package storage_ng

import (
	"bufio"
	"encoding/binary"
	"encoding/gob"
	"fmt"
	"io"
	"os"
	"path"

	"github.com/golang/glog"

	//"github.com/prometheus/prometheus/storage/metric"

	//"github.com/prometheus/client_golang/prometheus"

	clientmodel "github.com/prometheus/client_golang/model"

	"github.com/prometheus/prometheus/storage/metric"
	"github.com/prometheus/prometheus/utility"
)

const (
	seriesFileName     = "series.db"
	seriesTempFileName = "series.db.tmp"
	headsFileName      = "heads.db"
	indexFileName      = "index.db"

	indexFormatVersion = 1
	indexMagicString   = "PrometheusIndexes"
	indexBufSize       = 1 << 15 // 32kiB. TODO: Tweak.

	chunkHeaderLen             = 17
	chunkHeaderTypeOffset      = 0
	chunkHeaderFirstTimeOffset = 1
	chunkHeaderLastTimeOffset  = 9

	headsHeaderLen               = 9
	headsHeaderFingerprintOffset = 0
	headsHeaderTypeOffset        = 8
)

type diskPersistence struct {
	basePath string
	chunkLen int
	buf      []byte // Staging space for persisting indexes.
}

func NewDiskPersistence(basePath string, chunkLen int) (Persistence, error) {
	gob.Register(clientmodel.Fingerprint(0))
	gob.Register(clientmodel.LabelValue(""))

	err := os.MkdirAll(basePath, 0700)
	if err != nil {
		return nil, err
	}
	return &diskPersistence{
		basePath: basePath,
		chunkLen: chunkLen,
		buf:      make([]byte, binary.MaxVarintLen64), // Also sufficient for uint64.
	}, nil
}

func (p *diskPersistence) dirForFingerprint(fp clientmodel.Fingerprint) string {
	fpStr := fp.String()
	return fmt.Sprintf("%s/%c%c/%s", p.basePath, fpStr[0], fpStr[1], fpStr[2:])
}

// exists returns true when the given file or directory exists.
func exists(path string) (bool, error) {
	_, err := os.Stat(path)
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, nil
	}

	return false, err
}

func (p *diskPersistence) openChunkFileForWriting(fp clientmodel.Fingerprint) (*os.File, error) {
	dirname := p.dirForFingerprint(fp)
	ex, err := exists(dirname)
	if err != nil {
		return nil, err
	}
	if !ex {
		if err := os.MkdirAll(dirname, 0700); err != nil {
			return nil, err
		}
	}
	return os.OpenFile(path.Join(dirname, seriesFileName), os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0640)
}

func (p *diskPersistence) openChunkFileForReading(fp clientmodel.Fingerprint) (*os.File, error) {
	dirname := p.dirForFingerprint(fp)
	return os.Open(path.Join(dirname, seriesFileName))
}

func writeChunkHeader(w io.Writer, c chunk) error {
	header := make([]byte, chunkHeaderLen)
	header[chunkHeaderTypeOffset] = chunkType(c)
	binary.LittleEndian.PutUint64(header[chunkHeaderFirstTimeOffset:], uint64(c.firstTime()))
	binary.LittleEndian.PutUint64(header[chunkHeaderLastTimeOffset:], uint64(c.lastTime()))
	_, err := w.Write(header)
	return err
}

func (p *diskPersistence) PersistChunk(fp clientmodel.Fingerprint, c chunk) error {
	// 1. Open chunk file.
	f, err := p.openChunkFileForWriting(fp)
	if err != nil {
		return err
	}
	defer f.Close()

	b := bufio.NewWriterSize(f, chunkHeaderLen+p.chunkLen)
	defer b.Flush()

	// 2. Write the header (chunk type and first/last times).
	err = writeChunkHeader(b, c)
	if err != nil {
		return err
	}

	// 3. Write chunk into file.
	return c.marshal(b)
}

func (p *diskPersistence) offsetForChunkIndex(i int) int64 {
	return int64(i * (chunkHeaderLen + p.chunkLen))
}

func (p *diskPersistence) LoadChunks(fp clientmodel.Fingerprint, indexes []int) (chunks, error) {
	// TODO: we need to verify at some point that file length is a multiple of
	// the chunk size. When is the best time to do this, and where to remember
	// it? Right now, we only do it when loading chunkDescs.
	f, err := p.openChunkFileForReading(fp)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	chunks := make(chunks, 0, len(indexes))
	defer func() {
		if err == nil {
			return
		}
	}()

	typeBuf := make([]byte, 1)
	for _, idx := range indexes {
		_, err := f.Seek(p.offsetForChunkIndex(idx), os.SEEK_SET)
		if err != nil {
			return nil, err
		}
		// TODO: check seek offset too?

		n, err := f.Read(typeBuf)
		if err != nil {
			return nil, err
		}
		if n != 1 {
			// Shouldn't happen?
			panic("read returned != 1 bytes")
		}

		_, err = f.Seek(chunkHeaderLen-1, os.SEEK_CUR)
		if err != nil {
			return nil, err
		}
		chunk := chunkForType(typeBuf[0])
		chunk.unmarshal(f)
		chunks = append(chunks, chunk)
	}
	return chunks, nil
}

func (p *diskPersistence) LoadChunkDescs(fp clientmodel.Fingerprint, beforeTime clientmodel.Timestamp) (chunkDescs, error) {
	f, err := p.openChunkFileForReading(fp)
	if os.IsNotExist(err) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	defer f.Close()

	fi, err := f.Stat()
	if err != nil {
		return nil, err
	}
	totalChunkLen := chunkHeaderLen + p.chunkLen
	if fi.Size()%int64(totalChunkLen) != 0 {
		// TODO: record number of encountered corrupt series files in a metric?

		// Truncate the file size to the nearest multiple of chunkLen.
		truncateTo := fi.Size() - fi.Size()%int64(totalChunkLen)
		glog.Infof("Bad series file size for %s: %d bytes (no multiple of %d). Truncating to %d bytes.", fp, fi.Size(), totalChunkLen, truncateTo)
		// TODO: this doesn't work, as this is a read-only file handle.
		if err := f.Truncate(truncateTo); err != nil {
			return nil, err
		}
	}

	numChunks := int(fi.Size()) / totalChunkLen
	cds := make(chunkDescs, 0, numChunks)
	for i := 0; i < numChunks; i++ {
		_, err := f.Seek(p.offsetForChunkIndex(i)+chunkHeaderFirstTimeOffset, os.SEEK_SET)
		if err != nil {
			return nil, err
		}

		chunkTimesBuf := make([]byte, 16)
		_, err = io.ReadAtLeast(f, chunkTimesBuf, 16)
		if err != nil {
			return nil, err
		}
		cd := &chunkDesc{
			firstTimeField: clientmodel.Timestamp(binary.LittleEndian.Uint64(chunkTimesBuf)),
			lastTimeField:  clientmodel.Timestamp(binary.LittleEndian.Uint64(chunkTimesBuf[8:])),
		}
		if !cd.firstTime().Before(beforeTime) {
			// From here on, we have chunkDescs in memory already.
			break
		}
		cds = append(cds, cd)
	}
	return cds, nil
}

func (p *diskPersistence) indexPath() string {
	return path.Join(p.basePath, indexFileName)
}

// PersistIndexes persists the indexes to disk. Do not call it concurrently with
// LoadIndexes as they share a buffer for staging. This method depends on the
// following type conversions being possible:
//     clientmodel.LabelName -> string
//     clientmodel.LabelValue -> string
//     clientmodel.Fingerprint -> uint64
//
// Description of the on-disk format:
//
// Label names and label values are encoded as their varint-encoded length
// followed by their byte sequence.
//
// Fingerprints are encoded as big-endian uint64.
//
// The file starts with the 'magic' byte sequence "PrometheusIndexes", followed
// by a varint-encoded version number (currently 1).
//
// The indexes follow one after another in the order FingerprintToSeries,
// LabelPairToFingerprints, LabelNameToLabelValues. Each index starts with the
// varint-encoded number of entries in that index, followed by the corresponding
// number of entries.
//
// An entry in FingerprintToSeries consists of a fingerprint, followed by the
// number of label pairs, followed by those label pairs, each in order label
// name and then label value.
//
// An entry in LabelPairToFingerprints consists of a label name, then a label
// value, then a varint-encoded number of fingerprints, followed by those
// fingerprints.
//
// An entry in LabelNameToLabelValues consists of a label name, followed by the
// varint-encoded number of label values, followed by those label values.
func (p *diskPersistence) PersistIndexes(i *Indexes) error {
	f, err := os.OpenFile(p.indexPath(), os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0640)
	if err != nil {
		return err
	}
	defer f.Close()

	p.setBufLen(binary.MaxVarintLen64)

	w := bufio.NewWriterSize(f, indexBufSize)
	if _, err := w.WriteString(indexMagicString); err != nil {
		return err
	}
	if err := p.persistVarint(w, indexFormatVersion); err != nil {
		return err
	}

	if err := p.persistFingerprintToSeries(w, i.FingerprintToSeries); err != nil {
		return err
	}
	if err := p.persistLabelPairToFingerprints(w, i.LabelPairToFingerprints); err != nil {
		return err
	}
	if err := p.persistLabelNameToLabelValues(w, i.LabelNameToLabelValues); err != nil {
		return err
	}

	return w.Flush()
}

func (p *diskPersistence) persistVarint(w io.Writer, i int) error {
	bytesWritten := binary.PutVarint(p.buf, int64(i))
	_, err := w.Write(p.buf[:bytesWritten])
	return err
}

// persistFingerprint depends on clientmodel.Fingerprint to be convertible to
// uint64.
func (p *diskPersistence) persistFingerprint(w io.Writer, fp clientmodel.Fingerprint) error {
	binary.BigEndian.PutUint64(p.buf, uint64(fp))
	_, err := w.Write(p.buf[:8])
	return err
}

func (p *diskPersistence) persistString(w *bufio.Writer, s string) error {
	if err := p.persistVarint(w, len(s)); err != nil {
		return err
	}
	_, err := w.WriteString(s)
	return err
}

// persistFingerprintToSeries depends on clientmodel.LabelName and
// clientmodel.LabelValue to be convertible to string.
func (p *diskPersistence) persistFingerprintToSeries(w *bufio.Writer, index map[clientmodel.Fingerprint]*memorySeries) error {
	if err := p.persistVarint(w, len(index)); err != nil {
		return err
	}
	for fp, ms := range index {
		if err := p.persistFingerprint(w, fp); err != nil {
			return err
		}
		if err := p.persistVarint(w, len(ms.metric)); err != nil {
			return err
		}
		for n, v := range ms.metric {
			if err := p.persistString(w, string(n)); err != nil {
				return err
			}
			if err := p.persistString(w, string(v)); err != nil {
				return err
			}
		}
	}
	return nil
}

// persistLabelPairToFingerprints depends on clientmodel.LabelName and
// clientmodel.LabelValue to be convertible to string.
func (p *diskPersistence) persistLabelPairToFingerprints(w *bufio.Writer, index map[metric.LabelPair]utility.Set) error {
	if err := p.persistVarint(w, len(index)); err != nil {
		return err
	}
	for lp, fps := range index {
		if err := p.persistString(w, string(lp.Name)); err != nil {
			return err
		}
		if err := p.persistString(w, string(lp.Value)); err != nil {
			return err
		}
		if err := p.persistVarint(w, len(fps)); err != nil {
			return err
		}
		for fp := range fps {
			if err := p.persistFingerprint(w, fp.(clientmodel.Fingerprint)); err != nil {
				return err
			}
		}
	}
	return nil
}

// persistLabelNameToLabelValues depends on clientmodel.LabelValue to be convertible to string.
func (p *diskPersistence) persistLabelNameToLabelValues(w *bufio.Writer, index map[clientmodel.LabelName]utility.Set) error {
	if err := p.persistVarint(w, len(index)); err != nil {
		return err
	}
	for ln, lvs := range index {
		if err := p.persistString(w, string(ln)); err != nil {
			return err
		}
		if err := p.persistVarint(w, len(lvs)); err != nil {
			return err
		}
		for lv := range lvs {
			if err := p.persistString(w, string(lv.(clientmodel.LabelValue))); err != nil {
				return err
			}
		}
	}
	return nil
}

// LoadIndexes loads the indexes from disk. See PersistIndexes for details about
// the disk format. Do not call LoadIndexes and PersistIndexes concurrently as
// they share a buffer for staging.
func (p *diskPersistence) LoadIndexes() (*Indexes, error) {
	f, err := os.Open(p.indexPath())
	if os.IsNotExist(err) {
		return &Indexes{
			FingerprintToSeries:     map[clientmodel.Fingerprint]*memorySeries{},
			LabelPairToFingerprints: map[metric.LabelPair]utility.Set{},
			LabelNameToLabelValues:  map[clientmodel.LabelName]utility.Set{},
		}, nil
	}
	if err != nil {
		return nil, err
	}
	defer f.Close()

	r := bufio.NewReaderSize(f, indexBufSize)

	p.setBufLen(len(indexMagicString))
	if _, err := io.ReadFull(r, p.buf); err != nil {
		return nil, err
	}
	magic := string(p.buf)
	if magic != indexMagicString {
		return nil, fmt.Errorf(
			"unexpected magic string, want %q, got %q",
			indexMagicString, magic,
		)
	}
	if version, err := binary.ReadVarint(r); version != indexFormatVersion || err != nil {
		return nil, fmt.Errorf("unknown index format version, want %d", indexFormatVersion)
	}

	i := &Indexes{}

	if err := p.loadFingerprintToSeries(r, i); err != nil {
		return nil, err
	}
	if err := p.loadLabelPairToFingerprints(r, i); err != nil {
		return nil, err
	}
	if err := p.loadLabelNameToLabelValues(r, i); err != nil {
		return nil, err
	}

	return i, nil
}

func (p *diskPersistence) loadFingerprintToSeries(r *bufio.Reader, i *Indexes) error {
	length, err := binary.ReadVarint(r)
	if err != nil {
		return err
	}
	i.FingerprintToSeries = make(map[clientmodel.Fingerprint]*memorySeries, length)

	for ; length > 0; length-- {
		fp, err := p.loadFingerprint(r)
		if err != nil {
			return err
		}
		numLabelPairs, err := binary.ReadVarint(r)
		if err != nil {
			return err
		}
		m := make(clientmodel.Metric, numLabelPairs)
		i.FingerprintToSeries[fp] = &memorySeries{metric: m}
		for ; numLabelPairs > 0; numLabelPairs-- {
			ln, err := p.loadString(r)
			if err != nil {
				return err
			}
			lv, err := p.loadString(r)
			if err != nil {
				return err
			}
			m[clientmodel.LabelName(ln)] = clientmodel.LabelValue(lv)
		}
	}
	return nil
}

func (p *diskPersistence) loadLabelPairToFingerprints(r *bufio.Reader, i *Indexes) error {
	length, err := binary.ReadVarint(r)
	if err != nil {
		return err
	}
	i.LabelPairToFingerprints = make(map[metric.LabelPair]utility.Set, length)

	for ; length > 0; length-- {
		ln, err := p.loadString(r)
		if err != nil {
			return err
		}
		lv, err := p.loadString(r)
		if err != nil {
			return err
		}
		numFPs, err := binary.ReadVarint(r)
		if err != nil {
			return err
		}
		s := make(utility.Set, numFPs)
		i.LabelPairToFingerprints[metric.LabelPair{
			Name:  clientmodel.LabelName(ln),
			Value: clientmodel.LabelValue(lv),
		}] = s
		for ; numFPs > 0; numFPs-- {
			fp, err := p.loadFingerprint(r)
			if err != nil {
				return err
			}
			s.Add(fp)
		}
	}
	return nil
}

func (p *diskPersistence) loadLabelNameToLabelValues(r *bufio.Reader, i *Indexes) error {
	length, err := binary.ReadVarint(r)
	if err != nil {
		return err
	}
	i.LabelNameToLabelValues = make(map[clientmodel.LabelName]utility.Set, length)

	for ; length > 0; length-- {
		ln, err := p.loadString(r)
		if err != nil {
			return err
		}
		numLVs, err := binary.ReadVarint(r)
		if err != nil {
			return err
		}
		s := make(utility.Set, numLVs)
		i.LabelNameToLabelValues[clientmodel.LabelName(ln)] = s
		for ; numLVs > 0; numLVs-- {
			lv, err := p.loadString(r)
			if err != nil {
				return err
			}
			s.Add(clientmodel.LabelValue(lv))
		}
	}
	return nil
}

func (p *diskPersistence) loadFingerprint(r io.Reader) (clientmodel.Fingerprint, error) {
	p.setBufLen(8)
	if _, err := io.ReadFull(r, p.buf); err != nil {
		return 0, err
	}
	return clientmodel.Fingerprint(binary.BigEndian.Uint64(p.buf)), nil
}

func (p *diskPersistence) loadString(r *bufio.Reader) (string, error) {
	length, err := binary.ReadVarint(r)
	if err != nil {
		return "", err
	}
	p.setBufLen(int(length))
	if _, err := io.ReadFull(r, p.buf); err != nil {
		return "", err
	}
	return string(p.buf), nil
}

func (p *diskPersistence) setBufLen(l int) {
	if cap(p.buf) >= l {
		p.buf = p.buf[:l]
	} else {
		p.buf = make([]byte, l)
	}
}

func (p *diskPersistence) headsPath() string {
	return path.Join(p.basePath, headsFileName)
}

func (p *diskPersistence) PersistHeads(fpToSeries map[clientmodel.Fingerprint]*memorySeries) error {
	f, err := os.OpenFile(p.headsPath(), os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0640)
	if err != nil {
		return err
	}
	header := make([]byte, 9)
	for fp, series := range fpToSeries {
		head := series.head().chunk

		binary.LittleEndian.PutUint64(header[headsHeaderFingerprintOffset:], uint64(fp))
		header[headsHeaderTypeOffset] = chunkType(head)
		_, err := f.Write(header)
		if err != nil {
			return err
		}
		err = head.marshal(f)
		if err != nil {
			return err
		}
	}
	return nil
}

func (p *diskPersistence) DropChunks(fp clientmodel.Fingerprint, beforeTime clientmodel.Timestamp) error {
	f, err := p.openChunkFileForReading(fp)
	if os.IsNotExist(err) {
		return nil
	}
	if err != nil {
		return err
	}
	defer f.Close()

	// Find the first chunk that should be kept.
	for i := 0; ; i++ {
		_, err := f.Seek(p.offsetForChunkIndex(i)+chunkHeaderLastTimeOffset, os.SEEK_SET)
		if err != nil {
			return err
		}
		lastTimeBuf := make([]byte, 8)
		_, err = io.ReadAtLeast(f, lastTimeBuf, 8)
		if err == io.EOF {
			// We ran into the end of the file without finding any chunks that should
			// be kept. Remove the whole file.
			if err := os.Remove(f.Name()); err != nil {
				return err
			}
			return nil
		}
		if err != nil {
			return err
		}
		lastTime := clientmodel.Timestamp(binary.LittleEndian.Uint64(lastTimeBuf))
		if !lastTime.Before(beforeTime) {
			break
		}
	}

	// We've found the first chunk that should be kept. Seek backwards to the
	// beginning of its header and start copying everything from there into a new
	// file.
	_, err = f.Seek(-(chunkHeaderLastTimeOffset + 8), os.SEEK_CUR)
	if err != nil {
		return err
	}

	dirname := p.dirForFingerprint(fp)
	temp, err := os.OpenFile(path.Join(dirname, seriesTempFileName), os.O_WRONLY|os.O_CREATE, 0640)
	if err != nil {
		return err
	}
	defer temp.Close()

	if _, err := io.Copy(temp, f); err != nil {
		return err
	}

	os.Rename(path.Join(dirname, seriesTempFileName), path.Join(dirname, seriesFileName))
	return nil
}

func (p *diskPersistence) LoadHeads(fpToSeries map[clientmodel.Fingerprint]*memorySeries) error {
	f, err := os.Open(p.headsPath())
	if os.IsNotExist(err) {
		// TODO: this should only happen if there never was a shutdown before. In
		// that case, all heads should be in order already, since the series got
		// created during this process' runtime.
		// Still, make this more robust.
		return nil
	}

	header := make([]byte, headsHeaderLen)
	for {
		_, err := io.ReadAtLeast(f, header, headsHeaderLen)
		if err == io.ErrUnexpectedEOF {
			// TODO: this should only be ok if n is 0.
			break
		}
		if err != nil {
			return nil
		}
		// TODO: this relies on the implementation (uint64) of Fingerprint.
		fp := clientmodel.Fingerprint(binary.LittleEndian.Uint64(header[headsHeaderFingerprintOffset:]))
		chunk := chunkForType(header[headsHeaderTypeOffset])
		chunk.unmarshal(f)
		fpToSeries[fp].chunkDescs = append(fpToSeries[fp].chunkDescs, &chunkDesc{
			chunk:    chunk,
			refCount: 1,
		})
	}
	return nil
}