const c = @import("c.zig");
const builtin = @import("builtin");
const debug = @import("std").debug;
const math = @import("std").math;

pub const ClientApi = enum {
  Unknown,
  OpenGL,
  Vulkan,
};

// Data
var g_Window: ?*c.GLFWwindow = null;
var g_ClientApi: ClientApi = .Unknown;
var g_Time: f64 = 0.0;
var g_MouseJustPressed = [_]bool{ false } ** 5;
var g_MouseCursors = [_]?*c.GLFWcursor{ null } ** @enumToInt(c.ImGuiMouseCursor_COUNT);
var g_WantUpdateMonitors = true;

// Chain GLFW callbacks for main viewport:
// our callbacks will call the user's previously installed callbacks, if any.
var g_PrevUserCallbackMousebutton: c.GLFWmousebuttonfun = null;
var g_PrevUserCallbackScroll: c.GLFWscrollfun = null;
var g_PrevUserCallbackKey: c.GLFWkeyfun = null;
var g_PrevUserCallbackChar: c.GLFWcharfun = null;

pub fn Init(window: *c.GLFWwindow, install_callbacks: bool, client_api: ClientApi) void {
  g_Window = window;
  g_Time = 0.0;

  // Setup back-end capabilities flags
  const io = c.igGetIO();
  io.*.BackendFlags |= @enumToInt(c.ImGuiBackendFlags_HasMouseCursors); // We can honor GetMouseCursor() values (optional)
  io.*.BackendFlags |= @enumToInt(c.ImGuiBackendFlags_HasSetMousePos); // We can honor io.WantSetMousePos requests (optional, rarely used)
  if (false) io.*.BackendFlags |= @enumToInt(c.ImGuiBackendFlags_PlatformHasViewports); // We can create multi-viewports on the Platform side (optional)
  if (false and @hasField(c, "GLFW_HAS_GLFW_HOVERED") and builtin.os == builtin.Os.windows) {
    io.*.BackendFlags |= @enumToInt(ImGuiBackendFlags_HasMouseHoveredViewport); // We can set io.MouseHoveredViewport correctly (optional, not easy)
  }
  io.*.BackendPlatformName = c"imgui_impl_glfw.zig";

  // Keyboard mapping. ImGui will use those indices to peek into the io.KeysDown[] array.
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Tab)] = c.GLFW_KEY_TAB;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_LeftArrow)] = c.GLFW_KEY_LEFT;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_RightArrow)] = c.GLFW_KEY_RIGHT;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_UpArrow)] = c.GLFW_KEY_UP;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_DownArrow)] = c.GLFW_KEY_DOWN;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_PageUp)] = c.GLFW_KEY_PAGE_UP;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_PageDown)] = c.GLFW_KEY_PAGE_DOWN;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Home)] = c.GLFW_KEY_HOME;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_End)] = c.GLFW_KEY_END;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Insert)] = c.GLFW_KEY_INSERT;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Delete)] = c.GLFW_KEY_DELETE;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Backspace)] = c.GLFW_KEY_BACKSPACE;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Space)] = c.GLFW_KEY_SPACE;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Enter)] = c.GLFW_KEY_ENTER;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Escape)] = c.GLFW_KEY_ESCAPE;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_KeyPadEnter)] = c.GLFW_KEY_KP_ENTER;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_A)] = c.GLFW_KEY_A;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_C)] = c.GLFW_KEY_C;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_V)] = c.GLFW_KEY_V;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_X)] = c.GLFW_KEY_X;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Y)] = c.GLFW_KEY_Y;
  io.*.KeyMap[@enumToInt(c.ImGuiKey_Z)] = c.GLFW_KEY_Z;

  // @TODO: Clipboard
  // io.SetClipboardTextFn = ImGui_ImplGlfw_SetClipboardText;
  // io.GetClipboardTextFn = ImGui_ImplGlfw_GetClipboardText;
  io.*.ClipboardUserData = g_Window;

  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_Arrow)] = c.glfwCreateStandardCursor(c.GLFW_ARROW_CURSOR);
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_TextInput)] = c.glfwCreateStandardCursor(c.GLFW_IBEAM_CURSOR);
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_ResizeAll)] = c.glfwCreateStandardCursor(c.GLFW_ARROW_CURSOR); // FIXME: GLFW doesn't have this.
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_ResizeNS)] = c.glfwCreateStandardCursor(c.GLFW_VRESIZE_CURSOR);
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_ResizeEW)] = c.glfwCreateStandardCursor(c.GLFW_HRESIZE_CURSOR);
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_ResizeNESW)] = c.glfwCreateStandardCursor(c.GLFW_ARROW_CURSOR); // FIXME: GLFW doesn't have this.
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_ResizeNWSE)] = c.glfwCreateStandardCursor(c.GLFW_ARROW_CURSOR); // FIXME: GLFW doesn't have this.
  g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_Hand)] = c.glfwCreateStandardCursor(c.GLFW_HAND_CURSOR);

  // Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
  g_PrevUserCallbackMousebutton = null;
  g_PrevUserCallbackScroll = null;
  g_PrevUserCallbackKey = null;
  g_PrevUserCallbackChar = null;
  if (install_callbacks) {
    g_PrevUserCallbackMousebutton = c.glfwSetMouseButtonCallback(window, Callback_MouseButton);
    g_PrevUserCallbackScroll = c.glfwSetScrollCallback(window, Callback_Scroll);
    g_PrevUserCallbackKey = c.glfwSetKeyCallback(window, Callback_Key);
    g_PrevUserCallbackChar = c.glfwSetCharCallback(window, Callback_Char);
  }

  // Our mouse update function expect PlatformHandle to be filled for the main viewport
  const main_viewport = c.igGetMainViewport();
  main_viewport.*.PlatformHandle = g_Window;
  if (builtin.os == builtin.Os.windows)
    main_viewport.*.PlatformHandleRaw = c.glfwGetWin32Window(g_Window);

  // @TODO: Platform Interface (Viewport)
  if (io.*.ConfigFlags & @enumToInt(c.ImGuiConfigFlags_ViewportsEnable) != 0)
    unreachable;
    // ImGui_ImplGlfw_InitPlatformInterface();

  g_ClientApi = client_api;
}

pub fn Shutdown() void {
  // @TODO: Platform Interface (Viewport)
  // ImGui_ImplGlfw_ShutdownPlatformInterface();

  for (g_MouseCursors) |*cursor| {
    c.glfwDestroyCursor(cursor.*);
    cursor.* = null;
  }
  g_ClientApi = .Unknown;
}

pub fn NewFrame() void {
  const io = c.igGetIO();
  debug.assert(c.ImFontAtlas_IsBuilt(io.*.Fonts));

  var w : c_int = undefined;
  var h : c_int = undefined;
  var display_w : c_int = undefined;
  var display_h : c_int = undefined;
  c.glfwGetWindowSize(g_Window, &w, &h);
  c.glfwGetFramebufferSize(g_Window, &display_w, &display_h);
  io.*.DisplaySize = c.ImVec2{ .x = @intToFloat(f32, w), .y = @intToFloat(f32, h) };

  if (w > 0 and h > 0)
    io.*.DisplayFramebufferScale = c.ImVec2{
      .x = @intToFloat(f32, display_w) / @intToFloat(f32, w),
      .y = @intToFloat(f32, display_h) / @intToFloat(f32, h),
    };
  if (g_WantUpdateMonitors)
    UpdateMonitors();

  // Setup time step
  const current_time = c.glfwGetTime();
  io.*.DeltaTime = if (g_Time > 0.0) @floatCast(f32, current_time - g_Time) else 1.0 / 60.0;
  g_Time = current_time;

  UpdateMousePosAndButtons();
  UpdateMouseCursor();

  UpdateGamepads();
}

fn UpdateMonitors() void {
  const platform_io = c.igGetPlatformIO();
  var monitors_count : c_int = 0;
  const glfw_monitors = c.glfwGetMonitors(&monitors_count)[0..@intCast(usize, monitors_count)];

  c.ImVector_ImGuiPlatformMonitor_Resize(&platform_io.*.Monitors, monitors_count);
  for (glfw_monitors) |glfw_monitor, n| {
    var monitor = &platform_io.*.Monitors.Data[n];
    var x : c_int = undefined;
    var y : c_int = undefined;
    c.glfwGetMonitorPos(glfw_monitor, &x, &y);
    const vid_mode = c.glfwGetVideoMode(glfw_monitor); // glfw_monitors[n]);

    monitor.*.MainPos = c.ImVec2{ .x = @intToFloat(f32, x), .y = @intToFloat(f32, y) };
    monitor.*.MainSize = c.ImVec2{
      .x = @intToFloat(f32, vid_mode.*.width),
      .y = @intToFloat(f32, vid_mode.*.height),
    };
    if (false and c.GLFW_HAS_MONITOR_WORK_AREA) {
      var w : c_int = undefined;
      var h : c_int = undefined;
      c.glfwGetMonitorWorkarea(glfw_monitor, &x, &y, &w, &h);
      monitor.*.WorkPos = ImVec2{ .x = @intToFloat(f32, x), .y = @intToFloat(f32, y) };
      monitor.*.WorkSize = ImVec2{ .x = @intToFloat(f32, w), .y = @intToFloat(f32, h) };
    }
    if (false and c.GLFW_HAS_PER_MONITOR_DPI) {
      // Warning: the validity of monitor DPI information on Windows depends on the application DPI awareness settings,
      // which generally needs to be set in the manifest or at runtime.
      var x_scale : f32 = undefined;
      var y_scale : f32 = undefined;
      c.glfwGetMonitorContentScale(glfw_monitor, &x_scale, &y_scale);
      monitor.*.DpiScale = x_scale;
    }
  }
  g_WantUpdateMonitors = false;
}

fn UpdateMousePosAndButtons() void {
  // Update buttons
  const io = c.igGetIO();
  for (io.*.MouseDown) |*isDown, i| {
    // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
    isDown.* = g_MouseJustPressed[i] or c.glfwGetMouseButton(g_Window, @intCast(c_int, i)) != 0;
    g_MouseJustPressed[i] = false;
  }

  // Update mouse position
  const mouse_pos_backup = io.*.MousePos;
  io.*.MousePos = c.ImVec2{ .x = math.f32_min, .y = math.f32_min };
  io.*.MouseHoveredViewport = 0;
  const platform_io = c.igGetPlatformIO();
  var n : usize = 0;
  while (n < @intCast(usize, platform_io.*.Viewports.Size)) : (n += 1) {
    const viewport = platform_io.*.Viewports.Data[n];
    const window = @ptrCast(*c.GLFWwindow, viewport.*.PlatformHandle);
    const focused = c.glfwGetWindowAttrib(window, c.GLFW_FOCUSED) != 0;
    if (focused) {
      if (io.*.WantSetMousePos) {
        c.glfwSetCursorPos(window, mouse_pos_backup.x - viewport.*.Pos.x, mouse_pos_backup.y - viewport.*.Pos.y);
      } else {
        var mouse_x : f64 = undefined;
        var mouse_y : f64 = undefined;
        c.glfwGetCursorPos(window, &mouse_x, &mouse_y);
        if (io.*.ConfigFlags & @enumToInt(c.ImGuiConfigFlags_ViewportsEnable) != 0) {
          // Multi-viewport mode: mouse position in OS absolute coordinates (io.MousePos is (0,0) when the mouse is on the upper-left of the primary monitor)
          var window_x : c_int = undefined;
          var window_y : c_int = undefined;
          c.glfwGetWindowPos(window, &window_x, &window_y);
          io.*.MousePos = c.ImVec2{
            .x = @floatCast(f32, mouse_x) + @intToFloat(f32, window_x),
            .y = @floatCast(f32, mouse_y) + @intToFloat(f32, window_y),
          };
        } else {
          // Single viewport mode: mouse position in client window coordinates (io.MousePos is (0,0) when the mouse is on the upper-left corner of the app window)
          io.*.MousePos = c.ImVec2{ .x = @floatCast(f32, mouse_x), .y = @floatCast(f32, mouse_y) };
        }
      }

      for (io.*.MouseDown) |*isDown, i|
        isDown.* = isDown.* or c.glfwGetMouseButton(window, @intCast(c_int, i)) != 0;
    }
  }
}

fn UpdateMouseCursor() void {
  const io = c.igGetIO();
  if (io.*.ConfigFlags & @enumToInt(c.ImGuiConfigFlags_NoMouseCursorChange) != 0
      or c.glfwGetInputMode(g_Window, c.GLFW_CURSOR) == c.GLFW_CURSOR_DISABLED)
    return;

  const imgui_cursor = c.igGetMouseCursor();
  const platform_io = c.igGetPlatformIO();
  var n : usize = 0;
  while (n < @intCast(usize, platform_io.*.Viewports.Size)) : (n += 1) {
    const window = @ptrCast(*c.GLFWwindow, platform_io.*.Viewports.Data[n].*.PlatformHandle);
    if (imgui_cursor == @enumToInt(c.ImGuiMouseCursor_None) or io.*.MouseDrawCursor) {
      // Hide OS mouse cursor if imgui is drawing it or if it wants no cursor
      c.glfwSetInputMode(window, c.GLFW_CURSOR, c.GLFW_CURSOR_HIDDEN);
    } else {
      // Show OS mouse cursor
      // FIXME-PLATFORM: Unfocused windows seems to fail changing the mouse cursor with GLFW 3.2, but 3.3 works here.
      c.glfwSetCursor(window,
                      if (g_MouseCursors[@intCast(usize, imgui_cursor)]) |cursor| cursor
                      else g_MouseCursors[@enumToInt(c.ImGuiMouseCursor_Arrow)]);
      c.glfwSetInputMode(window, c.GLFW_CURSOR, c.GLFW_CURSOR_NORMAL);
    }
  }
}

fn UpdateGamepads() void {
  // @TODO
}

// GLFW Callbacks
extern fn Callback_MouseButton(window: ?*c.GLFWwindow, button: c_int, action: c_int, mods: c_int) void {
  if (g_PrevUserCallbackMousebutton) |prev| {
    prev(window, button, action, mods);
  }

  if (button < 0) 
    return;

  const button_u = @intCast(usize, button);
  if (action == c.GLFW_PRESS and button_u < g_MouseJustPressed.len)
    g_MouseJustPressed[button_u] = true;
}

extern fn Callback_Scroll(window: ?*c.GLFWwindow, dx: f64, dy: f64) void {
  if (g_PrevUserCallbackScroll) |prev| {
    prev(window, dx, dy);
  }

  const io = c.igGetIO();
  io.*.MouseWheelH += @floatCast(f32, dx);
  io.*.MouseWheel  += @floatCast(f32, dy);
}

extern fn Callback_Key(window: ?*c.GLFWwindow, key: c_int, scancode: c_int, action: c_int, modifiers: c_int) void {
  if (g_PrevUserCallbackKey) |prev| {
    prev(window, key, scancode, action, modifiers);
  }

  if (key < 0)
    unreachable;

  const key_u = @intCast(usize, key);

  const io = c.igGetIO();
  if (action == c.GLFW_PRESS)
    io.*.KeysDown[key_u] = true;
  if (action == c.GLFW_RELEASE)
    io.*.KeysDown[key_u] = false;

  // Modifiers are not reliable across systems
  io.*.KeyCtrl = io.*.KeysDown[c.GLFW_KEY_LEFT_CONTROL] or io.*.KeysDown[c.GLFW_KEY_RIGHT_CONTROL];
  io.*.KeyShift = io.*.KeysDown[c.GLFW_KEY_LEFT_SHIFT] or io.*.KeysDown[c.GLFW_KEY_RIGHT_SHIFT];
  io.*.KeyAlt = io.*.KeysDown[c.GLFW_KEY_LEFT_ALT] or io.*.KeysDown[c.GLFW_KEY_RIGHT_ALT];
  io.*.KeySuper = io.*.KeysDown[c.GLFW_KEY_LEFT_SUPER] or io.*.KeysDown[c.GLFW_KEY_RIGHT_SUPER];
}

extern fn Callback_Char(window: ?*c.GLFWwindow, char: c_uint) void {
  if (g_PrevUserCallbackChar) |prev| {
    prev(window, char);
  }

  const io = c.igGetIO();
  c.ImGuiIO_AddInputCharacter(io, char);
}