#include "qemu/osdep.h"
#include "hw/core/sysbus.h"
#include "hw/core/irq.h"
#include "hw/core/qdev-properties-system.h"
#include "qemu/log.h"
#include "qemu/module.h"
#include "chardev/char-fe.h"

#define TYPE_S5L8950X_UART "s5l8950x-uart"
OBJECT_DECLARE_SIMPLE_TYPE(S5L8950XUartState, S5L8950X_UART)

#define S5L8950X_UART_RX_FIFO_SIZE 16

struct S5L8950XUartState {
    SysBusDevice parent_obj;

    MemoryRegion iomem;
    CharFrontend chr;

    uint32_t ulcon;
    uint32_t ucon;
    uint32_t ufcon;
    uint32_t umcon;
    uint32_t ubrdiv;
    uint32_t ufracval;

    uint8_t rx_fifo[S5L8950X_UART_RX_FIFO_SIZE];
    int rx_count;
    qemu_irq irq;
};

#define UART_ULCON    0x00
#define UART_UCON     0x04
#define UART_UFCON    0x08
#define UART_UMCON    0x0C
#define UART_UTRSTAT  0x10
#define UART_UERSTAT  0x14
#define UART_UFSTAT   0x18
#define UART_UMSTAT   0x1C
#define UART_UTXH     0x20
#define UART_URXH     0x24
#define UART_UBRDIV   0x28
#define UART_UFRACVAL 0x2C

#define UART_UFCON_RX_FIFO_RESET BIT(1)
#define UART_UFCON_TX_FIFO_RESET BIT(2)

static void s5l8950x_uart_update_irq(S5L8950XUartState *s)
{
    if (s->rx_count > 0) {
        qemu_irq_raise(s->irq);
    } else {
        qemu_irq_lower(s->irq);
    }
}

static uint64_t s5l8950x_uart_read(void *opaque, hwaddr offset, unsigned size)
{
    S5L8950XUartState *s = S5L8950X_UART(opaque);
    uint32_t val = 0;

    switch (offset) {
    case UART_ULCON:
        val = s->ulcon;
        break;
    case UART_UCON:
        val = s->ucon;
        break;
    case UART_UFCON:
        val = s->ufcon;
        break;
    case UART_UMCON:
        val = s->umcon;
        break;
    case UART_UTRSTAT:
        /* Bit 0: rx ready, Bit 1: tx buf empty, Bit 2: tx empty */
        val = 0x6 | (s->rx_count > 0 ? 1 : 0);
        break;
    case UART_UERSTAT:
        val = 0;
        break;
    case UART_UFSTAT:
        /* Return rx count in low bits, no tx fifo used here */
        val = s->rx_count;
        break;
    case UART_UMSTAT:
        val = 0;
        break;
    case UART_UTXH:
        break;
    case UART_URXH:
        if (s->rx_count > 0) {
            val = s->rx_fifo[0];
            s->rx_count--;
            memmove(s->rx_fifo, s->rx_fifo + 1, s->rx_count);
            s5l8950x_uart_update_irq(s);
            qemu_chr_fe_accept_input(&s->chr);
        }
        break;
    case UART_UBRDIV:
        val = s->ubrdiv;
        break;
    case UART_UFRACVAL:
        val = s->ufracval;
        break;
    default:
        qemu_log_mask(LOG_UNIMP, "%s: Unimplemented read at offset 0x%" HWADDR_PRIx "\n",
                      __func__, offset);
        break;
    }
    return val;
}

static void s5l8950x_uart_write(void *opaque, hwaddr offset, uint64_t val, unsigned size)
{
    S5L8950XUartState *s = S5L8950X_UART(opaque);
    unsigned char c;

    switch (offset) {
    case UART_ULCON:
        s->ulcon = val;
        break;
    case UART_UCON:
        s->ucon = val;
        break;
    case UART_UFCON:
        if (val & UART_UFCON_RX_FIFO_RESET) {
            s->rx_count = 0;
            s5l8950x_uart_update_irq(s);
            qemu_chr_fe_accept_input(&s->chr);
        }
        /* FIFO reset bits are self-clearing; TX is unbuffered. */
        s->ufcon = val & ~(UART_UFCON_RX_FIFO_RESET |
                           UART_UFCON_TX_FIFO_RESET);
        break;
    case UART_UMCON:
        s->umcon = val;
        break;
    case UART_UTRSTAT:
    case UART_UERSTAT:
    case UART_UFSTAT:
    case UART_UMSTAT:
        /* Read-only registers */
        break;
    case UART_UTXH:
        c = val & 0xFF;
        qemu_chr_fe_write_all(&s->chr, &c, 1);
        break;
    case UART_URXH:
        break;
    case UART_UBRDIV:
        s->ubrdiv = val;
        break;
    case UART_UFRACVAL:
        s->ufracval = val;
        break;
    default:
        qemu_log_mask(LOG_UNIMP, "%s: Unimplemented write at offset 0x%" HWADDR_PRIx "\n",
                      __func__, offset);
        break;
    }
}

static const MemoryRegionOps s5l8950x_uart_ops = {
    .read = s5l8950x_uart_read,
    .write = s5l8950x_uart_write,
    .endianness = DEVICE_LITTLE_ENDIAN,
    .valid = {
        .min_access_size = 1,
        .max_access_size = 4,
    },
    .impl = {
        .min_access_size = 1,
        .max_access_size = 4,
    },
};

static int s5l8950x_uart_can_receive(void *opaque)
{
    S5L8950XUartState *s = S5L8950X_UART(opaque);

    return S5L8950X_UART_RX_FIFO_SIZE - s->rx_count;
}

static void s5l8950x_uart_receive(void *opaque, const uint8_t *buf, int size)
{
    S5L8950XUartState *s = S5L8950X_UART(opaque);
    int i;

    for (i = 0; i < size &&
                s->rx_count < S5L8950X_UART_RX_FIFO_SIZE; i++) {
        s->rx_fifo[s->rx_count++] = buf[i];
    }
    s5l8950x_uart_update_irq(s);
}

static void s5l8950x_uart_reset(DeviceState *dev)
{
    S5L8950XUartState *s = S5L8950X_UART(dev);

    s->ulcon = 0;
    s->ucon = 0;
    s->ufcon = 0;
    s->umcon = 0;
    s->ubrdiv = 0;
    s->ufracval = 0;
    s->rx_count = 0;
    s5l8950x_uart_update_irq(s);
}

static void s5l8950x_uart_realize(DeviceState *dev, Error **errp)
{
    S5L8950XUartState *s = S5L8950X_UART(dev);

    qemu_chr_fe_set_handlers(&s->chr, s5l8950x_uart_can_receive,
                             s5l8950x_uart_receive, NULL, NULL,
                             s, NULL, true);
}

static void s5l8950x_uart_init(Object *obj)
{
    SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
    S5L8950XUartState *s = S5L8950X_UART(obj);

    memory_region_init_io(&s->iomem, obj, &s5l8950x_uart_ops, s,
                          TYPE_S5L8950X_UART, 0x100);
    sysbus_init_mmio(sbd, &s->iomem);
    sysbus_init_irq(sbd, &s->irq);
}

static const Property s5l8950x_uart_properties[] = {
    DEFINE_PROP_CHR("chardev", S5L8950XUartState, chr),
};

static void s5l8950x_uart_class_init(ObjectClass *klass, const void *data)
{
    DeviceClass *dc = DEVICE_CLASS(klass);

    device_class_set_legacy_reset(dc, s5l8950x_uart_reset);
    dc->realize = s5l8950x_uart_realize;
    device_class_set_props(dc, s5l8950x_uart_properties);
}

static const TypeInfo s5l8950x_uart_info = {
    .name          = TYPE_S5L8950X_UART,
    .parent        = TYPE_SYS_BUS_DEVICE,
    .instance_size = sizeof(S5L8950XUartState),
    .instance_init = s5l8950x_uart_init,
    .class_init    = s5l8950x_uart_class_init,
};

static void s5l8950x_uart_register_types(void)
{
    type_register_static(&s5l8950x_uart_info);
}

type_init(s5l8950x_uart_register_types)