/*
 * texec.c - Minimal X11 tray applet with mandatory PNG icon (32x32)
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 *
 * Compile:
 *   gcc -o texec texec.c -lX11 -lpng
 *
 * Usage:
 *   ./texec "<command>" <icon.png>
 *
 * Left-click: execute command
 * Right-click: quit applet
 */

#include <png.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/Xutil.h>

#define WIDTH 24
#define HEIGHT 24

static Display *dpy;
static int screen;
static Window icon_win;
static char *x_command;

void execute_command() {
    if (!x_command) return;
    pid_t pid = fork();
    if (pid == 0) {
        setsid();
        execl("/bin/sh", "sh", "-c", x_command, (char *)NULL);
        _exit(127);
    }
}

/* Minimal PNG loader into XImage */
XImage *load_png(const char *filename) {
    FILE *fp = fopen(filename, "rb");
    if (!fp) return NULL;

    png_structp png = png_create_read_struct(PNG_LIBPNG_VER_STRING,NULL,NULL,NULL);
    png_infop info = png_create_info_struct(png);
    if (setjmp(png_jmpbuf(png))) return NULL;

    png_init_io(png, fp);
    png_read_info(png, info);

    int w = png_get_image_width(png, info);
    int h = png_get_image_height(png, info);
    png_byte color_type = png_get_color_type(png, info);
    png_byte bit_depth = png_get_bit_depth(png, info);

    if (bit_depth == 16) png_set_strip_16(png);
    if (color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png);
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png);
    if (png_get_valid(png, info, PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png);
    png_set_filler(png, 0xFF, PNG_FILLER_AFTER);
    png_read_update_info(png, info);

    png_bytep *rows = (png_bytep*)malloc(sizeof(png_bytep) * h);
    for (int y=0; y<h; y++) {
        rows[y] = (png_byte*)malloc(4*w);
    }

    png_read_image(png, rows);
    fclose(fp);

    XImage *img = XCreateImage(dpy, CopyFromParent, 24, ZPixmap, 0,
                               malloc(w*h*4), w, h, 32, 0);

    for (int y=0; y<h; y++) {
        for (int x=0; x<w; x++) {
            png_bytep px = &(rows[y][x*4]);
            unsigned long pixel = (px[0]<<16) | (px[1]<<8) | px[2];
            XPutPixel(img, x, y, pixel);
        }
    }

    for (int y=0; y<h; y++) {
        free(rows[y]);
    }
    free(rows);
    png_destroy_read_struct(&png, &info, NULL);
    return img;
}

void draw_icon(Window win, const char *icon_path) {
    GC gc = XCreateGC(dpy, win, 0, NULL);
    XImage *img = load_png(icon_path);
    if (!img) {
        fprintf(stderr,"Failed to load PNG icon: %s\n", icon_path);
        exit(1);
    }
    XPutImage(dpy, win, gc, img, 0,0,0,0, img->width, img->height);
    XDestroyImage(img);
    XFreeGC(dpy,gc);
}

int main(int argc, char *argv[]) {
    if (argc < 3) {
        fprintf(stderr,"Usage: %s <command> <icon.png>\n",argv[0]);
        return 1;
    }
    x_command = argv[1];
    char *icon_path = argv[2];

    signal(SIGCHLD, SIG_IGN);

    dpy = XOpenDisplay(NULL);
    if (!dpy) {
        fprintf(stderr,"Cannot open display\n");
        return 1;
    }
    screen = DefaultScreen(dpy);

    Atom _NET_SYSTEM_TRAY_S0 = XInternAtom(dpy, "_NET_SYSTEM_TRAY_S0", False);
    Window tray_win = XGetSelectionOwner(dpy, _NET_SYSTEM_TRAY_S0);
    if (tray_win == None) {
        fprintf(stderr,"No system tray found\n");
        return 1;
    }

    icon_win = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy),
                                   0,0, WIDTH, HEIGHT, 1,
                                   BlackPixel(dpy,screen),
                                   WhitePixel(dpy,screen));
    XSelectInput(dpy, icon_win, ExposureMask | ButtonPressMask);

    // Send dock request
    XEvent ev;
    memset(&ev, 0, sizeof(ev));
    ev.xclient.type = ClientMessage;
    ev.xclient.window = icon_win;
    ev.xclient.message_type = XInternAtom(dpy,"_NET_SYSTEM_TRAY_OPCODE",False);
    ev.xclient.format = 32;
    ev.xclient.data.l[0] = CurrentTime;
    ev.xclient.data.l[1] = 0; // SYSTEM_TRAY_REQUEST_DOCK
    ev.xclient.data.l[2] = icon_win;
    XSendEvent(dpy, tray_win, False, NoEventMask, &ev);

    XMapWindow(dpy, icon_win);
    draw_icon(icon_win, icon_path);

    XEvent xev;
    while (1) {
        XNextEvent(dpy, &xev);
        if (xev.xany.window == icon_win) {
            if (xev.type == Expose) draw_icon(icon_win, icon_path);
            else if (xev.type == ButtonPress) {
                if (xev.xbutton.button == 1) {
                    execute_command(); // left-click
                } else if (xev.xbutton.button == 3) {
                    break; // right-click: quit
                }
            }
        }
    }

    XDestroyWindow(dpy, icon_win);
    XCloseDisplay(dpy);
    return 0;
}