#include <model.h>

#include <filesystem.h>
// TODO: Update math/camera to explicitly expose ortho/perspective camera parameters,
//  not just a baked matrix.
//#include <math/camera.h>
#include <math/spatial3.h>
#include <math/vec2.h>
#include <swgfx.h>
#include <SDL3/SDL.h>
#include <SDL3/SDL_timer.h>

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

static constexpr int     BufferWidth  = 160;
static constexpr int     BufferHeight = 120;
static constexpr sgVec2i BufferDims   = (sgVec2i){.x = BufferWidth, .y = BufferHeight};
static constexpr R       Aspect       = (R)BufferWidth / (R)BufferHeight;

static const char*   WindowTitle  = "GAME";
// Window dimensions must be an integer scaling of buffer dimensions.
// TODO: Make window dimensions a function of DPI.
static constexpr int     WindowWidth  = 640;
static constexpr int     WindowHeight = 480;
static constexpr sgVec2i WindowDims   = (sgVec2i){.x = WindowWidth, .y = WindowHeight};

static const R Fovy = (R)(90 * TO_RAD);

#define DEBUG_EVENT_LOOP 1

#ifdef DEBUG_EVENT_LOOP
#define EVENT_LOOP_PRINT printf
#else
#define EVENT_LOOP_PRINT(...)
#endif // DEBUG_EVENT_LOOP

typedef struct CameraCommand {
  bool CameraMoveLeft     : 1;
  bool CameraMoveRight    : 1;
  bool CameraMoveForward  : 1;
  bool CameraMoveBackward : 1;
  bool CameraSlow         : 1; // When true, move more slowly.
  bool CameraRotate       : 1; // When true, subsequent mouse movements cause
                               // the camera to rotate.
} CameraCommand;

typedef struct CameraController {
  R speed;          // Camera movement speed.
  R rotation_speed; // Controls the degree with which mouse movements rotate
                    // the camera.
  vec2 prev_mouse_position; // Mouse position in the previous frame.
} CameraController;

typedef struct Camera {
  Spatial3 spatial;
  R        fovy;
  R        aspect;
  R        near;
  R        far;
} Camera;

typedef struct State {
  SDL_Window*      window;
  swgfx*           gfx;
  sgPixel*         colour;
  Model*           model;
  Camera           camera;
  CameraController camera_controller;
  Uint64           last_tick;
} State;

static sgVec3 SgVec3FromMathVec3(vec3 v) {
  return (sgVec3){v.x, v.y, v.z};
}

static CameraCommand CameraCommandFromInput(
    const bool* keyboard_state, const SDL_MouseButtonFlags mouse_flags) {
  assert(keyboard_state);
  if (keyboard_state[SDL_SCANCODE_W]) {
    printf("W: %d\n", keyboard_state[SDL_SCANCODE_W]);
  }
  return (CameraCommand){
    .CameraMoveLeft     = keyboard_state[SDL_SCANCODE_A],
    .CameraMoveRight    = keyboard_state[SDL_SCANCODE_D],
    .CameraMoveForward  = keyboard_state[SDL_SCANCODE_W],
    .CameraMoveBackward = keyboard_state[SDL_SCANCODE_S],
    .CameraSlow         = keyboard_state[SDL_SCANCODE_LSHIFT],
    .CameraRotate       = mouse_flags & SDL_BUTTON_MASK(SDL_BUTTON_LEFT),
  };
}

static void UpdateCamera(
    CameraController* controller, R dt, vec2 mouse_position,
    CameraCommand command, Camera* camera) {
  assert(controller);
  assert(camera);

  Spatial3* cam = &camera->spatial;

  // Translation.
  const R move_x = (R)(command.CameraMoveLeft ? -1 : 0) +
                   (R)(command.CameraMoveRight ? 1 : 0);
  const R move_y = (R)(command.CameraMoveForward ? 1 : 0) +
                   (R)(command.CameraMoveBackward ? -1 : 0);
  const R speed_factor = command.CameraSlow ? 0.3f : 1.f;
  const vec2 translation  = vec2_scale(
      vec2_normalize(vec2_make(move_x, move_y)),
      controller->speed * speed_factor * dt);
  spatial3_move_right(cam, translation.x);
  spatial3_move_forwards(cam, translation.y);

  // Rotation.
  if (command.CameraRotate) {
    const vec2 mouse_delta =
        vec2_sub(mouse_position, controller->prev_mouse_position);

    const vec2 rotation =
        vec2_scale(mouse_delta, controller->rotation_speed * dt);

    spatial3_global_yaw(cam, -rotation.x);
    spatial3_pitch(cam, -rotation.y);
  }

  // Update controller state.
  controller->prev_mouse_position = mouse_position;
}

static bool Update(State* state, R dt) {
  assert(state);

  int num_keys = 0;
  const bool* keyboard_state = SDL_GetKeyboardState(&num_keys);

  vec2 mouse = {0};
  const SDL_MouseButtonFlags mouse_flags = SDL_GetMouseState(&mouse.x, &mouse.y);

  const CameraCommand cmd = CameraCommandFromInput(keyboard_state, mouse_flags);
  UpdateCamera(&state->camera_controller, dt, mouse, cmd, &state->camera);

  return true;
}

static void RenderIndexedModel(swgfx* gfx, const IndexedModel* model) {
  assert(gfx);
  assert(model);
  const sgTriIdx*  tris   = (const sgTriIdx*)(model->data + model->offsetTris);
  const sgVec3* positions = (const sgVec3*)(model->data + model->offsetPositions);
  sgTrianglesIndexedNonUniform(gfx, model->numTris, tris, positions);
}

static void RenderModel(swgfx* gfx, const Model* model) {
  assert(gfx);
  assert(model);
  switch (model->type) {
  case ModelTypeIndexed: RenderIndexedModel(gfx, &model->indexed); break;
  case ModelTypeFlat: /* TODO: Render flat models. */ break;
  default: assert(false); break;
  }
}

static void RenderTriangle2d(swgfx* gfx) {
  assert(gfx);
  const sgVec2 p0  = (sgVec2){20, 20};
  const sgVec2 p1  = (sgVec2){80, 20};
  const sgVec2 p2  = (sgVec2){50, 50};
  const sgTri2 tri = (sgTri2){p0, p1, p2};
  sgTriangles2(gfx, 1, &tri);
}

static void Checkerboard(swgfx* gfx, int width, int height) {
  assert(gfx);
  const sgPixel colour = (sgPixel){255, 0, 255, 255};
  for (int y = 0; y < height; ++y) {
    for (int x = 0; x < width; ++x) {
      if (((x ^ y) & 1) == 1) {
        const sgVec2i position = (sgVec2i){x, y};
        sgPixels(gfx, 1, &position, colour);
      }
    }
  }
}

static bool Render(State* state) {
  assert(state);
  assert(state->window);
  assert(state->gfx);

  // Locking/unlocking SDL software surfaces is not necessary.
  // Probably also best to avoid SDL_BlitSurface(); it does pixel format
  // conversion while blitting one pixel at a time. Instead, make the UI pixel
  // format match the SDL window's and write to SDL's back buffer directly.
  SDL_Surface* window_surface = SDL_GetWindowSurface(state->window);
  assert(window_surface);
  
  // Until we make the window resizable, assert dimensions for safety.
  assert(window_surface->w == WindowWidth);
  assert(window_surface->h == WindowHeight);

#ifdef DEBUG_EVENT_LOOP
  EVENT_LOOP_PRINT(
      "Render: window surface: %dx%d\n",
      window_surface->w, window_surface->h);
#endif

  const Camera* cam = &state->camera;

  sgColourBuffer(state->gfx, BufferDims, state->colour);
  sgClear(state->gfx);
  sgViewport(state->gfx, 0, 0, BufferWidth, BufferHeight);
  sgCheck(state->gfx);
  // TODO: For easier debugging, overlay the checkerboard on top of the
  //  other rendered items with alpha blending.
  //Checkerboard(state->gfx, BufferWidth, BufferHeight);
  //RenderTriangle2d(state->gfx);
  sgModelId(state->gfx);
  sgView(state->gfx, SgVec3FromMathVec3(cam->spatial.p), SgVec3FromMathVec3(cam->spatial.f));
  sgPerspective(state->gfx, cam->fovy, cam->aspect, cam->near, cam->far);
  RenderModel(state->gfx, state->model);
  /*sgIdx indices[3] = {0, 1, 2};
  sgVec3 positions[3] = {
    (sgVec3){0, 0, 0},
    (sgVec3){5, 2, 0},
    (sgVec3){8, 8, 0},
  };
  sgTrianglesIndexed(state->gfx, 3, indices, positions);*/
  sgPresent(state->gfx, WindowDims, window_surface->pixels);

  if (!SDL_UpdateWindowSurface(state->window)) {
    return false;
  }

  return true;
}

static bool Resize(State* state) {
  assert(state);

  // int width, height;
  // SDL_GetWindowSize(state->window, &width, &height);

  const SDL_Surface* window_surface = SDL_GetWindowSurface(state->window);
  if (!window_surface) {
    return false;
  }
  const int width  = window_surface->w;
  const int height = window_surface->h;

  EVENT_LOOP_PRINT("Resize: %dx%d\n", width, height);

  return true;
}

static bool Initialize(State* state) {
  assert(state);

  if ((state->window = SDL_CreateWindow(
         WindowTitle,
         WindowWidth,
         WindowHeight,
         0)) == NULL) {
    fprintf(stderr, "SDL_CreateWindow failed\n");
    return false;
  }
  
  if (!(state->gfx = sgNew())) {
    fprintf(stderr, "sgNew failed\n");
    return false;
  }
  
  if (!(state->colour = SG_ALIGN_ALLOC(BufferWidth * BufferHeight, sgPixel))) {
    fprintf(stderr, "Failed to allocate colour buffer\n");
    return false;
  }
  
  sgColourBuffer(state->gfx, BufferDims, state->colour);

  const char* model_path = "/home/jeanne/blender/box.mdl";
  if (!(state->model = read_file(model_path))) {
    fprintf(stderr, "Failed to load model: [%s]\n", model_path);
    return false;
  }

  Camera* camera    = &state->camera;
  camera->fovy      = Fovy;
  camera->aspect    = Aspect;
  camera->near      = 0.1f;
  camera->far       = 1000.f;
  camera->spatial   = spatial3_make();
  camera->spatial.p = vec3_make(0, 1, 10);

  state->camera_controller = (CameraController){
    .speed = 7.f,
    .rotation_speed = (R)(90 * TO_RAD),
  };

  state->last_tick = SDL_GetPerformanceCounter();

  return true;
}

static void Shutdown(State* state) {
  assert(state);

  if (state->model) {
    free(state->model);
    state->model = nullptr;
  }
  
  if (state->colour) {
    SG_FREE(&state->colour);
  }
  
  if (state->gfx) {
    sgDel(&state->gfx);
  }
  
  if (state->window) {
    SDL_DestroyWindow(state->window);
    state->window = nullptr;
  }
}

static R GetDeltaTime(State* state) {
  assert(state);
  constexpr Uint64 NS_IN_SEC = 1'000'000'000;
  const Uint64 this_tick = SDL_GetPerformanceCounter();
  const Uint64 freq = SDL_GetPerformanceFrequency();
  const Uint64 elapsed_ns = (this_tick - state->last_tick) * NS_IN_SEC / freq;
  const R elapsed_sec = (R)elapsed_ns / (R)NS_IN_SEC;
  state->last_tick = this_tick;
  return elapsed_sec;
}

int main() {
  bool success = false;
  // Controls whether we should keep running.
  bool running = true;

  State state = {0};

  if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS)) {
    fprintf(stderr, "SDL_Init failed\n");
    goto cleanup;
  }

  if (!Initialize(&state)) {
    fprintf(stderr, "Initialization failed\n");
    goto cleanup;
  }

  if (!Resize(&state)) {
    goto cleanup;
  }
  
  success = true;

  while (success && running) {
    EVENT_LOOP_PRINT("loop\n");

    // Handle events.
    SDL_Event event = {0};
    while (SDL_PollEvent(&event)) {
      if ((event.type == SDL_EVENT_QUIT) ||
          (event.type == SDL_EVENT_WINDOW_CLOSE_REQUESTED)) {
        running = false;
        break;
      } else if ((event.window.type == SDL_EVENT_WINDOW_DISPLAY_CHANGED) ||
                 (event.window.type == SDL_EVENT_WINDOW_RESIZED) ||
                 (event.window.type == SDL_EVENT_WINDOW_MOVED)) {
        // When the window is maximized, an SDL_WINDOWEVENT_MOVED comes in
        // before an SDL_WINDOWEVENT_SIZE_CHANGED with the window already
        // resized. This is unfortunate because we cannot rely on the latter
        // event alone to handle resizing.
        if (!Resize(&state)) {
          success = false;
          break;
        }
      } else if (event.type == SDL_EVENT_KEY_DOWN) {
        if (event.key.mod & SDL_KMOD_LCTRL) {
          switch (event.key.key) {
          // Exit.
          case SDLK_C:
          case SDLK_D:
            running = false;
            break;
          default:
            break;
          }
        }
      } else if (event.type == SDL_EVENT_MOUSE_BUTTON_DOWN) {
        //
      } else if (event.type == SDL_EVENT_MOUSE_BUTTON_UP) {
        //
      } else if (event.type == SDL_EVENT_MOUSE_WHEEL) {
        //
      } else {
        EVENT_LOOP_PRINT("event.window.type = %d\n", event.window.type);
      }
    } // events

    // Draw and update if needed.
    if (success && running) {
      const R dt = GetDeltaTime(&state);
      success = Update(&state, dt);
    }
    if (success && running) {
      success = Render(&state);
    }
  } // loop

cleanup:
  if (!success) {
    fprintf(stderr, "%s\n", SDL_GetError());
  }
  Shutdown(&state);
  SDL_Quit();
  return success ? 0 : 1;
}