#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <linux/uhid.h>
#include <stdint.h>

static unsigned char rdesc[] = {
    #include "wheel_hid_report_desc.h"
};

static int uhid_write(int fd, const struct uhid_event *ev)
{
	ssize_t ret;

	ret = write(fd, ev, sizeof(*ev));
	if (ret < 0) {
		fprintf(stderr, "Cannot write to uhid: %m\n");
		return -errno;
	} else if (ret != sizeof(*ev)) {
		fprintf(stderr, "Wrong size written to uhid: %zd != %zu\n",
			ret, sizeof(ev));
		return -EFAULT;
	} else {
		return 0;
	}
}

static int create(int fd)
{
	struct uhid_event ev;

	memset(&ev, 0, sizeof(ev));
	ev.type = UHID_CREATE;
	strcpy((char*)ev.u.create.name, "test-uhid-device");
	ev.u.create.rd_data = rdesc;
	ev.u.create.rd_size = sizeof(rdesc);
	ev.u.create.bus = BUS_USB;
	ev.u.create.vendor = 0x15d9;
	ev.u.create.product = 0x0a37;
	ev.u.create.version = 0;
	ev.u.create.country = 0;

	return uhid_write(fd, &ev);
}

static void destroy(int fd)
{
	struct uhid_event ev;

	memset(&ev, 0, sizeof(ev));
	ev.type = UHID_DESTROY;

	uhid_write(fd, &ev);
}

/* This parses raw output reports sent by the kernel to the device. A normal
 * uhid program shouldn't do this but instead just forward the raw report.
 * However, for ducomentational purposes, we try to detect LED events here and
 * print debug messages for it. */
static void handle_output(struct uhid_event *ev)
{
	/* LED messages are adverised via OUTPUT reports; ignore the rest */
	if (ev->u.output.rtype != UHID_OUTPUT_REPORT)
		return;
	/* LED reports have length 2 bytes */
	if (ev->u.output.size != 2)
		return;
	/* first byte is report-id which is 0x02 for LEDs in our rdesc */
	if (ev->u.output.data[0] != 0x2)
		return;

	/* print flags payload */
	fprintf(stderr, "LED output report received with flags %x\n",
		ev->u.output.data[1]);
}

static int event(int fd)
{
	struct uhid_event ev;
	ssize_t ret;

	memset(&ev, 0, sizeof(ev));
	ret = read(fd, &ev, sizeof(ev));
	if (ret == 0) {
		fprintf(stderr, "Read HUP on uhid-cdev\n");
		return -EFAULT;
	} else if (ret < 0) {
		fprintf(stderr, "Cannot read uhid-cdev: %m\n");
		return -errno;
	} else if (ret != sizeof(ev)) {
		fprintf(stderr, "Invalid size read from uhid-dev: %zd != %zu\n",
			ret, sizeof(ev));
		return -EFAULT;
	}

	switch (ev.type) {
	case UHID_START:
		fprintf(stderr, "UHID_START from uhid-dev\n");
		break;
	case UHID_STOP:
		fprintf(stderr, "UHID_STOP from uhid-dev\n");
		break;
	case UHID_OPEN:
		fprintf(stderr, "UHID_OPEN from uhid-dev\n");
		break;
	case UHID_CLOSE:
		fprintf(stderr, "UHID_CLOSE from uhid-dev\n");
		break;
	case UHID_OUTPUT:
		fprintf(stderr, "UHID_OUTPUT from uhid-dev\n");
		handle_output(&ev);
		break;
	case UHID_OUTPUT_EV:
		fprintf(stderr, "UHID_OUTPUT_EV from uhid-dev\n");
		break;
	default:
		fprintf(stderr, "Invalid event from uhid-dev: %u\n", ev.type);
 	}

	return 0;
}

struct my_report {
    uint8_t reportid;
    int8_t a[4];
    uint16_t rest;
} __attribute__((packed)) r = {1};

static int send_event(int fd)
{
	struct uhid_event ev;

	memset(&ev, 0, sizeof(ev));
	ev.type = UHID_INPUT;
	ev.u.input.size = sizeof(r);
    memcpy(ev.u.input.data, &r, sizeof(r));
    
    printf("\n");
    for(size_t i = 0; i < sizeof(r); i++) {
        printf("0x%x ", ev.u.input.data[i]);
    }
    printf("\n");

    printf("Sending event\n");
	return uhid_write(fd, &ev);
}

static int keyboard(int fd)
{
    static int axisidx = 0;
	char buf[128];

	ssize_t ret = read(STDIN_FILENO, buf, sizeof(buf));
	if (ret == 0) {
		fprintf(stderr, "Read HUP on stdin\n");
		return -EFAULT;
	} else if (ret < 0) {
		fprintf(stderr, "Cannot read stdin: %m\n");
		return -errno;
	}

    for(size_t i = 0; i < ret; ++i) {
        if(buf[i] >= '1' && buf[i] <= '8') {
            axisidx = buf[i] - '0' - 1;
            continue;
        }
        
        switch(buf[i]) {
        case 'u': r.a[axisidx] += 2; send_event(fd); break;
        case 'd': r.a[axisidx] -= 2; send_event(fd); break;
        case 'q': return -ECANCELED;
        default:
            fprintf(stderr, "Unknown command %c\n", buf[i]);
        }
    }
    
	return 0;
}

int main(int argc, char **argv)
{
	int fd;
	const char *path = "/dev/uhid";
	struct pollfd pfds[2];
	int ret;
	struct termios state;

	ret = tcgetattr(STDIN_FILENO, &state);
	if (ret) {
		fprintf(stderr, "Cannot get tty state\n");
	} else {
		state.c_lflag &= ~ICANON;
		state.c_cc[VMIN] = 1;
		ret = tcsetattr(STDIN_FILENO, TCSANOW, &state);
		if (ret)
			fprintf(stderr, "Cannot set tty state\n");
	}

	if (argc >= 2) {
		if (!strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
			fprintf(stderr, "Usage: %s [%s]\n", argv[0], path);
			return EXIT_SUCCESS;
		} else {
			path = argv[1];
		}
	}

	fprintf(stderr, "Open uhid-cdev %s\n", path);
	fd = open(path, O_RDWR | O_CLOEXEC);
	if (fd < 0) {
		fprintf(stderr, "Cannot open uhid-cdev %s: %m\n", path);
		return EXIT_FAILURE;
	}

	fprintf(stderr, "Create uhid device\n");
	ret = create(fd);
	if (ret) {
		close(fd);
		return EXIT_FAILURE;
	}

	pfds[0].fd = STDIN_FILENO;
	pfds[0].events = POLLIN;
	pfds[1].fd = fd;
	pfds[1].events = POLLIN;

	fprintf(stderr, "Press 'q' to quit...\n");
	while (1) {
		ret = poll(pfds, 2, -1);
		if (ret < 0) {
			fprintf(stderr, "Cannot poll for fds: %m\n");
			break;
		}
		if (pfds[0].revents & POLLHUP) {
			fprintf(stderr, "Received HUP on stdin\n");
			break;
		}
		if (pfds[1].revents & POLLHUP) {
			fprintf(stderr, "Received HUP on uhid-cdev\n");
			break;
		}

		if (pfds[0].revents & POLLIN) {
			ret = keyboard(fd);
			if (ret)
				break;
		}
		if (pfds[1].revents & POLLIN) {
			ret = event(fd);
			if (ret)
				break;
		}
	}

	fprintf(stderr, "Destroy uhid device\n");
	destroy(fd);
	return EXIT_SUCCESS;
}