/* SPDX-License-Identifier: BSD-2-Clause */

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdbool.h>

#define CUR_PATH "/sys/class/backlight/intel_backlight/brightness"
#define MAX_PATH "/sys/class/backlight/intel_backlight/max_brightness"
#define STEP     10

struct brightness {
    int max_raw;
    int raw;
    int percents;
};



int readval(const char *path, int *dst)
{
    FILE *f = fopen(path, "r");
    int retval = 1;

    if (f == NULL) {
        perror(path);
        goto end;
    }

    int raw;
    if (fscanf(f, "%d", &raw) != 1) {
        perror(path);
        goto end;
    }

    *dst = raw;
    retval = 0;

end:
    if (f != NULL)
        fclose(f);
    return retval;
}


int get(struct brightness *dst)
{
    int retval = 1;
    if (readval(CUR_PATH, &dst->raw))
        goto end;
    if (readval(MAX_PATH, &dst->max_raw))
        goto end;

    dst->percents = (int)round((double)dst->raw*100/dst->max_raw);
    retval = 0;

end:
    return retval;
}

int set(struct brightness *src)
{
    int retval = 1;
    FILE *f = fopen(CUR_PATH, "w");
    if (!f) {
        perror(CUR_PATH);
        goto end;
    }

    fprintf(f, "%d", src->raw);
    retval = 0;

end:
    if (f != NULL)
        fclose(f);
    return retval;
}

void adjust(struct brightness *b, int value)
{
    b->percents += value;
    if (b->percents > 100)
        b->percents = 100;
    else if (b->percents < 0)
        b->percents = 0;
    b->raw = (int)ceil((double)b->percents*b->max_raw/100);
}


void dump(struct brightness *b)
{
    printf("%d (%d%%)\n", b->raw, b->percents);
}


int main(int argc, char** argv)
{
    int retval = 0;
    struct brightness b;
    int adjust_val = STEP;
    bool decr = false;

    if (argc > 1 && strcmp(argv[1], "-h") == 0) {
        printf("usage: %s [-h] [+/-]\n", argv[0]);
        goto end;
    }

    if (get(&b))
        goto end;

    if (argc <= 1) {
        dump(&b);
        goto end;
    }

    if (strcmp(argv[1], "-") == 0)
        decr = true;
    else if (strcmp(argv[1], "+") != 0) {
        fprintf(stderr, "%s: unknown argument\n", argv[1]);
        retval = 1;
        goto end;
    }

    if (decr)
        adjust_val *= -1;

    adjust(&b, adjust_val);
    if (set(&b)) {
        retval = 1;
        goto end;
    }

    dump(&b);

end:
    return retval;
}