logout.php

<?php
// we will only start the session with session_start() IF the session isn't started yet //
if (session_status() == PHP_SESSION_NONE) {
    session_start();
}
?>

<?php
// including the conn.php to establish connection with database //
  include "conn.php";
?>

<?php
// logout function specifically for cashier //
if (isset($_SESSION['order_id']) && (($_SESSION['order_id']) != "")) {
  // begin the query of deletion of the related order, and clearing the $_SESSION back to empty string, then replace them with the new value //
  // but first we have to update the Foreign Key of the related table to NULL in order to delete the order due to SYNTAX //
  $UPDATENULL = "UPDATE user_order SET user_id = NULL, brand_id = NULL, cashier_id = NULL WHERE order_id = '".$_SESSION["order_id"]."' AND paid = 0";
  $UPDATENULLQ = mysqli_query($con, $UPDATENULL);
  if (mysqli_affected_rows($con) < 1) {
    // if there's no result then inform the user and show the possible SQL error //
    echo "<script>alert('WARNING: Order ID can\'t be updated, you will be return back to Cashier Panel. Possible Error: ".mysqli_error($con)."');";
    echo "window.location.href='cashier_panel.html';</script>";
  } else {
    // if we're able to update the Foreign Key, proceeds to another related table to update their Foreign Key as well //
    echo "<script>alert('Notice: Order ID: ".$_SESSION['order_id']." updated, now updating another table\'s Foreign Key in order to proceed the deletion...');</script>";
    // then we've to first get the transaction_id from the related records in transaction_record table so in latter process we will able to delete the record specifically //
    // the variable will be an array to hold all the transaction_id //
    $transaction_id = "";
    // defining and execute the query which finds all the related transaction records //
    $TRANSID = "SELECT * FROM transaction_record WHERE order_id = '".$_SESSION["order_id"]."'";
    $TRANSIDQ = mysqli_query($con, $TRANSID);
    if (mysqli_num_rows($TRANSIDQ) < 1) {
      // if we're able to retrieve the transaction_id, alert the user about it //
      echo "<script>alert('WARNING: Unable to retrieve transaction_records under Order ID: ".$_SESSION['order_id'].", or there\'s no record existing in the transaction record table. Checking the types of error occured...');</script>";
      // if there's no record under transaction_record table, then we can straight delete the order_id //
      $DELETEORD = "DELETE FROM user_order WHERE paid < 1 AND order_id = '".$_SESSION["order_id"]."'";
      $DELETEORDQ = mysqli_query($con, $DELETEORD);
      if (mysqli_affected_rows($con) < 1) {
        // if there's no result then inform the user and show the possible SQL error //
        echo "<script>alert('WARNING: Order ID: ".$_SESSION['order_id']." can\'t be deleted, it\'s highly possible that the fault is on SQL Query. Possible Error: ".mysqli_error($con)."');";
        echo "window.location.href='cashier_panel.html';</script>";
      } else {
        // if the deletion is a success then exit() immediately, and declare the related $_SESSION to empty string //
        $_SESSION['brand_id'] = "";
        $_SESSION['order_id'] = "";
        $_SESSION['buyer_id'] = "";
        echo "<script>alert('Notice: Deletion Process completed. Continue to proceed your intended progress.');";
        echo "window.location.href='cashier_panel.html';</script>";
      }
    } else {
      $result = $con->query($TRANSID);
      if ($result->num_rows > 0) {
        // if there's a result then begin to put the related transaction id into the variable //
        while ($row = $result->fetch_assoc()) {
          $transaction_id[] = $row["transaction_id"];
        }
      }
      // once we got all the transaction_id then we proceed to update the transaction_record table //
      $UPDATENULL = "UPDATE transaction_record SET meal_id = NULL, meal_brand_id = NULL, order_id = NULL WHERE order_id = '".$_SESSION["order_id"]."'";
      $UPDATENULLQ = mysqli_query($con, $UPDATENULL);
      if (mysqli_affected_rows($con) < 1) {
        // if there's no result then inform the user and show the possible SQL error //
        echo "<script>alert('WARNING: Transaction Record ID can\'t be updated, you will be return back to Cashier Panel. Possible Error: ".mysqli_error($con)."');";
        echo "window.location.href='cashier_panel.html';</script>";
      } else {
        // if we've updated the table, begin the process of deletion //
        echo "<script>alert('Notice: Transaction Record ID updated, now begin the deletion of the related information.');</script>";
        $DELETEORD = "DELETE FROM user_order WHERE paid < 1 AND order_id = '".$_SESSION["order_id"]."'";
        $DELETEORDQ = mysqli_query($con, $DELETEORD);
        if (mysqli_affected_rows($con) < 1) {
          // if there's no result then inform the user and show the possible SQL error //
          echo "<script>alert('WARNING: Order ID: ".$_SESSION['order_id']." can\'t be deleted, you will be return back to Cashier Panel. Possible Error: ".mysqli_error($con)."');";
          echo "window.location.href='cashier_panel.html';</script>";
        } else {
          // if we've deleted the related info in order table, begin the final deletion on transaction_record table //
          echo "<script>alert('Notice: Order ID: ".$_SESSION['order_id']." deleted, now begin the deletion of the related information.');</script>";
          while (list($key,$val) = @each ($transaction_id)) {
            $DELETETRANS = "DELETE FROM transaction_record WHERE transaction_id = $val";
            $DELETETRANSQ = mysqli_query($con, $DELETETRANS);
            if (mysqli_affected_rows($con) < 1) {
              // if we are unable to delete the transaction record, something must gone wrong //
              echo "<script>alert('WARNING: Unable to delete the Transaction ID: ".$val.". Please try again. Possible Error: ".mysqli_error($con)."');";
              echo "</script>";
            } else {
              echo "<script>alert('Notice: Deleted Transaction ID: ".$val.".');";
              echo "</script>";
            }
          }
          // if we have reached this point then deletion process is completed, and begin to revert the $_SESSION back to empty string //
          $_SESSION['brand_id'] = "";
          $_SESSION['order_id'] = "";
          $_SESSION['buyer_id'] = "";
        }
      }
    }
  }
}
  session_destroy();
  echo "<script>alert('You\'ve logged out. See you next time.');";
  echo "window.location.href='homepage.html';</script>";
  exit();
 ?>