MVC Architecture

<?php
require_once 'Models/AuthModel.php';

class AuthController {
    private $model;

    public function __construct() {
        if (session_status() === PHP_SESSION_NONE) session_start();
        $this->model = new AuthModel();
    }

    public function index() {
        if (isset($_SESSION['logged_in'])) {
            $this->redirigirSegunGrado($_SESSION['grado']);
            return;
        }
        require_once 'Views/auth/login.php';
    }

    public function login() {
        header('Content-Type: application/json');
        
        if ($_SERVER['REQUEST_METHOD'] === 'POST') {
            $username = trim($_POST['username'] ?? '');
            $password = $_POST['password'] ?? '';

            $user = $this->model->buscarUsuario($username);

            if ($user && $password === $user['PAS']) {
                $_SESSION['user'] = $user['USR'];
                $_SESSION['nombre'] = $user['NOMBRE'];
                $_SESSION['grado'] = $user['GRADO'];
                $_SESSION['logged_in'] = true;
                $_SESSION['last_activity'] = time();
                
                session_regenerate_id(true);

                echo json_encode([
                    'success' => true,
                    'redirect' => $this->getRedirectUrl($user['GRADO'])
                ]);
            } else {
                echo json_encode([
                    'success' => false, 
                    'message' => 'Credenciales incorrectas'
                ]);
            }
        }
    }

    public function logout() {
        session_unset();
        session_destroy();
        header('Location: index.php?url=auth/index');
        exit;
    }

    private function getRedirectUrl($grado) {
        switch ($grado) {
            case 1: 
                return 'index.php?url=home/index'; 
            case 2: 
                return 'index.php?url=devolucion/crear'; 
            case 3: 
                return 'index.php?url=consulta/index';
            default: 
                return 'index.php?url=auth/index';
        }
    }

    private function redirigirSegunGrado($grado) {
        header('Location: ' . $this->getRedirectUrl($grado));
        exit;
    }
}

<?php
require_once 'Config/Conexion.php';

class DevolucionModel {
    private $db;

    public function __construct() {
        $this->db = Conexion::Conectar();
    }

    // ========================================
    // CREATE - Insert new deviation
    // ========================================
    
    public function guardar($datos) {
        $sql = "INSERT INTO devoluciones (
                    nit, nombre_cliente, direccion, item_producto, 
                    descripcion_producto, unidad, kg, motivo, 
                    cantidad_und, cantidad_kg, observacion, 
                    usuario_creador, estado, fecha_creacion, evidencia
                ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 'Pendiente', NOW(), ?)";
        
        $stmt = $this->db->prepare($sql);
        
        return $stmt->execute([
            $datos['nit'],
            $datos['nombre_cliente'],
            $datos['direccion'],
            $datos['item_producto'],
            $datos['descripcion_producto'],
            $datos['unidad'],
            $datos['kg'],
            $datos['motivo'],
            $datos['cantidad_und'],
            $datos['cantidad_kg'],
            $datos['observacion'],
            $datos['usuario_creador'],
            $datos['evidencia'] ?? null
        ]);
    }

    // ========================================
    // READ - Get pending deviations
    // ========================================

    public function obtenerPendientes() {
        $stmt = $this->db->prepare(
            "SELECT * FROM devoluciones 
             WHERE estado = 'Pendiente' 
             ORDER BY fecha_creacion ASC"
        );
        $stmt->execute();
        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }

    // ========================================
    // UPDATE - Process admin review
    // ========================================

    public function procesarRevision($id, $accion, $codigo, $obs, $revisor) {
        try {
            $this->db->beginTransaction();

            $sql = "UPDATE devoluciones 
                    SET estado = ?, 
                        codigo_admin = ?, 
                        observacion_admin = ?, 
                        usuario_revisor = ?, 
                        fecha_revision = NOW() 
                    WHERE id = ?";
            
            $stmt = $this->db->prepare($sql);
            $stmt->execute([$accion, $codigo, $obs, $revisor, $id]);

            $this->db->commit();
            return true;
        } catch (Exception $e) {
            $this->db->rollBack();
            return false;
        }
    }

    // ========================================
    // STATISTICS - Dashboard data
    // ========================================
    
    public function obtenerEstadisticas($fecha = null) {
        $where = $fecha ? "WHERE DATE(fecha_creacion) = :fecha" : "";
        
        $sql = "SELECT 
                    COUNT(*) as total,
                    COALESCE(SUM(cantidad_kg), 0) as total_kg,
                    COALESCE(SUM(cantidad_und), 0) as total_und,
                    
                    COUNT(CASE WHEN estado = 'Pendiente' THEN 1 END) as pendientes,
                    COUNT(CASE WHEN estado = 'Aprobado' THEN 1 END) as aprobados,
                    COUNT(CASE WHEN estado = 'Rechazado' THEN 1 END) as rechazados,
                    
                    COUNT(CASE WHEN motivo = 'Devolucion' THEN 1 END) as motivo_dev,
                    COUNT(CASE WHEN motivo = 'Faltante' THEN 1 END) as motivo_fal,
                    COUNT(CASE WHEN motivo = 'Sobrante' THEN 1 END) as motivo_sob
                FROM devoluciones 
                $where";

        $stmt = $this->db->prepare($sql);
        if ($fecha) $stmt->bindValue(':fecha', $fecha);
        $stmt->execute();
        return $stmt->fetch(PDO::FETCH_ASSOC);
    }

    public function obtenerFechas() {
        $stmt = $this->db->query(
            "SELECT DISTINCT DATE(fecha_creacion) as fecha 
             FROM devoluciones 
             ORDER BY fecha DESC"
        );
        return $stmt->fetchAll(PDO::FETCH_COLUMN);
    }
}