package txlog

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"math"
	"os"
	"path/filepath"
	"sync"

	bin "gordenko.dev/dima/bin/little"
	"gordenko.dev/dima/qb"
	"gordenko.dev/dima/qb/atree"
	"gordenko.dev/dima/qb/freelist"
	"gordenko.dev/dima/qb/util"
)

const (
	lsnSize          = 4
	packetPrefixSize = 12 // 4 lsn + 4 packet length + 4 crc32

	lengthIdx   = 0
	checksumIdx = 4
	lsnIdx      = 8

	filePerm = 0770

	dumpSnapshotAfterNBytes = 1024 * 1024 * 1024 // 1 GB

	writeBufferSize = 4 * 1024 * 1024
)

const (
	CodeAddedMetric      byte = 1
	CodeDeletedMetric    byte = 2
	CodeAppendedMeasure  byte = 4
	CodeAppendedMeasures byte = 5
	CodeAppendedPages    byte = 6
	CodeDeletedMeasures  byte = 7
)

type FreeList interface {
	// використовується в allocPage
	GetPageNumber() (uint32, error)
}

func JoinChangesFileName(dir string, logNumber int) string {
	return filepath.Join(dir, fmt.Sprintf("%d.changes", logNumber))
}

type MetricsState struct {
	Metrics []Metric
	WaitCh  chan struct{}
}

type Changes struct {
	Records   []any
	MetricsCh chan MetricsState
}

type Writer struct {
	mutex           sync.Mutex
	dataPagesCount  uint32
	indexPagesCount uint32
	dataFreeList    *freelist.FreeList
	indexFreeList   *freelist.FreeList
	atree           *atree.Atree
	logNumber       int
	dir             string
	w               *bytes.Buffer // wal буфер для упаковки даних перед записом на диск
	wal             *os.File
	dataFile        *os.File
	indexFile       *os.File
	// буфер для складання payload на сторінку, розрахунку CRC32 та інше
	pageBuffer          []byte
	input               []any
	appendToWorkerQueue func(any)
	//lsn                 uint32
	written   int64
	isExited  bool
	exitCh    chan struct{}
	waitGroup *sync.WaitGroup
	signalCh  chan struct{}
}

type WriterOptions struct {
	Dir                 string
	LogNumber           int // номер журнала
	AppendToWorkerQueue func(any)
	DataFreeList        *freelist.FreeList
	IndexFreeList       *freelist.FreeList
	Atree               *atree.Atree
	ExitCh              chan struct{}
	WaitGroup           *sync.WaitGroup
}

func NewWriter(opt WriterOptions) (*Writer, error) {
	if opt.Dir == "" {
		return nil, errors.New("Dir option is required")
	}
	if opt.AppendToWorkerQueue == nil {
		return nil, errors.New("AppendToWorkerQueue option is required")
	}
	if opt.DataFreeList == nil {
		return nil, errors.New("DataFreeList option is required")
	}
	if opt.IndexFreeList == nil {
		return nil, errors.New("IndexFreeList option is required")
	}
	if opt.Atree == nil {
		return nil, errors.New("Atree option is required")
	}
	if opt.ExitCh == nil {
		return nil, errors.New("ExitCh option is required")
	}
	if opt.WaitGroup == nil {
		return nil, errors.New("WaitGroup option is required")
	}

	s := &Writer{
		dir:                 opt.Dir,
		appendToWorkerQueue: opt.AppendToWorkerQueue,
		dataFreeList:        opt.DataFreeList,
		indexFreeList:       opt.IndexFreeList,
		atree:               opt.Atree,
		logNumber:           opt.LogNumber,
		exitCh:              opt.ExitCh,
		waitGroup:           opt.WaitGroup,
		signalCh:            make(chan struct{}, 1),
	}

	var err error

	if opt.LogNumber > 0 {
		s.wal, err = os.OpenFile(
			JoinChangesFileName(opt.Dir, s.logNumber),
			os.O_APPEND|os.O_WRONLY,
			filePerm,
		)
		if err != nil {
			return nil, err
		}
	} else {
		s.logNumber = 1
		s.wal, err = os.OpenFile(
			JoinChangesFileName(opt.Dir, s.logNumber),
			os.O_CREATE|os.O_WRONLY,
			filePerm,
		)
		if err != nil {
			return nil, err
		}
	}
	return s, nil
}

func (s *Writer) Run() {
	for {
		select {
		case <-s.signalCh:
			if err := s.packAndWrite(); err != nil {
				qb.Abort(qb.FailedWriteToTxLog, err)
			}

		case <-s.exitCh:
			s.exit()
			return
		}
	}
}

func (s *Writer) getDataPageNumber() (uint32, bool, error) {
	pageNo, err := s.dataFreeList.GetPageNumber()
	if err != nil {
		return 0, false, err
	}
	if pageNo > 0 {
		return pageNo, true, nil
	}
	if s.dataPagesCount < math.MaxUint32 {
		s.dataPagesCount++
		return s.dataPagesCount, false, nil
	}
	return 0, false, errors.New("no space")
}

func (s *Writer) getIndexPageNumber() (uint32, bool, error) {
	pageNo, err := s.indexFreeList.GetPageNumber()
	if err != nil {
		return 0, false, err
	}
	if pageNo > 0 {
		return pageNo, true, nil
	}
	if s.indexPagesCount < math.MaxUint32 {
		s.indexPagesCount++
		return s.indexPagesCount, false, nil
	}
	return 0, false, errors.New("no space")
}

func (s *Writer) packAndWrite() (err error) {
	s.mutex.Lock()
	//isExited := s.isExited
	input := s.input
	s.input = nil

	// var exitWaitGroup *sync.WaitGroup
	// if s.isExited {
	// 	exitWaitGroup = s.waitGroup
	// }
	s.mutex.Unlock()

	prepared := prepareData(input)

	// 3. Пишу на диск WAL (append)
	n, err := s.wal.Write(prepared.Packet)
	if err != nil {
		return
	}
	if n != len(prepared.Packet) {
		return fmt.Errorf("written %d != total size %d", n, len(prepared.Packet))
	}
	if err = s.wal.Sync(); err != nil {
		return
	}

	// 4. Пишу в atree сторінки
	err = s.writePagesToAtree(prepared.WriteToIndex, prepared.WriteToData)
	if err != nil {
		return
	}

	// 6. відправляю input - worker-у

	var (
		forceSnapshot bool
	)

	if s.written > dumpSnapshotAfterNBytes {
		forceSnapshot = true
	}

	// if isExited && s.written > 0 {
	// 	forceSnapshot = true
	// }

	if forceSnapshot {
		metricsStateCh := make(chan MetricsState)

		s.appendToWorkerQueue(Changes{
			Records:   prepared.ToWorker,
			MetricsCh: metricsStateCh,
		})

		if err := s.wal.Close(); err != nil {
			return fmt.Errorf("close changes file: %s", err)
		}

		state := <-metricsStateCh

		s.logNumber++

		// write snapshot FIX
		err = writeSnapshot(Snapshot{
			LogNumber:       s.logNumber,
			Dir:             s.dir,
			WriteBufferSize: writeBufferSize,
			Metrics:         state.Metrics,
			DataFreeList:    s.dataFreeList,
			IndexFreeList:   s.indexFreeList,
		})
		if err != nil {
			return fmt.Errorf("write snapshot file: %s", err)
		}

		var err error
		s.wal, err = os.OpenFile(
			JoinChangesFileName(s.dir, s.logNumber),
			os.O_CREATE|os.O_WRONLY,
			filePerm,
		)
		if err != nil {
			return fmt.Errorf("create new changes file: %s", err)
		}

		s.written = 0
		// release Worker
		close(state.WaitCh)
	} else {
		s.appendToWorkerQueue(Changes{
			Records: prepared.ToWorker,
		})
	}

	// Якщо потрібен снапшот - відправляю канал із буфером розміру 1,
	// в який воркер має покласти снапшот отриманий після застосування змін (records).
	// Після чого Writer створює нові файли snapshot і changes і працює далі.

	// flush
	// err = s.flush(w)
	// if err != nil {
	// 	return err
	// }

	// FIX send to worker workerReqs
	return nil
}

func (s *Writer) Append(req any) {
	s.mutex.Lock()
	s.input = append(s.input, req)
	s.mutex.Unlock()

	select {
	case s.signalCh <- struct{}{}:
	default:
	}
}

// func (s *Writer) reset() {
// 	s.buf.Reset()
// 	s.buf.Write([]byte{
// 		0, 0, 0, 0, // packet length
// 		0, 0, 0, 0, // crc32
// 		0, 0, 0, 0, // lsn

// 	})
// 	s.pagesToWrite = nil
// 	s.workerReqs = nil
// 	s.waitCh = make(chan struct{})
// }

// func (s *Writer) flush(w *bytes.Buffer) error {

// 	return nil
// }

func (s *Writer) exit() {
	s.mutex.Lock()
	s.isExited = true
	s.mutex.Unlock()

	if err := s.packAndWrite(); err != nil {
		qb.Abort(qb.FailedWriteToTxLog, err)
	}
}

type IndexPayloadToWrite struct {
	PageNo    uint32
	Payload   []byte
	ZeroLevel bool
}

type DataPayloadToWrite struct {
	PrevPageNo     uint32
	Timestamps     [][]byte // chunks
	TimestampsSize int
	Values         [][]byte // chunks
	ValuesSize     int
	PageNo         uint32
}

// writePagesToAtree - записує сторінки в .data та .index файли
func (s *Writer) writePagesToAtree(indexItems []IndexPayloadToWrite, dataItems []DataPayloadToWrite) (err error) {
	for _, p := range dataItems {
		atree.ChunksToDataPage(s.pageBuffer, atree.ChunksToDataPageReq{
			PrevPageNo:     p.PrevPageNo,
			Timestamps:     p.Timestamps,
			TimestampsSize: p.TimestampsSize,
			Values:         p.Values,
			ValuesSize:     p.ValuesSize,
		})
		var (
			off = (p.PageNo - 1) * atree.DataPageSize
			n   int
		)
		n, err = s.dataFile.WriteAt(s.pageBuffer, int64(off))
		if err != nil {
			return
		}
		if n != atree.DataPageSize {
			return fmt.Errorf("write %d instead of %d", n, atree.DataPageSize)
		}
	}
	for _, p := range indexItems {
		// if len(p.Payload) > atree.MaxIndexPayload {
		// 	return fmt.Errorf("wrong index payload size: %d", len(p.Payload))
		// }
		indexPageBuffer := s.pageBuffer[:atree.IndexPageSize]
		atree.DataToIndexPage(indexPageBuffer, p.Payload, p.ZeroLevel)
		var (
			off = (p.PageNo - 1) * atree.IndexPageSize
			n   int
		)
		n, err = s.indexFile.WriteAt(indexPageBuffer, int64(off))
		if err != nil {
			return
		}
		if n != atree.IndexPageSize {
			return fmt.Errorf("write %d instead of %d", n, atree.IndexPageSize)
		}
	}
	return nil
}

type AppendMeasuresSummary struct {
	MetricID uint32
	//TimestampsOffset int // (заповнені одразу)
	//ValuesOffset     int // (заповнені одразу)
	// Timestamps     [][]byte
	// TimestampsSize int
	// Values         [][]byte
	// ValuesSize     int
	LastPageNo   uint32
	Index        [][]byte
	ResultCode   int
	WrittenCount int
	ResultCh     chan struct{}
}

type AppendedMeasures struct {
	MetricID         uint32
	TimestampsOffset int // (заповнені одразу)
	ValuesOffset     int // (заповнені одразу)
	Timestamps       [][]byte
	TimestampsSize   int
	Values           [][]byte
	ValuesSize       int
	IndexLevels      []*atree.IndexLevel
	DataPages        []*atree.DataPage // fix - prevPageNo for the 1st data page
	ResultCode       int
	WrittenCount     int
	ResultCh         chan struct{}
}

func (s *Writer) packMeasuresIntoWALBuffer(req AppendedMeasures) (err error) {
	// fix write code
	bin.WriteUint32(s.w, req.MetricID)
	bin.WriteVarSize(s.w, len(req.DataPages))
	for idx, p := range req.DataPages {
		bin.WriteUint32(s.w, p.PageNo)
		var reused byte
		if p.IsReused {
			reused = 1
		}
		s.w.WriteByte(reused)
		bin.WriteUint32(s.w, p.PrevPageNo)
		//bin.WriteUint32(s.w, p.Checksum)
		var (
			timestampsOffset int
			valuesOffset     int
		)
		if idx == 0 {
			timestampsOffset = req.TimestampsOffset
			valuesOffset = req.ValuesOffset
		}
		copyPayloadFromChunks(s.w, p.Timestamps, p.TimestampsSize, timestampsOffset)
		copyPayloadFromChunks(s.w, p.Values, p.ValuesSize, valuesOffset)
	}
	bin.WriteUint16(s.w, uint16(req.TimestampsOffset))
	bin.WriteUint16(s.w, uint16(req.ValuesOffset))
	var (
		timestampsOffset int
		valuesOffset     int
	)
	if len(req.DataPages) == 0 {
		timestampsOffset = req.TimestampsOffset
		valuesOffset = req.ValuesOffset
	}
	copyPayloadFromChunks(s.w, req.Timestamps, req.TimestampsSize, timestampsOffset)
	copyPayloadFromChunks(s.w, req.Values, req.ValuesSize, valuesOffset)
	if len(req.DataPages) == 0 {
		return
	}
	// fix - levels reduced
	bin.WriteVarSize(s.w, len(req.IndexLevels))
	for _, level := range req.IndexLevels {
		bin.WriteVarSize(s.w, len(level.Filled))
		for idx, p := range level.Filled {
			bin.WriteUint32(s.w, p.PageNo)
			var reused byte
			if p.IsReused {
				reused = 1
			}
			s.w.WriteByte(reused)
			//bin.WriteUint32(s.w, p.Checksum)
			records := p.Data
			if idx == 0 {
				records = p.Data[level.Offset:]
			}
			if (len(records) % recordSize) != 0 {
				log.Fatalf("wrong records length: %d", len(records))
			}
			bin.WriteVarSize(s.w, len(records)/recordSize)
			s.w.Write(records)
		}
		records := level.Data
		if len(level.Filled) == 0 {
			records = level.Data[level.Offset:]
		}
		if (len(records) % recordSize) != 0 {
			log.Fatalf("wrong unfilled records length: %d", len(records))
		}
		bin.WriteVarSize(s.w, len(records)/recordSize)
		s.w.Write(records)
	}
	return
}

// API

// FIX - add
// type DeletedMeasuresSince struct {
// 	MetricID       uint32
// 	LastPageNo     uint32
// 	IsRootChanged  bool
// 	RootPageNo     uint32
// 	FreeDataPages  []uint32
// 	FreeIndexPages []uint32
// 	TimestampsBuf  []byte
// 	ValuesBuf      []byte
// }

func (s *Writer) sendSignal() {
	select {
	case s.signalCh <- struct{}{}:
	default:
	}
}

// Якщо (Pages) > 0 - незаповнену сторінку кодую в стисненому вигляді.
// Якщо (Pages) = 0 - кодую просто пари timestamp / value
// func (s *Writer) packWriteAppended(w *bytes.Buffer, req AppendedPagesReq) {
// 	// завантажений path. Отже просто додаємо в дерево data сторінки, створюємо нові індексні
// 	// без звернення до диску.
// 	report := s.atree.AppendDataPages(atree.AppendDataPagesReq{
// 		LastPageNo: req.LastPageNo,
// 		Legs:       req.Legs,
// 		DataPages:  req.Pages,
// 	})

// 	m := AppendedPages{
// 		MetricID:         req.MetricID,
// 		Timestamp:        req.Timestamp,
// 		Value:            req.Value,
// 		NewRootPageNo:    report.NewRootPageNo,
// 		LastPageNo:       report.LastPageNo,
// 		Pages:            report.Pages,
// 		TimestampsChunks: req.TimestampsChunks,
// 		TimestampsSize:   int(req.TimestampsSize),
// 		ValuesChunks:     req.ValuesChunks,
// 		ValuesSize:       int(req.ValuesSize),
// 	}
// 	m.Pack(w)
// }

// helpers

/*
Формат:
metricsQty - varuint
[metric]*
де metric - це:
metricID - 4b
metricType - 1b
fracDigits - 1b
lastPageNo - 4b
since - 4b
sinceValue - 8b
until - 4b
untilValue - 8b
timestamps size - 2b
values size - 2b
timestams payload - Nb
values payload - Nb
data free list frozen pages - varsize
dataFreeList size - varsize
dataFreeList - Nb
index free list frozen pages - varsize
indexFreeList size - varsize
indexFreeList - Nb
CRC32 - 4b
*/

const metricHeaderSize = 38

type Metric struct {
	MetricID       uint32
	MetricType     qb.MetricType
	FracDigits     byte
	LastPageNo     uint32
	Since          uint32
	SinceValue     float64
	Until          uint32
	UntilValue     float64
	Timestamps     [][]byte
	TimestampsSize int
	Values         [][]byte
	ValuesSize     int
}

type Snapshot struct {
	LogNumber       int
	Dir             string
	WriteBufferSize int
	Metrics         []Metric
	IndexFreeList   *freelist.FreeList
	DataFreeList    *freelist.FreeList
}

func writeSnapshot(snapshot Snapshot) (err error) {
	var (
		fileName = filepath.Join(snapshot.Dir, fmt.Sprintf("%d.snapshot", snapshot.LogNumber))
		hasher   = util.NewHasher()
		prefix   = make([]byte, metricHeaderSize)
	)

	file, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, 0770)
	if err != nil {
		return
	}

	dst := io.MultiWriter(bufio.NewWriterSize(file, snapshot.WriteBufferSize), hasher)

	_, err = bin.WriteVarSize(dst, len(snapshot.Metrics))
	if err != nil {
		return
	}

	for _, metric := range snapshot.Metrics {
		tSize := metric.TimestampsSize
		vSize := metric.ValuesSize

		bin.PutUint32(prefix[0:], metric.MetricID)
		prefix[4] = byte(metric.MetricType)
		prefix[5] = metric.FracDigits
		bin.PutUint32(prefix[6:], metric.LastPageNo)
		bin.PutUint32(prefix[10:], metric.Since)
		bin.PutFloat64(prefix[14:], metric.SinceValue)
		bin.PutUint32(prefix[22:], metric.Until)
		bin.PutFloat64(prefix[26:], metric.UntilValue)
		bin.PutUint16(prefix[34:], uint16(tSize))
		bin.PutUint16(prefix[36:], uint16(vSize))

		_, err = dst.Write(prefix)
		if err != nil {
			return
		}
		// copy timestamps
		writeChunks(dst, metric.Timestamps, tSize)
		// copy values
		writeChunks(dst, metric.Values, vSize)
	}
	// free data pages
	_, err = bin.WriteVarSize(dst, snapshot.DataFreeList.Pages())
	if err != nil {
		return
	}
	err = freeListWriteTo(snapshot.DataFreeList, dst)
	if err != nil {
		return
	}
	// free index pages
	_, err = bin.WriteVarSize(dst, snapshot.IndexFreeList.Pages())
	if err != nil {
		return
	}
	err = freeListWriteTo(snapshot.IndexFreeList, dst)
	if err != nil {
		return
	}

	bin.WriteUint32(file, hasher.Sum32())

	err = file.Sync()
	if err != nil {
		return
	}

	err = file.Close()
	if err != nil {
		return
	}
	// копіюю сторінки із delta файла в base файл і потім роблю Truncate
	err = snapshot.DataFreeList.Merge() // fix - get frozen pages count + unfilled
	if err != nil {
		return
	}
	err = snapshot.IndexFreeList.Merge()
	if err != nil {
		return
	}

	// prevLogNumber := logNumber - 1
	// prevChanges := filepath.Join(s.dir, fmt.Sprintf("%d.changes", prevLogNumber))
	// prevSnapshot := filepath.Join(s.dir, fmt.Sprintf("%d.snapshot", prevLogNumber))

	// isExist, err := isFileExist(prevChanges)
	// if err != nil {
	// 	return
	// }

	// if isExist {
	// 	err = os.Remove(prevChanges)
	// 	if err != nil {
	// 		qb.Abort(qb.DeletePrevChangesFileFailed, err)
	// 	}
	// }

	// isExist, err = isFileExist(prevSnapshot)
	// if err != nil {
	// 	return
	// }

	// if isExist {
	// 	err = os.Remove(prevSnapshot)
	// 	if err != nil {
	// 		qb.Abort(qb.DeletePrevSnapshotFileFailed, err)
	// 	}
	// }
	return
}

// HELPERS

func freeListWriteTo(freeList *freelist.FreeList, dst io.Writer) error {
	serialized, err := freeList.Serialize()
	if err != nil {
		qb.Abort(qb.FailedFreeListSerialize, err)
	}
	_, err = bin.WriteVarSize(dst, len(serialized))
	if err != nil {
		return err
	}
	_, err = dst.Write(serialized)
	if err != nil {
		return err
	}
	return nil
}

func writeChunks(dst io.Writer, chunks [][]byte, size int) (err error) {
	remaining := size
	for _, buf := range chunks {
		if remaining < len(buf) {
			buf = buf[:remaining]
		}
		_, err = dst.Write(buf)
		if err != nil {
			return
		}
		remaining -= len(buf)
		if remaining == 0 {
			break
		}
	}
	return
}