Include latest and earliest record times in state (#34)

Reviewed-on: #34
Co-authored-by: Natercio Moniz <[email protected]>

internal/json_store.go

@@ -96,11 +96,9 @@ func (fs *JSONStore) Load(ctx context.Context) (map[string]*FillerQueue, error)
 // the same directory followed by an atomic rename so a crash mid-write cannot
 // leave a half-written state file.
 func (fs *JSONStore) Save(ctx context.Context, queue map[string]*FillerQueue) error {
-	state := State{
-		Version:  StateVersion,
-		Platform: fs.platform,
-		Queues:   make(map[string][]persistedFiller),
-	}
+	queues := make(map[string][]persistedFiller)
+	latest := time.Time{}
+	earliest := time.Time{}
 
 	for symbol, q := range queue {
 		if q == nil || q.Len() == 0 {
@@ -119,8 +117,23 @@ func (fs *JSONStore) Save(ctx context.Context, queue map[string]*FillerQueue) er
 				Price:      f.Price(),
 				Filled:     f.Filled(),
 			})
+
+			if f.Timestamp().After(latest) {
+				latest = f.Timestamp()
+			}
+			if f.Timestamp().Before(earliest) || earliest.IsZero() {
+				earliest = f.Timestamp()
+			}
 		}
-		state.Queues[symbol] = persisted
+		queues[symbol] = persisted
+	}
+
+	state := State{
+		Version:  StateVersion,
+		Platform: fs.platform,
+		Queues:   queues,
+		Latest:   latest,
+		Earliest: earliest,
 	}
 
 	buf := &bytes.Buffer{}