// dear imgui: standalone example application for Android + OpenGL ES 3

// Learn about Dear ImGui:
// - FAQ                  https://dearimgui.com/faq
// - Getting Started      https://dearimgui.com/getting-started
// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
// - Introduction, links and more at the top of imgui.cpp

#include "imgui.h"
#include "imgui_impl_android.h"
#include "imgui_impl_opengl3.h"
#include <android/log.h>
#include <android_native_app_glue.h>
#include <android/asset_manager.h>
#include <EGL/egl.h>
#include <GLES3/gl3.h>
#include <string>

// Data
static EGLDisplay           g_EglDisplay = EGL_NO_DISPLAY;
static EGLSurface           g_EglSurface = EGL_NO_SURFACE;
static EGLContext           g_EglContext = EGL_NO_CONTEXT;
static struct android_app*  g_App = nullptr;
static bool                 g_Initialized = false;
static char                 g_LogTag[] = "ImGuiExample";
static std::string          g_IniFilename = "";

// Forward declarations of helper functions
static void Init(struct android_app* app);
static void Shutdown();
static void MainLoopStep();
static int ShowSoftKeyboardInput();
static int PollUnicodeChars();
static int GetAssetData(const char* filename, void** out_data);

// Main code
static void handleAppCmd(struct android_app* app, int32_t appCmd)
{
    switch (appCmd)
    {
    case APP_CMD_SAVE_STATE:
        break;
    case APP_CMD_INIT_WINDOW:
        Init(app);
        break;
    case APP_CMD_TERM_WINDOW:
        Shutdown();
        break;
    case APP_CMD_GAINED_FOCUS:
    case APP_CMD_LOST_FOCUS:
        break;
    }
}

static int32_t handleInputEvent(struct android_app* app, AInputEvent* inputEvent)
{
    return ImGui_ImplAndroid_HandleInputEvent(inputEvent);
}

void android_main(struct android_app* app)
{
    app->onAppCmd = handleAppCmd;
    app->onInputEvent = handleInputEvent;

    while (true)
    {
        int out_events;
        struct android_poll_source* out_data;

        // Poll all events. If the app is not visible, this loop blocks until g_Initialized == true.
        while (ALooper_pollOnce(g_Initialized ? 0 : -1, nullptr, &out_events, (void**)&out_data) >= 0)
        {
            // Process one event
            if (out_data != nullptr)
                out_data->process(app, out_data);

            // Exit the app by returning from within the infinite loop
            if (app->destroyRequested != 0)
            {
                // shutdown() should have been called already while processing the
                // app command APP_CMD_TERM_WINDOW. But we play save here
                if (!g_Initialized)
                    Shutdown();

                return;
            }
        }

        // Initiate a new frame
        MainLoopStep();
    }
}

void Init(struct android_app* app)
{
    if (g_Initialized)
        return;

    g_App = app;
    ANativeWindow_acquire(g_App->window);

    // Initialize EGL
    // This is mostly boilerplate code for EGL...
    {
        g_EglDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);
        if (g_EglDisplay == EGL_NO_DISPLAY)
            __android_log_print(ANDROID_LOG_ERROR, g_LogTag, "%s", "eglGetDisplay(EGL_DEFAULT_DISPLAY) returned EGL_NO_DISPLAY");

        if (eglInitialize(g_EglDisplay, 0, 0) != EGL_TRUE)
            __android_log_print(ANDROID_LOG_ERROR, g_LogTag, "%s", "eglInitialize() returned with an error");

        const EGLint egl_attributes[] = { EGL_BLUE_SIZE, 8, EGL_GREEN_SIZE, 8, EGL_RED_SIZE, 8, EGL_DEPTH_SIZE, 24, EGL_SURFACE_TYPE, EGL_WINDOW_BIT, EGL_NONE };
        EGLint num_configs = 0;
        if (eglChooseConfig(g_EglDisplay, egl_attributes, nullptr, 0, &num_configs) != EGL_TRUE)
            __android_log_print(ANDROID_LOG_ERROR, g_LogTag, "%s", "eglChooseConfig() returned with an error");
        if (num_configs == 0)
            __android_log_print(ANDROID_LOG_ERROR, g_LogTag, "%s", "eglChooseConfig() returned 0 matching config");

        // Get the first matching config
        EGLConfig egl_config;
        eglChooseConfig(g_EglDisplay, egl_attributes, &egl_config, 1, &num_configs);
        EGLint egl_format;
        eglGetConfigAttrib(g_EglDisplay, egl_config, EGL_NATIVE_VISUAL_ID, &egl_format);
        ANativeWindow_setBuffersGeometry(g_App->window, 0, 0, egl_format);

        const EGLint egl_context_attributes[] = { EGL_CONTEXT_CLIENT_VERSION, 3, EGL_NONE };
        g_EglContext = eglCreateContext(g_EglDisplay, egl_config, EGL_NO_CONTEXT, egl_context_attributes);

        if (g_EglContext == EGL_NO_CONTEXT)
            __android_log_print(ANDROID_LOG_ERROR, g_LogTag, "%s", "eglCreateContext() returned EGL_NO_CONTEXT");

        g_EglSurface = eglCreateWindowSurface(g_EglDisplay, egl_config, g_App->window, nullptr);
        eglMakeCurrent(g_EglDisplay, g_EglSurface, g_EglSurface, g_EglContext);
    }

    // Setup Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();

    // Redirect loading/saving of .ini file to our location.
    // Make sure 'g_IniFilename' persists while we use Dear ImGui.
    g_IniFilename = std::string(app->activity->internalDataPath) + "/imgui.ini";
    io.IniFilename = g_IniFilename.c_str();;

    // Setup Dear ImGui style
    ImGui::StyleColorsDark();
    //ImGui::StyleColorsLight();

    // Setup Platform/Renderer backends
    ImGui_ImplAndroid_Init(g_App->window);
    ImGui_ImplOpenGL3_Init("#version 300 es");

    // Setup scaling
    float main_scale = 2.0f;
    ImGuiStyle& style = ImGui::GetStyle();
    style.ScaleAllSizes(main_scale);        // Bake a fixed style scale. (until we have a solution for dynamic style scaling, changing this requires resetting Style + calling this again)
    style.FontScaleDpi = main_scale;        // Set initial font scale.

    // Load Fonts
    // - If fonts are not explicitly loaded, Dear ImGui will select an embedded font: either AddFontDefaultVector() or AddFontDefaultBitmap().
    //   This selection is based on (style.FontSizeBase * style.FontScaleMain * style.FontScaleDpi) reaching a small threshold.
    // - You can load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
    // - If a file cannot be loaded, AddFont functions will return a nullptr. Please handle those errors in your code (e.g. use an assertion, display an error and quit).
    // - Read 'docs/FONTS.md' for more instructions and details.
    // - Use '#define IMGUI_ENABLE_FREETYPE' in your imconfig file to use FreeType for higher quality font rendering.
    // - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
    // - Android: The TTF files have to be placed into the assets/ directory (android/app/src/main/assets), we use our GetAssetData() helper to retrieve them.
    //style.FontSizeBase = 20.0f;
    //io.Fonts->AddFontDefaultVector();
    //io.Fonts->AddFontDefaultBitmap();

    // Important: when calling AddFontFromMemoryTTF(), ownership of font_data is transferred by Dear ImGui by default (deleted is handled by Dear ImGui), unless we set FontDataOwnedByAtlas=false in ImFontConfig
    //void*   font_data;
    //int     font_data_size;
    //ImFont* font;
    //font_data_size = GetAssetData("segoeui.ttf", &font_data);
    //font = io.Fonts->AddFontFromMemoryTTF(font_data, font_data_size);
    //IM_ASSERT(font != nullptr);
    //font_data_size = GetAssetData("DroidSans.ttf", &font_data);
    //font = io.Fonts->AddFontFromMemoryTTF(font_data, font_data_size);
    //IM_ASSERT(font != nullptr);
    //font_data_size = GetAssetData("Roboto-Medium.ttf", &font_data);
    //font = io.Fonts->AddFontFromMemoryTTF(font_data, font_data_size);
    //IM_ASSERT(font != nullptr);
    //font_data_size = GetAssetData("Cousine-Regular.ttf", &font_data);
    //font = io.Fonts->AddFontFromMemoryTTF(font_data, font_data_size);
    //IM_ASSERT(font != nullptr);
    //font_data_size = GetAssetData("ArialUni.ttf", &font_data);
    //font = io.Fonts->AddFontFromMemoryTTF(font_data, font_data_size);
    //IM_ASSERT(font != nullptr);

    g_Initialized = true;
}

void MainLoopStep()
{
    ImGuiIO& io = ImGui::GetIO();
    if (g_EglDisplay == EGL_NO_DISPLAY)
        return;

    // Our state
    // (we use static, which essentially makes the variable globals, as a convenience to keep the example code easy to follow)
    static bool show_demo_window = true;
    static bool show_another_window = false;
    static ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    // Poll Unicode characters via JNI
    // FIXME: do not call this every frame because of JNI overhead
    PollUnicodeChars();

    // Open on-screen (soft) input if requested by Dear ImGui
    static bool WantTextInputLast = false;
    if (io.WantTextInput && !WantTextInputLast)
        ShowSoftKeyboardInput();
    WantTextInputLast = io.WantTextInput;

    // Start the Dear ImGui frame
    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplAndroid_NewFrame();
    ImGui::NewFrame();

    // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
    if (show_demo_window)
        ImGui::ShowDemoWindow(&show_demo_window);

    // 2. Show a simple window that we create ourselves. We use a Begin/End pair to create a named window.
    {
        static float f = 0.0f;
        static int counter = 0;

        ImGui::Begin("Hello, world!"); // Create a window called "Hello, world!" and append into it.

        ImGui::Text("This is some useful text.");               // Display some text (you can use a format strings too)
        ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our window open/close state
        ImGui::Checkbox("Another Window", &show_another_window);

        ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f
        ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color

        if (ImGui::Button("Button"))                            // Buttons return true when clicked (most widgets return true when edited/activated)
            counter++;
        ImGui::SameLine();
        ImGui::Text("counter = %d", counter);

        ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / io.Framerate, io.Framerate);
        ImGui::End();
    }

    // 3. Show another simple window.
    if (show_another_window)
    {
        ImGui::Begin("Another Window", &show_another_window);   // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
        ImGui::Text("Hello from another window!");
        if (ImGui::Button("Close Me"))
            show_another_window = false;
        ImGui::End();
    }

    // Rendering
    ImGui::Render();
    glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
    glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
    glClear(GL_COLOR_BUFFER_BIT);
    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
    eglSwapBuffers(g_EglDisplay, g_EglSurface);
}

void Shutdown()
{
    if (!g_Initialized)
        return;

    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplAndroid_Shutdown();
    ImGui::DestroyContext();

    if (g_EglDisplay != EGL_NO_DISPLAY)
    {
        eglMakeCurrent(g_EglDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);

        if (g_EglContext != EGL_NO_CONTEXT)
            eglDestroyContext(g_EglDisplay, g_EglContext);

        if (g_EglSurface != EGL_NO_SURFACE)
            eglDestroySurface(g_EglDisplay, g_EglSurface);

        eglTerminate(g_EglDisplay);
    }

    g_EglDisplay = EGL_NO_DISPLAY;
    g_EglContext = EGL_NO_CONTEXT;
    g_EglSurface = EGL_NO_SURFACE;
    ANativeWindow_release(g_App->window);

    g_Initialized = false;
}

// Helper functions

// Unfortunately, there is no way to show the on-screen input from native code.
// Therefore, we call ShowSoftKeyboardInput() of the main activity implemented in MainActivity.kt via JNI.
static int ShowSoftKeyboardInput()
{
    JavaVM* java_vm = g_App->activity->vm;
    JNIEnv* java_env = nullptr;

    jint jni_return = java_vm->GetEnv((void**)&java_env, JNI_VERSION_1_6);
    if (jni_return == JNI_ERR)
        return -1;

    jni_return = java_vm->AttachCurrentThread(&java_env, nullptr);
    if (jni_return != JNI_OK)
        return -2;

    jclass native_activity_clazz = java_env->GetObjectClass(g_App->activity->clazz);
    if (native_activity_clazz == nullptr)
        return -3;

    jmethodID method_id = java_env->GetMethodID(native_activity_clazz, "showSoftInput", "()V");
    if (method_id == nullptr)
        return -4;

    java_env->CallVoidMethod(g_App->activity->clazz, method_id);

    jni_return = java_vm->DetachCurrentThread();
    if (jni_return != JNI_OK)
        return -5;

    return 0;
}

// Unfortunately, the native KeyEvent implementation has no getUnicodeChar() function.
// Therefore, we implement the processing of KeyEvents in MainActivity.kt and poll
// the resulting Unicode characters here via JNI and send them to Dear ImGui.
static int PollUnicodeChars()
{
    JavaVM* java_vm = g_App->activity->vm;
    JNIEnv* java_env = nullptr;

    jint jni_return = java_vm->GetEnv((void**)&java_env, JNI_VERSION_1_6);
    if (jni_return == JNI_ERR)
        return -1;

    jni_return = java_vm->AttachCurrentThread(&java_env, nullptr);
    if (jni_return != JNI_OK)
        return -2;

    jclass native_activity_clazz = java_env->GetObjectClass(g_App->activity->clazz);
    if (native_activity_clazz == nullptr)
        return -3;

    jmethodID method_id = java_env->GetMethodID(native_activity_clazz, "pollUnicodeChar", "()I");
    if (method_id == nullptr)
        return -4;

    // Send the actual characters to Dear ImGui
    ImGuiIO& io = ImGui::GetIO();
    jint unicode_character;
    while ((unicode_character = java_env->CallIntMethod(g_App->activity->clazz, method_id)) != 0)
        io.AddInputCharacter(unicode_character);

    jni_return = java_vm->DetachCurrentThread();
    if (jni_return != JNI_OK)
        return -5;

    return 0;
}

// Helper to retrieve data placed into the assets/ directory (android/app/src/main/assets)
static int GetAssetData(const char* filename, void** outData)
{
    int num_bytes = 0;
    AAsset* asset_descriptor = AAssetManager_open(g_App->activity->assetManager, filename, AASSET_MODE_BUFFER);
    if (asset_descriptor)
    {
        num_bytes = AAsset_getLength(asset_descriptor);
        *outData = IM_ALLOC(num_bytes);
        int64_t num_bytes_read = AAsset_read(asset_descriptor, *outData, num_bytes);
        AAsset_close(asset_descriptor);
        IM_ASSERT(num_bytes_read == num_bytes);
    }
    return num_bytes;
}