// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <cassert>
#include <chrono>
#include <iostream>

#define GLFW_EXPOSE_NATIVE_EGL
#define GLFW_INCLUDE_GLEXT

#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <array>
#include <cstring>
#include <list>
#include <unordered_map>
#include "GLFW/glfw3.h"
#include "GLFW/glfw3native.h"
#include "embedder.h"

// This value is calculated after the window is created.
static double g_pixelRatio = 1.0;
static const size_t kInitialWindowWidth = 800;
static const size_t kInitialWindowHeight = 600;
// Maximum damage history - for triple buffering we need to store damage for
// last two frames; Some Android devices (Pixel 4) use quad buffering.
static const int kMaxHistorySize = 10;
static constexpr FlutterViewId kImplicitViewId = 0;

// Keeps track of the most recent frame damages so that existing damage can
// be easily computed.
std::list<FlutterRect> damage_history_;

// Keeps track of the existing damage associated with each FBO ID
std::unordered_map<intptr_t, FlutterRect*> existing_damage_map_;

EGLDisplay display_;
EGLSurface surface_;

static_assert(FLUTTER_ENGINE_VERSION == 1,
              "This Flutter Embedder was authored against the stable Flutter "
              "API at version 1. There has been a serious breakage in the "
              "API. Please read the ChangeLog and take appropriate action "
              "before updating this assertion");

void GLFWcursorPositionCallbackAtPhase(GLFWwindow* window,
                                       FlutterPointerPhase phase,
                                       double x,
                                       double y) {
  FlutterPointerEvent event = {};
  event.struct_size = sizeof(event);
  event.phase = phase;
  event.x = x * g_pixelRatio;
  event.y = y * g_pixelRatio;
  event.timestamp =
      std::chrono::duration_cast<std::chrono::microseconds>(
          std::chrono::high_resolution_clock::now().time_since_epoch())
          .count();
  // This example only supports a single window, therefore we assume the pointer
  // event occurred in the only view, the implicit view.
  event.view_id = kImplicitViewId;
  FlutterEngineSendPointerEvent(
      reinterpret_cast<FlutterEngine>(glfwGetWindowUserPointer(window)), &event,
      1);
}

void GLFWcursorPositionCallback(GLFWwindow* window, double x, double y) {
  GLFWcursorPositionCallbackAtPhase(window, FlutterPointerPhase::kMove, x, y);
}

void GLFWmouseButtonCallback(GLFWwindow* window,
                             int key,
                             int action,
                             int mods) {
  if (key == GLFW_MOUSE_BUTTON_1 && action == GLFW_PRESS) {
    double x, y;
    glfwGetCursorPos(window, &x, &y);
    GLFWcursorPositionCallbackAtPhase(window, FlutterPointerPhase::kDown, x, y);
    glfwSetCursorPosCallback(window, GLFWcursorPositionCallback);
  }

  if (key == GLFW_MOUSE_BUTTON_1 && action == GLFW_RELEASE) {
    double x, y;
    glfwGetCursorPos(window, &x, &y);
    GLFWcursorPositionCallbackAtPhase(window, FlutterPointerPhase::kUp, x, y);
    glfwSetCursorPosCallback(window, nullptr);
  }
}

static void GLFWKeyCallback(GLFWwindow* window,
                            int key,
                            int scancode,
                            int action,
                            int mods) {
  if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
    glfwSetWindowShouldClose(window, GLFW_TRUE);
  }
}

void GLFWwindowSizeCallback(GLFWwindow* window, int width, int height) {
  FlutterWindowMetricsEvent event = {};
  event.struct_size = sizeof(event);
  event.width = width * g_pixelRatio;
  event.height = height * g_pixelRatio;
  event.pixel_ratio = g_pixelRatio;
  // This example only supports a single window, therefore we assume the event
  // occurred in the only view, the implicit view.
  event.view_id = kImplicitViewId;
  FlutterEngineSendWindowMetricsEvent(
      reinterpret_cast<FlutterEngine>(glfwGetWindowUserPointer(window)),
      &event);
}

// Auxiliary function used to transform a FlutterRect into the format that is
// expected by the EGL functions (i.e. array of EGLint).
static std::array<EGLint, 4> RectToInts(const FlutterRect rect) {
  EGLint height;
  eglQuerySurface(display_, surface_, EGL_HEIGHT, &height);

  std::array<EGLint, 4> res{
      static_cast<int>(rect.left), height - static_cast<int>(rect.bottom),
      static_cast<int>(rect.right) - static_cast<int>(rect.left),
      static_cast<int>(rect.bottom) - static_cast<int>(rect.top)};
  return res;
}

// Auxiliary function to union the damage regions comprised by two FlutterRect
// element. It saves the result of this join in the rect variable.
static void JoinFlutterRect(FlutterRect* rect, FlutterRect additional_rect) {
  rect->left = std::min(rect->left, additional_rect.left);
  rect->top = std::min(rect->top, additional_rect.top);
  rect->right = std::max(rect->right, additional_rect.right);
  rect->bottom = std::max(rect->bottom, additional_rect.bottom);
}

// Auxiliary function used to check if the given list of extensions contains the
// requested extension name.
static bool HasExtension(const char* extensions, const char* name) {
  const char* r = strstr(extensions, name);
  auto len = strlen(name);
  // check that the extension name is terminated by space or null terminator
  return r != nullptr && (r[len] == ' ' || r[len] == 0);
}

bool RunFlutter(GLFWwindow* window,
                const std::string& project_path,
                const std::string& icudtl_path) {
  FlutterRendererConfig config = {};
  config.type = kOpenGL;
  config.open_gl.struct_size = sizeof(config.open_gl);
  config.open_gl.make_current = [](void* userdata) -> bool {
    glfwMakeContextCurrent(static_cast<GLFWwindow*>(userdata));
    return true;
  };
  config.open_gl.clear_current = [](void*) -> bool {
    glfwMakeContextCurrent(nullptr);  // is this even a thing?
    return true;
  };
  config.open_gl.present_with_info =
      [](void* userdata, const FlutterPresentInfo* info) -> bool {
    // Free the existing damage that was allocated to this frame.
    if (existing_damage_map_[info->fbo_id] != nullptr) {
      free(existing_damage_map_[info->fbo_id]);
      existing_damage_map_[info->fbo_id] = nullptr;
    }

    // Get list of extensions.
    const char* extensions = eglQueryString(display_, EGL_EXTENSIONS);

    // Retrieve the set damage region function.
    PFNEGLSETDAMAGEREGIONKHRPROC set_damage_region_ = nullptr;
    if (HasExtension(extensions, "EGL_KHR_partial_update")) {
      set_damage_region_ = reinterpret_cast<PFNEGLSETDAMAGEREGIONKHRPROC>(
          eglGetProcAddress("eglSetDamageRegionKHR"));
    }

    // Retrieve the swap buffers with damage function.
    PFNEGLSWAPBUFFERSWITHDAMAGEEXTPROC swap_buffers_with_damage_ = nullptr;
    if (HasExtension(extensions, "EGL_EXT_swap_buffers_with_damage")) {
      swap_buffers_with_damage_ =
          reinterpret_cast<PFNEGLSWAPBUFFERSWITHDAMAGEEXTPROC>(
              eglGetProcAddress("eglSwapBuffersWithDamageEXT"));
    } else if (HasExtension(extensions, "EGL_KHR_swap_buffers_with_damage")) {
      swap_buffers_with_damage_ =
          reinterpret_cast<PFNEGLSWAPBUFFERSWITHDAMAGEEXTPROC>(
              eglGetProcAddress("eglSwapBuffersWithDamageKHR"));
    }

    if (set_damage_region_) {
      // Set the buffer damage as the damage region.
      auto buffer_rects = RectToInts(info->buffer_damage.damage[0]);
      set_damage_region_(display_, surface_, buffer_rects.data(), 1);
    }

    // Add frame damage to damage history
    damage_history_.push_back(info->frame_damage.damage[0]);
    if (damage_history_.size() > kMaxHistorySize) {
      damage_history_.pop_front();
    }

    if (swap_buffers_with_damage_) {
      // Swap buffers with frame damage.
      auto frame_rects = RectToInts(info->frame_damage.damage[0]);
      return swap_buffers_with_damage_(display_, surface_, frame_rects.data(),
                                       1);
    } else {
      // If the required extensions for partial repaint were not provided, do
      // full repaint.
      return eglSwapBuffers(display_, surface_);
    }
  };
  config.open_gl.fbo_callback = [](void*) -> uint32_t {
    return 0;  // FBO0
  };
  config.open_gl.populate_existing_damage =
      [](void* userdata, intptr_t fbo_id,
         FlutterDamage* existing_damage) -> void {
    // Given the FBO age, create existing damage region by joining all frame
    // damages since FBO was last used
    EGLint age;
    if (glfwExtensionSupported("GL_EXT_buffer_age") == GLFW_TRUE) {
      eglQuerySurface(display_, surface_, EGL_BUFFER_AGE_EXT, &age);
    } else {
      age = 4;  // Virtually no driver should have a swapchain length > 4.
    }

    existing_damage->num_rects = 1;

    // Allocate the array of rectangles for the existing damage.
    existing_damage_map_[fbo_id] = static_cast<FlutterRect*>(
        malloc(sizeof(FlutterRect) * existing_damage->num_rects));
    existing_damage_map_[fbo_id][0] =
        FlutterRect{0, 0, kInitialWindowWidth, kInitialWindowHeight};
    existing_damage->damage = existing_damage_map_[fbo_id];

    if (age > 1) {
      --age;
      // join up to (age - 1) last rects from damage history
      for (auto i = damage_history_.rbegin();
           i != damage_history_.rend() && age > 0; ++i, --age) {
        if (i == damage_history_.rbegin()) {
          if (i != damage_history_.rend()) {
            existing_damage->damage[0] = {i->left, i->top, i->right, i->bottom};
          }
        } else {
          JoinFlutterRect(&(existing_damage->damage[0]), *i);
        }
      }
    }
  };
  config.open_gl.gl_proc_resolver = [](void*, const char* name) -> void* {
    return reinterpret_cast<void*>(glfwGetProcAddress(name));
  };
  config.open_gl.fbo_reset_after_present = true;

  // This directory is generated by `flutter build bundle`.
  std::string assets_path = project_path + "/build/flutter_assets";
  FlutterProjectArgs args = {
      .struct_size = sizeof(FlutterProjectArgs),
      .assets_path = assets_path.c_str(),
      .icu_data_path =
          icudtl_path.c_str(),  // Find this in your bin/cache directory.
  };
  FlutterEngine engine = nullptr;
  FlutterEngineResult result =
      FlutterEngineRun(FLUTTER_ENGINE_VERSION, &config,  // renderer
                       &args, window, &engine);
  if (result != kSuccess || engine == nullptr) {
    std::cout << "Could not run the Flutter Engine." << std::endl;
    return false;
  }

  glfwSetWindowUserPointer(window, engine);
  GLFWwindowSizeCallback(window, kInitialWindowWidth, kInitialWindowHeight);

  return true;
}

void printUsage() {
  std::cout
      << "usage: embedder_example_drm <path to project> <path to icudtl.dat>"
      << std::endl;
}

void GLFW_ErrorCallback(int error, const char* description) {
  std::cout << "GLFW Error: (" << error << ") " << description << std::endl;
}

int main(int argc, const char* argv[]) {
  if (argc != 3) {
    printUsage();
    return 1;
  }

  std::string project_path = argv[1];
  std::string icudtl_path = argv[2];

  glfwSetErrorCallback(GLFW_ErrorCallback);

  int result = glfwInit();
  if (result != GLFW_TRUE) {
    std::cout << "Could not initialize GLFW." << std::endl;
    return EXIT_FAILURE;
  }

#if defined(__linux__)
  glfwWindowHint(GLFW_CONTEXT_CREATION_API, GLFW_EGL_CONTEXT_API);
#endif

  GLFWwindow* window = glfwCreateWindow(
      kInitialWindowWidth, kInitialWindowHeight, "Flutter", NULL, NULL);
  if (window == nullptr) {
    std::cout << "Could not create GLFW window." << std::endl;
    return EXIT_FAILURE;
  }

  int framebuffer_width, framebuffer_height;
  glfwGetFramebufferSize(window, &framebuffer_width, &framebuffer_height);
  g_pixelRatio = framebuffer_width / kInitialWindowWidth;

  // Get the display and surface variables.
  display_ = glfwGetEGLDisplay();
  surface_ = glfwGetEGLSurface(window);

  bool run_result = RunFlutter(window, project_path, icudtl_path);
  if (!run_result) {
    std::cout << "Could not run the Flutter engine." << std::endl;
    return EXIT_FAILURE;
  }

  glfwSetKeyCallback(window, GLFWKeyCallback);
  glfwSetWindowSizeCallback(window, GLFWwindowSizeCallback);
  glfwSetMouseButtonCallback(window, GLFWmouseButtonCallback);

  while (!glfwWindowShouldClose(window)) {
    glfwWaitEvents();
  }

  glfwDestroyWindow(window);
  glfwTerminate();

  return EXIT_SUCCESS;
}