print("hello world")
You can run this script by typing the command /run print("hello world") in the chat window, or by binding it to a macro.

local function AutoReply(event, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12)
  if event == "CHAT_MSG_WHISPER" then
    SendChatMessage("I'm busy", "WHISPER", nil, arg2)
  end
end
 
ChatFrame_AddMessageEventFilter("CHAT_MSG_WHISPER", AutoReply)
 
You can run this script by typing the command /run AutoReply() in the chat window, or by binding it to a macro.
 
This script will work for whispers (private messages) only, if you want to reply to other type of chat messages you should replace "CHAT_MSG_WHISPER" with the appropriate event type.
 
You can also change the reply message from "I'm busy" to any other message you want.
 
Also, you might want to add a delay between the reply messages to avoid spamming.

local function CheckPowerInfusion()
    local name, _, _, _, _, _, _, _, _, spellId = UnitBuff("player", "Power Infusion")
    if spellId then
        UIErrorsFrame:AddMessage("Power Infusion is up!", 1.0, 1.0, 0.0, 53, 5)
    end
end
 
local frame = CreateFrame("Frame")
frame:RegisterEvent("UNIT_AURA")
frame:SetScript("OnEvent", function(self, event, ...)
    if event == "UNIT_AURA" and ... == "player" then
        CheckPowerInfusion()
    end
end)
You can run this script by typing the command /run CheckPowerInfusion() in the chat window, or by binding it to a macro.
 
This script uses the UnitBuff function to check if the "Power Infusion" aura is present on the player, and if it is, it uses the UIErrorsFrame:AddMessage function to display a notification in the middle of the screen. You can adjust the color and position of the message by changing the parameters of the UIErrorsFrame:AddMessage function.
 
Also, you can set a timer to check the buff every x seconds instead of using the UNIT_AURA event and also you could also use another function as UnitAura to check for the presence of the buff.

local function AutoReply(event, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12)
  if event == "CHAT_MSG_WHISPER" then
    SendChatMessage("I'm busy", "WHISPER", nil, arg2)
  end
end
 
ChatFrame_AddMessageEventFilter("CHAT_MSG_WHISPER", AutoReply)