#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#define BUF_SIZE 100
#define KBD_MAX_PATH        "/sys/class/leds/tpacpi::kbd_backlight/max_brightness"
#define KBD_BRIGHTNESS_PATH "/sys/class/leds/tpacpi::kbd_backlight/brightness"

#define KBD_ERROR_ARGS -1
#define KBD_ERROR_MEM  -2
#define KBD_SUCCESS    1

typedef enum direction { BL_DOWN, BL_UP, BL_OFF, BL_MAX } direction_t;

int read_int(const char *path, int *value);
int write_int(const char *path, int value);
int bl_new(int current, int max, direction_t direction);
void usage(const char *name);
int get_direction(const char *str, direction_t *dir);

int main(int argc, char *argv[]) {
    int bl_max = -1, bl_current = -1, bl;
    direction_t direction;

    if (argc < 2) {
        usage(argv[0]);
        return -1;
    }

    if (get_direction(argv[1], &direction) != KBD_SUCCESS) {
        fprintf(stderr, "E: Unexpected argument \"%s\"\n", argv[1]);
        usage(argv[0]);
        return 1;
    }

    if (read_int(KBD_MAX_PATH, &bl_max) != KBD_SUCCESS) {
        fprintf(stderr, "E: Failed to read maximum brightness from \"%s\"\n", KBD_MAX_PATH);
        usage(argv[0]);
        return 1;
    }

    if (read_int(KBD_BRIGHTNESS_PATH, &bl_current) != KBD_SUCCESS) {
        fprintf(stderr, "E: Failed to read current brightness from \"%s\"\n", KBD_BRIGHTNESS_PATH);
        usage(argv[0]);
        return 1;
    }

    bl = bl_new(bl_current, bl_max, direction);

    if (write_int(KBD_BRIGHTNESS_PATH, bl) != KBD_SUCCESS) {
        fprintf(stderr, "E: Failed to writing to \"%s\"\n", KBD_BRIGHTNESS_PATH);
        usage(argv[0]);
        return 1;
    }

    return 0;
}

int read_int(const char *path, int *value) {
    FILE *fp = fopen(path, "r");
    int pos;

    if (fp == NULL)
      return KBD_ERROR_MEM;

    char buf[BUF_SIZE];
    if (fread(buf, sizeof(char), BUF_SIZE, fp) == 0)
      return KBD_ERROR_MEM;

    int status = sscanf(buf, "%d%n", value, &pos);
    if (status == EOF || pos != 1) {
      return KBD_ERROR_MEM;
    }

    fclose(fp);
    return KBD_SUCCESS;
}

int write_int(const char *path, int value) {
    FILE *fp = fopen(path, "w");

    if (fp == NULL)
      return KBD_ERROR_MEM;

    int status = fprintf(fp, "%d", value);
    if (status < 0)
      return KBD_ERROR_MEM;

    fclose(fp);
    return KBD_SUCCESS;
}

int bl_new(int current, int max, direction_t direction) {
    switch(direction) {
        case BL_DOWN:
            return (current == 0 ? 0 : current - 1);
            break;
        case BL_UP:
            return (current == max ? max : current + 1);
            break;
        case BL_OFF:
            return 0;
            break;
        case BL_MAX:
            return max;
            break;
    }
    return 0;
}

void usage(const char *name) {
    fprintf(stderr, "Usage: %s [up|down|off|max]\n", name);
}

int get_direction(const char *str, direction_t *dir) {
    if (strcmp(str, "up") == 0) {
        *dir = BL_UP;
    } else if (strcmp(str, "down") == 0) {
        *dir = BL_DOWN;
    } else if (strcmp(str, "off") == 0) {
        *dir = BL_OFF;
    } else if (strcmp(str, "max") == 0) {
        *dir = BL_MAX;
    } else {
      return KBD_ERROR_ARGS;
    }
    return KBD_SUCCESS;
}