From a3d455e9d6632ea663a6875aaf1a3b69667b1b66 Mon Sep 17 00:00:00 2001
From: Tom Carman <tom.carman@gmail.com>
Date: Tue, 5 May 2026 11:49:11 +0100
Subject: [PATCH] feat: add in-memory cache for recently seen aircraft

---
 core/aircraft.go     | 51 +++++++++++++++++++++++++++++---------------
 core/db-connector.go | 14 ++++++++++--
 2 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/core/aircraft.go b/core/aircraft.go
index 720f809..4e19379 100644
--- a/core/aircraft.go
+++ b/core/aircraft.go
@@ -92,10 +92,23 @@ func (pg *postgres) updateDatabase(nowEpoch float64, aircrafts []Aircraft) {
 func getAircraftsRecentlySeen(pg *postgres, nowEpoch float64, aircrafts []Aircraft) map[string]*Aircraft {
 
 	existingAircrafts := make(map[string]*Aircraft)
+	now := time.Now()
+	newExpiry := now.Add(10 * time.Minute)
+
+	var uncachedHexes []string
 
-	var hexValues []string
 	for _, a := range aircrafts {
-		hexValues = append(hexValues, a.Hex)
+		entry, ok := pg.recentAircraftCache[a.Hex]
+		if ok && now.Before(entry.expiresAt) {
+			entry.expiresAt = newExpiry
+			existingAircrafts[a.Hex] = &entry.aircraft
+		} else {
+			uncachedHexes = append(uncachedHexes, a.Hex)
+		}
+	}
+
+	if len(uncachedHexes) == 0 {
+		return existingAircrafts
 	}
 
 	recentThreshold := int(nowEpoch) - 600
@@ -114,12 +127,12 @@ func getAircraftsRecentlySeen(pg *postgres, nowEpoch float64, aircrafts []Aircra
 			ias,
 			tas
 		FROM aircraft_data
-		WHERE hex = ANY($1::text[]) 
+		WHERE hex = ANY($1::text[])
 			AND last_seen_epoch > $2
 		ORDER BY hex, last_seen DESC;
 	`
 
-	rows, err := pg.db.Query(context.Background(), query, hexValues, recentThreshold)
+	rows, err := pg.db.Query(context.Background(), query, uncachedHexes, recentThreshold)
 	if err != nil {
 		fmt.Println("getAircraftsRecentlySeen() - Error querying db: ", err)
 		return nil
@@ -127,26 +140,30 @@ func getAircraftsRecentlySeen(pg *postgres, nowEpoch float64, aircrafts []Aircra
 	defer rows.Close()
 
 	for rows.Next() {
-		var existingAircraft Aircraft
+		var a Aircraft
 		err := rows.Scan(
-			&existingAircraft.Id,
-			&existingAircraft.Hex,
-			&existingAircraft.LastSeenEpoch,
-			&existingAircraft.LastSeenLat,
-			&existingAircraft.LastSeenLon,
-			&existingAircraft.LastSeenDistance,
-			&existingAircraft.AltBaro,
-			&existingAircraft.AltGeom,
-			&existingAircraft.Gs,
-			&existingAircraft.Ias,
-			&existingAircraft.Tas)
+			&a.Id,
+			&a.Hex,
+			&a.LastSeenEpoch,
+			&a.LastSeenLat,
+			&a.LastSeenLon,
+			&a.LastSeenDistance,
+			&a.AltBaro,
+			&a.AltGeom,
+			&a.Gs,
+			&a.Ias,
+			&a.Tas)
 
 		if err != nil {
 			log.Error().Err(err).Msg("getAircraftsRecentlySeen() - error scanning rows")
 			continue
 		}
 
-		existingAircrafts[existingAircraft.Hex] = &existingAircraft
+		pg.recentAircraftCache[a.Hex] = &aircraftCacheEntry{
+			aircraft:  a,
+			expiresAt: newExpiry,
+		}
+		existingAircrafts[a.Hex] = &pg.recentAircraftCache[a.Hex].aircraft
 	}
 
 	return existingAircrafts
diff --git a/core/db-connector.go b/core/db-connector.go
index e9e8bed..6ca06ce 100644
--- a/core/db-connector.go
+++ b/core/db-connector.go
@@ -4,13 +4,20 @@ import (
 	"context"
 	"os"
 	"sync"
+	"time"
 
 	"github.com/jackc/pgx/v5/pgxpool"
 	"github.com/rs/zerolog/log"
 )
 
+type aircraftCacheEntry struct {
+	aircraft  Aircraft
+	expiresAt time.Time
+}
+
 type postgres struct {
-	db *pgxpool.Pool
+	db                 *pgxpool.Pool
+	recentAircraftCache map[string]*aircraftCacheEntry
 }
 
 var (
@@ -25,7 +32,10 @@ func NewPG(ctx context.Context, connString string) (*postgres, error) {
 			log.Error().Err(err).Msg("Unable to connect to database")
 		}
 
-		pgInstance = &postgres{db}
+		pgInstance = &postgres{
+			db:                  db,
+			recentAircraftCache: make(map[string]*aircraftCacheEntry),
+		}
 	})
 
 	return pgInstance, nil