feat: add merchant price checking

now if no price on the TP is found, we should check the local merchant options, and use their price
instead of calculations

crafter.go

@@ -18,12 +18,34 @@ func NewCrafter(gw2APIClient APIClient, localCache LocalCache) *Crafter {
 	return &Crafter{gw2APIClient: gw2APIClient, localCache: localCache}
 }
 
+type NoPurchasingOptionsFoundError struct {
+	ItemID  int
+	Message string
+}
+
+func (e *NoPurchasingOptionsFoundError) Error() string {
+	return fmt.Sprintf("%s for ItemID=%d", e.Message, e.ItemID)
+}
+
 func (crafter *Crafter) fetchItemTPPrice(itemID int) (*ItemPrice, error) {
 	itemPrice, err := crafter.gw2APIClient.FetchItemPrice(itemID)
 	if err != nil {
 		apiErr, ok := err.(*APIError)
 		if ok && apiErr.StatusCode == http.StatusNotFound {
-			logger.Error("Item Price not found on TP", "itemID", itemID)
+			logger.Warn("Item Price not found on TP, checking merchant options", "itemID", itemID)
+			hasPurchaseOption, err := crafter.localCache.HasPurchaseOptionWithCurrency(itemID, "Coin")
+			if err != nil {
+				return nil, fmt.Errorf("Failed to check for purchasing options: %w", err)
+			}
+			if !hasPurchaseOption {
+				return nil, &NoPurchasingOptionsFoundError{ItemID: itemID, Message: "No purchasing options found"}
+			}
+			merchantPrice, err := crafter.localCache.GetMerchantItemPrice(itemID, "Coin")
+			if err != nil {
+				return nil, err
+			}
+			logger.Info("Found merchant price", "itemID", itemID)
+			return merchantPrice, nil
 		}
 		return nil, err
 	}

db.go

@@ -3,6 +3,7 @@ package main
 import (
 	"database/sql"
 	"errors"
+	"fmt"
 
 	"github.com/jmoiron/sqlx"
 )
@@ -112,3 +113,29 @@ func (lc *LocalCache) HasPurchaseOptionWithCurrency(itemId int, currencyName str
 	}
 	return count > 0, nil
 }
+
+func (lc *LocalCache) GetMerchantItemPrice(itemID int, currencyName string) (*ItemPrice, error) {
+	currencyId, err := lc.GetCurrencyIDByName(currencyName)
+	if err != nil {
+		return nil, err
+	}
+	var currencyPrice int
+	err = lc.db.QueryRowx(
+		`SELECT mp.count FROM merchant_prices merchant_prices
+    JOIN purchase_options po ON mp.purchase_option_id = po.recipe_id
+    WHERE po.item_id = ? AND mp.currency_id = ?`, itemID, currencyId).Scan(&currencyPrice)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			// No price was found with given currency
+			return nil, fmt.Errorf("No price found in %s for itemID %d", currencyName, itemID)
+		}
+		// An error has occurred during the query
+		return nil, err
+	}
+	// Price found, return a custom ItemPrice
+	return &ItemPrice{
+		ID:    itemID,
+		Buys:  TradingPostPrice{UnitPrice: currencyPrice},
+		Sells: TradingPostPrice{UnitPrice: currencyPrice},
+	}, nil
+}