1 files changed, 110 insertions, 0 deletions
diff --git a/bin/capsremap.c b/bin/capsremap.c
new file mode 100644
index 0000000..8a78f4b
--- /dev/null
+++ b/bin/capsremap.c
@@ -0,0 +1,110 @@
+// 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;
+
+	// Handle cases where caps lock is released before hjkl is released so
+	// the subsequent hjkl release is properly rewritten as an arrow key
+	int down_key = KEY_RESERVED;
+
+	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 {
+				if (event.type == EV_KEY && event.code == down_key && event.value == 0) {
+					hjkl_to_arrow(&event);
+					down_key = KEY_RESERVED;
+				}
+				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) {
+					down_key = event.code;
+					hjkl_to_arrow(&event);
+					state = CAPSLOCK_IS_MODIFIER;
+				}
+				if (event.type == EV_KEY && event.code == down_key && event.value == 0) {
+					down_key = KEY_RESERVED;
+					hjkl_to_arrow(&event);
+				}
+				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 {
+				if (event.type == EV_KEY && event.value) {
+					down_key = event.code;
+					hjkl_to_arrow(&event);
+				}
+				if (event.type == EV_KEY && event.code == down_key && event.value == 0) {
+					down_key = KEY_RESERVED;
+					hjkl_to_arrow(&event);
+				}
+				fwrite(&event, sizeof(event), 1, stdout);
+			}
+			break;
+		}
+	}
+}