#include "core/application.h"

#include "core/assert.h"
#include "core/log.h"
#include "core/window.h"
#include "core/window_manager.h"
#include "debugger/debugger.h"
#include "ui/ui.h"

#include <glad/gl.h>

#include <algorithm>
#include <charconv>
#include <chrono>
#include <cstdlib>
#include <fstream>
#include <vector>

namespace Hsdbg
{
    namespace
    {
        using Clock = std::chrono::steady_clock;

        constexpr float MAX_DELTA_TIME = 0.25f;
        constexpr double MINIMIZED_WAIT_TIMEOUT = 0.1;

        // dev aid: HSDBG_CAPTURE=<file.ppm> writes the frame numbered
        // HSDBG_CAPTURE_FRAME (default 240) as a binary ppm; returns true on
        // that frame so the caller can quit
        auto capture_frame(uint64_t frame, uint32_t width, uint32_t height) -> bool
        {
            static const char* path = std::getenv("HSDBG_CAPTURE");
            if (path == nullptr)
                return false;

            static const uint64_t target = [] {
                uint64_t value = 240;
                if (const char* text = std::getenv("HSDBG_CAPTURE_FRAME"))
                    std::from_chars(text, text + std::char_traits<char>::length(text), value);
                return value;
            }();

            if (frame != target)
                return false;

            const size_t stride = static_cast<size_t>(width) * 3;
            std::vector<unsigned char> pixels(stride * height);
            glPixelStorei(GL_PACK_ALIGNMENT, 1);
            glReadPixels(0, 0, static_cast<GLsizei>(width), static_cast<GLsizei>(height),
                         GL_RGB, GL_UNSIGNED_BYTE, pixels.data());

            std::ofstream out(path, std::ios::binary);
            out << "P6\n" << width << ' ' << height << "\n255\n";
            for (uint32_t y = height; y-- > 0;)
                out.write(reinterpret_cast<const char*>(pixels.data() + y * stride),
                          static_cast<std::streamsize>(stride));

            Log::info("capture: wrote '{}' ({}x{})", path, width, height);
            return true;
        }
    }

    Application* Application::s_instance = nullptr;

    Application::Application(const ApplicationSpec& spec)
        : m_spec(spec)
    {
        HSDBG_ASSERT(s_instance == nullptr, "an Application instance already exists");
        s_instance = this;

        Log::info("{}: starting up", m_spec.name);

        m_window_manager = std::make_unique<WindowManager>();

        WindowSpec window_spec;
        window_spec.title = m_spec.name;
        window_spec.width = m_spec.width;
        window_spec.height = m_spec.height;
        window_spec.vsync = m_spec.vsync;

        m_window = &m_window_manager->create_window(window_spec);

        m_debugger = std::make_unique<Debugger>();
        m_ui = std::make_unique<Ui>(*m_window);
    }

    Application::~Application()
    {
        m_ui.reset();
        m_debugger.reset();

        m_window = nullptr;
        m_window_manager.reset();

        Log::info("{}: shutting down after {} frames", m_spec.name, m_frame_count);

        s_instance = nullptr;
    }

    auto Application::get() -> Application&
    {
        HSDBG_ASSERT(s_instance != nullptr, "no Application instance has been created");
        return *s_instance;
    }

    auto Application::run() -> void
    {
        m_running = true;

        auto last_frame_time = Clock::now();

        while (m_running)
        {
            const auto now = Clock::now();
            const float elapsed = std::chrono::duration<float>(now - last_frame_time).count();
            last_frame_time = now;

            m_delta_time = elapsed < MAX_DELTA_TIME ? elapsed : MAX_DELTA_TIME;
            m_time += m_delta_time;
            m_frame_count += 1;

            m_window_manager->poll_events();

            if (m_window->should_close())
            {
                close();
                break;
            }

            if (m_window->is_minimized())
            {
                m_window_manager->wait_events(MINIMIZED_WAIT_TIMEOUT);
                continue;
            }

            update();
            render();

            m_window->swap_buffers();
        }
    }

    auto Application::close() -> void
    {
        m_running = false;
    }

    auto Application::update() -> void
    {
        m_debugger->update();

        // dev aid: HSDBG_STEP_AT=<frame>[,<frame>…] steps over a line on those
        // frames while stopped, so a capture can show a target that has moved
        static const std::vector<uint64_t> step_frames = [] {
            std::vector<uint64_t> frames;
            const char* text = std::getenv("HSDBG_STEP_AT");
            for (const char* at = text; at != nullptr && *at != '\0';)
            {
                uint64_t value = 0;
                const auto [next, error] = std::from_chars(at, at + std::char_traits<char>::length(at), value);
                if (error != std::errc{})
                    break;
                frames.push_back(value);
                at = *next == ',' ? next + 1 : next;
            }
            return frames;
        }();

        if (std::ranges::find(step_frames, m_frame_count) != step_frames.end() && m_debugger->is_stopped())
            (void)m_debugger->step_over();
    }

    auto Application::render() -> void
    {
        // clear the whole framebuffer at the very start of the frame, before any
        // drawing, so nothing from the previous frame can survive underneath
        glViewport(0, 0,
                   static_cast<GLsizei>(m_window->framebuffer_width()),
                   static_cast<GLsizei>(m_window->framebuffer_height()));
        glDisable(GL_SCISSOR_TEST);
        glClearColor(0.05f, 0.05f, 0.06f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        m_ui->begin_frame();
        m_ui->draw(*m_debugger);
        m_ui->end_frame();

        if (capture_frame(m_frame_count, m_window->framebuffer_width(), m_window->framebuffer_height()))
            close();
    }
}