#define _POSIX_C_SOURCE 200809L
#include "common/backend.h"

#include <X11/Xatom.h>
#include <X11/XKBlib.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/cursorfont.h>
#include <X11/keysym.h>
#include <xkbcommon/xkbcommon.h>

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <poll.h>
#include <stdlib.h>
#include <string.h>

#define INPUT_CAP 256
#define TEXT_LIMIT (16 * 1024 * 1024)

struct x11_surface {
    struct yasl_surface base;
    struct x11_surface *next;
    struct x11_surface *dead_next;
    Window window;
    GC gc;
    XIC ic;
    XImage *image;
    uint32_t *pixels;
    struct yasl_vector2i size;
    const struct yasl_surface_cbs *cbs;
    void *ud;
    struct yasl_input_event events[INPUT_CAP];
    char *event_text[INPUT_CAP];
    char *last_text;
    unsigned head, count;
    struct yasl_frame frame;
    struct yasl_damage_list damage;
    struct yasl_frame_clock clock;
    uint32_t state;
    bool want_draw, drawing, presented, destroyed;
};

struct x11_display {
    struct yasl_display base;
    Display *native;
    int screen;
    struct yasl_loop *loop;
    int watch;
    struct x11_surface *surfaces, *dead;
    int depth;
    XIM im;
    Window selection_window;
    Atom protocols, delete_window, utf8, clipboard, targets, paste_property;
    Atom net_name, net_state, fullscreen, maximized_h, maximized_v;
    char *selection[2];
    struct x11_surface *paste_target;
    uint32_t mods;
    char *app_id;
};

static struct x11_display *display_of(const struct yasl_surface *s)
{
    return (struct x11_display *)s->display;
}

static void leave(struct x11_display *d)
{
    if (--d->depth) return;
    while (d->dead) {
        struct x11_surface *s = d->dead;
        d->dead = s->dead_next;
        free(s);
    }
}

static void push(struct x11_surface *s, struct yasl_input_event event,
                 const char *text, size_t len)
{
    if (s->destroyed || s->count == INPUT_CAP) return;
    unsigned slot = (s->head + s->count) % INPUT_CAP;
    if (text) {
        char *copy = malloc(len + 1);
        if (!copy) return;
        memcpy(copy, text, len);
        copy[len] = 0;
        s->event_text[slot] = copy;
        if (event.kind == YASL_INPUT_TEXT) {
            event.text.text = copy;
            event.text.len = len;
        } else {
            event.paste.text = copy;
            event.paste.len = len;
        }
    }
    event.surface = &s->base;
    s->events[slot] = event;
    s->count++;
}

static uint32_t modifiers(unsigned state)
{
    return ((state & ShiftMask) ? YASL_MOD_SHIFT : 0) |
           ((state & ControlMask) ? YASL_MOD_CTRL : 0) |
           ((state & Mod1Mask) ? YASL_MOD_ALT : 0) |
           ((state & Mod4Mask) ? YASL_MOD_SUPER : 0) |
           ((state & LockMask) ? YASL_MOD_CAPS : 0);
}

static bool resize(struct x11_surface *s, struct yasl_vector2i size)
{
    if (size.x <= 0 || size.y <= 0 || size.x > 32767 || size.y > 32767 ||
        (size_t)size.x > SIZE_MAX / sizeof(uint32_t) / (size_t)size.y)
        return false;
    if (s->image && size.x == s->size.x && size.y == s->size.y) return true;
    struct x11_display *d = display_of(&s->base);
    uint64_t start = yasl_loop_now_ns();
    XImage *image = XCreateImage(d->native, DefaultVisual(d->native, d->screen),
            (unsigned)DefaultDepth(d->native, d->screen), ZPixmap, 0, NULL,
            (unsigned)size.x, (unsigned)size.y, 32, 0);
    uint32_t *pixels = calloc((size_t)size.x * (size_t)size.y, sizeof(*pixels));
    if (!image || !pixels) {
        if (image) XDestroyImage(image);
        free(pixels);
        return false;
    }
    image->data = calloc((size_t)image->bytes_per_line, (size_t)size.y);
    if (!image->data) {
        XDestroyImage(image);
        free(pixels);
        return false;
    }
    if (s->image) XDestroyImage(s->image);
    free(s->pixels);
    s->image = image;
    s->pixels = pixels;
    s->size = size;
    s->want_draw = true;
    yasl_clock_note_resize(&s->clock, yasl_loop_now_ns() - start);
    return true;
}

static void surface_destroy(struct yasl_surface *base)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (s->destroyed) return;
    struct x11_display *d = display_of(base);
    s->destroyed = true;
    for (struct x11_surface **p = &d->surfaces; *p; p = &(*p)->next) {
        if (*p == s) { *p = s->next; break; }
    }
    if (d->paste_target == s) d->paste_target = NULL;
    if (s->ic) XDestroyIC(s->ic);
    if (s->image) XDestroyImage(s->image);
    free(s->pixels);
    if (s->gc) XFreeGC(d->native, s->gc);
    if (s->window) XDestroyWindow(d->native, s->window);
    for (unsigned i = 0; i < INPUT_CAP; i++) free(s->event_text[i]);
    free(s->last_text);
    if (d->depth) {
        s->dead_next = d->dead;
        d->dead = s;
    } else free(s);
}

static void set_callbacks(struct yasl_surface *base,
        const struct yasl_surface_cbs *cbs, void *ud)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (s->destroyed) return;
    s->cbs = cbs;
    s->ud = ud;
}

static void set_title(struct yasl_surface *base, const char *title)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (s->destroyed || !title) return;
    struct x11_display *d = display_of(base);
    XStoreName(d->native, s->window, title);
    XChangeProperty(d->native, s->window, d->net_name, d->utf8, 8,
                    PropModeReplace, (const unsigned char *)title, (int)strlen(title));
}

static void net_message(struct x11_surface *s, Atom type,
                        long a, long b, long c, long e, long f)
{
    struct x11_display *d = display_of(&s->base);
    XEvent event = {0};
    event.xclient = (XClientMessageEvent){
        .type = ClientMessage, .display = d->native, .window = s->window,
        .message_type = type, .format = 32, .data.l = {a, b, c, e, f},
    };
    XSendEvent(d->native, RootWindow(d->native, d->screen), False,
               SubstructureRedirectMask | SubstructureNotifyMask, &event);
}

static struct yasl_surface *create_toplevel(struct yasl_display *base,
        const struct yasl_surface_spec *spec)
{
    if (!spec) return NULL;
    struct x11_display *d = (struct x11_display *)base;
    struct x11_surface *s = calloc(1, sizeof(*s));
    if (!s) return NULL;
    s->base.display = base;
    s->clock.refresh_ns = YASL_REFRESH_DEFAULT_NS;
    if (!resize(s, spec->size)) { free(s); return NULL; }
    s->window = XCreateSimpleWindow(d->native, RootWindow(d->native, d->screen),
            0, 0, (unsigned)spec->size.x, (unsigned)spec->size.y, 0, 0, 0);
    s->gc = XCreateGC(d->native, s->window, 0, NULL);
    XSelectInput(d->native, s->window, ExposureMask | StructureNotifyMask |
            FocusChangeMask | KeyPressMask | KeyReleaseMask | ButtonPressMask |
            ButtonReleaseMask | PointerMotionMask | LeaveWindowMask | PropertyChangeMask);
    XSetWMProtocols(d->native, s->window, &d->delete_window, 1);
    XClassHint hint = { .res_name = d->app_id, .res_class = d->app_id };
    XSetClassHint(d->native, s->window, &hint);
    if (d->im) {
        s->ic = XCreateIC(d->im, XNInputStyle, XIMPreeditNothing | XIMStatusNothing,
                XNClientWindow, s->window, XNFocusWindow, s->window, NULL);
    }
    s->next = d->surfaces;
    d->surfaces = s;
    set_title(&s->base, spec->title ? spec->title : "YASL");
    if (spec->fullscreen) {
        XChangeProperty(d->native, s->window, d->net_state, XA_ATOM, 32,
                PropModeReplace, (unsigned char *)&d->fullscreen, 1);
        s->state |= YASL_STATE_FULLSCREEN;
    }
    XMapWindow(d->native, s->window);
    XFlush(d->native);
    return &s->base;
}

static void update_state(struct x11_surface *s)
{
    struct x11_display *d = display_of(&s->base);
    Atom actual;
    int format;
    unsigned long count, left;
    unsigned char *data = NULL;
    uint32_t state = s->state & YASL_STATE_ACTIVATED;
    if (XGetWindowProperty(d->native, s->window, d->net_state, 0, 64, False,
            XA_ATOM, &actual, &format, &count, &left, &data) == Success && format == 32) {
        Atom *atoms = (Atom *)data;
        bool h = false, v = false;
        for (unsigned long i = 0; i < count; i++) {
            if (atoms[i] == d->fullscreen) state |= YASL_STATE_FULLSCREEN;
            if (atoms[i] == d->maximized_h) h = true;
            if (atoms[i] == d->maximized_v) v = true;
        }
        if (h && v) state |= YASL_STATE_MAXIMIZED;
    }
    if (data) XFree(data);
    if (state == s->state) return;
    s->state = state;
    if (s->cbs && s->cbs->state) s->cbs->state(&s->base, state, s->ud);
}

static void selection_request(struct x11_display *d, XSelectionRequestEvent *request)
{
    XEvent reply = {0};
    reply.xselection = (XSelectionEvent){
        .type = SelectionNotify, .display = d->native,
        .requestor = request->requestor, .selection = request->selection,
        .target = request->target, .time = request->time,
    };
    Atom property = request->property ? request->property : request->target;
    int slot = request->selection == XA_PRIMARY ? YASL_PRIMARY : YASL_CLIPBOARD;
    const char *text = d->selection[slot];
    if (text && request->target == d->targets) {
        Atom targets[] = {d->targets, d->utf8, XA_STRING};
        XChangeProperty(d->native, request->requestor, property, XA_ATOM, 32,
                PropModeReplace, (unsigned char *)targets, 3);
        reply.xselection.property = property;
    } else if (text && (request->target == d->utf8 || request->target == XA_STRING)) {
        size_t len = strlen(text);
        long max = XMaxRequestSize(d->native) * 4 - 128;
        if (len <= (size_t)max) {
            XChangeProperty(d->native, request->requestor, property, request->target,
                    8, PropModeReplace, (const unsigned char *)text, (int)len);
            reply.xselection.property = property;
        }
    }
    XSendEvent(d->native, request->requestor, False, 0, &reply);
}

static void selection_notify(struct x11_display *d, XSelectionEvent *event)
{
    struct x11_surface *s = d->paste_target;
    d->paste_target = NULL;
    if (!s || event->property == None) return;
    Atom actual;
    int format;
    unsigned long count, left;
    unsigned char *data = NULL;
    if (XGetWindowProperty(d->native, d->selection_window, event->property,
            0, TEXT_LIMIT / 4, True, AnyPropertyType,
            &actual, &format, &count, &left, &data) == Success &&
            (actual == d->utf8 || actual == XA_STRING) && format == 8 && !left) {
        push(s, (struct yasl_input_event){.kind = YASL_INPUT_PASTE},
                (const char *)data, count);
    }
    if (data) XFree(data);
}

static void key_event(struct x11_surface *s, XKeyEvent *key, bool repeat)
{
    struct x11_display *d = display_of(&s->base);
    d->mods = modifiers(key->state);
    KeySym sym = XLookupKeysym(key, (key->state & ShiftMask) ? 1 : 0);
    KeySym base = XLookupKeysym(key, 0), shifted = XLookupKeysym(key, 1);
    char local[128];
    char *text = local;
    int len = 0;
    if (key->type == KeyPress) {
        if (s->ic) {
            Status status;
            len = Xutf8LookupString(s->ic, key, local, sizeof(local), &sym, &status);
            if (status == XBufferOverflow && len > 0 && len < TEXT_LIMIT) {
                text = malloc((size_t)len + 1);
                if (text) len = Xutf8LookupString(s->ic, key, text, len + 1, &sym, &status);
                else len = 0;
            }
            if (status != XLookupChars && status != XLookupBoth) len = 0;
        } else len = XLookupString(key, local, sizeof(local), &sym, NULL);
    }
    uint32_t cp = xkb_keysym_to_utf32((xkb_keysym_t)base);
    if (!cp) cp = xkb_keysym_to_utf32((xkb_keysym_t)sym);
    push(s, (struct yasl_input_event){
        .kind = YASL_INPUT_KEY,
        .key = {.key = (uint32_t)sym, .codepoint = cp,
                .base = key->keycode >= 8 ? key->keycode - 8 : 0,
                .keypad = sym >= XK_KP_Space && sym <= XK_KP_Equal,
                .shifted = xkb_keysym_to_utf32((xkb_keysym_t)shifted),
                .text = xkb_keysym_to_utf32((xkb_keysym_t)sym), .mods = d->mods,
                .action = key->type == KeyRelease ? YASL_KEY_RELEASE :
                          repeat ? YASL_KEY_REPEAT : YASL_KEY_PRESS},
    }, NULL, 0);
    if (len > 0 && text)
        push(s, (struct yasl_input_event){.kind = YASL_INPUT_TEXT}, text, (size_t)len);
    if (text != local) free(text);
}

static void dispatch(struct yasl_display *base)
{
    struct x11_display *d = (struct x11_display *)base;
    d->depth++;
    while (XPending(d->native)) {
        XEvent event;
        XNextEvent(d->native, &event);
        if (XFilterEvent(&event, None)) continue;
        if (event.type == SelectionRequest) {
            selection_request(d, &event.xselectionrequest);
            continue;
        }
        if (event.type == SelectionNotify) {
            selection_notify(d, &event.xselection);
            continue;
        }
        struct x11_surface *s = d->surfaces;
        while (s && s->window != event.xany.window) s = s->next;
        if (!s) continue;
        switch (event.type) {
        case Expose: s->want_draw = true; break;
        case ConfigureNotify: {
            struct yasl_vector2i size = {event.xconfigure.width, event.xconfigure.height};
            if (size.x == s->size.x && size.y == s->size.y) break;
            if (resize(s, size) && s->cbs && s->cbs->configure)
                s->cbs->configure(&s->base, (struct yasl_geometry){size, YASL_SCALE_UNIT}, s->ud);
            break;
        }
        case ClientMessage:
            if (event.xclient.message_type == d->protocols &&
                (Atom)event.xclient.data.l[0] == d->delete_window && s->cbs && s->cbs->close)
                s->cbs->close(&s->base, s->ud);
            break;
        case FocusIn: case FocusOut: {
            bool focused = event.type == FocusIn;
            if (s->ic) { if (focused) XSetICFocus(s->ic); else XUnsetICFocus(s->ic); }
            if (focused) s->state |= YASL_STATE_ACTIVATED;
            else s->state &= ~YASL_STATE_ACTIVATED;
            push(s, (struct yasl_input_event){
                .kind = YASL_INPUT_FOCUS, .focus.focused = focused}, NULL, 0);
            if (s->cbs && s->cbs->state) s->cbs->state(&s->base, s->state, s->ud);
            break;
        }
        case PropertyNotify:
            if (event.xproperty.atom == d->net_state) update_state(s);
            break;
        case KeyPress: case KeyRelease: {
            bool repeat = false;
            if (event.type == KeyRelease && XPending(d->native)) {
                XEvent next;
                XPeekEvent(d->native, &next);
                if (next.type == KeyPress && next.xkey.window == event.xkey.window &&
                    next.xkey.keycode == event.xkey.keycode && next.xkey.time == event.xkey.time) {
                    XNextEvent(d->native, &event);
                    repeat = true;
                }
            }
            key_event(s, &event.xkey, repeat);
            break;
        }
        case MotionNotify: case LeaveNotify: case ButtonPress: case ButtonRelease: {
            struct yasl_mouse_event mouse = {.device = YASL_PTR_DEV_MOUSE};
            unsigned state;
            if (event.type == MotionNotify) {
                mouse.pos = (struct yasl_vector2i){event.xmotion.x, event.xmotion.y};
                mouse.kind = YASL_PTR_MOTION;
                state = event.xmotion.state;
            } else if (event.type == LeaveNotify) {
                mouse.pos = (struct yasl_vector2i){event.xcrossing.x, event.xcrossing.y};
                mouse.kind = YASL_PTR_LEAVE;
                state = event.xcrossing.state;
            } else {
                mouse.pos = (struct yasl_vector2i){event.xbutton.x, event.xbutton.y};
                state = event.xbutton.state;
                unsigned button = event.xbutton.button;
                if (button >= 4 && button <= 7) {
                    if (event.type == ButtonRelease) break;
                    mouse.kind = YASL_PTR_SCROLL;
                    mouse.scroll_lines = (button == 4 || button == 6) ? -1 : 1;
                } else {
                    mouse.kind = event.type == ButtonPress ? YASL_PTR_PRESS : YASL_PTR_RELEASE;
                    mouse.button = button == 1 ? 0x110 : button == 2 ? 0x112 :
                                   button == 3 ? 0x111 : (int)button + 0x10b;
                }
            }
            d->mods = mouse.mods = modifiers(state);
            push(s, (struct yasl_input_event){.kind = YASL_INPUT_MOUSE, .mouse = mouse}, NULL, 0);
            break;
        }
        }
    }
    leave(d);
}

static unsigned long component(uint32_t color, unsigned long mask)
{
    if (!mask) return 0;
    unsigned shift = 0;
    while (!(mask & 1)) { mask >>= 1; shift++; }
    return (((unsigned long)color * mask + 127) / 255) << shift;
}

static bool present(struct yasl_surface *base, const struct yasl_framebuffer *fb,
                    const struct yasl_damage_list *damage)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (s->destroyed || !s->drawing || s->presented || !fb || !damage ||
        fb->pixels != s->pixels || fb->size.x != s->size.x || fb->size.y != s->size.y ||
        damage->n < -1 || damage->n > YASL_DAMAGE_MAX) return false;
    struct x11_display *d = display_of(base);
    XImage *im = s->image;
    bool direct = im->bits_per_pixel == 32 && im->red_mask == 0xff0000 &&
                  im->green_mask == 0xff00 && im->blue_mask == 0xff;
    for (int y = 0; y < s->size.y; y++) {
        const uint32_t *row = s->pixels + (size_t)y * s->size.x;
        if (direct) memcpy(im->data + (size_t)y * im->bytes_per_line, row, (size_t)s->size.x * 4);
        else for (int x = 0; x < s->size.x; x++) {
            uint32_t p = row[x];
            XPutPixel(im, x, y, component((p >> 16) & 255, im->red_mask) |
                    component((p >> 8) & 255, im->green_mask) | component(p & 255, im->blue_mask));
        }
    }
    if (damage->n == -1)
        XPutImage(d->native, s->window, s->gc, im, 0, 0, 0, 0,
                  (unsigned)s->size.x, (unsigned)s->size.y);
    else for (int i = 0; i < damage->n; i++) {
        struct yasl_rect2i r = damage->rects[i];
        int64_t right = (int64_t)r.x + r.width, bottom = (int64_t)r.y + r.height;
        int x = r.x > 0 ? r.x : 0, y = r.y > 0 ? r.y : 0;
        int w = (int)(right < s->size.x ? right : s->size.x) - x;
        int h = (int)(bottom < s->size.y ? bottom : s->size.y) - y;
        if (w > 0 && h > 0)
            XPutImage(d->native, s->window, s->gc, im, x, y, x, y, (unsigned)w, (unsigned)h);
    }
    s->presented = true;
    yasl_clock_presented(&s->clock, yasl_loop_now_ns(), false);
    return true;
}

static void flush(struct yasl_display *base)
{
    struct x11_display *d = (struct x11_display *)base;
    d->depth++;
    for (struct x11_surface *s = d->surfaces, *next; s; s = next) {
        next = s->next;
        if (s->destroyed || !s->want_draw || !s->cbs || !s->cbs->draw || s->drawing) continue;
        s->want_draw = false;
        s->drawing = true;
        s->presented = false;
        s->damage = (struct yasl_damage_list){0};
        s->frame = (struct yasl_frame){
            .surface = &s->base,
            .target = {.pixels = s->pixels, .size = s->size, .damage = &s->damage},
        };
        s->cbs->draw(&s->base, &s->frame, s->ud);
        s->drawing = false;
    }
    XFlush(d->native);
    leave(d);
}

static int ready(int fd, short events, void *ud)
{
    (void)fd;
    struct yasl_display *base = ud;
    if (events & POLLIN) { dispatch(base); flush(base); }
    return 0;
}

static struct yasl_display *display_open(struct yasl_loop *loop,
        const struct yasl_display_spec *spec)
{
    struct x11_display *d = calloc(1, sizeof(*d));
    if (!d) return NULL;
    d->base.ops = &yasl_x11_backend;
    d->native = XOpenDisplay(NULL);
    if (!d->native) { free(d); errno = ENODEV; return NULL; }
    d->screen = DefaultScreen(d->native);
    d->loop = loop;
    d->app_id = strdup(spec && spec->app_id ? spec->app_id : "YASL");
    if (!d->app_id) { XCloseDisplay(d->native); free(d); return NULL; }
    d->im = XOpenIM(d->native, NULL, NULL, NULL);
    d->selection_window = XCreateSimpleWindow(d->native,
            RootWindow(d->native, d->screen), 0, 0, 1, 1, 0, 0, 0);
#define ATOM(field, name) d->field = XInternAtom(d->native, name, False)
    ATOM(protocols, "WM_PROTOCOLS");
    ATOM(delete_window, "WM_DELETE_WINDOW");
    ATOM(utf8, "UTF8_STRING");
    ATOM(clipboard, "CLIPBOARD");
    ATOM(targets, "TARGETS");
    ATOM(paste_property, "YASL_SELECTION");
    ATOM(net_name, "_NET_WM_NAME");
    ATOM(net_state, "_NET_WM_STATE");
    ATOM(fullscreen, "_NET_WM_STATE_FULLSCREEN");
    ATOM(maximized_h, "_NET_WM_STATE_MAXIMIZED_HORZ");
    ATOM(maximized_v, "_NET_WM_STATE_MAXIMIZED_VERT");
#undef ATOM
    if (loop) {
        d->watch = yasl_loop_add_fd(loop, ConnectionNumber(d->native), POLLIN, ready, &d->base);
        if (d->watch < 0) {
            if (d->im) XCloseIM(d->im);
            XDestroyWindow(d->native, d->selection_window);
            XCloseDisplay(d->native);
            free(d->app_id);
            free(d);
            return NULL;
        }
    }
    return &d->base;
}

static void display_close(struct yasl_display *base)
{
    struct x11_display *d = (struct x11_display *)base;
    assert(!d->surfaces && "destroy every surface before its display");
    if (d->loop) yasl_loop_del_fd(d->loop, d->watch);
    if (d->im) XCloseIM(d->im);
    XDestroyWindow(d->native, d->selection_window);
    XCloseDisplay(d->native);
    free(d->selection[0]);
    free(d->selection[1]);
    free(d->app_id);
    free(d);
}

static uint32_t caps(const struct yasl_display *d)
{
    (void)d;
    return YASL_CAP_PLACE_WINDOW | YASL_CAP_PRIMARY_SELECTION;
}

static void copy(struct yasl_display *base, enum yasl_selection sel, const char *text)
{
    if (!text || (sel != YASL_CLIPBOARD && sel != YASL_PRIMARY)) return;
    struct x11_display *d = (struct x11_display *)base;
    char *value = strdup(text);
    if (!value) return;
    free(d->selection[sel]);
    d->selection[sel] = value;
    XSetSelectionOwner(d->native, sel == YASL_PRIMARY ? XA_PRIMARY : d->clipboard,
                        d->selection_window, CurrentTime);
    XFlush(d->native);
}

static void paste(struct yasl_display *base, enum yasl_selection sel, struct yasl_surface *target)
{
    if (sel != YASL_CLIPBOARD && sel != YASL_PRIMARY) return;
    struct x11_display *d = (struct x11_display *)base;
    struct x11_surface *s = (struct x11_surface *)target;
    Atom selection = sel == YASL_PRIMARY ? XA_PRIMARY : d->clipboard;
    if (XGetSelectionOwner(d->native, selection) == d->selection_window) {
        const char *text = d->selection[sel];
        if (text) push(s, (struct yasl_input_event){.kind = YASL_INPUT_PASTE}, text, strlen(text));
    } else {
        d->paste_target = s;
        XConvertSelection(d->native, selection, d->utf8, d->paste_property,
                            d->selection_window, CurrentTime);
        XFlush(d->native);
    }
}

static bool input_poll(struct yasl_surface *base, struct yasl_input_event *event)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (!event || s->destroyed || !s->count) return false;
    free(s->last_text);
    s->last_text = s->event_text[s->head];
    s->event_text[s->head] = NULL;
    *event = s->events[s->head];
    s->head = (s->head + 1) % INPUT_CAP;
    s->count--;
    return true;
}

static void schedule_redraw(struct yasl_surface *base)
{
    struct x11_surface *s = (struct x11_surface *)base;
    if (!s->destroyed) s->want_draw = true;
}

static struct yasl_display *surface_display(const struct yasl_surface *s) { return s->display; }
static struct yasl_vector2i size(const struct yasl_surface *s) { return ((const struct x11_surface *)s)->size; }
static uint32_t scale(const struct yasl_surface *s) { (void)s; return YASL_SCALE_UNIT; }
static uint32_t state(const struct yasl_surface *s) { return ((const struct x11_surface *)s)->state; }
static int mods(const struct yasl_display *d) { return (int)((const struct x11_display *)d)->mods; }
static void *native_display(struct yasl_display *d) { return ((struct x11_display *)d)->native; }
static void *native_surface(struct yasl_surface *s) { return (void *)(uintptr_t)((struct x11_surface *)s)->window; }

static struct yasl_timing timing(const struct yasl_surface *base)
{
    const struct x11_surface *s = (const struct x11_surface *)base;
    struct yasl_timing t = {.refresh_ns = s->clock.refresh_ns,
        .last_present_ns = s->clock.last_present_ns,
        .next_present_ns = yasl_clock_next_present_ns(&s->clock)};
    yasl_clock_resize_stats(&s->clock, &t.resize);
    return t;
}

static uint64_t frame_time(struct yasl_surface *s, uint64_t now)
{
    return yasl_clock_frame_timestamp_ns(&((struct x11_surface *)s)->clock, now);
}

static void cursor(struct yasl_surface *base, enum yasl_cursor cursor)
{
    static const unsigned shapes[] = {XC_left_ptr, XC_xterm, XC_hand2, XC_crosshair,
        XC_fleur, XC_bottom_right_corner, XC_bottom_left_corner,
        XC_sb_h_double_arrow, XC_sb_v_double_arrow};
    struct x11_surface *s = (struct x11_surface *)base;
    if (s->destroyed || (unsigned)cursor > YASL_CURSOR_NONE) return;
    struct x11_display *d = display_of(base);
    Cursor native;
    if (cursor == YASL_CURSOR_NONE) {
        char bits[] = {0};
        Pixmap pixmap = XCreateBitmapFromData(d->native, s->window, bits, 1, 1);
        XColor color = {0};
        native = XCreatePixmapCursor(d->native, pixmap, pixmap, &color, &color, 0, 0);
        XFreePixmap(d->native, pixmap);
    } else native = XCreateFontCursor(d->native, shapes[cursor]);
    XDefineCursor(d->native, s->window, native);
    XFreeCursor(d->native, native);
}

static bool place(struct yasl_surface *base, struct yasl_vector2i at)
{
    struct x11_surface *s = (struct x11_surface *)base;
    struct x11_display *d = display_of(base);
    Window root, child;
    int root_x, root_y, x, y;
    unsigned mask;
    if (s->destroyed || !XQueryPointer(d->native, s->window,
            &root, &child, &root_x, &root_y, &x, &y, &mask)) return false;
    XMoveWindow(d->native, s->window, root_x - at.x, root_y - at.y);
    return true;
}

static bool interactive_move(struct yasl_surface *base)
{
    struct x11_surface *s = (struct x11_surface *)base;
    struct x11_display *d = display_of(base);
    Window root, child;
    int rx, ry, x, y;
    unsigned mask;
    if (s->destroyed || !XQueryPointer(d->native, s->window,
            &root, &child, &rx, &ry, &x, &y, &mask)) return false;
    XUngrabPointer(d->native, CurrentTime);
    net_message(s, XInternAtom(d->native, "_NET_WM_MOVERESIZE", False), rx, ry, 8, 1, 1);
    return true;
}

const struct yasl_backend_ops yasl_x11_backend = {
    .type = YASL_BACKEND_X11,
    .display_open = display_open,
    .display_close = display_close,
    .display_caps = caps,
    .display_dispatch = dispatch,
    .display_flush = flush,
    .display_modifiers = mods,
    .display_copy = copy,
    .display_paste = paste,
    .surface_create_toplevel = create_toplevel,
    .surface_destroy = surface_destroy,
    .surface_display = surface_display,
    .surface_set_callbacks = set_callbacks,
    .surface_set_title = set_title,
    .surface_schedule_redraw = schedule_redraw,
    .surface_present = present,
    .surface_input_poll = input_poll,
    .surface_size = size,
    .surface_scale_120 = scale,
    .surface_state = state,
    .surface_timing = timing,
    .surface_frame_time_ns = frame_time,
    .surface_set_cursor = cursor,
    .surface_place_under_pointer = place,
    .surface_start_interactive_move = interactive_move,
    .display_get_native_handle = native_display,
    .surface_get_native_handle = native_surface,
};