typedef struct ui_code_loc_t ui_code_loc_t;
struct ui_code_loc_t {
    char *file;
    int line;
    int counter;
};

typedef struct ui_id_t ui_id_t;
struct ui_id_t {
    u64 value;
};

typedef struct ui_box_flags_t ui_box_flags_t;
struct ui_box_flags_t {
    b8 draw_rect: 1;
    b8 draw_border: 1;
    b8 draw_text: 1;

    b8 clip_rect : 1;
};

typedef enum {
    ui_text_align_left,
    ui_text_align_center,
} ui_text_align_t;

typedef enum {
    ui_op_cut_top,
    ui_op_cut_bottom,
    ui_op_cut_left,
    ui_op_cut_right,
    ui_op_idle,
} ui_op_t;

typedef struct ui_box_t ui_box_t;
struct ui_box_t {
    ui_box_t *next;
    ui_box_t *prev;
    ui_box_t *first;
    ui_box_t *last;
    ui_box_t *parent;
    i32       node_count;

    ui_code_loc_t loc;
    s8_t          string;

    ui_box_flags_t  flags;
    b8              created_new;
    ui_text_align_t text_align;

    ui_op_t op;
    r2f32_t full_rect;
    r2f32_t rect;

    // state
    ui_id_t   id;
    ui_box_t *hash_next;
    ui_box_t *hash_prev;
    u64       last_touched_event_id;

    r2f32_t final_rect;
    b32     expanded;
};

typedef struct ui_signal_t ui_signal_t;
struct ui_signal_t {
    ui_box_t *box;
    b8 clicked;
    b8 dragging;
};

typedef struct ui_t ui_t;
struct ui_t {
    // building
    ui_box_t root;
    ui_box_t *top;
    app_event_t *event;
    stack_t(ui_id_t, 32) id_stack;
    ui_text_align_t pref_text_align;

    // allocation
    ma_arena_t *box_arena;
    i32 allocated_boxes;
    ui_box_t *free_first;
    ui_box_t *hash_first;
    ui_box_t *hash_last;

    // interaction
    ui_id_t hot;
    ui_id_t active;

    // drawing
    r2f32_t clip_rect;
};

ui_t *ui;

gb_read_only ui_id_t ui_null_id;
gb_read_only ui_box_t ui_null_box;
gb_read_only ui_box_flags_t ui_null_flags;

fn b32 ui_is_null_id(ui_id_t id) { return id.value == 0; }
fn b32 ui_is_null_box(ui_box_t *box) { return box->id.value == 0; }
fn b32 ui_is_hot_box(ui_box_t *box) { return !ui_is_null_box(box) && box->id.value == ui->hot.value; }
fn b32 ui_is_active_box(ui_box_t *box) { return !ui_is_null_box(box) && box->id.value == ui->active.value; }

#define ev_left(ev) ((ev)->mouse_button == app_mouse_button_left)
#define ev_left_up(ev) ((ev)->kind == app_event_kind_mouse_up && ev_left(ev))
#define ev_left_down(ev) ((ev)->kind == app_event_kind_mouse_down && ev_left(ev))

fn void ui_set_rect(ui_box_t *box, r2f32_t rect) { box->rect = box->full_rect = rect; }

#define UILOC (ui_code_loc_t){.file = __FILE__, .line = __LINE__, .counter = __COUNTER__}
#define ui_em(x) ((x) * rn_state.main_font->size)
#define ui_max 200000000.f
#define ui_box_flags(...) (ui_box_flag_t){__VA_ARGS__}