/*********************************************************************
 * \file   SerializationManager.cpp
 *
 * \author Romain BOULLARD
 * \date   August 2026
 *********************************************************************/
#include <Engine/SerializationManager/SerializationManager.hpp>

#include <Engine/Asset/AssetLibrary.hpp>
#include <Engine/DataAccessor/DataAccessor.hpp>

#include <Utils/Algorithm/Graph.hpp>

#include <ankerl/unordered_dense.h>

namespace Bigfoot::SerializationManager
{
/*
 * Build the transitive HardReference graph reachable from p_roots
 *
 * \param p_roots The assets to start the discovery from
 * \param p_discovered Every discovered asset that isn't already loaded, including p_roots
 * \return Every asset's HardReferences
 */
[[nodiscard]]
ankerl::unordered_dense::map<UUID, eastl::vector<UUID>> BuildDependencyGraph(
    const eastl::span<const UUID> p_roots,
    ankerl::unordered_dense::set<UUID>& p_discovered)
{
    ankerl::unordered_dense::map<UUID, eastl::vector<UUID>> graph;

    eastl::vector<UUID> toQuery;
    toQuery.reserve(p_roots.size());
    for (const UUID& uuid: p_roots)
    {
        if (!g_activeAssetLibrary->IsLoaded(uuid) && p_discovered.insert(uuid).second)
        {
            toQuery.push_back(uuid);
        }
    }

    while (!toQuery.empty())
    {
        eastl::vector<eastl::vector<UUID>> hardReferencesBatch = g_dataAccessor->GetAssetsHardReferences(toQuery);

        eastl::vector<UUID> nextToQuery;
        for (std::size_t i = 0; i < toQuery.size(); ++i)
        {
            eastl::vector<UUID>& hardReferences = graph[toQuery[i]];
            hardReferences = std::move(hardReferencesBatch[i]);

            for (const UUID& hardReference: hardReferences)
            {
                if (!g_activeAssetLibrary->IsLoaded(hardReference) && p_discovered.insert(hardReference).second)
                {
                    nextToQuery.push_back(hardReference);
                }
            }
        }

        toQuery = std::move(nextToQuery);
    }

    return graph;
}

/****************************************************************************************/

void LoadAssets(const eastl::span<const UUID> p_uuids)
{
    ankerl::unordered_dense::set<UUID> discovered;
    const ankerl::unordered_dense::map<UUID, eastl::vector<UUID>> graph = BuildDependencyGraph(p_uuids, discovered);

    // Assets that are part of a cyclic HardReference dependency are left out of waves and simply never loaded.
    eastl::vector<eastl::vector<UUID>> waves;
    eastl::vector<UUID> cyclicUuids;
    std::ignore = LayeredTopologicalSort(graph, discovered, waves, cyclicUuids);
    BIGFOOT_LOG_ERROR_IF(!cyclicUuids.empty(),
                         ENGINE_LOGGER,
                         "Cyclic HardReference dependency detected while loading assets, involved UUIDs: {}",
                         cyclicUuids);

    // Waves are loaded one after another since a wave's assets may HardReference the previous wave's; within a
    // wave, every asset is independent of the others, so this is where loading could later be parallelized.
    for (const eastl::vector<UUID>& wave: waves)
    {
        const eastl::vector<eastl::vector<std::byte>> assetFlatbuffers = g_dataAccessor->GetAssetFlatbuffers(wave);
        for (const eastl::vector<std::byte>& flatbuffer: assetFlatbuffers)
        {
            if (flatbuffer.empty())
            {
                continue;
            }

#ifdef BIGFOOT_NOT_OPTIMIZED
            flatbuffers::Verifier verifier {std::bit_cast<std::uint8_t*>(flatbuffer.data()), flatbuffer.size()};
            const bool assetVerified = ::Flat::Bigfoot::VerifyAssetBuffer(verifier);
            CRITICAL_ASSERT(EngineAssertHandler, assetVerified, "Given asset could not be verified!");
#endif

            const ::Flat::Bigfoot::Asset* asset = flatbuffers::GetRoot<::Flat::Bigfoot::Asset>(flatbuffer.data());

            AssetContainerBase* container = g_activeAssetLibrary->GetAssetContainer(
                flatbuffers::UnPack(*asset->header()->type_id()));
            std::ignore = container->Insert(flatbuffer);
        }
    }
}

/****************************************************************************************/

void LoadAsset(const UUID& p_uuid)
{
    ankerl::unordered_dense::set<UUID> discovered;
    const ankerl::unordered_dense::map<UUID, eastl::vector<UUID>> graph = BuildDependencyGraph(
        eastl::span<const UUID> {&p_uuid, 1},
        discovered);

    // Assets that are part of a cyclic HardReference dependency are left out of waves and simply never loaded.
    eastl::vector<eastl::vector<UUID>> waves;
    eastl::vector<UUID> cyclicUuids;
    std::ignore = LayeredTopologicalSort(graph, discovered, waves, cyclicUuids);
    BIGFOOT_LOG_ERROR_IF(!cyclicUuids.empty(),
                         ENGINE_LOGGER,
                         "Cyclic HardReference dependency detected while loading asset {}, involved UUIDs: {}",
                         p_uuid,
                         cyclicUuids);

    // Waves are loaded one after another since a wave's assets may HardReference the previous wave's; within a
    // wave, every asset is independent of the others, so this is where loading could later be parallelized.
    for (const eastl::vector<UUID>& wave: waves)
    {
        for (const UUID& uuid: wave)
        {
            const eastl::vector<std::byte> flatbuffer = g_dataAccessor->GetAssetFlatbuffer(uuid);
            if (flatbuffer.empty())
            {
                continue;
            }

#ifdef BIGFOOT_NOT_OPTIMIZED
            flatbuffers::Verifier verifier {std::bit_cast<std::uint8_t*>(flatbuffer.data()), flatbuffer.size()};
            const bool assetVerified = ::Flat::Bigfoot::VerifyAssetBuffer(verifier);
            CRITICAL_ASSERT(EngineAssertHandler, assetVerified, "Given asset could not be verified!");
#endif

            const ::Flat::Bigfoot::Asset* asset = flatbuffers::GetRoot<::Flat::Bigfoot::Asset>(flatbuffer.data());

            AssetContainerBase* container = g_activeAssetLibrary->GetAssetContainer(
                flatbuffers::UnPack(*asset->header()->type_id()));
            std::ignore = container->Insert(flatbuffer);
        }
    }
}

/****************************************************************************************/

#if defined BIGFOOT_TOOLMODE
/*
 * Finds the cyclic dependencies that may exist in Assets
 *
 * \param p_uuids The assets we want to explore
 * \param p_hardReferences The HardReferences of p_uuids, matching by index
 * \return Every UUID caught in a cyclic dependency
 */
[[nodiscard]]
eastl::vector<UUID> FindCyclicDependencies(const eastl::span<const UUID> p_uuids,
                                           const eastl::span<const eastl::vector<UUID>> p_hardReferences)
{
    ankerl::unordered_dense::map<UUID, eastl::vector<UUID>> graph;
    ankerl::unordered_dense::set<UUID> discovered;

    eastl::vector<UUID> toQuery;
    for (std::size_t i = 0; i < p_uuids.size(); ++i)
    {
        discovered.insert(p_uuids[i]);
        graph[p_uuids[i]] = p_hardReferences[i];
    }
    for (const eastl::vector<UUID>& hardReferences: p_hardReferences)
    {
        for (const UUID& hardReference: hardReferences)
        {
            if (discovered.insert(hardReference).second)
            {
                toQuery.push_back(hardReference);
            }
        }
    }

    while (!toQuery.empty())
    {
        eastl::vector<eastl::vector<UUID>> hardReferencesBatch = g_dataAccessor->GetAssetsHardReferences(toQuery);

        eastl::vector<UUID> nextToQuery;
        for (std::size_t i = 0; i < toQuery.size(); ++i)
        {
            eastl::vector<UUID>& hardReferences = graph[toQuery[i]];
            hardReferences = std::move(hardReferencesBatch[i]);

            for (const UUID& hardReference: hardReferences)
            {
                if (discovered.insert(hardReference).second)
                {
                    nextToQuery.push_back(hardReference);
                }
            }
        }

        toQuery = std::move(nextToQuery);
    }

    eastl::vector<eastl::vector<UUID>> waves;
    eastl::vector<UUID> cyclicUuids;
    std::ignore = LayeredTopologicalSort(graph, discovered, waves, cyclicUuids);
    return cyclicUuids;
}

/****************************************************************************************/

bool SaveAsset(const UUID& p_uuid)
{
    AssetContainerBase* container = g_activeAssetLibrary->GetAssetContainer(p_uuid);
    const AssetBase* asset = container->AcquireContainerHandle(p_uuid)->GetAsset();

    const eastl::vector<std::byte> flatbuffer = asset->Pack();
    const eastl::vector<UUID> hardReferences = asset->GetHardReferences(flatbuffer);

    const eastl::vector<UUID> cyclicUuids = FindCyclicDependencies(
        eastl::span<const UUID> {&p_uuid, 1},
        eastl::span<const eastl::vector<UUID>> {&hardReferences, 1});
    BIGFOOT_LOG_ERROR_IF(!cyclicUuids.empty(),
                         ENGINE_LOGGER,
                         "Cyclic HardReference dependency detected while saving asset {}, involved UUIDs: {}",
                         p_uuid,
                         cyclicUuids);
    if (!cyclicUuids.empty())
    {
        return false;
    }

    g_dataAccessor->SaveAssetFlatbuffer(p_uuid, flatbuffer, hardReferences);
    return true;
}

/****************************************************************************************/

bool SaveAssets(const eastl::span<const UUID> p_uuids)
{
    eastl::vector<eastl::vector<std::byte>> flatbuffers;
    eastl::vector<eastl::vector<UUID>> hardReferences;

    flatbuffers.reserve(p_uuids.size());
    hardReferences.reserve(p_uuids.size());
    for (const UUID& uuid: p_uuids)
    {
        AssetContainerBase* container = g_activeAssetLibrary->GetAssetContainer(uuid);
        const AssetBase* asset = container->AcquireContainerHandle(uuid)->GetAsset();

        const eastl::vector<std::byte> flatbuffer = asset->Pack();

        flatbuffers.push_back(flatbuffer);
        hardReferences.push_back(asset->GetHardReferences(flatbuffer));
    }

    const eastl::vector<UUID> cyclicUuids = FindCyclicDependencies(p_uuids, hardReferences);
    BIGFOOT_LOG_ERROR_IF(!cyclicUuids.empty(),
                         ENGINE_LOGGER,
                         "Cyclic HardReference dependency detected while saving assets, involved UUIDs: {}",
                         cyclicUuids);
    if (!cyclicUuids.empty())
    {
        return false;
    }

    g_dataAccessor->SaveAssetFlatbuffers(p_uuids, flatbuffers, hardReferences);
    return true;
}
#endif
}   // namespace Bigfoot::SerializationManager