// SPDX-FIleCopyrightText: 2017 Francisco Lopes da Silva
// SPDX-FIleCopyrightText: 2023 Sam Nystrom <sam@samnystrom.dev>
// SPDX-License-Identifier: MIT

// Map the caps lock key to escape and caps+hjkl to the arrow keys

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <linux/input.h>

const struct input_event
syn       = {.type = EV_SYN, .code = SYN_REPORT, .value = 0},
esc_up    = {.type = EV_KEY, .code = KEY_ESC   , .value = 0},
esc_down  = {.type = EV_KEY, .code = KEY_ESC   , .value = 1};

const int delay = 10000;

void hjkl_to_arrow(struct input_event *event) {
	switch (event->code) {
	case KEY_H:
		event->code = KEY_LEFT;
		break;
	case KEY_J:
		event->code = KEY_DOWN;
		break;
	case KEY_K:
		event->code = KEY_UP;
		break;
	case KEY_L:
		event->code = KEY_RIGHT;
		break;
	}
}

int main(int argc, char** argv) {
	setbuf(stdin, NULL);
	setbuf(stdout, NULL);

	enum { START, CAPSLOCK_HELD, CAPSLOCK_IS_MODIFIER } state = START;

	struct input_event event;
	while (fread(&event, sizeof(event), 1, stdin) == 1) {
		if (event.type == EV_MSC && event.code == MSC_SCAN) {
			continue;
		}
		if (event.type != EV_KEY && event.type != EV_REL && event.type != EV_ABS) {
			fwrite(&event, sizeof(event), 1, stdout);
			continue;
		}

		switch (state) {
		case START:
			if (event.type == EV_KEY && event.code == KEY_CAPSLOCK && event.value) {
				state = CAPSLOCK_HELD;
			} else {
				fwrite(&event, sizeof(event), 1, stdout);
			}
			break;
		case CAPSLOCK_HELD:
			if (event.type == EV_KEY && event.code == KEY_CAPSLOCK) {
				if (event.value == 0) {
					fwrite(&esc_down, sizeof(esc_down), 1, stdout);
					fwrite(&syn, sizeof(syn), 1, stdout);
					usleep(delay);
					fwrite(&esc_up, sizeof(esc_up), 1, stdout);
					state = START;
				}
			} else if (event.type == EV_KEY && event.value) {
				hjkl_to_arrow(&event);
				fwrite(&event, sizeof(event), 1, stdout);
				state = CAPSLOCK_IS_MODIFIER;
			} else {
				fwrite(&event, sizeof(event), 1, stdout);
			}
			break;
		case CAPSLOCK_IS_MODIFIER:
			if (event.type == EV_KEY && event.code == KEY_CAPSLOCK) {
				if (event.value == 0) {
					state = START;
				}
			} else {
				hjkl_to_arrow(&event);
				fwrite(&event, sizeof(event), 1, stdout);
			}
			break;
		}
	}
}