#include "BuiltInIcons.h"

#include "ImGuiBackendBridge.h"
#include "BuiltInIconLayoutUtils.h"
#include "Platform/Win32Utf8.h"
#include "StyleTokens.h"

#include <algorithm>
#include <array>
#include <condition_variable>
#include <cstdint>
#include <cwctype>
#include <deque>
#include <cstring>
#include <filesystem>
#include <fstream>
#include <limits>
#include <memory>
#include <string>
#include <thread>
#include <unordered_map>
#include <vector>

#include <stb_image.h>

namespace XCEngine {
namespace Editor {
namespace UI {

namespace {

using BuiltInTexture = ImGuiBackendBridge::UploadedTexture;
using PreviewGpuUpload = ImGuiBackendBridge::PendingTextureUpload;

struct LoadedTexturePixels {
    std::vector<stbi_uc> rgbaPixels;
    int width = 0;
    int height = 0;
};

struct PreviewDecodeJob {
    std::string key;
    std::filesystem::path filePath;
    std::filesystem::path cacheFilePath;
    std::string relativePathKey;
    std::uint64_t fileSize = 0;
    std::int64_t lastWriteTimeTicks = 0;
    bool useDiskCache = false;
};

struct PreviewDecodeResult {
    std::string key;
    LoadedTexturePixels pixels;
    std::uint64_t fileSize = 0;
    std::int64_t lastWriteTimeTicks = 0;
    bool success = false;
};

struct SourceFileFingerprint {
    std::uint64_t fileSize = 0;
    std::int64_t lastWriteTimeTicks = 0;

    bool IsValid() const {
        return fileSize > 0 && lastWriteTimeTicks != 0;
    }
};

bool operator==(const SourceFileFingerprint& lhs, const SourceFileFingerprint& rhs) {
    return lhs.fileSize == rhs.fileSize && lhs.lastWriteTimeTicks == rhs.lastWriteTimeTicks;
}

bool operator!=(const SourceFileFingerprint& lhs, const SourceFileFingerprint& rhs) {
    return !(lhs == rhs);
}

struct PreviewDiskCacheEntry {
    std::filesystem::path filePath;
    std::string relativePathKey;
};

#pragma pack(push, 1)
struct ThumbnailCacheFileHeader {
    char magic[8];
    std::uint32_t version = 1;
    std::uint64_t fileSize = 0;
    std::int64_t lastWriteTimeTicks = 0;
    std::uint32_t width = 0;
    std::uint32_t height = 0;
    std::uint32_t relativePathSize = 0;
    std::uint32_t pixelDataSize = 0;
};
#pragma pack(pop)

struct BuiltInIconState {
    ImGuiBackendBridge* backend = nullptr;
    ID3D12Device* device = nullptr;
    ID3D12CommandQueue* commandQueue = nullptr;
    BuiltInTexture folder;
    BuiltInTexture gameObject;
    BuiltInTexture scene;
    BuiltInTexture cameraGizmo;
    BuiltInTexture directionalLightGizmo;
    BuiltInTexture pointLightGizmo;
    BuiltInTexture spotLightGizmo;
    struct CachedAssetPreview {
        BuiltInTexture texture;
        std::unique_ptr<LoadedTexturePixels> decodedPixels;
        std::unique_ptr<PreviewGpuUpload> pendingUpload;
        SourceFileFingerprint sourceFingerprint;
        bool decodeQueued = false;
        bool hasStaleTexture = false;
        bool loadFailed = false;
        int lastUsedFrame = -1;
        int lastSourceValidationFrame = -1;
    };
    std::unordered_map<std::string, CachedAssetPreview> assetPreviews;
    std::vector<std::unique_ptr<PreviewGpuUpload>> pendingIconUploads;
    std::vector<std::thread> previewWorkers;
    std::deque<PreviewDecodeJob> previewDecodeQueue;
    std::deque<PreviewDecodeResult> previewDecodeResults;
    std::mutex previewQueueMutex;
    std::condition_variable previewQueueEvent;
    bool previewWorkersRunning = false;
    size_t pendingPreviewDecodeJobs = 0;
    int lastPreviewBudgetFrame = -1;
    int previewLoadsThisFrame = 0;
    int lastMaintenanceFrame = -1;
};

BuiltInIconState g_icons;

constexpr size_t kMaxCachedAssetPreviews = 40;
constexpr int kMaxPreviewLoadsPerFrame = 64;
constexpr size_t kMaxQueuedPreviewDecodeJobs = 64;
constexpr int kMaxPreviewThumbnailExtent = 192;
constexpr size_t kPreviewWorkerCount = 2;
constexpr int kPreviewSourceValidationIntervalFrames = 30;
constexpr std::uint32_t kThumbnailCacheVersion = 1;
constexpr std::array<char, 8> kThumbnailCacheMagic = { 'X', 'C', 'T', 'H', 'M', 'B', '1', '\0' };
constexpr std::uint32_t kMaxThumbnailCacheRelativePathBytes = 16u * 1024u;

std::filesystem::path ResolveFolderIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "folder_icon.png").lexically_normal();
}

std::filesystem::path ResolveGameObjectIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "gameobject_icon.png").lexically_normal();
}

std::filesystem::path ResolveSceneIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "scene_icon.png").lexically_normal();
}

std::filesystem::path ResolveCameraGizmoIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "camera_gizmo.png").lexically_normal();
}

std::filesystem::path ResolveDirectionalLightGizmoIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "directional_light_gizmo.png").lexically_normal();
}

std::filesystem::path ResolvePointLightGizmoIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "point_light_gizmo.png").lexically_normal();
}

std::filesystem::path ResolveSpotLightGizmoIconPath() {
    const std::filesystem::path exeDir(Platform::GetExecutableDirectoryUtf8());
    return (exeDir / ".." / ".." / "resources" / "Icons" / "spot_light_gizmo.png").lexically_normal();
}

std::string NormalizePathKey(const std::filesystem::path& path) {
    std::wstring key = path.lexically_normal().generic_wstring();
    std::transform(key.begin(), key.end(), key.begin(), ::towlower);
    return Platform::WideToUtf8(key);
}

std::string MakeAssetPreviewKey(const std::string& filePath) {
    return NormalizePathKey(std::filesystem::path(Platform::Utf8ToWide(filePath)));
}

SourceFileFingerprint MakeSourceFingerprint(
    std::uint64_t fileSize,
    std::int64_t lastWriteTimeTicks) {
    SourceFileFingerprint fingerprint;
    fingerprint.fileSize = fileSize;
    fingerprint.lastWriteTimeTicks = lastWriteTimeTicks;
    return fingerprint;
}

bool QuerySourceFileFingerprint(
    const std::filesystem::path& filePath,
    SourceFileFingerprint& outFingerprint) {
    std::error_code ec;
    if (!std::filesystem::exists(filePath, ec) || ec) {
        return false;
    }

    ec.clear();
    if (!std::filesystem::is_regular_file(filePath, ec) || ec) {
        return false;
    }

    ec.clear();
    const auto fileSize = std::filesystem::file_size(filePath, ec);
    if (ec || fileSize == static_cast<std::uintmax_t>(-1)) {
        return false;
    }

    ec.clear();
    const auto lastWriteTime = std::filesystem::last_write_time(filePath, ec);
    if (ec) {
        return false;
    }

    outFingerprint.fileSize = static_cast<std::uint64_t>(fileSize);
    outFingerprint.lastWriteTimeTicks = static_cast<std::int64_t>(lastWriteTime.time_since_epoch().count());
    return outFingerprint.IsValid();
}

std::uint64_t ComputeFnv1a64(const std::string& value) {
    constexpr std::uint64_t kOffsetBasis = 14695981039346656037ull;
    constexpr std::uint64_t kPrime = 1099511628211ull;

    std::uint64_t hash = kOffsetBasis;
    for (unsigned char ch : value) {
        hash ^= static_cast<std::uint64_t>(ch);
        hash *= kPrime;
    }
    return hash;
}

std::string FormatHashHex(std::uint64_t value) {
    static constexpr char kHexDigits[] = "0123456789abcdef";

    std::string result(16, '0');
    for (int index = 15; index >= 0; --index) {
        result[static_cast<size_t>(index)] = kHexDigits[value & 0xFu];
        value >>= 4u;
    }
    return result;
}

bool IsProjectRelativePath(const std::filesystem::path& relativePath) {
    if (relativePath.empty()) {
        return false;
    }

    const std::wstring generic = relativePath.generic_wstring();
    return generic != L"." && generic != L".." && generic.rfind(L"../", 0) != 0;
}

bool ResolvePreviewDiskCacheEntry(
    const std::string& projectPath,
    const std::string& filePath,
    PreviewDiskCacheEntry& outEntry) {
    if (projectPath.empty() || filePath.empty()) {
        return false;
    }

    std::error_code ec;
    const std::filesystem::path rootPath = std::filesystem::weakly_canonical(
        std::filesystem::path(Platform::Utf8ToWide(projectPath)),
        ec);
    if (ec || rootPath.empty()) {
        return false;
    }

    ec.clear();
    const std::filesystem::path assetPath = std::filesystem::weakly_canonical(
        std::filesystem::path(Platform::Utf8ToWide(filePath)),
        ec);
    if (ec || assetPath.empty()) {
        return false;
    }

    ec.clear();
    std::filesystem::path relativePath = std::filesystem::relative(assetPath, rootPath, ec);
    if (ec) {
        return false;
    }

    relativePath = relativePath.lexically_normal();
    if (!IsProjectRelativePath(relativePath)) {
        return false;
    }

    outEntry.relativePathKey = NormalizePathKey(relativePath);
    const std::string hashFileName = FormatHashHex(ComputeFnv1a64(outEntry.relativePathKey)) + ".thumb";
    outEntry.filePath =
        (rootPath / L".xceditor" / L"thumbs" / std::filesystem::path(Platform::Utf8ToWide(hashFileName)))
            .lexically_normal();
    return true;
}

bool ReadThumbnailCacheFile(
    const std::filesystem::path& cacheFilePath,
    const std::string& relativePathKey,
    const SourceFileFingerprint& sourceFingerprint,
    LoadedTexturePixels& outTexturePixels) {
    std::ifstream stream(cacheFilePath, std::ios::binary | std::ios::in);
    if (!stream.is_open()) {
        return false;
    }

    ThumbnailCacheFileHeader header = {};
    if (!stream.read(reinterpret_cast<char*>(&header), sizeof(header)).good()) {
        return false;
    }

    if (std::memcmp(header.magic, kThumbnailCacheMagic.data(), kThumbnailCacheMagic.size()) != 0 ||
        header.version != kThumbnailCacheVersion ||
        header.fileSize != sourceFingerprint.fileSize ||
        header.lastWriteTimeTicks != sourceFingerprint.lastWriteTimeTicks ||
        header.relativePathSize == 0 ||
        header.relativePathSize > kMaxThumbnailCacheRelativePathBytes ||
        header.width == 0 ||
        header.height == 0 ||
        header.width > static_cast<std::uint32_t>(kMaxPreviewThumbnailExtent) ||
        header.height > static_cast<std::uint32_t>(kMaxPreviewThumbnailExtent)) {
        return false;
    }

    const std::uint64_t expectedPixelBytes =
        static_cast<std::uint64_t>(header.width) * static_cast<std::uint64_t>(header.height) * 4ull;
    if (expectedPixelBytes == 0 ||
        expectedPixelBytes > static_cast<std::uint64_t>((std::numeric_limits<size_t>::max)()) ||
        header.pixelDataSize != expectedPixelBytes) {
        return false;
    }

    std::string cachedRelativePath(header.relativePathSize, '\0');
    if (!stream.read(cachedRelativePath.data(), static_cast<std::streamsize>(cachedRelativePath.size())).good()) {
        return false;
    }
    if (cachedRelativePath != relativePathKey) {
        return false;
    }

    outTexturePixels.width = static_cast<int>(header.width);
    outTexturePixels.height = static_cast<int>(header.height);
    outTexturePixels.rgbaPixels.resize(static_cast<size_t>(header.pixelDataSize));
    if (!stream.read(
            reinterpret_cast<char*>(outTexturePixels.rgbaPixels.data()),
            static_cast<std::streamsize>(outTexturePixels.rgbaPixels.size())).good()) {
        outTexturePixels.rgbaPixels.clear();
        outTexturePixels.width = 0;
        outTexturePixels.height = 0;
        return false;
    }

    return true;
}

void RemoveDiskCacheFile(const std::filesystem::path& cacheFilePath) {
    std::error_code ec;
    std::filesystem::remove(cacheFilePath, ec);
}

bool WriteThumbnailCacheFile(
    const std::filesystem::path& cacheFilePath,
    const std::string& relativePathKey,
    const SourceFileFingerprint& sourceFingerprint,
    const LoadedTexturePixels& texturePixels) {
    if (cacheFilePath.empty() ||
        relativePathKey.empty() ||
        relativePathKey.size() > kMaxThumbnailCacheRelativePathBytes ||
        !sourceFingerprint.IsValid() ||
        texturePixels.width <= 0 ||
        texturePixels.height <= 0 ||
        texturePixels.rgbaPixels.empty()) {
        return false;
    }

    const std::uint64_t pixelDataSize = static_cast<std::uint64_t>(texturePixels.rgbaPixels.size());
    if (pixelDataSize !=
            static_cast<std::uint64_t>(texturePixels.width) * static_cast<std::uint64_t>(texturePixels.height) * 4ull ||
        pixelDataSize > static_cast<std::uint64_t>((std::numeric_limits<std::uint32_t>::max)())) {
        return false;
    }

    std::error_code ec;
    std::filesystem::create_directories(cacheFilePath.parent_path(), ec);
    if (ec) {
        return false;
    }

    const std::filesystem::path tempPath = cacheFilePath.parent_path() / (cacheFilePath.filename().wstring() + L".tmp");
    std::ofstream stream(tempPath, std::ios::binary | std::ios::out | std::ios::trunc);
    if (!stream.is_open()) {
        return false;
    }

    ThumbnailCacheFileHeader header = {};
    std::memcpy(header.magic, kThumbnailCacheMagic.data(), kThumbnailCacheMagic.size());
    header.version = kThumbnailCacheVersion;
    header.fileSize = sourceFingerprint.fileSize;
    header.lastWriteTimeTicks = sourceFingerprint.lastWriteTimeTicks;
    header.width = static_cast<std::uint32_t>(texturePixels.width);
    header.height = static_cast<std::uint32_t>(texturePixels.height);
    header.relativePathSize = static_cast<std::uint32_t>(relativePathKey.size());
    header.pixelDataSize = static_cast<std::uint32_t>(pixelDataSize);

    const bool writeSucceeded =
        stream.write(reinterpret_cast<const char*>(&header), sizeof(header)).good() &&
        stream.write(relativePathKey.data(), static_cast<std::streamsize>(relativePathKey.size())).good() &&
        stream.write(
            reinterpret_cast<const char*>(texturePixels.rgbaPixels.data()),
            static_cast<std::streamsize>(texturePixels.rgbaPixels.size())).good();
    stream.close();
    if (!writeSucceeded) {
        RemoveDiskCacheFile(tempPath);
        return false;
    }

    ec.clear();
    std::filesystem::remove(cacheFilePath, ec);
    ec.clear();
    std::filesystem::rename(tempPath, cacheFilePath, ec);
    if (ec) {
        RemoveDiskCacheFile(tempPath);
        return false;
    }
    return true;
}

bool ReadFileBytes(const std::filesystem::path& filePath, std::vector<stbi_uc>& bytes) {
    std::ifstream stream(filePath, std::ios::binary | std::ios::ate);
    if (!stream.is_open()) {
        return false;
    }

    const std::streamsize size = stream.tellg();
    if (size <= 0) {
        return false;
    }

    bytes.resize(static_cast<size_t>(size));
    stream.seekg(0, std::ios::beg);
    return stream.read(reinterpret_cast<char*>(bytes.data()), size).good();
}

void ResizeRgbaImageBilinear(
    const stbi_uc* srcPixels,
    int srcWidth,
    int srcHeight,
    int dstWidth,
    int dstHeight,
    std::vector<stbi_uc>& dstPixels) {
    dstPixels.resize(static_cast<size_t>(dstWidth) * static_cast<size_t>(dstHeight) * 4u);
    if (!srcPixels || srcWidth <= 0 || srcHeight <= 0 || dstWidth <= 0 || dstHeight <= 0) {
        return;
    }

    for (int dstY = 0; dstY < dstHeight; ++dstY) {
        const float srcY = dstHeight > 1
            ? static_cast<float>(dstY) * static_cast<float>(srcHeight - 1) / static_cast<float>(dstHeight - 1)
            : 0.0f;
        const int y0 = static_cast<int>(srcY);
        const int y1 = (std::min)(y0 + 1, srcHeight - 1);
        const float ty = srcY - static_cast<float>(y0);

        for (int dstX = 0; dstX < dstWidth; ++dstX) {
            const float srcX = dstWidth > 1
                ? static_cast<float>(dstX) * static_cast<float>(srcWidth - 1) / static_cast<float>(dstWidth - 1)
                : 0.0f;
            const int x0 = static_cast<int>(srcX);
            const int x1 = (std::min)(x0 + 1, srcWidth - 1);
            const float tx = srcX - static_cast<float>(x0);

            const size_t dstOffset =
                (static_cast<size_t>(dstY) * static_cast<size_t>(dstWidth) + static_cast<size_t>(dstX)) * 4u;
            const size_t srcOffset00 =
                (static_cast<size_t>(y0) * static_cast<size_t>(srcWidth) + static_cast<size_t>(x0)) * 4u;
            const size_t srcOffset10 =
                (static_cast<size_t>(y0) * static_cast<size_t>(srcWidth) + static_cast<size_t>(x1)) * 4u;
            const size_t srcOffset01 =
                (static_cast<size_t>(y1) * static_cast<size_t>(srcWidth) + static_cast<size_t>(x0)) * 4u;
            const size_t srcOffset11 =
                (static_cast<size_t>(y1) * static_cast<size_t>(srcWidth) + static_cast<size_t>(x1)) * 4u;

            for (size_t channel = 0; channel < 4u; ++channel) {
                const float top =
                    static_cast<float>(srcPixels[srcOffset00 + channel]) * (1.0f - tx) +
                    static_cast<float>(srcPixels[srcOffset10 + channel]) * tx;
                const float bottom =
                    static_cast<float>(srcPixels[srcOffset01 + channel]) * (1.0f - tx) +
                    static_cast<float>(srcPixels[srcOffset11 + channel]) * tx;
                dstPixels[dstOffset + channel] = static_cast<stbi_uc>(top * (1.0f - ty) + bottom * ty + 0.5f);
            }
        }
    }
}

bool DownscalePreviewTextureIfNeeded(LoadedTexturePixels& texturePixels) {
    if (texturePixels.width <= 0 || texturePixels.height <= 0 || texturePixels.rgbaPixels.empty()) {
        return false;
    }

    const int maxExtent = (std::max)(texturePixels.width, texturePixels.height);
    if (maxExtent <= kMaxPreviewThumbnailExtent) {
        return true;
    }

    const float scale = static_cast<float>(kMaxPreviewThumbnailExtent) / static_cast<float>(maxExtent);
    const int dstWidth = (std::max)(1, static_cast<int>(static_cast<float>(texturePixels.width) * scale + 0.5f));
    const int dstHeight = (std::max)(1, static_cast<int>(static_cast<float>(texturePixels.height) * scale + 0.5f));

    std::vector<stbi_uc> resizedPixels;
    ResizeRgbaImageBilinear(
        texturePixels.rgbaPixels.data(),
        texturePixels.width,
        texturePixels.height,
        dstWidth,
        dstHeight,
        resizedPixels);
    if (resizedPixels.empty()) {
        return false;
    }

    texturePixels.rgbaPixels = std::move(resizedPixels);
    texturePixels.width = dstWidth;
    texturePixels.height = dstHeight;
    return true;
}

void ResetTexture(BuiltInTexture& texture);

void InvalidateAssetPreview(BuiltInIconState::CachedAssetPreview& preview) {
    if (preview.pendingUpload) {
        preview.hasStaleTexture = true;
    } else {
        ResetTexture(preview.texture);
        preview.hasStaleTexture = false;
    }

    preview.decodedPixels.reset();
    preview.decodeQueued = false;
    preview.loadFailed = false;
}

bool RefreshAssetPreviewSourceFingerprint(
    const std::filesystem::path& filePath,
    BuiltInIconState::CachedAssetPreview& preview) {
    SourceFileFingerprint currentFingerprint;
    if (!QuerySourceFileFingerprint(filePath, currentFingerprint)) {
        InvalidateAssetPreview(preview);
        preview.sourceFingerprint = {};
        preview.loadFailed = true;
        return false;
    }

    if (preview.sourceFingerprint != currentFingerprint) {
        InvalidateAssetPreview(preview);
        preview.sourceFingerprint = currentFingerprint;
    }
    return true;
}

void ResetTexture(BuiltInTexture& texture) {
    if (g_icons.backend != nullptr) {
        g_icons.backend->ResetUploadedTexture(&texture);
        return;
    }

    texture = {};
}

void ResetAssetPreviewCache() {
    for (auto& entry : g_icons.assetPreviews) {
        ResetTexture(entry.second.texture);
    }
    g_icons.assetPreviews.clear();
}

bool DecodeTextureFromFile(
    const std::filesystem::path& filePath,
    LoadedTexturePixels& outTexturePixels) {
    if (!std::filesystem::exists(filePath)) {
        return false;
    }

    std::vector<stbi_uc> fileData;
    if (!ReadFileBytes(filePath, fileData)) {
        return false;
    }

    int width = 0;
    int height = 0;
    int channels = 0;
    stbi_uc* pixels = stbi_load_from_memory(
        fileData.data(),
        static_cast<int>(fileData.size()),
        &width,
        &height,
        &channels,
        STBI_rgb_alpha);
    if (!pixels || width <= 0 || height <= 0) {
        if (pixels) {
            stbi_image_free(pixels);
        }
        return false;
    }

    outTexturePixels.width = width;
    outTexturePixels.height = height;
    outTexturePixels.rgbaPixels.assign(
        pixels,
        pixels + static_cast<size_t>(width) * static_cast<size_t>(height) * 4u);
    stbi_image_free(pixels);

    return DownscalePreviewTextureIfNeeded(outTexturePixels);
}

bool LoadTextureFromFile(
    ImGuiBackendBridge& backend,
    ID3D12Device* device,
    ID3D12CommandQueue* commandQueue,
    const std::filesystem::path& filePath,
    BuiltInTexture& outTexture,
    std::unique_ptr<PreviewGpuUpload>& outPendingUpload) {
    LoadedTexturePixels texturePixels;
    if (!DecodeTextureFromFile(filePath, texturePixels)) {
        return false;
    }

    return backend.UploadRgbaTexture(
        device,
        commandQueue,
        texturePixels.rgbaPixels.data(),
        texturePixels.width,
        texturePixels.height,
        &outTexture,
        &outPendingUpload);
}

void PreviewWorkerMain() {
    while (true) {
        PreviewDecodeJob job;
        {
            std::unique_lock<std::mutex> lock(g_icons.previewQueueMutex);
            g_icons.previewQueueEvent.wait(lock, [] {
                return !g_icons.previewWorkersRunning || !g_icons.previewDecodeQueue.empty();
            });

            if (!g_icons.previewWorkersRunning && g_icons.previewDecodeQueue.empty()) {
                return;
            }

            job = std::move(g_icons.previewDecodeQueue.front());
            g_icons.previewDecodeQueue.pop_front();
        }

        PreviewDecodeResult result;
        result.key = std::move(job.key);
        result.fileSize = job.fileSize;
        result.lastWriteTimeTicks = job.lastWriteTimeTicks;

        if (job.useDiskCache) {
            result.success = ReadThumbnailCacheFile(
                job.cacheFilePath,
                job.relativePathKey,
                MakeSourceFingerprint(job.fileSize, job.lastWriteTimeTicks),
                result.pixels);
            if (!result.success) {
                RemoveDiskCacheFile(job.cacheFilePath);
            }
        }

        if (!result.success) {
            result.success = DecodeTextureFromFile(job.filePath, result.pixels);
            if (result.success && job.useDiskCache) {
                WriteThumbnailCacheFile(
                    job.cacheFilePath,
                    job.relativePathKey,
                    MakeSourceFingerprint(job.fileSize, job.lastWriteTimeTicks),
                    result.pixels);
            }
        }

        {
            std::lock_guard<std::mutex> lock(g_icons.previewQueueMutex);
            g_icons.previewDecodeResults.push_back(std::move(result));
        }
    }
}

void StartPreviewWorkers() {
    if (g_icons.previewWorkersRunning) {
        return;
    }

    g_icons.previewWorkersRunning = true;
    g_icons.previewWorkers.reserve(kPreviewWorkerCount);
    for (size_t workerIndex = 0; workerIndex < kPreviewWorkerCount; ++workerIndex) {
        g_icons.previewWorkers.emplace_back(PreviewWorkerMain);
    }
}

void StopPreviewWorkers() {
    {
        std::lock_guard<std::mutex> lock(g_icons.previewQueueMutex);
        g_icons.previewWorkersRunning = false;
        g_icons.previewDecodeQueue.clear();
        g_icons.previewDecodeResults.clear();
        g_icons.pendingPreviewDecodeJobs = 0;
    }
    g_icons.previewQueueEvent.notify_all();

    for (std::thread& worker : g_icons.previewWorkers) {
        if (worker.joinable()) {
            worker.join();
        }
    }
    g_icons.previewWorkers.clear();
}

bool QueuePreviewDecode(
    const std::string& key,
    const std::filesystem::path& filePath,
    const SourceFileFingerprint& sourceFingerprint,
    const std::string& projectPath,
    const std::string& filePathUtf8) {
    PreviewDiskCacheEntry diskCacheEntry;
    const bool useDiskCache = ResolvePreviewDiskCacheEntry(projectPath, filePathUtf8, diskCacheEntry);

    std::lock_guard<std::mutex> lock(g_icons.previewQueueMutex);
    if (!g_icons.previewWorkersRunning || g_icons.pendingPreviewDecodeJobs >= kMaxQueuedPreviewDecodeJobs) {
        return false;
    }

    PreviewDecodeJob job;
    job.key = key;
    job.filePath = filePath;
    job.fileSize = sourceFingerprint.fileSize;
    job.lastWriteTimeTicks = sourceFingerprint.lastWriteTimeTicks;
    if (useDiskCache) {
        job.cacheFilePath = std::move(diskCacheEntry.filePath);
        job.relativePathKey = std::move(diskCacheEntry.relativePathKey);
        job.useDiskCache = true;
    }

    g_icons.previewDecodeQueue.push_back(std::move(job));
    ++g_icons.pendingPreviewDecodeJobs;
    g_icons.previewQueueEvent.notify_one();
    return true;
}

void DrainPreviewDecodeResults() {
    std::deque<PreviewDecodeResult> completedResults;
    {
        std::lock_guard<std::mutex> lock(g_icons.previewQueueMutex);
        completedResults.swap(g_icons.previewDecodeResults);
    }

    for (PreviewDecodeResult& result : completedResults) {
        if (g_icons.pendingPreviewDecodeJobs > 0) {
            --g_icons.pendingPreviewDecodeJobs;
        }

        auto it = g_icons.assetPreviews.find(result.key);
        if (it == g_icons.assetPreviews.end()) {
            continue;
        }

        BuiltInIconState::CachedAssetPreview& preview = it->second;
        preview.decodeQueued = false;
        if (preview.sourceFingerprint != MakeSourceFingerprint(result.fileSize, result.lastWriteTimeTicks)) {
            continue;
        }

        if (!result.success) {
            preview.loadFailed = true;
            preview.decodedPixels.reset();
            continue;
        }

        preview.loadFailed = false;
        preview.decodedPixels = std::make_unique<LoadedTexturePixels>(std::move(result.pixels));
    }
}

void PollCompletedUploads() {
    if (g_icons.backend == nullptr) {
        return;
    }

    for (auto& entry : g_icons.assetPreviews) {
        auto& preview = entry.second;
        if (preview.pendingUpload && g_icons.backend->IsTextureUploadComplete(*preview.pendingUpload)) {
            preview.pendingUpload.reset();
            if (preview.hasStaleTexture) {
                ResetTexture(preview.texture);
                preview.hasStaleTexture = false;
            }
        }
    }

    g_icons.backend->RemoveCompletedTextureUploads(&g_icons.pendingIconUploads);
}

void MaintainIconRuntimeState() {
    const int frame = ImGui::GetFrameCount();
    if (g_icons.lastMaintenanceFrame == frame) {
        return;
    }

    g_icons.lastMaintenanceFrame = frame;
    DrainPreviewDecodeResults();
    PollCompletedUploads();
}

void DrawTextureIcon(ImDrawList* drawList, const BuiltInTexture& texture, const ImVec2& min, const ImVec2& max) {
    if (!drawList || !texture.IsValid()) {
        return;
    }

    const ImVec2 size = ComputeFittedIconSize(texture.width, texture.height, min, max);
    const float x = min.x + ((max.x - min.x) - size.x) * 0.5f;
    const float y = min.y + ((max.y - min.y) - size.y) * 0.5f;
    drawList->AddImage(texture.textureId, ImVec2(x, y), ImVec2(x + size.x, y + size.y));
}

void DrawBuiltInFolderFallback(ImDrawList* drawList, const ImVec2& min, const ImVec2& max) {
    if (!drawList) {
        return;
    }

    const float width = max.x - min.x;
    const float height = max.y - min.y;
    if (width <= 0.0f || height <= 0.0f) {
        return;
    }

    const float rounding = (std::max)(1.0f, (std::min)(width, height) * 0.18f);
    const ImU32 tabColor = ImGui::GetColorU32(BuiltInFolderIconTabColor());
    const ImU32 topColor = ImGui::GetColorU32(BuiltInFolderIconTopColor());
    const ImU32 bodyColor = ImGui::GetColorU32(BuiltInFolderIconBodyColor());

    const ImVec2 tabMin(min.x + width * 0.08f, min.y + height * 0.14f);
    const ImVec2 tabMax(min.x + width * 0.48f, min.y + height * 0.38f);
    const ImVec2 topMin(min.x + width * 0.24f, min.y + height * 0.22f);
    const ImVec2 topMax(min.x + width * 0.90f, min.y + height * 0.42f);
    const ImVec2 bodyMin(min.x + width * 0.06f, min.y + height * 0.32f);
    const ImVec2 bodyMax(min.x + width * 0.94f, min.y + height * 0.88f);

    drawList->AddRectFilled(tabMin, tabMax, tabColor, rounding);
    drawList->AddRectFilled(
        topMin,
        topMax,
        topColor,
        rounding,
        ImDrawFlags_RoundCornersTopLeft | ImDrawFlags_RoundCornersTopRight);
    drawList->AddRectFilled(bodyMin, bodyMax, bodyColor, rounding);
}

void DrawBuiltInFileIcon(ImDrawList* drawList, const ImVec2& min, const ImVec2& max) {
    if (!drawList) {
        return;
    }

    const ImU32 fillColor = ImGui::GetColorU32(AssetFileIconFillColor());
    const ImU32 lineColor = ImGui::GetColorU32(AssetFileIconLineColor());
    const ImVec2 foldA(max.x - 8.0f, min.y);
    const ImVec2 foldB(max.x, min.y + 8.0f);
    drawList->AddRectFilled(min, max, fillColor, 2.0f);
    drawList->AddRect(min, max, lineColor, 2.0f);
    drawList->AddTriangleFilled(foldA, ImVec2(max.x, min.y), foldB, ImGui::GetColorU32(AssetFileFoldColor()));
    drawList->AddLine(foldA, foldB, lineColor);
}

BuiltInIconState::CachedAssetPreview* GetOrCreateAssetPreview(
    const std::string& filePath,
    const std::string& projectPath) {
    if (!g_icons.backend || !g_icons.device || !g_icons.commandQueue || filePath.empty()) {
        return nullptr;
    }

    MaintainIconRuntimeState();

    const std::filesystem::path filePathW(Platform::Utf8ToWide(filePath));
    const std::string key = MakeAssetPreviewKey(filePath);
    auto [it, inserted] = g_icons.assetPreviews.try_emplace(key);
    BuiltInIconState::CachedAssetPreview& preview = it->second;
    preview.lastUsedFrame = ImGui::GetFrameCount();

    const int frame = ImGui::GetFrameCount();
    if (inserted ||
        preview.lastSourceValidationFrame < 0 ||
        frame - preview.lastSourceValidationFrame >= kPreviewSourceValidationIntervalFrames) {
        preview.lastSourceValidationFrame = frame;
        if (!RefreshAssetPreviewSourceFingerprint(filePathW, preview)) {
            return &preview;
        }
    }

    if (!preview.sourceFingerprint.IsValid()) {
        return &preview;
    }

    if (preview.texture.IsValid() && !preview.hasStaleTexture) {
        if (preview.pendingUpload && g_icons.backend->IsTextureUploadComplete(*preview.pendingUpload)) {
            preview.pendingUpload.reset();
        }
        return &preview;
    }

    if (preview.decodedPixels && !preview.pendingUpload) {
        std::unique_ptr<PreviewGpuUpload> pendingUpload;
        if (!g_icons.backend->UploadRgbaTexture(
                g_icons.device,
                g_icons.commandQueue,
                preview.decodedPixels->rgbaPixels.data(),
                preview.decodedPixels->width,
                preview.decodedPixels->height,
                &preview.texture,
                &pendingUpload)) {
            preview.decodedPixels.reset();
            preview.loadFailed = true;
            return &preview;
        }

        preview.decodedPixels.reset();
        preview.loadFailed = false;
        preview.pendingUpload = std::move(pendingUpload);
        return &preview;
    }

    if (preview.decodeQueued || preview.loadFailed) {
        return &preview;
    }

    if (g_icons.lastPreviewBudgetFrame != frame) {
        g_icons.lastPreviewBudgetFrame = frame;
        g_icons.previewLoadsThisFrame = 0;
    }
    if (g_icons.previewLoadsThisFrame >= kMaxPreviewLoadsPerFrame) {
        return &preview;
    }

    if (QueuePreviewDecode(key, filePathW, preview.sourceFingerprint, projectPath, filePath)) {
        preview.decodeQueued = true;
        ++g_icons.previewLoadsThisFrame;
    }
    return &preview;
}

void PruneAssetPreviewCache() {
    if (g_icons.assetPreviews.size() <= kMaxCachedAssetPreviews) {
        return;
    }

    std::vector<std::pair<std::string, int>> candidates;
    candidates.reserve(g_icons.assetPreviews.size());
    for (const auto& entry : g_icons.assetPreviews) {
        if (entry.second.pendingUpload || entry.second.decodeQueued) {
            continue;
        }
        candidates.emplace_back(entry.first, entry.second.lastUsedFrame);
    }

    std::sort(
        candidates.begin(),
        candidates.end(),
        [](const auto& lhs, const auto& rhs) {
            return lhs.second < rhs.second;
        });

    size_t removeCount = g_icons.assetPreviews.size() - kMaxCachedAssetPreviews;
    for (size_t i = 0; i < removeCount && i < candidates.size(); ++i) {
        auto it = g_icons.assetPreviews.find(candidates[i].first);
        if (it == g_icons.assetPreviews.end()) {
            continue;
        }

        ResetTexture(it->second.texture);
        g_icons.assetPreviews.erase(it);
    }
}

BuiltInTexture* ResolveEditorTexture(EditorTextureIconKind kind) {
    switch (kind) {
    case EditorTextureIconKind::CameraGizmo:
        return &g_icons.cameraGizmo;
    case EditorTextureIconKind::DirectionalLightGizmo:
        return &g_icons.directionalLightGizmo;
    case EditorTextureIconKind::PointLightGizmo:
        return &g_icons.pointLightGizmo;
    case EditorTextureIconKind::SpotLightGizmo:
        return &g_icons.spotLightGizmo;
    default:
        return nullptr;
    }
}

} // namespace

void InitializeBuiltInIcons(
    ImGuiBackendBridge& backend,
    ID3D12Device* device,
    ID3D12CommandQueue* commandQueue) {
    ShutdownBuiltInIcons();
    g_icons.backend = &backend;
    g_icons.device = device;
    g_icons.commandQueue = commandQueue;
    StartPreviewWorkers();

    std::unique_ptr<PreviewGpuUpload> pendingUpload;
    if (LoadTextureFromFile(backend, device, commandQueue, ResolveFolderIconPath(), g_icons.folder, pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(backend, device, commandQueue, ResolveGameObjectIconPath(), g_icons.gameObject, pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(backend, device, commandQueue, ResolveSceneIconPath(), g_icons.scene, pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(
            backend,
            device,
            commandQueue,
            ResolveCameraGizmoIconPath(),
            g_icons.cameraGizmo,
            pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(
            backend,
            device,
            commandQueue,
            ResolveDirectionalLightGizmoIconPath(),
            g_icons.directionalLightGizmo,
            pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(
            backend,
            device,
            commandQueue,
            ResolvePointLightGizmoIconPath(),
            g_icons.pointLightGizmo,
            pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }

    pendingUpload.reset();
    if (LoadTextureFromFile(
            backend,
            device,
            commandQueue,
            ResolveSpotLightGizmoIconPath(),
            g_icons.spotLightGizmo,
            pendingUpload)) {
        g_icons.pendingIconUploads.push_back(std::move(pendingUpload));
    }
}

void ShutdownBuiltInIcons() {
    if (g_icons.backend && g_icons.device && g_icons.commandQueue) {
        g_icons.backend->WaitForQueueIdle(g_icons.device, g_icons.commandQueue);
    }
    StopPreviewWorkers();
    ResetAssetPreviewCache();
    g_icons.pendingIconUploads.clear();
    ResetTexture(g_icons.folder);
    ResetTexture(g_icons.gameObject);
    ResetTexture(g_icons.scene);
    ResetTexture(g_icons.cameraGizmo);
    ResetTexture(g_icons.directionalLightGizmo);
    ResetTexture(g_icons.pointLightGizmo);
    ResetTexture(g_icons.spotLightGizmo);
    g_icons.backend = nullptr;
    g_icons.device = nullptr;
    g_icons.commandQueue = nullptr;
    g_icons.lastMaintenanceFrame = -1;
    g_icons.lastPreviewBudgetFrame = -1;
    g_icons.previewLoadsThisFrame = 0;
}

void DrawAssetIcon(ImDrawList* drawList, const ImVec2& min, const ImVec2& max, AssetIconKind kind) {
    MaintainIconRuntimeState();

    if (kind == AssetIconKind::Folder) {
        if (g_icons.folder.IsValid()) {
            DrawTextureIcon(drawList, g_icons.folder, min, max);
            return;
        }

        DrawBuiltInFolderFallback(drawList, min, max);
        return;
    }

    if (kind == AssetIconKind::GameObject) {
        if (g_icons.gameObject.IsValid()) {
            DrawTextureIcon(drawList, g_icons.gameObject, min, max);
            return;
        }

        DrawBuiltInFileIcon(drawList, min, max);
        return;
    }

    if (kind == AssetIconKind::Scene) {
        if (g_icons.scene.IsValid()) {
            DrawTextureIcon(drawList, g_icons.scene, min, max);
            return;
        }

        DrawBuiltInFileIcon(drawList, min, max);
        return;
    }

    DrawBuiltInFileIcon(drawList, min, max);
}

bool DrawEditorTextureIcon(
    ImDrawList* drawList,
    const ImVec2& min,
    const ImVec2& max,
    EditorTextureIconKind kind) {
    MaintainIconRuntimeState();

    const BuiltInTexture* texture = ResolveEditorTexture(kind);
    if (texture == nullptr || !texture->IsValid()) {
        return false;
    }

    DrawTextureIcon(drawList, *texture, min, max);
    return true;
}

bool DrawTextureAssetPreview(
    ImDrawList* drawList,
    const ImVec2& min,
    const ImVec2& max,
    const std::string& filePath,
    const std::string& projectPath) {
    BuiltInIconState::CachedAssetPreview* preview = GetOrCreateAssetPreview(filePath, projectPath);
    if (!preview || !preview->texture.IsValid() || preview->hasStaleTexture) {
        return false;
    }

    DrawTextureIcon(drawList, preview->texture, min, max);
    PruneAssetPreviewCache();
    return true;
}

} // namespace UI
} // namespace Editor
} // namespace XCEngine