/scrobble/worker_test.go

@@ -0,0 +1,31 @@
+package scrobble
+
+import (
+	"testing"
+	"time"
+)
+
+func TestBackoffDelay(t *testing.T) {
+	cases := []struct {
+		attempts int
+		want     time.Duration
+		ok       bool
+	}{
+		{1, 1 * time.Minute, true},
+		{2, 5 * time.Minute, true},
+		{3, 30 * time.Minute, true},
+		{4, 2 * time.Hour, true},
+		{5, 6 * time.Hour, true},
+		{6, 0, false},
+		{99, 0, false},
+	}
+	for _, c := range cases {
+		got, ok := backoffDelay(c.attempts)
+		if ok != c.ok {
+			t.Errorf("backoffDelay(%d) ok = %v, want %v", c.attempts, ok, c.ok)
+		}
+		if got != c.want {
+			t.Errorf("backoffDelay(%d) = %v, want %v", c.attempts, got, c.want)
+		}
+	}
+}