Add GetItemId overloads, like we have for locations

Archipelago.MultiClient.Net/DataPackage/ItemInfoResolver.cs

@@ -22,6 +22,20 @@ public interface IItemInfoResolver
 		/// </returns>
 		string GetItemName(long itemId, string game = null);
 
+		/// <summary>
+		///     Perform a lookup using the DataPackage sent as a source of truth to lookup a particular item name for a particular game.
+		/// </summary>
+		/// <param name="itemName">
+		///     Name of the item to lookup.
+		/// </param>
+		/// <param name="game">
+		///     The game to lookup the item name for, if null will look in the game the local player is connected to.
+		/// </param>
+		/// <returns>
+		///     The id of the item as a long, or -1 if no such item is found.
+		/// </returns>
+		long GetItemId(string itemName, string game = null);
+
 		/// <summary>
 		///     Get the name of a location from its id. Useful when receiving a packet and it is necessary to find the name of the location.
 		/// </summary>
@@ -81,6 +95,23 @@ public string GetItemName(long itemId, string game = null)
 				: null;
 		}
 
+		/// <inheritdoc/>
+		public long GetItemId(string itemName, string game = null)
+		{
+			if (game == null)
+				game = connectionInfoProvider.Game ?? "Archipelago";
+
+			if (string.IsNullOrEmpty(itemName))
+				return -1;
+
+			if (!cache.TryGetGameDataFromCache(game, out var dataPackage))
+				return -1;
+
+			return dataPackage.Items.TryGetValue(itemName, out var itemId)
+				? itemId
+				: -1;
+		}
+
 		/// <inheritdoc/>
 		public string GetLocationName(long locationId, string game = null)
 		{

Archipelago.MultiClient.Net/Helpers/ReceivedItemsHelper.cs

@@ -31,6 +31,20 @@ public interface IReceivedItemsHelper
 		/// </returns>
 		string GetItemName(long id, string game = null);
 
+		/// <summary>
+		///     Perform a lookup using the DataPackage sent as a source of truth to lookup a particular item name for a particular game.
+		/// </summary>
+		/// <param name="name">
+		///     Name of the item to lookup.
+		/// </param>
+		/// <param name="game">
+		///     The game to lookup the item name for, if null will look in the game the local player is connected to.
+		/// </param>
+		/// <returns>
+		///     The id of the item as a string, or -1 if no such item is found.
+		/// </returns>
+		long GetItemId(string name, string game = null);
+
 		/// <summary>
 		/// Total number of items received
 		/// </summary>
@@ -141,6 +155,9 @@ public ItemInfo DequeueItem()
 		/// <inheritdoc/>
         public string GetItemName(long id, string game = null) => itemInfoResolver.GetItemName(id, game);
 
+        /// <inheritdoc/>
+        public long GetItemId(string name, string game = null) => itemInfoResolver.GetItemId(name, game);
+
 		void Socket_PacketReceived(ArchipelagoPacketBase packet)
         {
             switch (packet.PacketType)