Destrum/destrum/src/Assets/AssetDatabase.cpp

#include <destrum/Assets/AssetDatabase.h>

#include <charconv>
#include <filesystem>
#include <format>
#include <random>

#include <spdlog/spdlog.h>

#include <destrum/Assets/AssetTypes.h>
#include <destrum/FS/AssetFS.h>

namespace {
    [[nodiscard]] bool IsVirtualPath(std::string_view path)
    {
        return path.find("://") != std::string_view::npos;
    }

    [[nodiscard]] std::optional<AssetGuid> ReadMetaFile(const std::filesystem::path& path)
    {
        try {
            const std::vector<std::uint8_t> bytes = AssetFS::GetInstance().ReadFile(path);
            const auto meta = nlohmann::json::parse(bytes.begin(), bytes.end());
            return AssetGuid::Parse(meta.at("guid").get<std::string>());
        } catch (const std::exception& exception) {
            spdlog::warn("Ignoring broken asset meta file {}: {}", path.string(), exception.what());
            return std::nullopt;
        }
    }
}

AssetGuid AssetGuid::Generate()
{
    static std::mt19937_64 random{std::random_device{}() ^ (static_cast<std::uint64_t>(std::random_device{}()) << 32)};
    AssetGuid guid;
    while (!guid.IsValid()) {
        guid = {random(), random()};
    }
    return guid;
}

std::optional<AssetGuid> AssetGuid::Parse(std::string_view text)
{
    if (text.size() != 32) {
        return std::nullopt;
    }
    AssetGuid guid;
    const auto parseHalf = [](std::string_view half, std::uint64_t& out) {
        const auto [end, error] = std::from_chars(half.data(), half.data() + half.size(), out, 16);
        return error == std::errc{} && end == half.data() + half.size();
    };
    if (!parseHalf(text.substr(0, 16), guid.high) || !parseHalf(text.substr(16), guid.low) || !guid.IsValid()) {
        return std::nullopt;
    }
    return guid;
}

std::string AssetGuid::ToString() const
{
    return std::format("{:016x}{:016x}", high, low);
}

AssetDatabase::MetaFileScope::MetaFileScope()
{
    ++AssetDatabase::GetInstance().m_MetaFileScopes;
}

AssetDatabase::MetaFileScope::~MetaFileScope()
{
    --AssetDatabase::GetInstance().m_MetaFileScopes;
}

void AssetDatabase::Clear()
{
    m_Guids.clear();
    m_Paths.clear();
}

void AssetDatabase::Refresh()
{
    Clear();
    const auto& assetFs = AssetFS::GetInstance();
    for (const FSMount& mount : assetFs.GetMounts()) {
        for (const std::filesystem::path& file : assetFs.ListFiles(mount)) {
            if (!AssetTypes::IsMeta(file.string())) {
                continue;
            }
            if (const auto guid = ReadMetaFile(file)) {
                std::filesystem::path asset = file;
                asset.replace_extension();
                Register(mount.scheme + "://" + asset.lexically_relative(mount.root).generic_string(), *guid);
            }
        }
    }
}

void AssetDatabase::Register(std::string_view path, const AssetGuid& guid)
{
    if (const auto existing = m_Paths.find(guid); existing != m_Paths.end() && existing->second != path) {
        spdlog::warn("Assets {} and {} share the id {}, copy assets without their .meta file",
                     existing->second, path, guid.ToString());
        return;
    }
    m_Guids.insert_or_assign(std::string{path}, guid);
    m_Paths.insert_or_assign(guid, std::string{path});
}

std::optional<AssetGuid> AssetDatabase::FindGuid(std::string_view path) const
{
    const auto it = m_Guids.find(std::string{path});
    return it != m_Guids.end() ? std::optional{it->second} : std::nullopt;
}

std::optional<std::string> AssetDatabase::FindPath(const AssetGuid& guid) const
{
    const auto it = m_Paths.find(guid);
    return it != m_Paths.end() ? std::optional{it->second} : std::nullopt;
}

std::optional<AssetGuid> AssetDatabase::GuidForSave(std::string_view path)
{
    if (auto guid = FindGuid(path)) {
        return guid;
    }
    if (m_MetaFileScopes == 0 || !IsVirtualPath(path)) {
        return std::nullopt;
    }

    auto& assetFs = AssetFS::GetInstance();
    if (!assetFs.Exists(assetFs.GetFullPath(path))) {
        return std::nullopt;
    }

    const AssetGuid guid = AssetGuid::Generate();
    const nlohmann::json meta{{"guid", guid.ToString()}};
    if (!assetFs.WriteFile(std::string{path} + std::string{AssetTypes::MetaExtension}, meta.dump(4))) {
        return std::nullopt;
    }
    Register(path, guid);
    return guid;
}

nlohmann::json AssetDatabase::WriteReference(std::string_view path, std::string_view subresource)
{
    nlohmann::json reference{{"path", path}};
    if (!subresource.empty()) {
        reference["sub"] = subresource;
    }
    if (const auto guid = GuidForSave(path)) {
        reference["guid"] = guid->ToString();
    }
    return reference;
}

std::optional<AssetReference> AssetDatabase::ReadReference(const nlohmann::json& reference) const
{
    if (!reference.is_object() || !reference.contains("path") || !reference.at("path").is_string()) {
        return std::nullopt;
    }

    AssetReference result{
        .path = reference.at("path").get<std::string>(),
        .subresource = reference.value("sub", std::string{}),
    };
    if (const auto guid = AssetGuid::Parse(reference.value("guid", std::string{}))) {
        if (auto current = FindPath(*guid); current && *current != result.path) {
            spdlog::info("{} moved to {}, following its id", result.path, *current);
            result.path = std::move(*current);
        }
    }
    return result;
}