<?php
//#########################
//### GLOBALS CONSTANTS ###
//#########################

  //Number of characters in a generated session key
  $KEY_LENGTH = 6;

  //All possible characters to exist within session keys
  $VALID_CHAR = "0123456789abcdefghijkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ";

  //Default session end time in seconds if no end time specified
  $END_TIME_OFFSET = "5400";

  //DBA Creds
  $SERVERNAME = "#########";
  $USERNAME = "###########";
  $PASSWORD = "###########";
  $DATABASE = "###########";

//###############
//### GLOBALS ###
//###############

  $conn = 0;




connect();

// Creates a new session with random session key and start time
// endTime is OPTIONAL, if provided will use that as end time OTHERWISE sets end time to (startTime + END_TIME_OFFSET)
// RETURNS:
//    Success: Success message stating: sessionKey, startTime, and endTime;
//    Failure: Error message stating what went wrong;

  function createSession($endTime) {
    global $conn;
    global $END_TIME_OFFSET;

    $sessionKey = "";
    // start time is now
    $startTime = date('Y-m-d H:i:s');

    //If no end time given, use default end time offset
    if (!isset($endTime))
      $endTime = date('Y-m-d H:i:s', time()+$END_TIME_OFFSET);

    //Generate Session key, if key exists on active session, repeat till good key
    do {
      $sessionKey = keyGen();
    } while (checkSession($sessionKey));

    //Run query
    $sql = "INSERT INTO session (class_key, start_time, end_time) VALUES ('$sessionKey', '$startTime', '$endTime');";
    if ($conn->query($sql) === TRUE){
      $insertResponse = "Session created with session_key: $sessionKey, start_time: $startTime, and end_time: $endTime";
    }
    else {
      $insertResponse = $conn->error;
    }
    echo $insertResponse;
    return $insertResponse;
  }

// returns randomly generated session key
  function keyGen() {
    global $VALID_CHAR;
    global $KEY_LENGTH;
    for ($i = 0; $i < $KEY_LENGTH; $i++)
      $sessionKey .= substr( $VALID_CHAR, rand( 0, strlen( $VALID_CHAR)-1), 1);
    return $sessionKey;

  }

// INPUT sessionKey (CASE SENSITIVE)
// RETURN VALUES
//    valid session:           >=1
//    invalid/expired session: 0
  function checkSession($sessionKey) {
    global $conn;

    $now = date('Y-m-d H:i:s');

    $sql = "SELECT * FROM session WHERE class_key = BINARY '$sessionKey' AND end_time > '$now';";
    $result = $conn->query($sql);

    //echo $now;
    //echo $sql;
    //echo $result->num_rows;
    return $result->num_rows;
    }

  function connect() {
    global $conn;
    global $SERVERNAME;
    global $USERNAME;
    global $PASSWORD;
    global $DATABASE;

    $conn = new mysqli( $SERVERNAME, $USERNAME, $PASSWORD, $DATABASE );
    if ($conn->connect_err) {
      die( "Connection Failed: " . $conn->connect_error);
    }
  }

  function disconnect() {
    global $conn;
    $conn->close();
  }

?>