#include <XCEngine/UI/Runtime/UISystem.h>

#include <utility>

namespace XCEngine {
namespace UI {
namespace Runtime {

namespace {

std::size_t FindTopInputLayerIndex(
    const std::vector<UIScreenLayerOptions>& layerOptions,
    std::size_t lowestPresentedIndex) {
    if (layerOptions.empty() || lowestPresentedIndex >= layerOptions.size()) {
        return static_cast<std::size_t>(-1);
    }

    for (std::size_t index = layerOptions.size(); index-- > lowestPresentedIndex;) {
        if (layerOptions[index].visible && layerOptions[index].acceptsInput) {
            return index;
        }
    }

    return static_cast<std::size_t>(-1);
}

std::size_t FindLowestPresentedLayerIndex(const std::vector<UIScreenLayerOptions>& layerOptions) {
    if (layerOptions.empty()) {
        return 0u;
    }

    for (std::size_t index = layerOptions.size(); index-- > 0u;) {
        if (layerOptions[index].visible && layerOptions[index].blocksLayersBelow) {
            return index;
        }
    }

    return 0u;
}

} // namespace

UISystem::UISystem(IUIScreenDocumentHost& documentHost)
    : m_documentHost(&documentHost) {
}

UIScreenPlayer& UISystem::CreatePlayer(const UIScreenLayerOptions& options) {
    m_players.push_back(std::make_unique<UIScreenPlayer>(*m_documentHost));
    m_layerIds.push_back(m_nextLayerId++);
    m_layerOptions.push_back(options);
    return *m_players.back();
}

UIScreenLayerId UISystem::PushScreen(
    const UIScreenAsset& asset,
    const UIScreenLayerOptions& options) {
    UIScreenPlayer& player = CreatePlayer(options);
    if (!player.Load(asset)) {
        m_players.pop_back();
        m_layerIds.pop_back();
        m_layerOptions.pop_back();
        return 0;
    }

    return m_layerIds.back();
}

bool UISystem::RemoveLayer(UIScreenLayerId layerId) {
    const std::size_t index = FindLayerIndex(layerId);
    if (index >= m_players.size()) {
        return false;
    }

    m_players.erase(m_players.begin() + static_cast<std::ptrdiff_t>(index));
    m_layerIds.erase(m_layerIds.begin() + static_cast<std::ptrdiff_t>(index));
    m_layerOptions.erase(m_layerOptions.begin() + static_cast<std::ptrdiff_t>(index));
    return true;
}

bool UISystem::SetLayerVisibility(UIScreenLayerId layerId, bool visible) {
    const std::size_t index = FindLayerIndex(layerId);
    if (index >= m_layerOptions.size()) {
        return false;
    }

    m_layerOptions[index].visible = visible;
    return true;
}

bool UISystem::SetLayerOptions(UIScreenLayerId layerId, const UIScreenLayerOptions& options) {
    const std::size_t index = FindLayerIndex(layerId);
    if (index >= m_layerOptions.size()) {
        return false;
    }

    m_layerOptions[index] = options;
    return true;
}

const UIScreenLayerOptions* UISystem::FindLayerOptions(UIScreenLayerId layerId) const {
    const std::size_t index = FindLayerIndex(layerId);
    return index < m_layerOptions.size() ? &m_layerOptions[index] : nullptr;
}

UIScreenLayerId UISystem::GetLayerId(std::size_t index) const {
    return index < m_layerIds.size() ? m_layerIds[index] : 0;
}

void UISystem::DestroyAllPlayers() {
    m_players.clear();
    m_layerIds.clear();
    m_layerOptions.clear();
    m_lastFrame = {};
}

std::size_t UISystem::GetPlayerCount() const {
    return m_players.size();
}

std::size_t UISystem::GetLayerCount() const {
    return m_layerIds.size();
}

const UISystemFrameResult& UISystem::Update(const UIScreenFrameInput& input) {
    m_lastFrame = {};
    m_lastFrame.frameIndex = input.frameIndex;
    m_lastFrame.viewportRect = input.viewportRect;
    m_lastFrame.submittedInputEventCount = input.events.size();
    m_lastFrame.deltaTimeSeconds = input.deltaTimeSeconds;
    m_lastFrame.focused = input.focused;

    if (m_players.empty()) {
        return m_lastFrame;
    }

    const std::size_t lowestPresentedIndex = FindLowestPresentedLayerIndex(m_layerOptions);
    const std::size_t inputLayerIndex = FindTopInputLayerIndex(m_layerOptions, lowestPresentedIndex);

    for (std::size_t index = 0; index < lowestPresentedIndex && index < m_players.size(); ++index) {
        ++m_lastFrame.skippedLayerCount;
    }

    for (std::size_t index = lowestPresentedIndex; index < m_players.size(); ++index) {
        if (!m_layerOptions[index].visible) {
            ++m_lastFrame.skippedLayerCount;
            continue;
        }

        UIScreenFrameInput layerInput = input;
        if (index != inputLayerIndex) {
            layerInput.events.clear();
            layerInput.focused = false;
        }

        const UIScreenFrameResult& layerFrame = m_players[index]->Update(layerInput);
        for (const UIDrawList& drawList : layerFrame.drawData.GetDrawLists()) {
            m_lastFrame.drawData.AddDrawList(drawList);
        }

        UISystemPresentedLayer presentedLayer = {};
        presentedLayer.layerId = m_layerIds[index];
        if (const UIScreenAsset* asset = m_players[index]->GetAsset(); asset != nullptr) {
            presentedLayer.asset = *asset;
        }
        presentedLayer.options = m_layerOptions[index];
        presentedLayer.stats = layerFrame.stats;
        m_lastFrame.layers.push_back(std::move(presentedLayer));
        ++m_lastFrame.presentedLayerCount;

        if (m_lastFrame.errorMessage.empty() && !layerFrame.errorMessage.empty()) {
            m_lastFrame.errorMessage = layerFrame.errorMessage;
        }
    }

    return m_lastFrame;
}

void UISystem::Tick(const UIScreenFrameInput& input) {
    Update(input);
}

const UISystemFrameResult& UISystem::GetLastFrame() const {
    return m_lastFrame;
}

UISystemFrameResult UISystem::ConsumeLastFrame() {
    UISystemFrameResult frame = std::move(m_lastFrame);
    m_lastFrame = {};
    return frame;
}

const std::vector<std::unique_ptr<UIScreenPlayer>>& UISystem::GetPlayers() const {
    return m_players;
}

std::size_t UISystem::FindLayerIndex(UIScreenLayerId layerId) const {
    for (std::size_t index = 0; index < m_layerIds.size(); ++index) {
        if (m_layerIds[index] == layerId) {
            return index;
        }
    }

    return static_cast<std::size_t>(-1);
}

} // namespace Runtime
} // namespace UI
} // namespace XCEngine