include latest and earliest record times in state

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()
 			}
-		state.Queues[symbol] = persisted
+			if f.Timestamp().Before(earliest) || earliest.IsZero() {
+				earliest = f.Timestamp()
+			}
+		}
+		queues[symbol] = persisted
+	}
+
+	state := State{
+		Version:  StateVersion,
+		Platform: fs.platform,
+		Queues:   queues,
+		Latest:   latest,
+		Earliest: earliest,
 	}
 
 	buf := &bytes.Buffer{}

internal/state.go

@@ -3,6 +3,7 @@ package internal
 import (
 	"context"
 	"encoding/json"
+	"time"
 
 	"github.com/shopspring/decimal"
 )
@@ -15,6 +16,8 @@ const StateVersion = "2"
 type State struct {
 	Version  string                       `json:"version"`
 	Platform string                       `json:"platform"`
+	Latest   time.Time                    `json:"latest"`
+	Earliest time.Time                    `json:"earliest"`
 	Queues   map[string][]persistedFiller `json:"queues"`
 }