/*
 * gpro-battery-openbsd.c
 *
 * Minimal OpenBSD userland tool: Logitech G PRO X Wireless battery via /dev/uhidX
 * heavily inspired by 
 * https://github.com/Sapd/HeadsetControl/blob/master/src/devices/logitech_gpro.c
 *
 * TX (19 bytes): ff 06 0d 00...
 * RX (19 bytes): on this device, voltage/status are at:
 *   voltage_raw = (rx[3] << 8) | rx[4]
 *   charging    = (rx[5] == 0x03)
 *
 * Prints:
 *   voltage_raw=<u16>
 *   percent_est=<0..100>   (simple linear approximation)
 *   charging=yes|no
 */

#include <err.h>
#include <fcntl.h>
#include <poll.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

static int
read_timeout(int fd, uint8_t *buf, size_t len, int ms)
{
    struct pollfd pfd = { .fd = fd, .events = POLLIN };
    int r = poll(&pfd, 1, ms);
    if (r == -1)
        err(1, "poll");
    if (r == 0)
        return 0;

    ssize_t n = read(fd, buf, len);
    if (n == -1)
        err(1, "read");
    return (int)n;
}

static double
percent_estimate(uint16_t vraw)
{
    /* Linear clamp: 3300 -> 0%, 4200 -> 100% (approximation) */
    const double vmin = 3300.0, vmax = 4200.0;
    if ((double)vraw <= vmin) return 0.0;
    if ((double)vraw >= vmax) return 100.0;
    return ((double)vraw - vmin) * 100.0 / (vmax - vmin);
}

int
main(int argc, char **argv)
{
    const char *dev = (argc > 1) ? argv[1] : "/dev/uhid0";

    int fd = open(dev, O_RDWR | O_NONBLOCK);
    if (fd == -1)
        err(1, "open %s", dev);

    uint8_t tx[19];
    memset(tx, 0, sizeof(tx));
    tx[0] = 0xff;
    tx[1] = 0x06;
    tx[2] = 0x0d;

    if (write(fd, tx, sizeof(tx)) != (ssize_t)sizeof(tx))
        err(1, "write");

    uint8_t rx[19];
    int n = read_timeout(fd, rx, sizeof(rx), 500);
    if (n <= 0)
        errx(1, "no response");
    if (n != (int)sizeof(rx))
        errx(1, "short read: %d bytes", n);

    uint16_t voltage_raw = (uint16_t)((rx[3] << 8) | rx[4]);
    int charging = (rx[5] == 0x03);
    double pct = percent_estimate(voltage_raw);

    printf("voltage_raw=%u\n", voltage_raw);
    printf("percent_est=%.1f\n", pct);
    printf("charging=%s\n", charging ? "yes" : "no");

    close(fd);
    return 0;
}