feat(behaviors): Add local ID system for behaviors

* Add a new feature for tracking a given behavior by a new concept
  of a "behavior local ID" which is a stable 16-bit identifier for
  a given behavior, that is resilient to new behaviors being added
  and requires no additional work on the part of the behavior
  authors.
* Add implementations for either settings lookup table, or CRC16
  hashing of behavior device names for generating behavior local
  IDs.

app/src/behavior.c

@@ -6,9 +6,17 @@
 
 #include <zephyr/device.h>
 #include <zephyr/init.h>
+#include <zephyr/sys/crc.h>
 #include <zephyr/sys/util_macro.h>
 #include <string.h>
 
+#if IS_ENABLED(CONFIG_ZMK_BEHAVIOR_LOCAL_IDS) &&                                                   \
+    IS_ENABLED(CONFIG_ZMK_BEHAVIOR_LOCAL_ID_TYPE_SETTINGS_TABLE)
+
+#include <zephyr/settings/settings.h>
+
+#endif
+
 #include <drivers/behavior.h>
 #include <zmk/behavior.h>
 #include <zmk/hid.h>
@@ -185,6 +193,133 @@ int zmk_behavior_validate_binding(const struct zmk_behavior_binding *binding) {
 #endif // IS_ENABLED(CONFIG_ZMK_BEHAVIOR_METADATA)
 }
 
+#if IS_ENABLED(CONFIG_ZMK_BEHAVIOR_LOCAL_IDS)
+
+zmk_behavior_local_id_t zmk_behavior_get_local_id(const char *name) {
+    if (!name) {
+        return UINT16_MAX;
+    }
+
+    STRUCT_SECTION_FOREACH(zmk_behavior_local_id_map, item) {
+        if (z_device_is_ready(item->device) && strcmp(item->device->name, name) == 0) {
+            return item->local_id;
+        }
+    }
+
+    return UINT16_MAX;
+}
+
+const char *zmk_behavior_find_behavior_name_from_local_id(zmk_behavior_local_id_t local_id) {
+    STRUCT_SECTION_FOREACH(zmk_behavior_local_id_map, item) {
+        if (z_device_is_ready(item->device) && item->local_id == local_id) {
+            return item->device->name;
+        }
+    }
+
+    return NULL;
+}
+
+#if IS_ENABLED(CONFIG_ZMK_BEHAVIOR_LOCAL_ID_TYPE_CRC16)
+
+static int behavior_local_id_init(void) {
+    STRUCT_SECTION_FOREACH(zmk_behavior_local_id_map, item) {
+        item->local_id = crc16_ansi(item->device->name, strlen(item->device->name));
+    }
+
+    return 0;
+}
+
+#elif IS_ENABLED(CONFIG_ZMK_BEHAVIOR_LOCAL_ID_TYPE_SETTINGS_TABLE)
+
+static zmk_behavior_local_id_t largest_local_id = 0;
+
+static int behavior_handle_set(const char *name, size_t len, settings_read_cb read_cb,
+                               void *cb_arg) {
+    const char *next;
+
+    if (settings_name_steq(name, "local_id", &next) && next) {
+        char *endptr;
+        uint8_t local_id = strtoul(next, &endptr, 10);
+        if (*endptr != '\0') {
+            LOG_WRN("Invalid behavior local ID: %s with endptr %s", next, endptr);
+            return -EINVAL;
+        }
+
+        if (len >= 64) {
+            LOG_ERR("Too large binding setting size (got %d expected less than %d)", len, 64);
+            return -EINVAL;
+        }
+
+        char name[len + 1];
+
+        int err = read_cb(cb_arg, name, len);
+        if (err <= 0) {
+            LOG_ERR("Failed to handle keymap binding from settings (err %d)", err);
+            return err;
+        }
+
+        name[len] = '\0';
+        STRUCT_SECTION_FOREACH(zmk_behavior_local_id_map, item) {
+            if (strcmp(name, item->device->name) == 0) {
+                item->local_id = local_id;
+                largest_local_id = MAX(largest_local_id, local_id);
+                return 0;
+            }
+        }
+
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static int behavior_handle_commit(void) {
+    STRUCT_SECTION_FOREACH(zmk_behavior_local_id_map, item) {
+        if (item->local_id != 0) {
+            continue;
+        }
+
+        if (!item->device || !item->device->name || !device_is_ready(item->device)) {
+            LOG_WRN("Skipping ID for device that doesn't exist or isn't ready");
+            continue;
+        }
+
+        item->local_id = ++largest_local_id;
+        char setting_name[32];
+        sprintf(setting_name, "behavior/local_id/%d", item->local_id);
+
+        // If the `device->name` is readonly in flash, settings save can fail to copy/read it while
+        // persisting to flash, so copy the device name into memory first before saving.
+        char device_name[32];
+        snprintf(device_name, ARRAY_SIZE(device_name), "%s", item->device->name);
+
+        settings_save_one(setting_name, device_name, strlen(device_name));
+    }
+
+    return 0;
+}
+
+SETTINGS_STATIC_HANDLER_DEFINE(behavior, "behavior", NULL, behavior_handle_set,
+                               behavior_handle_commit, NULL);
+
+static int behavior_local_id_init(void) {
+    settings_subsys_init();
+
+    settings_load_subtree("behavior");
+
+    return 0;
+}
+
+#else
+
+#error "A behavior local ID mechanism must be selected"
+
+#endif
+
+SYS_INIT(behavior_local_id_init, APPLICATION, CONFIG_APPLICATION_INIT_PRIORITY);
+
+#endif
+
 #if IS_ENABLED(CONFIG_LOG)
 static int check_behavior_names(void) {
     // Behavior names must be unique, but we don't have a good way to enforce this