//
// SuspensionManager.cpp
// Implementation of the SuspensionManager class
//

#include "pch.h"
#include "SuspensionManager.h"

#include <collection.h>
#include <algorithm>

using namespace $safeprojectname$::Common;

using namespace Concurrency;
using namespace Platform;
using namespace Platform::Collections;
using namespace Windows::Foundation;
using namespace Windows::Foundation::Collections;
using namespace Windows::Storage;
using namespace Windows::Storage::FileProperties;
using namespace Windows::Storage::Streams;
using namespace Windows::UI::Xaml;
using namespace Windows::UI::Xaml::Controls;
using namespace Windows::UI::Xaml::Interop;

namespace
{
	Map<String^, Object^>^ _sessionState = ref new Map<String^, Object^>();
	String^ sessionStateFilename = "_sessionState.dat";

	// Forward declarations for object object read / write support
	void WriteObject(Windows::Storage::Streams::DataWriter^ writer, Platform::Object^ object);
	Platform::Object^ ReadObject(Windows::Storage::Streams::DataReader^ reader);
}

/// <summary>
/// Provides access to global session state for the current session.  This state is serialized by
/// <see cref="SaveAsync"/> and restored by <see cref="RestoreAsync"/> which require values to be
/// one of the following: boxed values including integers, floating-point singles and doubles,
/// wide characters, boolean, Strings and Guids, or Map<String^, Object^> where map values are
/// subject to the same constraints.  Session state should be as compact as possible.
/// </summary>
IMap<String^, Object^>^ SuspensionManager::SessionState::get(void)
{
	return _sessionState;
}

/// <summary>
/// Wrap a WeakReference as a reference object for use in a collection.
/// </summary>
private ref class WeakFrame sealed
{
private:
	WeakReference _frameReference;

internal:
	WeakFrame(Frame^ frame) { _frameReference = frame; }
	property Frame^ ResolvedFrame
	{
		Frame^ get(void) { return _frameReference.Resolve<Frame>(); }
	};
};

namespace
{
	std::vector<WeakFrame^> _registeredFrames;
	DependencyProperty^ FrameSessionStateKeyProperty =
		DependencyProperty::RegisterAttached("_FrameSessionStateKeyProperty",
		TypeName(String::typeid), TypeName(SuspensionManager::typeid), nullptr);
	DependencyProperty^ FrameSessionStateProperty =
		DependencyProperty::RegisterAttached("_FrameSessionStateProperty",
		TypeName(IMap<String^, Object^>::typeid), TypeName(SuspensionManager::typeid), nullptr);
}

/// <summary>
/// Registers a <see cref="Frame"/> instance to allow its navigation history to be saved to
/// and restored from <see cref="SessionState"/>.  Frames should be registered once
/// immediately after creation if they will participate in session state management.  Upon
/// registration if state has already been restored for the specified key
/// the navigation history will immediately be restored.  Subsequent invocations of
/// <see cref="RestoreAsync(String)"/> will also restore navigation history.
/// </summary>
/// <param name="frame">An instance whose navigation history should be managed by
/// <see cref="SuspensionManager"/></param>
/// <param name="sessionStateKey">A unique key into <see cref="SessionState"/> used to
/// store navigation-related information.</param>
void SuspensionManager::RegisterFrame(Frame^ frame, String^ sessionStateKey)
{
	if (frame->GetValue(FrameSessionStateKeyProperty) != nullptr)
	{
		throw ref new FailureException("Frames can only be registered to one session state key");
	}

	if (frame->GetValue(FrameSessionStateProperty) != nullptr)
	{
		throw ref new FailureException("Frames must be either be registered before accessing frame session state, or not registered at all");
	}

	// Use a dependency property to associate the session key with a frame, and keep a list of frames whose
	// navigation state should be managed
	frame->SetValue(FrameSessionStateKeyProperty, sessionStateKey);
	_registeredFrames.insert(_registeredFrames.begin(), ref new WeakFrame(frame));

	// Check to see if navigation state can be restored
	RestoreFrameNavigationState(frame);
}

/// <summary>
/// Disassociates a <see cref="Frame"/> previously registered by <see cref="RegisterFrame"/>
/// from <see cref="SessionState"/>.  Any navigation state previously captured will be
/// removed.
/// </summary>
/// <param name="frame">An instance whose navigation history should no longer be
/// managed.</param>
void SuspensionManager::UnregisterFrame(Frame^ frame)
{
	// Remove session state and remove the frame from the list of frames whose navigation
	// state will be saved (along with any weak references that are no longer reachable)
	auto key = safe_cast<String^>(frame->GetValue(FrameSessionStateKeyProperty));
	if (SessionState->HasKey(key)) SessionState->Remove(key);
	_registeredFrames.erase(
		std::remove_if(_registeredFrames.begin(), _registeredFrames.end(), [=](WeakFrame^& e)
		{
			auto testFrame = e->ResolvedFrame;
			return testFrame == nullptr || testFrame == frame;
		}),
		_registeredFrames.end()
	);
}

/// <summary>
/// Provides storage for session state associated with the specified <see cref="Frame"/>.
/// Frames that have been previously registered with <see cref="RegisterFrame"/> have
/// their session state saved and restored automatically as a part of the global
/// <see cref="SessionState"/>.  Frames that are not registered have transient state
/// that can still be useful when restoring pages that have been discarded from the
/// navigation cache.
/// </summary>
/// <remarks>Apps may choose to rely on <see cref="LayoutAwarePage"/> to manage
/// page-specific state instead of working with frame session state directly.</remarks>
/// <param name="frame">The instance for which session state is desired.</param>
/// <returns>A collection of state subject to the same serialization mechanism as
/// <see cref="SessionState"/>.</returns>
IMap<String^, Object^>^ SuspensionManager::SessionStateForFrame(Frame^ frame)
{
	auto frameState = safe_cast<IMap<String^, Object^>^>(frame->GetValue(FrameSessionStateProperty));

	if (frameState == nullptr)
	{
		auto frameSessionKey = safe_cast<String^>(frame->GetValue(FrameSessionStateKeyProperty));
		if (frameSessionKey != nullptr)
		{
			// Registered frames reflect the corresponding session state
			if (!_sessionState->HasKey(frameSessionKey))
			{
				_sessionState->Insert(frameSessionKey, ref new Map<String^, Object^>());
			}
			frameState = safe_cast<IMap<String^, Object^>^>(_sessionState->Lookup(frameSessionKey));
		}
		else
		{
			// Frames that aren't registered have transient state
			frameState = ref new Map<String^, Object^>();
		}
		frame->SetValue(FrameSessionStateProperty, frameState);
	}
	return frameState;
}

void SuspensionManager::RestoreFrameNavigationState(Frame^ frame)
{
	auto frameState = SessionStateForFrame(frame);
	if (frameState->HasKey("Navigation"))
	{
		frame->SetNavigationState(safe_cast<String^>(frameState->Lookup("Navigation")));
	}
}

void SuspensionManager::SaveFrameNavigationState(Frame^ frame)
{
	auto frameState = SessionStateForFrame(frame);
	frameState->Insert("Navigation", frame->GetNavigationState());
}

/// <summary>
/// Save the current <see cref="SessionState"/>.  Any <see cref="Frame"/> instances
/// registered with <see cref="RegisterFrame"/> will also preserve their current
/// navigation stack, which in turn gives their active <see cref="Page"/> an opportunity
/// to save its state.
/// </summary>
/// <returns>An asynchronous task that reflects when session state has been saved.</returns>
task<void> SuspensionManager::SaveAsync(void)
{
	// Save the navigation state for all registered frames
	for (auto&& weakFrame : _registeredFrames)
	{
		auto frame = weakFrame->ResolvedFrame;
		if (frame != nullptr) SaveFrameNavigationState(frame);
	}

	// Serialize the session state synchronously to avoid asynchronous access to shared
	// state
	auto sessionData = ref new InMemoryRandomAccessStream();
	auto sessionDataWriter = ref new DataWriter(sessionData->GetOutputStreamAt(0));
	WriteObject(sessionDataWriter, _sessionState);

	// Once session state has been captured synchronously, begin the asynchronous process
	// of writing the result to disk
	return task<unsigned int>(sessionDataWriter->StoreAsync()).then([=](unsigned int)
	{
		return sessionDataWriter->FlushAsync();
	}).then([=](bool flushSucceeded)
	{
		(void)flushSucceeded; // Unused parameter
		return ApplicationData::Current->LocalFolder->CreateFileAsync(sessionStateFilename,
			CreationCollisionOption::ReplaceExisting);
	}).then([=](StorageFile^ createdFile)
	{
		return createdFile->OpenAsync(FileAccessMode::ReadWrite);
	}).then([=](IRandomAccessStream^ newStream)
	{
		return RandomAccessStream::CopyAndCloseAsync(
			sessionData->GetInputStreamAt(0), newStream->GetOutputStreamAt(0));
	}).then([=](UINT64 copiedBytes)
	{
		(void)copiedBytes; // Unused parameter
		return;
	});
}

/// <summary>
/// Restores previously saved <see cref="SessionState"/>.  Any <see cref="Frame"/> instances
/// registered with <see cref="RegisterFrame"/> will also restore their prior navigation
/// state, which in turn gives their active <see cref="Page"/> an opportunity restore its
/// state.
/// </summary>
/// <param name="version">A version identifer compared to the session state to prevent
/// incompatible versions of session state from reaching app code.  Saved state with a
/// different version will be ignored, resulting in an empty <see cref="SessionState"/>
/// dictionary.</param>
/// <returns>An asynchronous task that reflects when session state has been read.  The
/// content of <see cref="SessionState"/> should not be relied upon until this task
/// completes.</returns>
task<void> SuspensionManager::RestoreAsync(void)
{
	_sessionState->Clear();

	task<StorageFile^> getFileTask(ApplicationData::Current->LocalFolder->GetFileAsync(sessionStateFilename));
	return getFileTask.then([=](StorageFile^ stateFile)
	{
		task<BasicProperties^> getBasicPropertiesTask(stateFile->GetBasicPropertiesAsync());
		return getBasicPropertiesTask.then([=](BasicProperties^ stateFileProperties)
		{
			auto size = unsigned int(stateFileProperties->Size);
			if (size != stateFileProperties->Size) throw ref new FailureException("Session state larger than 4GB");
			task<IRandomAccessStreamWithContentType^> openReadTask(stateFile->OpenReadAsync());
			return openReadTask.then([=](IRandomAccessStreamWithContentType^ stateFileStream)
			{
				auto stateReader = ref new DataReader(stateFileStream);
				return task<unsigned int>(stateReader->LoadAsync(size)).then([=](unsigned int bytesRead)
				{
					(void)bytesRead; // Unused parameter
					// Deserialize the Session State
					Object^ content = ReadObject(stateReader);
					_sessionState = (Map<String^, Object^>^)content;

					// Restore any registered frames to their saved state
					for (auto&& weakFrame : _registeredFrames)
					{
						auto frame = weakFrame->ResolvedFrame;
						if (frame != nullptr)
						{
							frame->ClearValue(FrameSessionStateProperty);
							RestoreFrameNavigationState(frame);
						}
					}
				}, task_continuation_context::use_current());
			});
		});
	});
}

#pragma region Object serialization for a known set of types

namespace
{
	// Codes used for identifying serialized types
	enum StreamTypes {
		NullPtrType = 0,

		// Supported IPropertyValue types
		UInt8Type, UInt16Type, UInt32Type, UInt64Type, Int16Type, Int32Type, Int64Type,
		SingleType, DoubleType, BooleanType, Char16Type, GuidType, StringType,

		// Additional supported types
		StringToObjectMapType,

		// Marker values used to ensure stream integrity
		MapEndMarker
	};

	void WriteString(DataWriter^ writer, String^ string)
	{
		writer->WriteByte(StringType);
		writer->WriteUInt32(writer->MeasureString(string));
		writer->WriteString(string);
	}

	void WriteProperty(DataWriter^ writer, IPropertyValue^ propertyValue)
	{
		switch (propertyValue->Type)
		{
		case PropertyType::UInt8:
			writer->WriteByte(UInt8Type);
			writer->WriteByte(propertyValue->GetUInt8());
			return;
		case PropertyType::UInt16:
			writer->WriteByte(UInt16Type);
			writer->WriteUInt16(propertyValue->GetUInt16());
			return;
		case PropertyType::UInt32:
			writer->WriteByte(UInt32Type);
			writer->WriteUInt32(propertyValue->GetUInt32());
			return;
		case PropertyType::UInt64:
			writer->WriteByte(UInt64Type);
			writer->WriteUInt64(propertyValue->GetUInt64());
			return;
		case PropertyType::Int16:
			writer->WriteByte(Int16Type);
			writer->WriteUInt16(propertyValue->GetInt16());
			return;
		case PropertyType::Int32:
			writer->WriteByte(Int32Type);
			writer->WriteUInt32(propertyValue->GetInt32());
			return;
		case PropertyType::Int64:
			writer->WriteByte(Int64Type);
			writer->WriteUInt64(propertyValue->GetInt64());
			return;
		case PropertyType::Single:
			writer->WriteByte(SingleType);
			writer->WriteSingle(propertyValue->GetSingle());
			return;
		case PropertyType::Double:
			writer->WriteByte(DoubleType);
			writer->WriteDouble(propertyValue->GetDouble());
			return;
		case PropertyType::Boolean:
			writer->WriteByte(BooleanType);
			writer->WriteBoolean(propertyValue->GetBoolean());
			return;
		case PropertyType::Char16:
			writer->WriteByte(Char16Type);
			writer->WriteUInt16(propertyValue->GetChar16());
			return;
		case PropertyType::Guid:
			writer->WriteByte(GuidType);
			writer->WriteGuid(propertyValue->GetGuid());
			return;
		case PropertyType::String:
			WriteString(writer, propertyValue->GetString());
			return;
		default:
			throw ref new InvalidArgumentException("Unsupported property type");
		}
	}

	void WriteStringToObjectMap(DataWriter^ writer, IMap<String^, Object^>^ map)
	{
		writer->WriteByte(StringToObjectMapType);
		writer->WriteUInt32(map->Size);
		for (auto&& pair : map)
		{
			WriteObject(writer, pair->Key);
			WriteObject(writer, pair->Value);
		}
		writer->WriteByte(MapEndMarker);
	}

	void WriteObject(DataWriter^ writer, Object^ object)
	{
		if (object == nullptr)
		{
			writer->WriteByte(NullPtrType);
			return;
		}

		auto propertyObject = dynamic_cast<IPropertyValue^>(object);
		if (propertyObject != nullptr)
		{
			WriteProperty(writer, propertyObject);
			return;
		}

		auto mapObject = dynamic_cast<IMap<String^, Object^>^>(object);
		if (mapObject != nullptr)
		{
			WriteStringToObjectMap(writer, mapObject);
			return;
		}

		throw ref new InvalidArgumentException("Unsupported data type");
	}

	String^ ReadString(DataReader^ reader)
	{
		int length = reader->ReadUInt32();
		String^ string = reader->ReadString(length);
		return string;
	}

	IMap<String^, Object^>^ ReadStringToObjectMap(DataReader^ reader)
	{
		auto map = ref new Map<String^, Object^>();
		auto size = reader->ReadUInt32();
		for (unsigned int index = 0; index < size; index++)
		{
			auto key = safe_cast<String^>(ReadObject(reader));
			auto value = ReadObject(reader);
			map->Insert(key, value);
		}
		if (reader->ReadByte() != MapEndMarker)
		{
			throw ref new InvalidArgumentException("Invalid stream");
		}
		return map;
	}

	Object^ ReadObject(DataReader^ reader)
	{
		auto type = reader->ReadByte();
		switch (type)
		{
		case NullPtrType:
			return nullptr;
		case UInt8Type:
			return reader->ReadByte();
		case UInt16Type:
			return reader->ReadUInt16();
		case UInt32Type:
			return reader->ReadUInt32();
		case UInt64Type:
			return reader->ReadUInt64();
		case Int16Type:
			return reader->ReadInt16();
		case Int32Type:
			return reader->ReadInt32();
		case Int64Type:
			return reader->ReadInt64();
		case SingleType:
			return reader->ReadSingle();
		case DoubleType:
			return reader->ReadDouble();
		case BooleanType:
			return reader->ReadBoolean();
		case Char16Type:
			return (char16_t)reader->ReadUInt16();
		case GuidType:
			return reader->ReadGuid();
		case StringType:
			return ReadString(reader);
		case StringToObjectMapType:
			return ReadStringToObjectMap(reader);
		default:
			throw ref new InvalidArgumentException("Unsupported property type");
		}
	}
}

#pragma endregion
