Tactility/TactilityKernel/include/tactility/drivers/keyboard.h

// SPDX-License-Identifier: Apache-2.0
#pragma once

#ifdef __cplusplus
extern "C" {
#endif

#include <stdint.h>
#include <stdbool.h>

#include <tactility/device.h>
#include <tactility/error.h>

/**
 * @brief Named Unicode codepoints for KeyboardKeyData::key.
 *
 * Some common codepoints.
 * There are no official codepoints for arrow keys, so we use the symbols as placeholder.
 * Subsystems like LVGL can translate these special codepoints to specific actions.
 */
typedef enum {
    CODEPOINT_ENTER       = '\r',
    CODEPOINT_ESCAPE      = '\x1B',
    CODEPOINT_BACKSPACE   = '\b',
    CODEPOINT_DELETE      = '\x7F',
    CODEPOINT_TAB         = '\t',
    CODEPOINT_ARROW_LEFT  = 0x2190,
    CODEPOINT_ARROW_UP    = 0x2191,
    CODEPOINT_ARROW_RIGHT = 0x2192,
    CODEPOINT_ARROW_DOWN  = 0x2193,
    CODEPOINT_HOME        = 0x21F1,
    CODEPOINT_END         = 0x21F2,
} CodePoint;

/**
 * @brief A single key event read from a keyboard device.
 */
struct KeyboardKeyData {
    /**
     * @brief The key. Always a Unicode codepoint - never a raw scan code.
     *
     * For a key that produces a character, this is that character's codepoint (e.g. 'a', ' '). For
     * a key with no character representation, or one of the handful of C0 control keys every
     * driver needs, this is one of the CodePoint enum values above - never an LVGL LV_KEY_*
     * constant directly. See ctrl's doc comment below for the CodePoint values that numerically
     * collide with real C0 control codes.
     */
    uint32_t key;
    /** @brief True if the key was pressed, false if released. */
    bool pressed;
    /**
     * @brief True if another key event is already queued and read_key() should be called again
     * immediately to drain it. False if this was the last pending event.
     */
    bool continue_reading;
    /**
     * @brief True if Ctrl was held when this key was pressed.
     *
     * Reported separately rather than folded into `key` because the two encodings collide: the C0
     * control codes a terminal expects for Ctrl chords (Ctrl+C is 0x03, Ctrl+K is 0x0B, ...) overlap
     * the four CodePoint values that remain in true C0 range (CODEPOINT_ENTER is Ctrl+M/13,
     * CODEPOINT_BACKSPACE is Ctrl+H/8, CODEPOINT_TAB is Ctrl+I/9, CODEPOINT_ESCAPE is Ctrl+[/27), so
     * a single uint32_t cannot express both. Consumers that want control codes derive them here, e.g.
     * `((key >= 'a' && key <= 'z') || (key >= 'A' && key <= 'Z')) ? (key & 0x1F) : key`
     * when ctrl is set.
     *
     * Drivers whose hardware cannot report Ctrl leave this false.
     */
    bool ctrl;
    /**
     * @brief True if Alt was held when this key was pressed. See ctrl for why modifiers are reported
     * separately. Drivers whose hardware cannot report Alt leave this false.
     */
    bool alt;
    /**
     * @brief Standard USB HID keyboard usage code for this key (USB HID Usage Tables, page 0x07),
     * or 0 if this driver doesn't compute one (most don't - `key` is the only field most consumers need).
     * Populated by drivers whose hardware layout maps cleanly onto HID usage codes, so consumers that
     * want to mirror physical key presses as real HID reports (e.g. USB HID output) don't have to
     * reverse-engineer one out of `key`'s codepoint encoding.
     * Encoding is lossy for keys with no Unicode/LVGL representation at all, e.g. F1-F12.
     */
    uint8_t hid_keycode;
    /**
     * @brief HID modifier bitmask (report byte 0: bit0=LeftCtrl, bit1=LeftShift, bit2=LeftAlt,
     * bit3=LeftGui, bit4-7=Right variants) matching hid_keycode, or 0 if hid_keycode is 0.
     */
    uint8_t hid_modifier;
};

/**
 * @brief Number of key events that can be queued per subscription in the default
 * subscribe/unsubscribe/poll implementation before older subscribers' fanned-out events start
 * being dropped for that subscriber (silently, preserving FIFO order of what's already queued).
 */
#define KEYBOARD_EVENT_QUEUE_CAPACITY 4

/**
 * @brief Caller-owned subscription node for keyboard_subscribe()/keyboard_unsubscribe()/
 * keyboard_poll().
 * @warning `internal` is private to keyboard.cpp; do not read or write it directly.
 */
struct KeyboardEventSubscription {
    struct {
        struct Device* device;
        struct KeyboardKeyData queue[KEYBOARD_EVENT_QUEUE_CAPACITY];
        uint8_t head;
        uint8_t count;
        struct KeyboardEventSubscription* next;
    } internal;
};

/**
 * @brief API for keyboard drivers.
 */
struct KeyboardApi {
    /**
     * @brief Reads the next pending key event, if any.
     * May be NULL if the driver instead pushes events itself via keyboard_emit_key() (e.g. from a dedicated interrupt-handling task).
     * @param[in] device the keyboard device
     * @param[out] data the key event data
     * @retval ERROR_NONE when the operation was successful
     */
    error_t (*read_key)(struct Device* device, struct KeyboardKeyData* data);

    /**
     * @brief Returns the backlight if the keyboard has one.
     * @warning Returns a referenced device. Must call device_put() afterwards.
     * @param[in] device the keyboard device
     * @param[out] backlight_device the output backlight device
     * @retval ERROR_NONE when the backlight_device was set
     * @retval ERROR_NOT_SUPPORTED when this device has no backlight
     */
    error_t (*get_backlight)(struct Device* device, struct Device** backlight_device);

    /**
     * @deprecated Use Driver::probe + device_hotplug_register() instead (see DEVICE_FLAG_HOTPLUG)
     * The kernel then starts/stops the device itself instead of leaving it started forever.
     * When DEVICE_FLAG_HOTPLUG is used, use device_is_ready() only for checking if a keyboard is usable.
     */
    bool (*is_present)(struct Device* device);
};

/**
 * @brief Reads the next pending key event using the specified keyboard device. Also fans the
 * result out to every keyboard_subscribe()'d subscriber, same as keyboard_emit_key().
 * @retval ERROR_NONE @a data filled - key == 0 if nothing is pending
 * @retval ERROR_INVALID_STATE @a device isn't currently started (e.g. hotplug-absent)
 * @retval ERROR_NOT_SUPPORTED the driver has no KeyboardApi::read_key (it pushes events via
 * keyboard_emit_key() instead)
 */
error_t keyboard_read_key(struct Device* device, struct KeyboardKeyData* data);

/**
 * @brief Push a key event from @a device to every current subscriber (see keyboard_subscribe()).
 * For a driver whose hardware delivers key events asynchronously (e.g. from a dedicated
 * interrupt-handling task) rather than on demand - KeyboardApi::read_key may be left NULL when
 * the driver calls this instead.
 * @warning Not ISR-safe (takes a mutex); call from a task, not directly from interrupt context.
 * @param[in] device the keyboard device the event originated from
 * @param[in] data the key event
 */
void keyboard_emit_key(struct Device* device, struct KeyboardKeyData data);

/**
 * @brief Returns the backlight if the keyboard has one.
 * @warning Returns a referenced device. Must call device_put() afterwards.
 * @param[in] device the keyboard device
 * @param[out] backlight_device the output backlight device
 * @retval ERROR_NONE when the backlight_device was set
 * @retval ERROR_NOT_SUPPORTED when this device has no backlight
 */
error_t keyboard_get_backlight(struct Device* device, struct Device** backlight_device);

/**
 * @deprecated See KeyboardApi::is_present.
 * @param[in] device the keyboard device
 */
bool keyboard_is_present(struct Device* device);

/**
 * @brief Register @a sub for async key events from @a device, derived from `read_key`.
 * @param[in,out] sub subscription to register; owns the storage, must stay alive (and stationary)
 * until unsubscribed
 * @retval ERROR_NONE on success
 */
error_t keyboard_subscribe(struct Device* device, struct KeyboardEventSubscription* sub);

/**
 * @brief Remove a subscription previously registered with keyboard_subscribe().
 * @retval ERROR_NONE on success
 */
error_t keyboard_unsubscribe(struct Device* device, struct KeyboardEventSubscription* sub);

/**
 * @brief Non-blocking: pop the next event for @a sub if one is already queued.
 * @warning Never blocks.
 * @retval ERROR_NONE @a out_data was filled
 * @retval ERROR_TIMEOUT nothing queued right now
 */
error_t keyboard_poll(struct Device* device, struct KeyboardEventSubscription* sub, struct KeyboardKeyData* out_data);

extern const struct DeviceType KEYBOARD_TYPE;

#ifdef __cplusplus
}
#endif