<?php
    class DB {


      private $connection;
      private static $_instance;
      private $dbhost = ""; // Ip Address of database if external connection.
      private $dbuser = ""; // Username for DB
      private $dbpass = ""; // Password for DB
      private $dbname = ""; // DB Name
      private $query = "";


      /*
      Get an instance of the Database
      @return Instance
      */
      public static function getInstance(){
        if(!self::$_instance) {
              self::$_instance = new self();

           }
          return self::$_instance;
        }
      // Constructor
      private function __construct() {
        try{

        $this->connection = new PDO('mysql:host='.$this->dbhost.';dbname='.$this->dbname, $this->dbuser, $this->dbpass);
        $this->connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

	// Error handling
        }catch(PDOException $e){
          die("Failed to connect to DB: ". $e->getMessage());
        }
      }
      // Magic method clone is empty to prevent duplication of connection
      private function __clone(){}

      // Get the connection
      public function getConnection(){
        return $this->connection;
      }







      //[C] REATE
      public function insert($table, $params = []){ //insert $db->insert('table',['key'=>'value']);
         $con = self::getConnection();

        if($this->tableExists($table)){

            try
            {
                $sql = 'INSERT INTO `'.$table.'` (`' . implode('`, `',array_keys($params)) . '`) VALUES (' . $this->placeholders($params)  . ')';
                $stmt = $con->prepare($sql);
                try{
                  $con->beginTransaction();
                   $stmt->execute(array_values($params));
                  $con->commit();
                }
                catch( PDOException $e)
                {
                  $con->rollback();
                  return $e->getMessage() . "</br>";
                }
            }
            catch( PDOException $e){
                 return $e->getMessage() . "</br>";
            }

            return true;
        }
        else
        {
            return false;
        }


      }




      //[R] ETRIEVE
      public function select()
      {




      }



      //[U] PDATE
      public function update($table, $params = [], $where = null){ //$db->update('table',[],where);
          $con = self::getConnection();

          if($this->tableExists($table)){
                try
                {
                  $a = array();

                  foreach($params as $f=>$v){
                  // Seperate each column out with it's corresponding value
                      $a[] = $f.'='.$this->placeholders($v);
                  }

                  $sql = 'UPDATE '.$table.' SET '.implode(',',$a).' WHERE '.$where;
                  $stmt =  $con->prepare($sql);
                    try{
                      $con->beginTransaction();
                       $stmt->execute(array_values($params));
                      $con->commit();
                    }
                     catch( PDOException $e)
                    {
                      $con->rollback();
                      return $e->getMessage() . "</br>";
                    }
                }
                catch(PDOException $e){
                  return $e->getMessage() ."</br>";
                }

            return true;
          }
          else{
            return false;
          }

      }


      //[D] ELETE
      public function delete($table, $where = null){
        $del='';
        $con = self::getConnection();

        if($this->tableExists($table)){
            if($where == null)
              {
                //$delete = 'DROP TABLE '.$table;
              }
            else{
                $del = 'DELETE FROM '.$table.' WHERE '.$where;
            }
            try
              {
                  $stmt = $con->prepare($del);
                      try{
                        $con->beginTransaction();
                         $stmt->execute();
                        $con->commit();
                      }
                      catch( PDOException $e)
                      {
                        $con->rollback();
                        return $e->getMessage() . "</br>";
                      }
              }
            catch(PDOException $e)
            {
              return $e->getMessage()."</br>";
            }
        }
        else{
          return false;
        }

      }






    private function tableExists($tbl) //find table if exists
      {

       try{

            $tablesInDb = self::getConnection()->query('SHOW TABLES FROM '.$this->dbname.' LIKE "'.$tbl.'"');
            if($tablesInDb)
            {
              if($tablesInDb->fetch() > 0){
                return true;
              }
              else{
                return false;
              }
            }

       }
       catch(PDOException $e){
          return 'error: '.$e->getMessage();
       }


      }


/*
 *   extra functions
 */


      //placeholders for binding params
      public function placeholders($a = []){

        $bind = [];

        for($i = 0; $i < count($a); $i++){
            $bind[$i] = '?';
        }

        return implode(',',$bind);

      }

      //escapes strings and date values
      public function escapeString($val)
      {

        $new_val = self::getConnection()->quote($val);
        return $new_val;


      }




    }





?>