$filePath = 'c:\Users\MyName\Desktop\PLC_Comm_D13_VCL\uMain.pas'
$lines = Get-Content $filePath -Encoding Default
$startIdx = -1
$endIdx = -1

for ($i = 0; $i -lt $lines.Count; $i++) {
    if ($lines[$i] -match '^procedure TfMain\.OnMQTTMessage\(const ATopic, APayload: string\);') {
        $startIdx = $i
    }
    if ($startIdx -ne -1 -and $lines[$i] -match '^end;') {
        $endIdx = $i
        break
    }
}

if ($startIdx -ne -1 -and $endIdx -ne -1) {
    $newCode = @"
procedure TfMain.OnMQTTMessage(const ATopic, APayload: string);
var
  JsonObj: TJSONObject;
  i, DONum: Integer;
  Pair: TJSONPair;
  KeyStr, ValStr: string;
begin
//  mmMQTTmsg.Lines.Add(ATopic+'   '+APayload);
  Edit2.Text := ATopic+'   '+APayload;

  try
    JsonObj := TJSONObject.ParseJSONValue(APayload) as TJSONObject;
    if Assigned(JsonObj) then
    begin
      try
        for i := 0 to JsonObj.Count - 1 do
        begin
          Pair := JsonObj.Pairs[i];
          KeyStr := Pair.JsonString.Value;
          ValStr := Pair.JsonValue.Value;

          if (Length(KeyStr) >= 5) and (Copy(KeyStr, 1, 3) = 'DO_') then
          begin
            DONum := StrToIntDef(Copy(KeyStr, 4, Length(KeyStr) - 3), -1);
            if DONum > 0 then
            begin
              if ValStr = '1' then
                SendModbus(slvID, cmdFSC, 15 + DONum, 1)
              else if ValStr = '0' then
                SendModbus(slvID, cmdFSC, 15 + DONum, 0);
            end;
          end;
        end;
      finally
        JsonObj.Free;
      end;
    end;
  except
    on E: Exception do printlog('MQTT Msg Error: ' + E.Message);
  end;
end;
"@
    
    $head = @($lines[0..($startIdx - 1)])
    $tail = @($lines[($endIdx + 1)..($lines.Count - 1)])
    
    $newLines = @()
    $newLines += $head
    $newLines += $newCode -split "`r?`n"
    $newLines += $tail
    
    Set-Content -Path $filePath -Value $newLines -Encoding Default
    Write-Host "Replaced successfully. Start: $startIdx, End: $endIdx"
} else {
    Write-Host "Could not find OnMQTTMessage function bounds. Start: $startIdx, End: $endIdx"
}