implement redis inventory with threadsafe reservation

cmd/inventory/main.go

@@ -2,8 +2,9 @@ package main
 
 import (
 	"context"
-	"fmt"
+	"log"
 
+	"git.tornberg.me/go-cart-actor/pkg/inventory"
 	"github.com/redis/go-redis/v9"
 	"github.com/redis/go-redis/v9/maintnotifications"
 )
@@ -18,24 +19,36 @@ func main() {
 			Mode: maintnotifications.ModeDisabled,
 		},
 	})
-
+	s, err := inventory.NewRedisInventoryService(rdb, ctx)
-	err := rdb.Set(ctx, "key", "value", 0).Err()
 	if err != nil {
-		panic(err)
+		log.Fatalf("Unable to connect to inventory redis", err)
+		return
 	}
-
+	rdb.Pipelined(ctx, func(p redis.Pipeliner) error {
-	val, err := rdb.Get(ctx, "key").Result()
+		s.UpdateInventory(p, "1", "1", 10)
+		s.UpdateInventory(p, "2", "2", 20)
+		s.UpdateInventory(p, "3", "3", 30)
+		s.UpdateInventory(p, "4", "4", 40)
+		return nil
+	})
+	err = s.ReserveInventory(inventory.ReserveRequest{
+		SKU:        "1",
+		LocationID: "1",
+		Quantity:   3,
+	}, inventory.ReserveRequest{
+		SKU:        "2",
+		LocationID: "2",
+		Quantity:   15,
+	})
 	if err != nil {
-		panic(err)
+		log.Printf("Unable to reserve inventory: %v", err)
+		return
 	}
-	fmt.Println("key", val)
+	v, err := s.GetInventory("1", "1")
+	if err != nil {
+		log.Printf("Unable to get inventory: %v", err)
+		return
+	}
+	log.Printf("Inventory after reservation: %v", v)
 
-	val2, err := rdb.Get(ctx, "key2").Result()
-	if err == redis.Nil {
-		fmt.Println("key2 does not exist")
-	} else if err != nil {
-		panic(err)
-	} else {
-		fmt.Println("key2", val2)
-	}
 }

pkg/inventory/redis_service.go

@@ -2,8 +2,9 @@ package inventory
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
+	"fmt"
+	"strconv"
 
 	"github.com/redis/go-redis/v9"
 )
@@ -56,52 +57,124 @@ func (s *RedisInventoryService) AddWarehouse(warehouse *Warehouse) error {
 	return err
 }
 
-func (s *RedisInventoryService) GetInventory(sku SKU, locationID LocationID) (*InventoryItem, error) {
+func (s *RedisInventoryService) GetInventory(sku SKU, locationID LocationID) (int64, error) {
-	// Get the warehouse from Redis
+
-	key := "warehouse:" + string(locationID)
+	cmd := s.client.Get(s.ctx, getInventoryKey(sku, locationID))
-	result, err := s.client.HGetAll(s.ctx, key).Result()
+	if err := cmd.Err(); err != nil {
+		return 0, err
+	}
+
+	i, err := cmd.Int64()
 	if err != nil {
-		return nil, err
+		return 0, err
 	}
 
-	// Parse the inventory items
+	return i, nil
-	var inventoryItems []InventoryItem
-	for _, itemData := range result {
-		var item InventoryItem
-		if err := json.Unmarshal([]byte(itemData), &item); err == nil {
-			inventoryItems = append(inventoryItems, item)
-		}
-	}
-
-	// Find the requested SKU
-	for _, item := range inventoryItems {
-		if item.SKU == sku {
-			return &item, nil
-		}
-	}
-
-	return nil, errors.New("sku not found in warehouse")
 }
 
-func (s *RedisInventoryService) ReserveInventory(req ReserveRequest) error {
+func getInventoryKey(sku SKU, locationID LocationID) string {
+	return fmt.Sprintf("inventory:%s:%s", sku, locationID)
+}
+
+func (s *RedisInventoryService) UpdateInventory(rdb redis.Pipeliner, sku SKU, locationID LocationID, quantity int64) error {
+	key := getInventoryKey(sku, locationID)
+	cmd := rdb.Set(s.ctx, key, quantity, 0)
+	return cmd.Err()
+}
+
+var (
+	ErrInsufficientInventory = errors.New("insufficient inventory")
+	ErrInvalidQuantity       = errors.New("invalid quantity")
+	ErrMissingReservation    = errors.New("missing reservation")
+)
+
+func (s *RedisInventoryService) ReserveInventory(req ...ReserveRequest) error {
+	if len(req) == 0 {
+		return ErrMissingReservation
+	}
+
+	keys := make([]string, len(req))
+	args := make([]string, len(req))
+	for i, r := range req {
+		if r.Quantity <= 0 {
+			return ErrInvalidQuantity
+		}
+		keys[i] = getInventoryKey(r.SKU, r.LocationID)
+		args[i] = strconv.Itoa(int(r.Quantity))
+	}
+	cmd := reserveScript.Run(s.ctx, s.client, keys, args)
+	if err := cmd.Err(); err != nil {
+		return err
+	}
+	if val, err := cmd.Int(); err != nil {
+		return err
+	} else if val != 1 {
+		return ErrInsufficientInventory
+	}
 	return nil
-	// Get the Lua script from Redis
-	// key := "lua:reserve_inventory"
-	// script, err := s.client.Get(s.ctx, key).Result()
-	// if err != nil {
-	// 	return err
-	// }
-
-	// luaScript := redis.NewScript(script)
-
-	// // Prepare arguments for the Lua script
-	// args := []interface{}{
-	// 	string(req.LocationID),
-	// 	string(req.SKU),
-	// 	req.Quantity,
-	// }
-
-	// // Execute the Lua script
-	// cmd := s.client.Eval(s.ctx, luaScript, len(args), args...)
-	//return err
 }
+
+var reserveScript = redis.NewScript(`
+-- Get the number of keys passed
+local num_keys = #KEYS
+
+-- Ensure the number of keys matches the number of quantities
+if num_keys ~= #ARGV then
+  return {err = "Script requires the same number of keys and quantities."}
+end
+
+local new_values = {}
+local payload = {}
+
+-- ---
+-- 1. CHECK PHASE
+-- ---
+-- Loop through all keys to check their values first
+for i = 1, num_keys do
+  local key = KEYS[i]
+  local quantity_to_check = tonumber(ARGV[i])
+
+  -- Fail if the quantity is not a valid number
+  if not quantity_to_check then
+    return {err = "Invalid quantity provided for key: " .. key}
+  end
+
+  -- Get the current value stored at the key
+  local current_val = tonumber(redis.call('GET', key))
+
+  -- Check the condition
+  -- Fail if:
+  -- 1. The key doesn't exist (current_val is nil)
+  -- 2. The value is not > the required quantity
+  if not current_val or current_val <= quantity_to_check then
+    -- Return 0 to indicate the operation failed and no changes were made
+    return 0
+  end
+
+  -- If the check passes, store the new value
+  local new_val = current_val - quantity_to_check
+  table.insert(new_values, new_val)
+
+  -- Add this key and its *new* value to our payload map
+  payload[key] = new_val
+end
+
+-- ---
+-- 2. UPDATE PHASE
+-- ---
+-- If the script reaches this point, all checks passed.
+-- Now, loop again and apply all the updates.
+for i = 1, num_keys do
+  local key = KEYS[i]
+  local new_val = new_values[i]
+
+  -- Set the key to its new calculated value
+  redis.call('SET', key, new_val)
+end
+local message_payload = cjson.encode(payload)
+
+-- Publish the JSON-encoded message to the specified channel
+redis.call('PUBLISH', "inventory_changed", message_payload)
+-- Return 1 to indicate the operation was successful
+return 1
+`)

pkg/inventory/types.go

@@ -19,7 +19,7 @@ type Warehouse struct {
 }
 
 type InventoryService interface {
-	GetInventory(sku SKU, locationID LocationID) (uint32, error)
+	GetInventory(sku SKU, locationID LocationID) (int64, error)
 	ReserveInventory(req ...ReserveRequest) error
 }