Platform :: struct { // UNIX
  window: *SDL_Window;
  gpu_device: *SDL_GPUDevice;
  tray: *SDL_Tray;
  tray_image: Image_Data;
  tray_icon_surface: *SDL_Surface;
  tray_menu: *SDL_TrayMenu;
  tray_icon_failed: bool; // set on the first failure, so minimizing stops retrying and re-logging it
  app_icon_surface: *SDL_Surface;
  app_icon_pending: bool;          // set again at the start of the next frame, once the window is up

  #if OS == .LINUX {
    desktop_environment: Linux_Desktop_Environment;
    display_backend: Linux_Display_Backend;
  }
  #if OS == .MACOS {
    main_context: *#Context;
    polling_events: bool;         // inside the main loop's SDL_PollEvent, where a live-resize frame may run
    in_live_resize_frame: bool;
    live_resize_frame_drawn: bool;   // during this poll; the frame polling must then end, see app_frame
  }
}

// Calls SDL_GetError then SDL_ClearError
//
// The returned string is owned by SDL and only valid until the next SDL call
consume_sdl_error :: () -> string {
    data := SDL_GetError();
    SDL_ClearError();
    return to_string(data);
}

ok_or_exit :: inline (success: bool, err_msg_format: string, args: ..Any, flags := Log_Flags.ERROR, exit_code : s32 = 1) {
    if success return;

    log(err_msg_format, ..args, flags=flags);
    exit(exit_code);
} @PrintLike

platform_restore_window :: () {
  using app;
  SDL_ShowWindow(platform.window);
  SDL_RestoreWindow(platform.window);
  SDL_RaiseWindow(platform.window);
  #if OS == .MACOS {
    NSApplication.setActivationPolicy(NSApplication.sharedApplication(), NSApplicationActivationPolicyRegular);
    // The Dock tile is made anew and takes the bundle's icon, which a bare executable lacks.
    platform.app_icon_pending = true;
    // A global hotkey arrives while another app is active, and raising the window alone does not
    // make this the active app.
    NSApplication.activateIgnoringOtherApps(NSApplication.sharedApplication(), YES);
    platform_hide_tray_icon();
  }
  #if OS == .LINUX {
    // Right now, this doesn't work on my XFCE Arch Desktop, so I'm just going to leave the icon in the tray. Sad.
    if platform.desktop_environment == .XFCE {
      log("platform_hide_tray_icon is broken on XFCE, so it is currently disabled!");
    } else platform_hide_tray_icon();
  }
  
  app.minimized_to_tray = false;
}

// The display with the most area, as Windows opens on its largest monitor. The primary when SDL
// cannot list them.
sdl_largest_display :: () -> SDL_DisplayID {
  largest := SDL_GetPrimaryDisplay();
  count: s32;
  displays := SDL_GetDisplays(*count);
  if !displays  return largest;
  defer SDL_free(displays);

  largest_area: s64 = -1;
  for i: 0..count-1 {
    bounds: SDL_Rect;
    if !SDL_GetDisplayBounds(displays[i], *bounds)  continue;
    area := cast(s64) bounds.w * bounds.h;
    if area > largest_area {
      largest = displays[i];
      largest_area = area;
    }
  }
  return largest;
}

// SDL converts the whole surface on every set, so icon.png is scaled down once; 512 is plenty
// for the Dock and the taskbar.
APP_ICON_PIXELS :: 512;

// The window's icon. On macOS, run outside the .app (a debug build), it stands in for the Dock
// icon. Kept for sdl_apply_pending_app_icon.
sdl_set_app_icon :: () { using platform;
  #if OS == .MACOS  if app_running_from_app_bundle()  return;   // the Dock takes the bundle's own icon
  path := tprint("%images/icon.png", app_install_directory());
  image := Load_Image(path);
  if !image.data  return;
  defer stbi_image_free(image.data);

  full := SDL_CreateSurfaceFrom(image.width, image.height, .RGBA32, image.data, image.width * 4);
  if !full {
    log_error("[sdl_set_app_icon] SDL_CreateSurfaceFrom failed for `%`: %", path, consume_sdl_error());
    return;
  }
  defer SDL_DestroySurface(full);

  app_icon_surface = SDL_ScaleSurface(full, APP_ICON_PIXELS, APP_ICON_PIXELS, .LINEAR);
  if !app_icon_surface {
    log_error("[sdl_set_app_icon] SDL_ScaleSurface failed for `%`: %", path, consume_sdl_error());
    return;
  }
  app_icon_pending = true;
  sdl_apply_pending_app_icon();
}

sdl_apply_pending_app_icon :: () { using platform;
  if !app_icon_pending || !app_icon_surface  return;
  app_icon_pending = false;
  if !SDL_SetWindowIcon(window, app_icon_surface)  log_error("[sdl_set_app_icon] SDL_SetWindowIcon failed: %", consume_sdl_error());
}

#if OS == .MACOS {

  // While a window edge is dragged, the main loop is held inside SDL_PollEvent. SDL sends a window
  // exposed event with data1 = 1 from there and allows drawing from an event watch for it.
  sdl_live_resize_watch :: (userdata: *void, event: *SDL_Event) -> bool #c_call {
    using platform;
    if event.type != xx SDL_EventType.WINDOW_EXPOSED || event.window.data1 != 1  return true;
    if !polling_events || in_live_resize_frame || !main_context  return true;

    in_live_resize_frame = true;
    live_resize_frame_drawn = true;
    push_context main_context.* {
      auto_release_temp();
      app_frame(in_live_resize = true);
    }
    in_live_resize_frame = false;
    return true;
  }
}

sdl_default_window_size :: (mode: *SDL_DisplayMode) -> w: s32, h: s32 {
  w := cast(s32) (mode.w * app_user_settings.window_width_fraction);
  h := cast(s32) (mode.h * app_user_settings.window_height_fraction);
  return w, h;
}

// Back to the size and place the window starts at.
platform_reset_window_placement :: () -> bool { using platform;
  display := sdl_largest_display();
  mode := SDL_GetCurrentDisplayMode(display);
  if !mode {
    log_error("SDL_GetCurrentDisplayMode failed: %; the window was not reset.", consume_sdl_error());
    return false;
  }
  w, h := sdl_default_window_size(mode);

  flags := SDL_GetWindowFlags(window);
  if flags & SDL_WINDOW_FULLSCREEN  SDL_SetWindowFullscreen(window, false);
  if flags & SDL_WINDOW_MAXIMIZED   SDL_RestoreWindow(window);

  // Sized first: centering uses the window's size.
  centered := SDL_WINDOWPOS_CENTERED_DISPLAY(display);
  if !SDL_SetWindowSize(window, w, h) || !SDL_SetWindowPosition(window, xx centered, xx centered) {
    log_error("Could not reset the window: %", consume_sdl_error());
    return false;
  }
  log("Window reset: size: %x%", w, h);
  return true;
}

// Returns as soon as an event is queued, or after timeout_ms. The event stays queued for the next
// frame's SDL_PollEvent.
platform_wait_while_hidden :: (timeout_ms: u32) {
  SDL_WaitEventTimeout(null, xx timeout_ms);
}

platform_minimize_to_tray :: inline () {
  if !platform_show_tray_icon() {
    SDL_MinimizeWindow(platform.window);
    return;
  }

  SDL_HideWindow(platform.window);
  // Hidden in the menu bar, the app leaves the Dock and Cmd+Tab, as menu bar apps do.
  #if OS == .MACOS  NSApplication.setActivationPolicy(NSApplication.sharedApplication(), NSApplicationActivationPolicyAccessory);
  app.minimized_to_tray = true;
}

create_tray_from_image :: (image_path: string) -> bool { using platform;
  if tray_icon_surface  return true;

  tray_image = Load_Image(image_path);
  if !tray_image.data  return false;

  tray_icon_surface = SDL_CreateSurfaceFrom(tray_image.width, tray_image.height, .RGBA32, tray_image.data, tray_image.width * 4);
  if !tray_icon_surface {
    log_error("[create_tray_from_image] SDL_CreateSurfaceFrom failed for `%`: %", image_path, consume_sdl_error());
    stbi_image_free(tray_image.data);
    tray_image.data = null;
    return false;
  }
  return true;
}

// False when there is no tray to minimize to (e.g. GNOME without an AppIndicator extension)
platform_show_tray_icon :: () -> bool { using platform;
  if tray               return true;
  if tray_icon_failed   return false;

  if !create_tray_from_image(get_app_tray_icon_path()) {
    log_error("[platform_show_tray_icon] No tray icon image; minimizing instead of hiding to the tray.");
    tray_icon_failed = true;
    return false;
  }

  tray = SDL_CreateTray(tray_icon_surface, APP_TRAY_TOOLTIP_TEXT);
  if !tray {
    log_error("[platform_show_tray_icon] SDL_CreateTray failed: %. Minimizing instead of hiding to the tray.", consume_sdl_error());
    tray_icon_failed = true;
    return false;
  }

  tray_menu = SDL_CreateTrayMenu(tray);
  show_entry := ifx tray_menu then SDL_InsertTrayEntryAt(tray_menu, -1, "Show", 0) else null;
  if !show_entry {
    log_error("[platform_show_tray_icon] Could not build the tray menu: %. Minimizing instead of hiding to the tray.", consume_sdl_error());
    SDL_DestroyTray(tray);
    tray = null;
    tray_menu = null;
    tray_icon_failed = true;
    return false;
  }
  SDL_SetTrayEntryCallback(show_entry, tray_show, *app);

  quit_entry := SDL_InsertTrayEntryAt(tray_menu, -1, "Quit", 0);
  if quit_entry  SDL_SetTrayEntryCallback(quit_entry, tray_quit, *app);
  else           log_error("[platform_show_tray_icon] Could not add the tray's Quit entry: %", consume_sdl_error());

  return true;
}

platform_hide_tray_icon :: () {
  if !platform.tray return;
  // Maybe I need to unparent menu items first:
  SDL_DestroyTray(platform.tray);
  platform.tray = null;
  SDL_PumpEvents();
}

tray_show :: (userdata: *void, te: *SDL_TrayEntry) -> void #c_call {
  new_context: #Context;
  use_app_logger(*new_context);
  push_context,defer_pop new_context;
  app := cast(*App)userdata;
  app.restore_window_this_frame = true;
}

tray_quit :: (userdata: *void, te: *SDL_TrayEntry) -> void #c_call {
  using app := cast(*App)userdata;
  app.should_exit = true;
}

Image_Data :: struct {
  data: *u8;
  width: s32;
  height: s32;
  depth: s32;
  scale_factor: float32 = 1.0;
}

Load_Image :: (path: string) -> Image_Data {
  id: Image_Data = ---;
  
  path_c_string := to_c_string(path,, temp);
  
  id.data = stbi_load(path_c_string, *id.width, *id.height, *id.depth, 4);
  if id.data {
    log("% loaded: %x%x%\n", path, id.width, id.height, id.depth);
  } else {
    log_error("failed to load %\n", path);
  }
  
  return id;
}
// A texture from tightly packed RGBA pixels, at most GPU_TEXTURE_MAX_SIDE a side. Its handle is the
// SDL_GPUTexture, which is what the ImGui SDL_GPU backend draws. A zero handle when it failed.
// Modeled on ImGui_ImplSDLGPU3_UpdateTexture.
gpu_texture_create :: (pixels: *u8, width: s32, height: s32) -> Gpu_Texture {
  result: Gpu_Texture;
  device := platform.gpu_device;
  if !device || width <= 0 || height <= 0 || width > GPU_TEXTURE_MAX_SIDE || height > GPU_TEXTURE_MAX_SIDE  return result;
  size := cast(s64) width * height * 4;

  texture_info: SDL_GPUTextureCreateInfo;
  texture_info.type                 = ._2D;
  texture_info.format               = .R8G8B8A8_UNORM;
  texture_info.usage                = SDL_GPU_TEXTUREUSAGE_SAMPLER;
  texture_info.width                = xx width;
  texture_info.height               = xx height;
  texture_info.layer_count_or_depth = 1;
  texture_info.num_levels           = 1;
  texture_info.sample_count         = ._1;
  texture := SDL_CreateGPUTexture(device, *texture_info);
  if !texture {
    log_error("[SDL] SDL_CreateGPUTexture (%x%) failed: %", width, height, consume_sdl_error());
    return result;
  }

  transfer_info: SDL_GPUTransferBufferCreateInfo;
  transfer_info.usage = .UPLOAD;
  transfer_info.size  = xx size;
  transfer_buffer := SDL_CreateGPUTransferBuffer(device, *transfer_info);
  if !transfer_buffer {
    log_error("[SDL] SDL_CreateGPUTransferBuffer failed: %", consume_sdl_error());
    SDL_ReleaseGPUTexture(device, texture);
    return result;
  }
  defer SDL_ReleaseGPUTransferBuffer(device, transfer_buffer);

  mapped := SDL_MapGPUTransferBuffer(device, transfer_buffer, false);
  if !mapped {
    log_error("[SDL] SDL_MapGPUTransferBuffer failed: %", consume_sdl_error());
    SDL_ReleaseGPUTexture(device, texture);
    return result;
  }
  memcpy(mapped, pixels, size);
  SDL_UnmapGPUTransferBuffer(device, transfer_buffer);

  source: SDL_GPUTextureTransferInfo;
  source.transfer_buffer = transfer_buffer;
  destination: SDL_GPUTextureRegion;
  destination.texture = texture;
  destination.w       = xx width;
  destination.h       = xx height;
  destination.d       = 1;

  // Submitted before the frame's own command buffer, so the texture is ready when ImGui draws it.
  command_buffer := SDL_AcquireGPUCommandBuffer(device);
  if !command_buffer {
    log_error("[SDL] SDL_AcquireGPUCommandBuffer failed: %", consume_sdl_error());
    SDL_ReleaseGPUTexture(device, texture);
    return result;
  }
  copy_pass := SDL_BeginGPUCopyPass(command_buffer);
  SDL_UploadToGPUTexture(copy_pass, *source, *destination, false);
  SDL_EndGPUCopyPass(copy_pass);
  SDL_SubmitGPUCommandBuffer(command_buffer);

  result.handle = texture;
  result.width  = width;
  result.height = height;
  return result;
}

gpu_texture_release :: (texture: *Gpu_Texture) {
  if texture.handle  SDL_ReleaseGPUTexture(platform.gpu_device, cast(*SDL_GPUTexture) texture.handle);
  texture.* = .{};
}