Added a few restrictions

Only one arrow can be spawned on the map at a time. Players cannot spawn the arrow if there is more than one player online, but admins can.

lua/autorun/client/cl_gravity_arrow.lua

@@ -103,3 +103,16 @@ properties.Add( "gravityarrow", {
 	end
 
 } )
+
+net.Receive( "gravityArrowNotify", function( length )
+
+	-- Read the notification text
+	local message = net.ReadString()
+
+	-- Add the notification for 3 seconds
+	notification.AddLegacy( message, NOTIFY_ERROR, 3 )
+
+	-- Play a sound
+	surface.PlaySound("buttons/button10.wav")
+
+end )

lua/autorun/server/sv_gravity_arrow.lua

@@ -20,15 +20,73 @@ along with this program. If not, see https://www.gnu.org/licenses.
 resource.AddSingleFile( "materials/vgui/entities/gravity_arrow.vtf" )
 resource.AddSingleFile( "materials/vgui/entities/gravity_arrow.vmt" )
 
--- Add the network string for enabling or disabling the arrow
-util.AddNetworkString( "gravityArrowToggle" )
+-- Add the network strings
+util.AddNetworkString( "gravityArrowToggle" ) -- Enabling or disabling the arrow
+util.AddNetworkString( "gravityArrowNotify" ) -- Sending notifiations to the client
 
 -- Runs when the client requests that the arrow be enabled or disabled
 net.Receive( "gravityArrowToggle", function( length, player )
+
 	-- Read the network variables
 	local entity = net.ReadEntity()
 	local state = net.ReadBool()
 
 	-- Update the arrow's network var
 	entity:SetEnabled( state )
+
+end )
+
+-- Runs when an entity is attempting to be spawned by a player
+hook.Add( "PlayerSpawnSENT", "gravityArrowSpawn", function( ply, entityClass )
+
+	-- Prevent further execution if this isn't for the gravity arrow
+	if entityClass ~= "gravity_arrow" then return end
+
+	-- Is there at least one arrow already on the map?
+	if #ents.FindByClass( "gravity_arrow" ) > 0 then
+
+		-- Send them a notification
+		net.Start( "gravityArrowNotify" )
+		net.WriteString( "Only one arrow can be spawned on the map, please remove the existing one first." )
+		net.Send( ply )
+
+		-- Prevent them from spawning it
+		return false
+
+	end
+
+	-- Is there more than one player & are they not an admin?
+	if #player.GetHumans() > 1 and not ply:IsAdmin() then
+
+		-- Send them a notification
+		net.Start( "gravityArrowNotify" )
+		net.WriteString( "You cannot spawn this when there are multiple players online." )
+		net.Send( ply )
+
+		-- Prevent them from spawning it
+		return false
+
+	end
+
+end )
+
+-- Runs when a player initally spawns in the server
+hook.Add( "PlayerInitialSpawn", "gravityArrowRemove", function( ply )
+
+	-- Is there now more than one player?
+	if #player.GetHumans() > 1 then
+
+		-- Find all the spawned gravity arrows
+		local arrows = ents.FindByClass( "gravity_arrow" )
+
+		-- Loop through them
+		for _, arrow in ipairs( arrows ) do
+
+			-- Remove the arrow
+			arrow:Remove()
+
+		end
+
+	end
+
 end )