/***
    Copyright (C) 2022 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: Watcher.NT.cpp
    Date: 2022-4-1
    Author: Reece
    Note: FindFirstChangeNotification locks the parent directory, every other library is garbage 
          Aurora shall implement this sewage instead
***/
#include <Source/RuntimeInternal.hpp>
#include "FS.hpp"
#include <Source/Loop/Loop.hpp>
#include <Source/Loop/LSEvent.hpp>
#include "winioctl.h"

namespace Aurora::IO::FS
{
    struct NTWatchObject;
    struct NTWatcher;

    struct NTWatchhandle
    {
        NTWatcher *object;
    };

    struct NTEvent : Loop::LSEvent
    {
        NTEvent(AuSPtr<NTWatchhandle> parent);

        bool IsSignaled() override;
        Loop::ELoopSource GetType() override;

        void OnPresleep() override;
        bool OnTrigger(AuUInt handle) override;

    private:
        AuWPtr<NTWatchhandle> parent_;
    };

    struct NTWatchObject
    {
        OVERLAPPED ntOverlapped {};
        bool bBroken {};
        bool bReschedule {};
        NTWatcher *parent;
        AuString strBaseDir;
        HANDLE hFileHandle {INVALID_HANDLE_VALUE};
        AuUInt32 dwReferences {};

        ~NTWatchObject()
        {
            Cancel();
        }

        bool Init(const AuString &usrStr);
        bool ScheduleOnce();
        bool CheckBroken();
        void Cancel();

    private:
        REQUEST_OPLOCK_OUTPUT_BUFFER whoAsked_;

    };  

    struct NTCachedPath
    {
        AuString strNormalizedPath;
        AuString strTheCakeIsALie;
        AuSPtr<UserWatchData> userData;
        AuSPtr<NTWatchObject> watcher;
        bool bIsDirectory {};

        AuList<AuTuple<AuString, bool, AuUInt64>> lastTick;

        FILETIME lastFileTime {};

        AuList<AuTuple<AuString, bool, AuUInt64>> GetCurrentState();

        bool CheckDirDelta();
        void Warm();
        bool CheckRun(NTWatcher *parent);
        bool AddEvent(NTWatcher *parent, EWatchEvent type, const AuString &path);
    };

    struct NTWatcher : IWatcher
    {
        virtual bool                      AddWatch(const WatchRequest &file) override;

        virtual bool                      RemoveByName(const AuString &path) override;
        virtual bool                      RemoveByPrivateContext(const AuSPtr<UserWatchData> &file) override;

        virtual AuSPtr<Loop::ILoopSource> AsLoopSource() override;

        virtual AuList<WatchEvent>        QueryUpdates() override;

        bool Init();
        bool GoBrr();

    private:

        // we don't expect to yield to another thread to hit our vector 
        // these apis are generally expected to be called from a single thread
        AuThreadPrimitives::SpinLock spinlock_;
        AuBST<AuString, AuWPtr<NTWatchObject>> cachedWatchers_;

    public:

        AuList<WatchEvent>  triggered_;
        AuSPtr<NTEvent>      ntEvent_;
        AuList<NTCachedPath> paths_;

    private:
        AuSPtr<NTWatchhandle> watchHandler_;

    };

    // NT Event class

    NTEvent::NTEvent(AuSPtr<NTWatchhandle> parent) : LSEvent(false, true /*[1]*/, true), parent_(parent)
    {
        // [1] Functions such as GetOverlappedResult and the synchronization wait functions reset auto-reset events to the nonsignaled state. Therefore, you should use a manual reset event; if you use an auto-reset event, your application can stop responding if you wait for the operation to complete and then call GetOverlappedResult with the bWait parameter set to TRUE.
        //   - https://docs.microsoft.com/en-us/windows/win32/api/minwinbase/ns-minwinbase-overlapped
    }

    bool NTEvent::IsSignaled()
    {
        return LSEvent::IsSignaled();
    }

    Loop::ELoopSource NTEvent::GetType()
    {
        return Loop::ELoopSource::eSourceFileWatcher;
    }

    // Event type is latching, sort of like binary semaphore
    // Resignal if work is still available
    void NTEvent::OnPresleep()
    {
        if (auto watcher = parent_.lock())
        {
            if (watcher->object->triggered_.size())
            {
                Set();
            }
        }
    }

    // Filter the latching events signal state once 
    // based on the availability of work
    // ...
    /// also, this is kind of like a tick
    bool NTEvent::OnTrigger(AuUInt handle)
    {
        bool ret {};

        if (auto watcher = parent_.lock())
        {
            ret = watcher->object->GoBrr();
        }
        else
        {
            ret = true;
        }

        return ret;
    }


    // NT Cached Path / File Watch Item class

    void NTCachedPath::Warm()
    {
        HANDLE hFile;
        hFile = CreateFileW(AuLocale::ConvertFromUTF8(this->strNormalizedPath).c_str(),
                                  GENERIC_READ,
                                  FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
                                  NULL,
                                  OPEN_EXISTING,
                                  FILE_ATTRIBUTE_NORMAL | (this->bIsDirectory ? FILE_FLAG_BACKUP_SEMANTICS : 0),
                                  NULL);

        if (hFile != INVALID_HANDLE_VALUE)
        {
            GetFileTime(hFile, NULL, NULL, &this->lastFileTime);
            CloseHandle(hFile);
        }

        this->lastTick = GetCurrentState();
    }

    AuList<AuTuple<AuString, bool, AuUInt64>> NTCachedPath::GetCurrentState()
    {
        return {};
    }

    bool NTCachedPath::CheckDirDelta()
    {
        auto next = GetCurrentState();
        auto currentState = next;
        auto oldState     = AuExchange(this->lastTick, AuMove(next));

        return false;
    }

    bool NTCachedPath::AddEvent(NTWatcher *parent, EWatchEvent type, const AuString &path)
    {
        AuCtorCode_t code;
        auto watchedFile = AuTryConstruct<WatchedFile>(code, this->userData, this->strTheCakeIsALie);
        if (!code)
        {
            return false;
        }

        WatchEvent event;
        event.event = type;
        event.watch = AuMove(watchedFile);
        event.file = AuTryConstruct<AuString>(code, path);
        if (!code)
        {
            return false;
        }

        if (!AuTryInsert(parent->triggered_, AuMove(event)))
        {
            return false;
        }

        return true;
    }

    bool NTCachedPath::CheckRun(NTWatcher *parent)
    {
        FILETIME curFileTime {};
        HANDLE hFile;

        hFile = CreateFileW(AuLocale::ConvertFromUTF8(this->strNormalizedPath).c_str(),
                                  GENERIC_READ,
                                  FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
                                  NULL,
                                  OPEN_EXISTING,
                                  FILE_ATTRIBUTE_NORMAL | (this->bIsDirectory ? FILE_FLAG_BACKUP_SEMANTICS : 0),
                                  NULL);

        if (hFile == INVALID_HANDLE_VALUE)
        {
            if (GetLastError() == ERROR_FILE_NOT_FOUND)
            {
                // NOTE: we might want to add a check to prevent double dispatch
                return AddEvent(parent, EWatchEvent::eSelfDelete, this->strTheCakeIsALie);
            }
            else
            {
                return false;
            }
        }

        bool bDirChanged = this->bIsDirectory ? CheckDirDelta() : false;

        if (!GetFileTime(hFile, NULL, NULL, &curFileTime))
        {
            CloseHandle(hFile);
            return true;
        }

        bool ret = !((this->lastFileTime.dwLowDateTime == curFileTime.dwLowDateTime) &&
                     (this->lastFileTime.dwHighDateTime == curFileTime.dwHighDateTime));

        this->lastFileTime = curFileTime;

        CloseHandle(hFile);

        if (!ret)
        {
            return bDirChanged;
        }

        // Send a self modified update once the timestamp changes 
        return AddEvent(parent,this->bIsDirectory ? EWatchEvent::eSelfModify : EWatchEvent::eFileModify, this->strTheCakeIsALie) || bDirChanged;
    }

    // Directory Watcher Object

    bool NTWatchObject::Init(const AuString &usrStr)
    {
        AuCtorCode_t code;
        
        this->strBaseDir = AuTryConstruct<AuString>(code, usrStr);
        if (!code)
        {
            return false;
        }

        auto c =  this->strBaseDir[this->strBaseDir.size() - 1];
        if ((c == '\\') ||
            (c == '/'))
        {
            this->strBaseDir.pop_back();
        }
        
        this->hFileHandle = CreateFileW(AuLocale::ConvertFromUTF8(this->strBaseDir.c_str()).c_str(),
                                        GENERIC_READ,
                                        FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
                                        NULL,
                                        OPEN_EXISTING,
                                        FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED | FILE_FLAG_BACKUP_SEMANTICS,
                                        NULL);
        if (this->hFileHandle == INVALID_HANDLE_VALUE)
        {
            return false;
        }


        AuMemset(&this->ntOverlapped, 0, sizeof(this->ntOverlapped));

        return ScheduleOnce();
    }

    // Request OP lock
    bool NTWatchObject::ScheduleOnce()
    {
        bool firstTime = !this->ntOverlapped.hEvent;
        this->ntOverlapped.hEvent = (HANDLE)this->parent->ntEvent_->GetHandle();

        REQUEST_OPLOCK_INPUT_BUFFER input
        {
            REQUEST_OPLOCK_CURRENT_VERSION,
            sizeof(REQUEST_OPLOCK_INPUT_BUFFER),
            OPLOCK_LEVEL_CACHE_READ | OPLOCK_LEVEL_CACHE_HANDLE,
            firstTime ? REQUEST_OPLOCK_INPUT_FLAG_REQUEST : REQUEST_OPLOCK_INPUT_FLAG_ACK,
        };

        DWORD bytesReturned;
        if (DeviceIoControl(this->hFileHandle, FSCTL_REQUEST_OPLOCK, &input, sizeof(input), &whoAsked_, sizeof(whoAsked_), &bytesReturned, &this->ntOverlapped))
        {
            this->CheckBroken();
        }
        else
        {
            if (GetLastError() != ERROR_IO_PENDING)
            {
                SysPushErrorIO();
                return false;
            }
        }
        
        return true;
    }

    bool NTWatchObject::CheckBroken()
    {
        DWORD bytesTransferred;

        if (this->bBroken || GetOverlappedResult(this->hFileHandle, &this->ntOverlapped, &bytesTransferred, false))
        {
            bool bSuccess {true};
            this->bBroken = true;

            bool bAnyTriggered {};

            for (auto &filesWatched : this->parent->paths_)
            {
                if (!AuStartsWith(filesWatched.strNormalizedPath, this->strBaseDir))
                {
                    continue;
                }

                if (!filesWatched.CheckRun(this->parent))
                {
                    continue;
                }

                bAnyTriggered = true;
            }

            if (this->whoAsked_.Flags & REQUEST_OPLOCK_OUTPUT_FLAG_ACK_REQUIRED)
            {
                this->whoAsked_.Flags = 0;
                bSuccess = ScheduleOnce();
            }
           
            this->bBroken = false;
            return bSuccess;
        }

        return true;
    }

    void NTWatchObject::Cancel()
    {
        CancelIoEx(this->hFileHandle, &this->ntOverlapped);
        AuWin32CloseHandle(this->hFileHandle);
    }

    // NT Watcher - primary interface implementation

    bool NTWatcher::AddWatch(const WatchRequest &request)
    {
        AuCtorCode_t code;
        AuSPtr<NTWatchObject> watcher;
        NTCachedPath cached;

        auto &file = request.watch;

        AU_LOCK_GUARD(this->spinlock_);

        AuString translated;
        if (!AuIOFS::NormalizePath(translated, file.path))
        {
            translated = file.path;
        }

        // Create the NT path in the midst of path normalization
        cached.strNormalizedPath = AuTryConstruct<AuString>(code, translated);
        if (!code)
        {
            return false;
        }

        cached.strTheCakeIsALie = AuTryConstruct<AuString>(code, file.path);
        if (!code)
        {
            return false;
        }

        cached.userData = file.userData;

        // Continue normalizing the parent path

        if (AuIOFS::FileExists(translated))
        {
            AuIOFS::GetDirectoryFromPath(translated, translated);
        }
        else
        {
            // dammit, had to move checkrun
            cached.bIsDirectory = true;
        }

        // Update the last edited timestamp as a frame of reference for fast compare of 
        // directory entries upon lock breakage
        cached.Warm();

        // Attempt to locate a watcher for the directoy

        for (const auto &[base, wptr] : this->cachedWatchers_)
        {
            if (AuStartsWith(translated, base))
            {
                watcher = wptr.lock();
                break;
            }
        }

        // Create one, if missing

        if (!watcher)
        {
            auto item = AuMakeShared<NTWatchObject>();

            if (!item)
            {
                SysPushErrorMem();
                return false;
            }

            item->parent = this;

            if (!item->Init(translated))
            {
                SysPushErrorGen();
                return false;
            }

            watcher = item;

            if (!AuTryInsert(this->cachedWatchers_, AuMove(translated), AuMove(item)))
            {
                return false;
            }
        }

        cached.watcher = watcher;

        // Append path / user private pair alongside the watcher for book keeping

        if (!AuTryInsert(this->paths_, AuMove(cached)))
        {
            return false;
        }

        // Done

        return true;
    }

    // Post-event trigger processor and filterer
    bool NTWatcher::GoBrr()
    {
        AU_LOCK_GUARD(this->spinlock_);

        for (auto &[dir, weakWatcher] : this->cachedWatchers_)
        {
            if (auto watcher = weakWatcher.lock())
            {
                if (!watcher->CheckBroken())
                {
                    this->ntEvent_->Set();
                }
            }
        }

        return this->triggered_.size();
    }

    bool NTWatcher::RemoveByName(const AuString &path)
    {
        AU_LOCK_GUARD(this->spinlock_);
        AuString strNormalized;

        if (!AuIOFS::NormalizePath(strNormalized, path))
        {
            return false;
        }

        return AuRemoveIf(this->paths_, [&](const NTCachedPath &object) -> bool
        {
            if ((strNormalized == object.strNormalizedPath) || 
                (strNormalized.empty() && object.strNormalizedPath == path))
            {
                return true;
            }
            
            return false;
        });
    }

    bool NTWatcher::RemoveByPrivateContext(const AuSPtr<UserWatchData> &file)
    {
        AU_LOCK_GUARD(this->spinlock_);

        return AuRemoveIf(this->paths_, [&](const NTCachedPath &object) -> bool
        {
            return file == object.userData;
        });
    }

    bool NTWatcher::Init()
    {
        this->watchHandler_ = AuMakeShared<NTWatchhandle>();
        if (!this->watchHandler_)
        {
            return false;
        }

        this->watchHandler_->object = this;

        this->ntEvent_ = AuMakeShared<NTEvent>(this->watchHandler_);
        if (!this->ntEvent_)
        {
            return false;
        }

        if (!this->ntEvent_->HasValidHandle())
        {
            return false;
        }

        return true;
    }

    AuSPtr<Loop::ILoopSource> NTWatcher::AsLoopSource()
    {
        return AuStaticCast<Loop::ILSEvent>(this->ntEvent_);
    }

    AuList<WatchEvent> NTWatcher::NTWatcher::QueryUpdates()
    {
        AsLoopSource()->IsSignaled(); // poke work queue
        AU_LOCK_GUARD(this->spinlock_);
        return AuExchange(this->triggered_, {});
    }

    AUKN_SYM IWatcher *NewWatcherNew()
    {
        auto watcher = _new NTWatcher();
        if (!watcher)
        {
            return {};
        }

        if (!watcher->Init())
        {
            delete watcher;
            return {};
        }

        return watcher;
    }

    AUKN_SYM void NewWatcherRelease(IWatcher *watcher)
    {
        AuSafeDelete<NTWatcher *>(watcher);
    }
}