From 44d7c1faadca06a6665f0afe40e95786d207a452 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mats=20T=C3=B6rnberg?= <mats@tornberg.me>
Date: Mon, 10 Nov 2025 19:47:15 +0100
Subject: [PATCH] add listener and remove memory inventory service

---
 cmd/inventory/main.go           | 15 ++++++
 pkg/inventory/listener.go       | 85 +++++++++++++++++++++++++++++++++
 pkg/inventory/memory_service.go | 47 ------------------
 3 files changed, 100 insertions(+), 47 deletions(-)
 create mode 100644 pkg/inventory/listener.go
 delete mode 100644 pkg/inventory/memory_service.go

diff --git a/cmd/inventory/main.go b/cmd/inventory/main.go
index c8b4a8e..fa07589 100644
--- a/cmd/inventory/main.go
+++ b/cmd/inventory/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"log"
+	"time"
 
 	"git.tornberg.me/go-cart-actor/pkg/inventory"
 	"github.com/redis/go-redis/v9"
@@ -24,6 +25,18 @@ func main() {
 		log.Fatalf("Unable to connect to inventory redis: %v", err)
 		return
 	}
+
+	// Start inventory change listener
+	listener := inventory.NewInventoryChangeListener(rdb, ctx, func(changes []inventory.InventoryChange) {
+		for _, change := range changes {
+			log.Printf("Inventory change detected: SKU %s at location %s now has %d", change.SKU, change.StockLocationID, change.Value)
+		}
+	})
+	log.Println("Starting inventory change listener...")
+	go listener.Start()
+	listener.WaitReady()
+	log.Println("Listener is ready, proceeding with inventory operations...")
+
 	rdb.Pipelined(ctx, func(p redis.Pipeliner) error {
 		s.UpdateInventory(p, "1", "1", 10)
 		s.UpdateInventory(p, "2", "2", 20)
@@ -51,4 +64,6 @@ func main() {
 	}
 	log.Printf("Inventory after reservation: %v", v)
 
+	// Wait a bit for listener to process messages
+	time.Sleep(2 * time.Second)
 }
diff --git a/pkg/inventory/listener.go b/pkg/inventory/listener.go
new file mode 100644
index 0000000..41b32d2
--- /dev/null
+++ b/pkg/inventory/listener.go
@@ -0,0 +1,85 @@
+package inventory
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"strings"
+
+	"github.com/redis/go-redis/v9"
+)
+
+type InventoryChange struct {
+	SKU             string `json:"sku"`
+	StockLocationID string `json:"stock_location_id"`
+	Value           int64  `json:"value"`
+}
+
+type InventoryChangeHandler func(changes []InventoryChange)
+
+type InventoryChangeListener struct {
+	client  *redis.Client
+	ctx     context.Context
+	handler InventoryChangeHandler
+	ready   chan struct{}
+}
+
+func NewInventoryChangeListener(client *redis.Client, ctx context.Context, handler InventoryChangeHandler) *InventoryChangeListener {
+	return &InventoryChangeListener{
+		client:  client,
+		ctx:     ctx,
+		handler: handler,
+		ready:   make(chan struct{}),
+	}
+}
+
+func (l *InventoryChangeListener) WaitReady() {
+	<-l.ready
+}
+
+func (l *InventoryChangeListener) Start() error {
+	pubsub := l.client.Subscribe(l.ctx, "inventory_changed")
+	defer pubsub.Close()
+
+	// Signal that we're ready to receive messages
+	close(l.ready)
+
+	ch := pubsub.Channel()
+
+	for msg := range ch {
+		var payload map[string]int64
+		if err := json.Unmarshal([]byte(msg.Payload), &payload); err != nil {
+			log.Printf("Failed to unmarshal inventory change message: %v", err)
+			continue
+		}
+
+		changes := make([]InventoryChange, 0, len(payload))
+		for key, newValue := range payload {
+			// Parse key: "inventory:sku:location"
+			parts := strings.Split(key, ":")
+			if len(parts) != 3 || parts[0] != "inventory" {
+				log.Printf("Invalid inventory key format: %s", key)
+				continue
+			}
+			sku := parts[1]
+			locationID := parts[2]
+			changes = append(changes, InventoryChange{
+				SKU:             sku,
+				StockLocationID: locationID,
+				Value:           newValue,
+			})
+		}
+
+		if l.handler != nil {
+			l.handler(changes)
+		} else {
+			// Default logging
+			for _, change := range changes {
+				fmt.Printf("Inventory changed: SKU %s at location %s -> %d\n", change.SKU, change.StockLocationID, change.Value)
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/pkg/inventory/memory_service.go b/pkg/inventory/memory_service.go
deleted file mode 100644
index d3f6a70..0000000
--- a/pkg/inventory/memory_service.go
+++ /dev/null
@@ -1,47 +0,0 @@
-package inventory
-
-import (
-	"errors"
-	"sync"
-)
-
-type MemoryInventoryService struct {
-	warehouses map[LocationID]*Warehouse
-	mu         sync.RWMutex
-}
-
-func NewMemoryInventoryService() *MemoryInventoryService {
-	return &MemoryInventoryService{
-		warehouses: make(map[LocationID]*Warehouse),
-	}
-}
-
-func (s *MemoryInventoryService) AddWarehouse(warehouse *Warehouse) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.warehouses[warehouse.ID] = warehouse
-}
-
-func (s *MemoryInventoryService) GetInventory(sku SKU, locationID LocationID) (*InventoryItem, error) {
-	s.mu.RLock()
-	defer s.mu.RUnlock()
-
-	warehouse, ok := s.warehouses[locationID]
-	if !ok {
-		return nil, errors.New("warehouse not found")
-	}
-
-	for _, item := range warehouse.Inventory {
-		if item.SKU == sku {
-			return &item, nil
-		}
-	}
-	return nil, errors.New("sku not found in warehouse")
-}
-
-func (s *MemoryInventoryService) ReserveInventory(req ...ReserveRequest) error {
-	// We'll implement the reservation logic using Lua script execution here
-
-	// For now, let's just return an error indicating it's not implemented
-	return errors.New("reservation not implemented yet")
-}