[Commands] Add #countitem Command. (#1842)

* [Commands] Add #countitem Command.
- Add #countitem [Item ID] command to count an item by ID on yourself or your player/NPC target.

* Cleanup.

zone/gm_commands/countitem.cpp

@@ -0,0 +1,64 @@
+#include "../client.h"
+
+void command_countitem(Client *c, const Seperator *sep)
+{
+	int arguments = sep->argnum;
+	if (!arguments || !sep->IsNumber(1)) {
+		c->Message(Chat::White, "Usage: #countitem [Item ID]");
+		return;
+	}
+
+	Mob* target = c;
+	if (
+		c->GetTarget() &&
+		(
+			c->GetTarget()->IsClient() ||
+			c->GetTarget()->IsNPC()
+		)
+	) {
+		target = c->GetTarget();
+	}
+	
+	auto item_id = std::stoul(sep->arg[1]);
+	if (!database.GetItem(item_id)) {
+		c->Message(
+			Chat::White,
+			fmt::format(
+				"Item ID {} could not be found.",
+				item_id
+			).c_str()
+		);
+		return;
+	}
+
+	uint16 item_count = 0;
+	if (target->IsClient()) {
+		item_count = target->CastToClient()->CountItem(item_id);
+	} else if (target->IsNPC()) {
+		item_count = target->CastToNPC()->CountItem(item_id);
+	}
+
+	c->Message(
+		Chat::White,
+		fmt::format(
+			"{} {} {} {}.",
+			(
+				c == target ?
+				"You" :
+				fmt::format(
+					"{} ({})",
+					target->GetCleanName(),
+					target->GetID()
+				)
+			),
+			c == target ? "have" : "has",
+			(
+				item_count ?
+				std::to_string(item_count) :
+				"no"
+			),
+			database.CreateItemLink(item_id)
+		).c_str()
+	);
+}
+