implement dumb non-truncating oplog for cache-service

render-2023-10-11/cmd/cache-service/oplog.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"render231011/internal/thestore"
+	"slices"
+	"time"
+)
+
+type Oplog struct {
+	events []timestampedEvent
+}
+
+type timestampedEvent struct {
+	t time.Time
+	e thestore.Event
+}
+
+// gotcha duration? bigger N? whatever
+func NewOplog() Oplog {
+	return Oplog{
+		events: make([]timestampedEvent, 0, 1024),
+	}
+}
+
+// todo circular queue if we got time
+func (oplog *Oplog) Push(event thestore.Event) {
+	oplog.push(time.Now(), event)
+}
+
+func (oplog *Oplog) push(t time.Time, event thestore.Event) {
+	oplog.events = append(oplog.events, timestampedEvent{
+		t: t,
+		e: event,
+	})
+}
+
+func (oplog *Oplog) Since(t time.Time) []thestore.Event {
+	result := make([]thestore.Event, 0, 5)
+	for i := len(oplog.events) - 1; i >= 0; i-- {
+		if !oplog.events[i].t.After(t) {
+			break
+		}
+		result = append(result, oplog.events[i].e)
+	}
+	slices.Reverse(result)
+	return result
+}

render-2023-10-11/cmd/cache-service/oplog_test.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"render231011/internal/thestore"
+	"testing"
+	"time"
+)
+
+func TestOplog(t *testing.T) {
+	oplog := NewOplog()
+	oplog.push(time.Unix(1, 0), thestore.Event{ID: "1"})
+	oplog.push(time.Unix(2, 0), thestore.Event{ID: "2"})
+	oplog.push(time.Unix(3, 0), thestore.Event{ID: "3"})
+	oplog.push(time.Unix(4, 0), thestore.Event{ID: "4"})
+
+	got := oplog.Since(time.Unix(2, 0))
+	if len(got) != 2 {
+		t.Error(got)
+	} else if got[0].ID != "3" {
+		t.Error(got[0])
+	} else if got[1].ID != "4" {
+		t.Error(got[1])
+	}
+	t.Logf("%+v", got)
+}