<?php
class DB {
    private static $instance = null;
    private $pdo;
    private $query;
    private $error = false;
    private $results;
    private $count = 0;
    
    private function __construct() {
        try {
            $this->pdo = new PDO("mysql:host=" . DB_HOST . ";dbname=" . DB_NAME, DB_USER, DB_PASS);
            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $this->pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);
        } catch(PDOException $e) {
            die("Database connection failed: " . $e->getMessage());
        }
    }
    
    public static function getInstance() {
        if(!self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    
    public function query($sql, $params = []) {
        $this->error = false;
        if($this->query = $this->pdo->prepare($sql)) {
            $x = 1;
            if(count($params)) {
                foreach($params as $param) {
                    $this->query->bindValue($x, $param);
                    $x++;
                }
            }
            if($this->query->execute()) {
                $this->results = $this->query->fetchAll();
                $this->count = $this->query->rowCount();
            } else {
                $this->error = true;
            }
        }
        return $this;
    }
    
    public function action($action, $table, $where = []) {
        if(count($where) === 3) {
            $operators = ["=", ">", "<", ">=", "<=", "<>", "LIKE", "NOT LIKE"];
            $field = $where[0];
            $operator = $where[1];
            $value = $where[2];
            
            if(in_array($operator, $operators)) {
                $sql = "{$action} FROM {$table} WHERE {$field} {$operator} ?";
                if(!$this->query($sql, [$value])->error()) {
                    return $this;
                }
            }
        }
        return false;
    }
    
    public function get($table, $where) {
        return $this->action("SELECT *", $table, $where);
    }
    
    public function delete($table, $where) {
        return $this->action("DELETE", $table, $where);
    }
    
    public function insert($table, $fields = []) {
        $keys = array_keys($fields);
        $values = "";
        $x = 1;
        
        foreach($fields as $field) {
            $values .= "?";
            if($x < count($fields)) {
                $values .= ", ";
            }
            $x++;
        }
        
        $sql = "INSERT INTO {$table} (`" . implode("`, `", $keys) . "`) VALUES ({$values})";
        
        if(!$this->query($sql, $fields)->error()) {
            return $this->pdo->lastInsertId();
        }
        return false;
    }
    
    public function update($table, $id, $fields) {
        $set = "";
        $x = 1;
        
        foreach($fields as $name => $value) {
            $set .= "{$name} = ?";
            if($x < count($fields)) {
                $set .= ", ";
            }
            $x++;
        }
        
        $sql = "UPDATE {$table} SET {$set} WHERE id = {$id}";
        if(!$this->query($sql, $fields)->error()) {
            return true;
        }
        return false;
    }
    
    public function results() {
        return $this->results;
    }
    
    public function first() {
        return $this->results()[0] ?? null;
    }
    
    public function count() {
        return $this->count;
    }
    
    public function error() {
        return $this->error;
    }
}