#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
#include <zephyr/usb/usb_device.h>
#include <zephyr/drivers/uart.h>
#include <zephyr/sys/ring_buffer.h> /* NEU */

#include <io.h>

LOG_MODULE_REGISTER(usb, LOG_LEVEL_INF);

K_SEM_DEFINE(usb_rx_sem, 0, 1);
K_SEM_DEFINE(usb_tx_sem, 0, 1);

#define UART_NODE DT_ALIAS(usb_uart)
const struct device *cdc_dev = DEVICE_DT_GET(UART_NODE);

/* NEU: Ringbuffer für stabilen asynchronen USB-Empfang */
#define RX_RING_BUF_SIZE 4096
RING_BUF_DECLARE(rx_ringbuf, RX_RING_BUF_SIZE);

static void cdc_acm_irq_cb(const struct device *dev, void *user_data)
{
    ARG_UNUSED(user_data);

    if (!uart_irq_update(dev)) {
        return;
    }

    if (uart_irq_rx_ready(dev)) {
        uint8_t buffer[64];
        uint32_t space = ring_buf_space_get(&rx_ringbuf);
        
        if (space == 0) {
            /* Backpressure anwenden: Ringpuffer ist voll.
               Interrupt deaktivieren, damit Daten im HW-FIFO bleiben 
               und der USB-Stack den Host drosselt (NAK). */
            uart_irq_rx_disable(dev);
        } else {
            /* Nur so viele Daten lesen, wie Platz im Ringpuffer ist */
            int to_read = MIN(sizeof(buffer), space);
            int len = uart_fifo_read(dev, buffer, to_read);
            
            if (len > 0) {
                ring_buf_put(&rx_ringbuf, buffer, len);
                k_sem_give(&usb_rx_sem);
            }
        }
    }

    if (uart_irq_tx_ready(dev)) {
        uart_irq_tx_disable(dev);
        k_sem_give(&usb_tx_sem);
    }
}

bool usb_wait_for_data(k_timeout_t timeout)
{
    if (!ring_buf_is_empty(&rx_ringbuf)) {
        return true;
    }
    
    /* Wenn der Puffer leer ist, sicherstellen, dass der RX-Interrupt 
       aktiviert ist, da sonst keine neuen Daten empfangen werden können. */
    if (device_is_ready(cdc_dev)) {
        uart_irq_rx_enable(cdc_dev);
    }
    
    return (k_sem_take(&usb_rx_sem, timeout) == 0);
}

int usb_read_char(uint8_t *c)
{
    int ret = ring_buf_get(&rx_ringbuf, c, 1);
    if (ret > 0 && device_is_ready(cdc_dev)) {
        /* Platz geschaffen -> Empfang wieder aktivieren */
        uart_irq_rx_enable(cdc_dev);
    }
    return ret;
}

int usb_read_buffer(uint8_t *buf, size_t max_len)
{
    int ret = ring_buf_get(&rx_ringbuf, buf, max_len);
    if (ret > 0 && device_is_ready(cdc_dev)) {
        /* Platz geschaffen -> Empfang wieder aktivieren */
        uart_irq_rx_enable(cdc_dev);
    }
    return ret;
}

void usb_resume_rx(void)
{
    if (device_is_ready(cdc_dev)) {
        uart_irq_rx_enable(cdc_dev);
    }
}

void usb_write_char(uint8_t c)
{
    if (!device_is_ready(cdc_dev)) {
        return;
    }
    uart_poll_out(cdc_dev, c);
}

void usb_write_buffer(const uint8_t *buf, size_t len)
{
    if (!device_is_ready(cdc_dev))
    {
        return;
    }

    size_t written;
    while (len > 0)
    {
        written = uart_fifo_fill(cdc_dev, buf, len);

        len -= written;
        buf += written;

        if (len > 0)
        {
            uart_irq_tx_enable(cdc_dev);
            if (k_sem_take(&usb_tx_sem, K_MSEC(100)) != 0)
            {
                LOG_WRN("USB TX timeout - consumer not reading?");
                return;
            }
        }
    }
}

void usb_flush_rx(void)
{
    uint8_t dummy;
    if (!device_is_ready(cdc_dev)) return;
    
    /* Hardware-FIFO leeren, falls Reste vorhanden */
    while (uart_fifo_read(cdc_dev, &dummy, 1) > 0);
    
    /* Ringpuffer und Semaphore zurücksetzen */
    ring_buf_reset(&rx_ringbuf);
    k_sem_reset(&usb_rx_sem);
}

static void usb_status_cb(enum usb_dc_status_code cb_status, const uint8_t *param)
{
    switch (cb_status) {
    case USB_DC_CONNECTED:
        /* VBUS wurde vom Zephyr-Stack erkannt */
        LOG_DBG("VBUS detected, USB device connected");
        break;
    case USB_DC_CONFIGURED:
        LOG_DBG("USB device configured by host");
        io_usb_status(true);
        if (device_is_ready(cdc_dev)) {
            (void)uart_line_ctrl_set(cdc_dev, UART_LINE_CTRL_DCD, 1);
            (void)uart_line_ctrl_set(cdc_dev, UART_LINE_CTRL_DSR, 1);
            
            /* Interrupt-Handler binden und initial aktivieren */
            uart_irq_callback_set(cdc_dev, cdc_acm_irq_cb);
            uart_irq_rx_enable(cdc_dev);
        }
        break;
    case USB_DC_DISCONNECTED:
        /* Kabel wurde gezogen */
        LOG_DBG("VBUS removed, USB device disconnected");
        if (device_is_ready(cdc_dev)) {
            uart_irq_rx_disable(cdc_dev);
        }
        io_usb_status(false);
        break;
    case USB_DC_RESET:
        LOG_DBG("USB bus reset");
        break;
    default:
        break;
    }
}

int usb_cdc_acm_init(void)
{
    LOG_DBG("Initializing USB Stack...");

    /* Zephyr-Treiber registrieren. Verbraucht keinen Strom ohne VBUS. */
    int ret = usb_enable(usb_status_cb);
    if (ret != 0) {
        LOG_ERR("Failed to enable USB (%d)", ret);
        return ret;
    }

#if DT_NODE_HAS_STATUS(DT_NODELABEL(cdc_acm_uart0), okay)
    const struct device *cdc_dev = DEVICE_DT_GET(DT_NODELABEL(cdc_acm_uart0));

    if (!device_is_ready(cdc_dev)) {
        LOG_ERR("CDC ACM device not ready");
        return -ENODEV;
    }

#else
    LOG_ERR("CDC ACM UART device not found in devicetree");
    return -ENODEV;
#endif

    LOG_DBG("USB Stack enabled and waiting for VBUS in hardware");
    return 0;
}