#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#include <linux/spi/spidev.h>

#include <gpiod.h>
#include <pthread.h>

#include "msgq.h"
#include "tun.h"
#include "spi.h"

static pthread_t worker_thd;
static pthread_t rtscts_thd;
static pthread_t msg_handler_thd;
static pthread_t tun_handler_thd;
static pthread_mutex_t mutex;
static pthread_cond_t cond;

static MSGQueue spi_bufq;
static unsigned char *spi_bufq_array[SPI_SIZE_BUFQ];

static MSGQueue spi_msgq_in;
static unsigned char *spi_msgq_in_array[SPI_SIZE_MSGQ_IN];

static MSGQueue spi_msgq_out;
static unsigned char *spi_msgq_out_array[SPI_SIZE_MSGQ_OUT];

static uint32_t spi_speed = SPI_SPEED;
static int spi_fd;
static volatile int spi_cts;

struct gpiod_line_request *request = NULL;

static void _spi_wait4cts(void) {
    pthread_mutex_lock(&mutex);
    while (!spi_cts) {
        pthread_cond_wait(&cond, &mutex);
    }
    spi_cts = 0;
    pthread_mutex_unlock(&mutex);
}

static int _spi_xchg(unsigned char *buffer) {
    int rv;
    uint16_t len_tx;
    uint16_t len_rx;
    struct spi_ioc_transfer tr;

    memset(&tr, 0, sizeof(tr));
    tr.tx_buf = (unsigned long)buffer;
    tr.rx_buf = (unsigned long)buffer;
    tr.speed_hz = spi_speed;

    len_tx  = (uint16_t)buffer[1] << 8;
    len_tx |= (uint16_t)buffer[2] & 0xFF;
    if (len_tx > SPI_MTU) return SPI_ERR;

    if (buffer[0]) {
        len_tx += SPI_SIZE_HDR;
        // esp32 dma workaraund
        if (len_tx < 8) {
            len_tx = 8;
        } else if (len_tx % 4 != 0) {
            len_tx = (len_tx / 4 + 1) * 4;
        }

        tr.len = len_tx;
    } else {
        /* nothing to send, reset esp32 spi transaction */
        tr.len = 1;

        _spi_wait4cts();
        rv = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr);
        if (rv < 0) return SPI_ERR_MSG;

        /* receive SPI_SIZE_RECEIVE bytes in first transaction (estimate) */
        len_tx = SPI_SIZE_RECEIVE + SPI_SIZE_HDR;
        tr.len = len_tx;
        buffer[1] = 0;
        buffer[2] = 0;
    }

    _spi_wait4cts();
    rv = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr);
    if (rv < 0) return SPI_ERR_MSG;

    len_rx  = (uint16_t)buffer[1] << 8;
    len_rx |= (uint16_t)buffer[2] & 0xFF;
    if (len_rx > SPI_MTU) return SPI_ERR;

    len_rx += SPI_SIZE_HDR;
    if (len_rx > len_tx) {
        tr.tx_buf = (unsigned long)NULL;
        tr.rx_buf = (unsigned long)(buffer + len_tx);

        len_tx = len_rx - len_tx;
        // esp32 dma workaraund
        if (len_tx < 8) {
            len_tx = 8;
        } else if (len_tx % 4 != 0) {
            len_tx = (len_tx / 4 + 1) * 4;
        }

        tr.len = len_tx;

        _spi_wait4cts();
        rv = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr);
        if (rv < 0) return SPI_ERR_MSG;
    }

    return SPI_OK;
}

static void *worker(void *arg) {
    MSGQueue *bufq = &spi_bufq;
    MSGQueue *msgq_in = &spi_msgq_in;
    MSGQueue *msgq_out = &spi_msgq_out;
    int rv;
    unsigned char *buffer;

    while (1) {
        pthread_mutex_lock(&msgq_out->mutex);
        buffer = msgq_pop(msgq_out);
        if ((buffer == NULL) && (gpiod_line_request_get_value(request, SPI_GPIO_RTS) == GPIOD_LINE_VALUE_INACTIVE)) {
            pthread_mutex_lock(&bufq->mutex);
            buffer = msgq_pop(bufq);
            pthread_mutex_unlock(&bufq->mutex);
        }
        if (buffer == NULL) {
            pthread_cond_wait(&msgq_out->cond, &msgq_out->mutex);
            buffer = msgq_pop(msgq_out);
        }
        pthread_mutex_unlock(&msgq_out->mutex);
        if (buffer) {
            rv = _spi_xchg(buffer);
            if (rv || (buffer[0] == 0)) {
                buffer[0] = 0;
                buffer[1] = 0;
                buffer[2] = 0;
                pthread_mutex_lock(&bufq->mutex);
                msgq_push(bufq, buffer);
                pthread_mutex_unlock(&bufq->mutex);
            } else {
                pthread_mutex_lock(&msgq_in->mutex);
                rv = msgq_push(msgq_in, buffer);
                if (rv == MSGQ_OK) pthread_cond_signal(&msgq_in->cond);
                pthread_mutex_unlock(&msgq_in->mutex);

                if (rv) {
                    pthread_mutex_lock(&bufq->mutex);
                    msgq_push(bufq, buffer);
                    pthread_mutex_unlock(&bufq->mutex);
                }
            }
        }
    }

    return NULL;
}

static void *rtscts_handler(void *arg) {
    MSGQueue *msgq_out = &spi_msgq_out;
    struct gpiod_edge_event_buffer *event_buffer;
    struct gpiod_edge_event *event;
    int rv;

    event_buffer = gpiod_edge_event_buffer_new(1);

    while (1) {
        rv = gpiod_line_request_read_edge_events(request, event_buffer, 1);
        if (rv != 1) continue;

        event = gpiod_edge_event_buffer_get_event(event_buffer, 0);
        switch (gpiod_edge_event_get_line_offset(event)) {
            case SPI_GPIO_RTS: {
                pthread_mutex_lock(&msgq_out->mutex);
                pthread_cond_signal(&msgq_out->cond);
                pthread_mutex_unlock(&msgq_out->mutex);
                break;
            }

            case SPI_GPIO_CTS: {
                pthread_mutex_lock(&mutex);
                spi_cts = 1;
                pthread_cond_signal(&cond);
                pthread_mutex_unlock(&mutex);
                break;
            }
        }
    }

    gpiod_edge_event_buffer_free(event_buffer);
    return NULL;
}

static void *msg_handler(void *arg) {
    MSGQueue *bufq = &spi_bufq;
    MSGQueue *msgq_in = &spi_msgq_in;
    unsigned char *buffer;
    unsigned char mtype;
    uint16_t len;
    int rv;

    while (1) {
        pthread_mutex_lock(&msgq_in->mutex);
        buffer = msgq_pop(msgq_in);
        if (buffer == NULL) {
            pthread_cond_wait(&msgq_in->cond, &msgq_in->mutex);
            buffer = msgq_pop(msgq_in);
        }
        pthread_mutex_unlock(&msgq_in->mutex);
        if (buffer) {
            mtype = buffer[0];
            len  = (uint16_t)buffer[1] << 8;
            len |= (uint16_t)buffer[2] & 0xFF;

            switch (mtype) {
                case SPI_MTYPE_TUN:
                    tun_write(buffer + SPI_SIZE_HDR, len);
                    break;
            }
            buffer[0] = 0;
            buffer[1] = 0;
            buffer[2] = 0;
            pthread_mutex_lock(&bufq->mutex);
            msgq_push(bufq, buffer);
            pthread_mutex_unlock(&bufq->mutex);
        }
    }

    return NULL;
}

static void *tun_handler(void *arg) {
    unsigned char *buffer;
    ssize_t len;

    while (1) {
        buffer = spi_alloc();
        if (buffer == NULL) continue;

        len = tun_read(buffer + SPI_SIZE_HDR, SPI_SIZE_BUF - SPI_SIZE_HDR);
        if (len < 0) {
            perror("tun read");
            continue;
        }
        spi_xchg(SPI_MTYPE_TUN, buffer, len);
    }

    return NULL;
}

unsigned char *spi_alloc(void) {
    MSGQueue *bufq = &spi_bufq;
    unsigned char *buffer;

    pthread_mutex_lock(&bufq->mutex);
    buffer = msgq_pop(bufq);
    pthread_mutex_unlock(&bufq->mutex);

    return buffer;
}

void spi_free(unsigned char *buffer) {
    MSGQueue *bufq = &spi_bufq;

    buffer[0] = 0;
    buffer[1] = 0;
    buffer[2] = 0;
    pthread_mutex_lock(&bufq->mutex);
    msgq_push(bufq, buffer);
    pthread_mutex_unlock(&bufq->mutex);
}

int spi_xchg(unsigned char mtype, unsigned char *buffer, uint16_t len) {
    MSGQueue *bufq = &spi_bufq;
    MSGQueue *msgq_out = &spi_msgq_out;
    int rv;

    buffer[0] = mtype;
    buffer[1] = len >> 8;
    buffer[2] = len & 0xFF;

    pthread_mutex_lock(&msgq_out->mutex);
    rv = msgq_push(msgq_out, buffer);
    if (rv == MSGQ_OK) pthread_cond_signal(&msgq_out->cond);
    pthread_mutex_unlock(&msgq_out->mutex);

    if (rv) {
        pthread_mutex_lock(&bufq->mutex);
        msgq_push(bufq, buffer);
        pthread_mutex_unlock(&bufq->mutex);
    }

    return rv;
}

int gpio_init(void) {
    struct gpiod_chip *chip = NULL;
    struct gpiod_line_settings *line_settings = NULL;
    struct gpiod_line_config *line_cfg = NULL;
    struct gpiod_request_config *req_cfg = NULL;
    int rv;

    unsigned int line_offsets[2] = { SPI_GPIO_RTS, SPI_GPIO_CTS };

    chip = gpiod_chip_open(SPI_GPIO_DEV);
    if (chip == NULL) goto gpio_init_fin;

    line_settings = gpiod_line_settings_new();
    if (line_settings == NULL) goto gpio_init_fin;

    gpiod_line_settings_set_direction(line_settings, GPIOD_LINE_DIRECTION_INPUT);
    gpiod_line_settings_set_edge_detection(line_settings, GPIOD_LINE_EDGE_FALLING);
    gpiod_line_settings_set_bias(line_settings, GPIOD_LINE_BIAS_PULL_UP);

    line_cfg = gpiod_line_config_new();
    if (line_cfg == NULL) goto gpio_init_fin;

    rv = gpiod_line_config_add_line_settings(line_cfg, line_offsets, 2, line_settings);
    if (rv) goto gpio_init_fin;

    req_cfg = gpiod_request_config_new();
    if (req_cfg == NULL) goto gpio_init_fin;

    gpiod_request_config_set_consumer(req_cfg, "rts-cts");

    request = gpiod_chip_request_lines(chip, req_cfg, line_cfg);

gpio_init_fin:
    rv = (request ? SPI_OK : (chip ? SPI_ERR : SPI_ERR_OPEN));

    if (req_cfg) gpiod_request_config_free(req_cfg);
    if (line_cfg) gpiod_line_config_free(line_cfg);
    if (line_settings) gpiod_line_settings_free(line_settings);
    if (chip) gpiod_chip_close(chip);

    return rv;
}

int spi_init(void) {
    unsigned char *buffer;
    int rv, i;

    spi_fd = open(SPI_DEV, O_RDWR);
    if (spi_fd < 0) return SPI_ERR_OPEN;

    rv = ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &spi_speed);
    if (rv == -1) return SPI_ERR;

    rv = msgq_init(&spi_bufq, spi_bufq_array, SPI_SIZE_BUFQ);
    assert(rv == MSGQ_OK);

    rv = msgq_init(&spi_msgq_in, spi_msgq_in_array, SPI_SIZE_MSGQ_IN);
    assert(rv == MSGQ_OK);

    rv = msgq_init(&spi_msgq_out, spi_msgq_out_array, SPI_SIZE_MSGQ_OUT);
    assert(rv == MSGQ_OK);

    for (i=0; i<SPI_SIZE_BUFQ; i++) {
        buffer = malloc(SPI_SIZE_BUF);
        assert(buffer);
        msgq_push(&spi_bufq, buffer);
    }

    rv = pthread_mutex_init(&mutex, NULL);
    assert(rv == 0);

    rv = pthread_cond_init(&cond, NULL);
    assert(rv == 0);

    /* assret initial contitions */
    pthread_mutex_lock(&mutex);
    spi_cts = (gpiod_line_request_get_value(request, SPI_GPIO_CTS) == GPIOD_LINE_VALUE_INACTIVE);
    pthread_mutex_unlock(&mutex);

    rv = pthread_create(&worker_thd, NULL, worker, NULL);
    assert(rv == 0);

    rv = pthread_create(&rtscts_thd, NULL, rtscts_handler, NULL);
    assert(rv == 0);

    rv = pthread_create(&msg_handler_thd, NULL, msg_handler, NULL);
    assert(rv == 0);

    rv = pthread_create(&tun_handler_thd, NULL, tun_handler, NULL);
    assert(rv == 0);

    return SPI_OK;
}

int main(int argc, char *argv[]) {
    int rv;

    rv = tun_init(SPI_TUN_NAME);
    if (rv) printf("TUN INIT ERR\n");

    rv = gpio_init();
    if (rv) printf("GPIO INIT ERR\n");

    rv = spi_init();
    if (rv) printf("SPI INIT ERR\n");

    while (1);
}