#include "Core/UndoManager.h"

#include "Core/ISelectionManager.h"
#include "Managers/SceneManager.h"

#include <algorithm>

namespace XCEngine {
namespace Editor {

namespace {

constexpr size_t kMaxUndoHistory = 128;

} // namespace

UndoManager::UndoManager(SceneManager& sceneManager, ISelectionManager& selectionManager)
    : m_sceneManager(sceneManager)
    , m_selectionManager(selectionManager) {}

void UndoManager::ClearHistory() {
    m_history.clear();
    m_nextIndex = 0;
    m_pendingInteractiveChange.reset();
}

bool UndoManager::CanUndo() const {
    return m_nextIndex > 0;
}

bool UndoManager::CanRedo() const {
    return m_nextIndex < m_history.size();
}

const std::string& UndoManager::GetUndoLabel() const {
    return CanUndo() ? m_history[m_nextIndex - 1].label : m_emptyLabel;
}

const std::string& UndoManager::GetRedoLabel() const {
    return CanRedo() ? m_history[m_nextIndex].label : m_emptyLabel;
}

void UndoManager::Undo() {
    if (HasPendingInteractiveChange()) {
        FinalizeInteractiveChange();
    }

    if (!CanUndo()) {
        return;
    }

    --m_nextIndex;
    ApplyState(m_history[m_nextIndex].before);
}

void UndoManager::Redo() {
    if (HasPendingInteractiveChange()) {
        FinalizeInteractiveChange();
    }

    if (!CanRedo()) {
        return;
    }

    ApplyState(m_history[m_nextIndex].after);
    ++m_nextIndex;
}

UndoStateSnapshot UndoManager::CaptureCurrentState() const {
    UndoStateSnapshot snapshot;
    snapshot.scene = m_sceneManager.CaptureSceneSnapshot();

    if (!snapshot.scene.hasScene) {
        return snapshot;
    }

    for (uint64_t entityId : m_selectionManager.GetSelectedEntities()) {
        if (m_sceneManager.GetEntity(entityId)) {
            snapshot.selectionIds.push_back(entityId);
        }
    }

    return snapshot;
}

void UndoManager::PushCommand(const std::string& label, UndoStateSnapshot before, UndoStateSnapshot after) {
    if (AreStatesEqual(before, after)) {
        return;
    }

    if (m_nextIndex < m_history.size()) {
        m_history.erase(m_history.begin() + static_cast<std::ptrdiff_t>(m_nextIndex), m_history.end());
    }

    m_history.push_back(CommandEntry{ label, std::move(before), std::move(after) });
    if (m_history.size() > kMaxUndoHistory) {
        m_history.erase(m_history.begin());
        if (m_nextIndex > 0) {
            --m_nextIndex;
        }
    }

    m_nextIndex = m_history.size();
}

void UndoManager::BeginInteractiveChange(const std::string& label) {
    if (m_pendingInteractiveChange.has_value()) {
        return;
    }

    m_pendingInteractiveChange = PendingInteractiveChange{ label, CaptureCurrentState() };
}

bool UndoManager::HasPendingInteractiveChange() const {
    return m_pendingInteractiveChange.has_value();
}

void UndoManager::FinalizeInteractiveChange() {
    if (!m_pendingInteractiveChange.has_value()) {
        return;
    }

    PushCommand(
        m_pendingInteractiveChange->label,
        std::move(m_pendingInteractiveChange->before),
        CaptureCurrentState());
    m_pendingInteractiveChange.reset();
}

void UndoManager::CancelInteractiveChange() {
    m_pendingInteractiveChange.reset();
}

bool UndoManager::ApplyState(const UndoStateSnapshot& state) {
    if (!m_sceneManager.RestoreSceneSnapshot(state.scene)) {
        return false;
    }

    std::vector<uint64_t> validSelection;
    validSelection.reserve(state.selectionIds.size());
    for (uint64_t entityId : state.selectionIds) {
        if (m_sceneManager.GetEntity(entityId)) {
            validSelection.push_back(entityId);
        }
    }

    if (validSelection.empty()) {
        m_selectionManager.ClearSelection();
    } else {
        m_selectionManager.SetSelectedEntities(validSelection);
    }

    return true;
}

bool UndoManager::AreStatesEqual(const UndoStateSnapshot& lhs, const UndoStateSnapshot& rhs) {
    return lhs.scene.hasScene == rhs.scene.hasScene &&
        lhs.scene.scenePath == rhs.scene.scenePath &&
        lhs.scene.sceneData == rhs.scene.sceneData &&
        lhs.scene.dirty == rhs.scene.dirty &&
        lhs.selectionIds == rhs.selectionIds;
}

} // namespace Editor
} // namespace XCEngine