#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#include <raylib.h>
#include <raymath.h>
#include "spotlight.frag.c"

#define KEY_MOD_ROTATION KEY_LEFT_ALT
#define KEY_MOD_RADIUS   KEY_CAPS_LOCK

// NOTE(cmmm): GetMousePosition returns actual value only after
// certain amount of frames
#define STARTUP_FRAME_COUNT 3

#define SPOTLIGHT_SPEED_MAX  2000

#define SPOTLIGHT_TARGET_INITIAL_ZOOM     1
#define SPOTLIGHT_TARGET_INITIAL_ROTATION 0
#define SPOTLIGHT_TARGET_INITIAL_FOCUSED  false

#define SPOTLIGHT_ROTATION_MULTIPLIER 45
#define SPOTLIGHT_ROTATION_SPEED_MAX  180

#define SPOTLIGHT_ZOOM_SPEED_MAX       4
#define SPOTLIGHT_ZOOM_MIN             1
#define SPOTLIGHT_ZOOM_MAX            64

#define SPOTLIGHT_RADIUS_MULTIPLIER 50
#define SPOTLIGHT_RADIUS_SPEED_MAX  10
#define SPOTLIGHT_RADIUS_MIN       100

#define SPOTLIGHT_DIMNESS_MIN .25
#define SPOTLIGHT_DIMNESS_MAX .75

#define SPOTLIGHT_FOCUS_SPEED_MAX 2000

#define END_DURATION (.5)

#define EXECLP(P, ...) execlp ((P), (P), __VA_ARGS__, NULL)

static Texture2D screenshot;


static Vector2 translation_target = {0};
static Vector2 spotlight_pos;
static Vector2 spotlight_pos_initial;
static float   spotlight_radius;
static bool    spotlight_focused         = SPOTLIGHT_TARGET_INITIAL_FOCUSED;
static float   spotlight_target_zoom     = SPOTLIGHT_TARGET_INITIAL_ZOOM;
static float   spotlight_target_rotation = SPOTLIGHT_TARGET_INITIAL_ROTATION;
static float   spotlight_target_radius;
static Vector2 spotlight_target_pos;
static float spotlight_radius_unfocused;
static float spotlight_radius_initial_focused;

static Shader shader;
static int shader_location_target;
static int shader_location_dimness;
static int shader_location_radius;

static Camera2D camera = {
    .rotation = 0,
    .zoom     = 1,
};

static Vector2 screen_size = {0};
static float frame_time;

static void
update_frame_info (void)
{
  frame_time = GetFrameTime ();
  if (screen_size.x != GetScreenWidth  () ||
      screen_size.y != GetScreenHeight ()) {
    screen_size.x = GetScreenWidth  ();
    screen_size.y = GetScreenHeight ();

    spotlight_radius_unfocused = Vector2Length (screen_size);
    spotlight_radius_initial_focused = fminf (screen_size.x, screen_size.y)/2;
  }
}

static void
handle_input (void)
{
  spotlight_target_pos = GetMousePosition ();

  if (IsMouseButtonDown (MOUSE_BUTTON_RIGHT))
    translation_target = Vector2Add (translation_target, GetMouseDelta ());

  float wheel_move = GetMouseWheelMove ();
  if (wheel_move) {
    if (IsKeyDown (KEY_MOD_ROTATION)) {
      spotlight_target_rotation += SPOTLIGHT_ROTATION_MULTIPLIER*wheel_move;
    } else if (IsKeyDown (KEY_MOD_RADIUS)) {
      if (!spotlight_focused) {
        spotlight_focused = true;
        spotlight_target_radius = spotlight_radius_initial_focused;
        HideCursor ();
      }

      spotlight_target_radius += SPOTLIGHT_RADIUS_MULTIPLIER*wheel_move;
      float spotlight_radius_max = spotlight_radius_unfocused;
      spotlight_target_radius = Clamp (spotlight_target_radius,
                                       SPOTLIGHT_RADIUS_MIN,
                                       spotlight_radius_max);
    } else {
      float scale_factor = 1 + fabsf (wheel_move)/4;
      if (!signbit (wheel_move)) scale_factor = 1/scale_factor;
      spotlight_target_zoom = Clamp (spotlight_target_zoom*scale_factor,
                                     SPOTLIGHT_ZOOM_MIN,
                                     SPOTLIGHT_ZOOM_MAX);
    }
  }

  if (IsKeyPressed (KEY_F)) {
    spotlight_focused ^= 1;
    if (spotlight_focused) {
      spotlight_target_radius = spotlight_radius_initial_focused;
      HideCursor ();
    } else
      ShowCursor ();
  }
}

static void
update (void)
{
  spotlight_pos = Vector2MoveTowards (spotlight_pos, spotlight_target_pos,
                                      SPOTLIGHT_SPEED_MAX*frame_time);

  Vector2 translation_delta = Vector2MoveTowards (translation_delta, translation_target,
                                                  SPOTLIGHT_SPEED_MAX*frame_time);
  translation_target = Vector2Subtract (translation_target, translation_delta);
  Vector2 delta_target = Vector2Rotate (Vector2Scale (translation_delta,
                                                      -1/camera.zoom),
                                        -camera.rotation*DEG2RAD);
  camera.target = Vector2Add (camera.target, delta_target);


  if (!spotlight_focused) {
    spotlight_target_radius = spotlight_radius_unfocused;
  }

  camera.rotation += Clamp (spotlight_target_rotation - camera.rotation,
                            -SPOTLIGHT_ROTATION_SPEED_MAX*frame_time,
                            +SPOTLIGHT_ROTATION_SPEED_MAX*frame_time);

  camera.zoom += Clamp (spotlight_target_zoom - camera.zoom,
                        -SPOTLIGHT_ZOOM_SPEED_MAX*frame_time,
                        +SPOTLIGHT_ZOOM_SPEED_MAX*frame_time);
  camera.target = GetScreenToWorld2D (spotlight_pos, camera);
  camera.offset = spotlight_pos;

  spotlight_radius += Clamp (spotlight_target_radius - spotlight_radius,
                             -SPOTLIGHT_FOCUS_SPEED_MAX*frame_time,
                             +SPOTLIGHT_FOCUS_SPEED_MAX*frame_time);
}

static void
draw (void)
{
  Vector2 target = { spotlight_pos.x, screen_size.y - spotlight_pos.y, };
  float dimness = Remap (spotlight_radius,
                         spotlight_radius_initial_focused,
                         SPOTLIGHT_RADIUS_MIN,
                         SPOTLIGHT_DIMNESS_MIN,
                         SPOTLIGHT_DIMNESS_MAX);
  SetShaderValue (shader, shader_location_target,  &target,           SHADER_UNIFORM_VEC2);
  SetShaderValue (shader, shader_location_dimness, &dimness,          SHADER_UNIFORM_FLOAT);
  SetShaderValue (shader, shader_location_radius,  &spotlight_radius, SHADER_UNIFORM_FLOAT);

  BeginDrawing (); {
    ClearBackground (BLANK);
    BeginMode2D (camera); {
      BeginShaderMode (shader); {
        DrawTextureV (screenshot, Vector2Zero (), WHITE);
      } EndShaderMode ();
    } EndMode2D ();
  } EndDrawing ();
}

int
main (int argc, char *argv[])
{
  char tmpname[] = "/tmp/spotlight.png";
  // {
  //   int tmp_fd;
  //   do tmp_fd = mkstemp (tmpname);
  //   while (tmp_fd == -1);
  //   close (tmp_fd);
  // }

  {
    pid_t grim_pid = fork ();
    if (!grim_pid) EXECLP ("grim", tmpname);
    int grim_exit_status;
    waitpid (grim_pid, &grim_exit_status, 0);
    if (grim_exit_status) {
      TraceLog (LOG_ERROR, "GRIM: Unable to capture screenshot (%s)", tmpname);
      exit (EXIT_FAILURE);
    } TraceLog (LOG_INFO, "GRIM: Screenshot captured (%s)", tmpname);
  }

  SetConfigFlags (FLAG_FULLSCREEN_MODE |
                  FLAG_MSAA_4X_HINT |
                  FLAG_WINDOW_UNDECORATED |
                  FLAG_VSYNC_HINT);
  InitWindow (0, 0, NULL);
  SetMouseCursor (MOUSE_CURSOR_CROSSHAIR);
  screenshot = LoadTexture (tmpname);

  // shader = LoadShader (NULL, "./spotlight.frag");
  shader = LoadShaderFromMemory (NULL, (void *) SPOTLIGHT_FRAG_DATA);
  shader_location_target  = GetShaderLocation (shader, "target");
  shader_location_dimness = GetShaderLocation (shader, "dimness");
  shader_location_radius  = GetShaderLocation (shader, "radius");

  spotlight_radius =
    Vector2Length ((Vector2) { GetScreenWidth (), GetScreenHeight () });
  for (int i = 0; i < STARTUP_FRAME_COUNT; ++i) draw ();
  spotlight_pos = spotlight_pos_initial = GetMousePosition ();
  camera.target = GetScreenToWorld2D (spotlight_pos, camera);
  camera.offset =                     spotlight_pos;
  while (!WindowShouldClose ()) {
    update_frame_info ();
    handle_input ();
    update ();
    draw   ();
  }

  Vector2 camera_target = GetMousePosition ();
  Camera2D start_camera = camera;
  float start_spotlight_radius = spotlight_radius;
  float distances[5] = {
    Remap (Vector2Distance (start_camera.target, camera_target), 0, Vector2Length (screen_size), 0, 1),
    Remap (Vector2Distance (start_camera.offset, camera_target), 0, Vector2Length (screen_size), 0, 1),
    start_camera.rotation/SPOTLIGHT_ROTATION_MULTIPLIER,
    Remap (start_camera.zoom, SPOTLIGHT_ZOOM_MIN, SPOTLIGHT_ZOOM_MAX, 0, 1),
    Remap (start_spotlight_radius - spotlight_radius_unfocused, 0, spotlight_radius_unfocused - SPOTLIGHT_RADIUS_MIN, 0, 1),
  };
  float max_distance = 0;
  for (int i = 0; i < 5; ++i) {
    if (distances[i] > max_distance)
      max_distance = distances[i];
  }

  if (max_distance) {
    float end_speed = 4/(1 + fminf ( max_distance, 1));
    for (float progress  = end_speed*frame_time; progress < 1
      ;        progress += end_speed*frame_time) {
      update_frame_info ();

      Vector2 spotlight_pos_world = GetScreenToWorld2D (spotlight_pos, camera);
      camera.target    = Vector2Lerp (start_camera.target,                 camera_target,  progress);
      camera.offset    = Vector2Lerp (start_camera.offset,                 camera_target,  progress);
      camera.rotation  =        Lerp (start_camera.rotation,                           0,  progress);
      camera.zoom      =        Lerp (start_camera.zoom,                               1,  progress);
      spotlight_radius =        Lerp (start_spotlight_radius, spotlight_radius_unfocused, progress);
      spotlight_pos = GetWorldToScreen2D (spotlight_pos_world, camera);

      draw ();
    }
  }

  UnloadTexture (screenshot);
  CloseWindow ();

  return EXIT_SUCCESS;
}