#include "UI.hpp"

#include "Model/Filter.hpp"
#include "Model/Project.hpp"
#include "UI/Localization.hpp"
#include "UI/States.hpp"
#include "Utils/ScopeGuard.hpp"
#include "cplt_fwd.hpp"

#include <IconsFontAwesome.h>
#include <SQLiteCpp/Statement.h>
#include <imgui.h>
#include <chrono>
#include <cstdint>
#include <ctime>
#include <memory>
#include <vector>

namespace {

// TODO move to Settings
constexpr int kMaxEntriesPerPage = 20;

class SaleEntry {
public:
	std::string Customer;
	std::string Deadline;
	std::string DeliveryTime;
};

class PurchaseEntry {
public:
	std::string Factory;
	std::string OrderTime;
	std::string DeliveryTime;
};

class SalesViewTab {
private:
	Project* mProject;

	/// Current active filter object, or \c nullptr.
	std::unique_ptr<TableRowsFilter> mActiveFilter;

	/// Inclusive.
	/// \see mLastCachedRowId
	int64_t mFirstCachedRowId;
	/// Inclusive.
	/// \see mFirstCachedRowId
	int64_t mLastCachedRowId;

	/// A cached, contiguous (row id of each entry is monotonically increasing, but not necessarily starts at 0) list ready-to-be-presented entries. May be incomplete.
	std::vector<SaleEntry> mEntries;

	/// A vector of row ids of entries (in \c mEntries) that are visible under the current filter. To use these indices, the elements should be mapped to \c mEntries
	/// index by offsetting by \c mFirstCachedRowId.
	std::vector<int> mActiveEntries;

	/// Last possible page for the current set table and filter (inclusive).
	int mLastPage;
	/// The current page the user is on.
	int mCurrentPage;

	int mSelectedEntryRowId;

public:
	Project* GetProject() const {
		return mProject;
	}

	void OnProjectChanged(Project* newProject) {
		mProject = newProject;

		mFirstCachedRowId = 0;
		mLastCachedRowId = 0;

		mEntries.clear();
		mActiveEntries.clear();

		UpdateLastPage();
		SetPage(0);

		mSelectedEntryRowId = -1;
	}

	TableRowsFilter* GetFilter() const {
		return mActiveFilter.get();
	}

	void OnFilterChanged() {
		auto& stmt = mProject->GetTransactionsModel().GetSales().FilterRowsStatement;
		DEFER {
			stmt.reset();
		};

		// TODO lazy loading when too many results
		mActiveEntries.clear();
		int columnIdx = stmt.getColumnIndex("rowid");
		while (stmt.executeStep()) {
			mActiveEntries.push_back(stmt.getColumn(columnIdx).getInt());
		}

		UpdateLastPage();
		SetPage(0);

		mSelectedEntryRowId = -1;
	}

	void OnFilterChanged(std::unique_ptr<TableRowsFilter> filter) {
		mActiveFilter = std::move(filter);
		OnFilterChanged();
	}

	void Draw() {
		bool dummy = true;
		auto ls = LocaleStrings::Instance.get();

		if (ImGui::Button(ICON_FA_ARROW_LEFT, mCurrentPage == 0)) {
			SetPage(mCurrentPage - 1);
		}

		ImGui::SameLine();
		// +1 to convert from 0-based indices to 1-based, for human legibility
		ImGui::Text("%d/%d", mCurrentPage + 1, mLastPage + 1);

		ImGui::SameLine();
		if (ImGui::Button(ICON_FA_ARROW_RIGHT, mCurrentPage == mLastPage)) {
			SetPage(mCurrentPage + 1);
		}

		ImGui::SameLine();
		if (ImGui::Button(ls->Edit.Get(), mSelectedEntryRowId == -1)) {
			ImGui::OpenPopup(ls->EditSaleEntryDialogTitle.Get());
		}
		if (ImGui::BeginPopupModal(ls->EditSaleEntryDialogTitle.Get(), &dummy, ImGuiWindowFlags_AlwaysAutoResize)) {
			// TODO
			ImGui::EndPopup();
		}

		if (ImGui::BeginTable("##SalesTable", 3)) {

			ImGui::TableSetupColumn(ls->DatabaseCustomerColumn.Get());
			ImGui::TableSetupColumn(ls->DatabaseDeadlineColumn.Get());
			ImGui::TableSetupColumn(ls->DatabaseDeliveryTimeColumn.Get());
			ImGui::TableHeadersRow();

			auto [begin, end] = CalcRangeForPage(mCurrentPage);
			if (mActiveFilter) {
				end = std::min(end, (int64_t)mActiveEntries.size() - 1);
				for (int i = begin; i < end; ++i) {
					int rowId = mActiveEntries[i];
					DrawEntry(GetEntry(rowId), rowId);
				}
			} else {
				end = std::min(end, mLastCachedRowId);
				for (int rowId = begin; rowId < end; ++rowId) {
					DrawEntry(GetEntry(rowId), rowId);
				}
			}

			ImGui::EndTable();
		}
	}

	void DrawEntry(const SaleEntry& entry, int rowId) {
		auto ls = LocaleStrings::Instance.get();

		ImGui::TableNextColumn();
		if (ImGui::Selectable(entry.Customer.c_str(), mSelectedEntryRowId == rowId, ImGuiSelectableFlags_SpanAllColumns)) {
			mSelectedEntryRowId = rowId;
		}

		ImGui::TableNextColumn();
		ImGui::Text("%s", entry.Deadline.c_str());

		ImGui::TableNextColumn();
		if (entry.DeliveryTime.empty()) {
			ImGui::Text("%s", ls->NotDeliveredMessage.Get());
		} else {
			ImGui::Text("%s", entry.DeliveryTime.c_str());
		}
	}

	const SaleEntry& GetEntry(int64_t rowId) const {
		return mEntries[RowIdToIndex(rowId)];
	}

	SaleEntry& GetEntry(int64_t rowId) {
		return mEntries[RowIdToIndex(rowId)];
	}

private:
	void SetPage(int page) {
		mCurrentPage = page;
		EnsureCacheCoversPage(page);
	}

	void UpdateLastPage() {
		mLastPage = mActiveEntries.empty()
			? 0 // TODO calc page
			: CalcPageForRowId(mActiveEntries.back());
	}

	void EnsureCacheCoversPage(int page) {
		auto [begin, end] = CalcRangeForPage(page);
		EnsureCacheCovers(begin, end - 1);
	}

	void EnsureCacheCovers(int64_t firstRow, int64_t lastRow) {
		if (firstRow > lastRow) {
			std::swap(firstRow, lastRow);
		}

		int newFirst = mFirstCachedRowId;
		int newLast = mLastCachedRowId;

		bool doRebuild = false;
		if (firstRow < mFirstCachedRowId) {
			newFirst = (CalcPageForRowId(firstRow) + 1) * kMaxEntriesPerPage;
			doRebuild = true;
		}
		if (lastRow > mLastCachedRowId) {
			newLast = (CalcPageForRowId(lastRow) + 1) * kMaxEntriesPerPage;
			doRebuild = true;
		}
		if (!doRebuild) return;

		auto front = LoadRange(newFirst, mFirstCachedRowId);
		auto back = LoadRange(mLastCachedRowId + 1, newLast + 1);

		mFirstCachedRowId -= front.size();
		mLastCachedRowId += back.size();

		// TODO don't reallocate buffer/move elements around all the time. Maybe use a linked list of buckets?
		mEntries.insert(mEntries.begin(), std::make_move_iterator(front.begin()), std::make_move_iterator(front.end()));
		mEntries.insert(mEntries.end(), std::make_move_iterator(back.begin()), std::make_move_iterator(back.end()));
	}

	std::vector<SaleEntry> LoadRange(int64_t begin, int64_t end) {
		std::vector<SaleEntry> result;

		size_t size = end - begin;
		if (size == 0) {
			return result;
		}

		result.reserve(size);

		auto& stmt = mProject->GetTransactionsModel().GetSales().GetRowsStatement;
		DEFER {
			stmt.reset();
		};

		stmt.bind(1, begin);
		stmt.bind(2, end);

		auto StringifyEpochTime = [](int64_t epoch) -> std::string {
			if (epoch == 0) {
				return "";
			}

			namespace chrono = std::chrono;
			using Clock = chrono::system_clock;

			chrono::milliseconds d{ epoch };
			chrono::time_point<chrono::system_clock> tp{ d };
			auto t = chrono::system_clock::to_time_t(tp);

			char data[32];
			std::strftime(data, sizeof(data), "%Y-%m-%d %H:%M:%S", std::localtime(&t));

			return std::string(data);
		};

		int customerCol = stmt.getColumnIndex("Customer");
		int deadlineCol = stmt.getColumnIndex("Deadline");
		int deliveryTimeCol = stmt.getColumnIndex("DeliveryTime");

		while (stmt.executeStep()) {
			auto customer = stmt.getColumn(customerCol).getInt();
			auto deadline = stmt.getColumn(deadlineCol).getInt64();
			auto deliveryTime = stmt.getColumn(deliveryTimeCol).getInt64();
			result.push_back(SaleEntry{
				.Customer = mProject->Customers.Find(customer)->GetName(),
				.Deadline = StringifyEpochTime(deadline),
				.DeliveryTime = StringifyEpochTime(deliveryTime),
			});
		}
		return result;
	}

	int RowIdToIndex(int64_t rowId) const {
		return rowId - mFirstCachedRowId;
	}

	int64_t IndexToRowId(int index) const {
		return index + mFirstCachedRowId;
	}

	static int CalcPageForRowId(int64_t rowId) {
		return rowId / kMaxEntriesPerPage;
	}

	/// Calculate range [begin, end) of index for the list of entries that are currently visible that the path-th page would show.
	/// i.e. when there is a filter, look into \c mActiveEntryIndices; when there is no filter, use directly.
	static std::pair<int64_t, int64_t> CalcRangeForPage(int page) {
		int begin = page * kMaxEntriesPerPage;
		return { begin, begin + kMaxEntriesPerPage };
	}
};

class PurchasesViewTab {
private:
	std::vector<PurchaseEntry> mEntries;
	int mCurrentPage = 0;

public:
	void OnProjectChanged(Project* newProject) {
		// TODO
	}

	void Draw() {
		auto ls = LocaleStrings::Instance.get();
		if (ImGui::BeginTable("##PurcahsesTable", 4)) {
			ImGui::EndTable();
		}
	}
};
} // namespace

void UI::DatabaseViewTab() {
	auto ls = LocaleStrings::Instance.get();
	auto& uis = UIState::GetInstance();

	static Project* currentProject = nullptr;
	static SalesViewTab salesView;
	static PurchasesViewTab purchasesView;

	if (currentProject != uis.CurrentProject.get()) {
		currentProject = uis.CurrentProject.get();
		salesView.OnProjectChanged(currentProject);
		purchasesView.OnProjectChanged(currentProject);
	}

	if (ImGui::BeginTabBar("##DatabaseViewTabs")) {
		if (ImGui::BeginTabItem(ls->SalesViewTab.Get())) {
			salesView.Draw();
			ImGui::EndTabItem();
		}
		if (ImGui::BeginTabItem(ls->PurchasesViewTab.Get())) {
			purchasesView.Draw();
			ImGui::EndTabItem();
		}

		ImGui::EndTabBar();
	}
}