// Copyright 2017 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tsdb

import (
	"bufio"
	"encoding/binary"
	"fmt"
	"hash"
	"hash/crc32"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"unsafe"

	"math"

	"github.com/coreos/etcd/pkg/fileutil"
	"github.com/pkg/errors"
	"github.com/prometheus/tsdb/labels"
)

const (
	// MagicIndex 4 bytes at the head of an index file.
	MagicIndex = 0xBAAAD700

	indexFormatV1 = 1
)

const compactionPageBytes = minSectorSize * 64

type indexWriterSeries struct {
	labels labels.Labels
	chunks []*ChunkMeta // series file offset of chunks
	offset uint32       // index file offset of series reference
}

type indexWriterSeriesSlice []*indexWriterSeries

func (s indexWriterSeriesSlice) Len() int      { return len(s) }
func (s indexWriterSeriesSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

func (s indexWriterSeriesSlice) Less(i, j int) bool {
	return labels.Compare(s[i].labels, s[j].labels) < 0
}

type indexWriterStage uint8

const (
	idxStagePopulate indexWriterStage = iota
	idxStageLabelIndex
	idxStagePostings
	idxStageDone
)

func (s indexWriterStage) String() string {
	switch s {
	case idxStagePopulate:
		return "populate"
	case idxStageLabelIndex:
		return "label index"
	case idxStagePostings:
		return "postings"
	case idxStageDone:
		return "done"
	}
	return "<unknown>"
}

// IndexWriter serializes the index for a block of series data.
// The methods must generally be called in the order they are specified in.
type IndexWriter interface {
	// AddSeries populates the index writer with a series and its offsets
	// of chunks that the index can reference.
	// The reference number is used to resolve a series against the postings
	// list iterator. It only has to be available during the write processing.
	AddSeries(ref uint32, l labels.Labels, chunks ...*ChunkMeta) error

	// WriteLabelIndex serializes an index from label names to values.
	// The passed in values chained tuples of strings of the length of names.
	WriteLabelIndex(names []string, values []string) error

	// WritePostings writes a postings list for a single label pair.
	// The Postings here contain refs to the series that were added.
	WritePostings(name, value string, it Postings) error

	// Close writes any finalization and closes the resources associated with
	// the underlying writer.
	Close() error
}

// indexWriter implements the IndexWriter interface for the standard
// serialization format.
type indexWriter struct {
	f    *os.File
	fbuf *bufio.Writer
	pos  uint64

	toc   indexTOC
	stage indexWriterStage

	// Reusable memory.
	buf1    encbuf
	buf2    encbuf
	uint32s []uint32

	series       map[uint32]*indexWriterSeries
	symbols      map[string]uint32 // symbol offsets
	labelIndexes []hashEntry       // label index offsets
	postings     []hashEntry       // postings lists offsets

	crc32 hash.Hash
}

type indexTOC struct {
	symbols           uint64
	series            uint64
	labelIndices      uint64
	labelIndicesTable uint64
	postings          uint64
	postingsTable     uint64
}

func newIndexWriter(dir string) (*indexWriter, error) {
	df, err := fileutil.OpenDir(dir)
	if err != nil {
		return nil, err
	}
	f, err := os.OpenFile(filepath.Join(dir, "index"), os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		return nil, err
	}
	if err := fileutil.Fsync(df); err != nil {
		return nil, errors.Wrap(err, "sync dir")
	}

	iw := &indexWriter{
		f:     f,
		fbuf:  bufio.NewWriterSize(f, 1<<22),
		pos:   0,
		stage: idxStagePopulate,

		// Reusable memory.
		buf1:    encbuf{b: make([]byte, 0, 1<<22)},
		buf2:    encbuf{b: make([]byte, 0, 1<<22)},
		uint32s: make([]uint32, 0, 1<<15),

		// Caches.
		symbols: make(map[string]uint32, 1<<13),
		series:  make(map[uint32]*indexWriterSeries, 1<<16),
		crc32:   crc32.New(crc32.MakeTable(crc32.Castagnoli)),
	}
	if err := iw.writeMeta(); err != nil {
		return nil, err
	}
	return iw, nil
}

func (w *indexWriter) write(bufs ...[]byte) error {
	for _, b := range bufs {
		n, err := w.fbuf.Write(b)
		w.pos += uint64(n)
		if err != nil {
			return err
		}
		// For now the index file must not grow beyond 4GiB. Some of the fixed-sized
		// offset references in v1 are only 4 byte large.
		// Once we move to compressed/varint representations in those areas, this limitation
		// can be lifted.
		if w.pos > math.MaxUint32 {
			return errors.Errorf("exceeding max size of 4GiB")
		}
	}
	return nil
}

// ensureStage handles transitions between write stages and ensures that IndexWriter
// methods are called in an order valid for the implementation.
func (w *indexWriter) ensureStage(s indexWriterStage) error {
	if w.stage == s {
		return nil
	}
	if w.stage > s {
		return errors.Errorf("invalid stage %q, currently at %q", s, w.stage)
	}

	// Complete population stage by writing symbols and series.
	if w.stage == idxStagePopulate {
		w.toc.symbols = w.pos
		if err := w.writeSymbols(); err != nil {
			return err
		}
		w.toc.series = w.pos
		if err := w.writeSeries(); err != nil {
			return err
		}
	}

	// Mark start of sections in table of contents.
	switch s {
	case idxStageLabelIndex:
		w.toc.labelIndices = w.pos

	case idxStagePostings:
		w.toc.labelIndicesTable = w.pos
		if err := w.writeOffsetTable(w.labelIndexes); err != nil {
			return err
		}
		w.toc.postings = w.pos

	case idxStageDone:
		w.toc.postingsTable = w.pos
		if err := w.writeOffsetTable(w.postings); err != nil {
			return err
		}
		if err := w.writeTOC(); err != nil {
			return err
		}
	}

	w.stage = s
	return nil
}

func (w *indexWriter) writeMeta() error {
	w.buf1.reset()
	w.buf1.putBE32(MagicIndex)
	w.buf1.putByte(indexFormatV1)

	return w.write(w.buf1.get())
}

func (w *indexWriter) AddSeries(ref uint32, lset labels.Labels, chunks ...*ChunkMeta) error {
	if _, ok := w.series[ref]; ok {
		return errors.Errorf("series with reference %d already added", ref)
	}
	// Populate the symbol table from all label sets we have to reference.
	for _, l := range lset {
		w.symbols[l.Name] = 0
		w.symbols[l.Value] = 0
	}

	w.series[ref] = &indexWriterSeries{
		labels: lset,
		chunks: chunks,
	}
	return nil
}

func (w *indexWriter) writeSymbols() error {
	// Generate sorted list of strings we will store as reference table.
	symbols := make([]string, 0, len(w.symbols))
	for s := range w.symbols {
		symbols = append(symbols, s)
	}
	sort.Strings(symbols)

	const headerSize = 8

	w.buf1.reset()
	w.buf2.reset()

	for _, s := range symbols {
		w.symbols[s] = uint32(w.pos) + headerSize + uint32(w.buf2.len())

		// NOTE: len(s) gives the number of runes, not the number of bytes.
		// Therefore the read-back length for strings with unicode characters will
		// be off when not using putCstr.
		w.buf2.putUvarintStr(s)
	}

	w.buf1.putBE32int(len(symbols))
	w.buf1.putBE32int(w.buf2.len())

	w.buf2.putHash(w.crc32)

	err := w.write(w.buf1.get(), w.buf2.get())
	return errors.Wrap(err, "write symbols")
}

func (w *indexWriter) writeSeries() error {
	// Series must be stored sorted along their labels.
	series := make(indexWriterSeriesSlice, 0, len(w.series))

	for _, s := range w.series {
		series = append(series, s)
	}
	sort.Sort(series)

	// Header holds number of series.
	w.buf1.reset()
	w.buf1.putBE32int(len(series))
	if err := w.write(w.buf1.get()); err != nil {
		return errors.Wrap(err, "write series count")
	}

	for _, s := range series {
		w.buf2.reset()
		w.buf2.putUvarint(len(s.labels))

		for _, l := range s.labels {
			w.buf2.putUvarint32(w.symbols[l.Name])
			w.buf2.putUvarint32(w.symbols[l.Value])
		}

		w.buf2.putUvarint(len(s.chunks))

		for _, c := range s.chunks {
			w.buf2.putVarint64(c.MinTime)
			w.buf2.putVarint64(c.MaxTime)
			w.buf2.putUvarint64(c.Ref)

			w.crc32.Reset()
			c.hash(w.crc32)
			w.buf2.putBytes(w.crc32.Sum(nil))
		}

		s.offset = uint32(w.pos)

		w.buf1.reset()
		w.buf1.putUvarint(w.buf2.len())

		w.buf2.putHash(w.crc32)

		if err := w.write(w.buf1.get(), w.buf2.get()); err != nil {
			return errors.Wrap(err, "write series data")
		}
	}

	return nil
}

func (w *indexWriter) WriteLabelIndex(names []string, values []string) error {
	if err := w.ensureStage(idxStageLabelIndex); err != nil {
		return errors.Wrap(err, "ensure stage")
	}

	valt, err := newStringTuples(values, len(names))
	if err != nil {
		return err
	}
	sort.Sort(valt)

	w.labelIndexes = append(w.labelIndexes, hashEntry{
		keys:   names,
		offset: w.pos,
	})

	w.buf2.reset()
	w.buf2.putUvarint(len(names))

	for _, v := range valt.s {
		w.buf2.putBE32(w.symbols[v])
	}

	w.buf1.reset()
	w.buf1.putUvarint(w.buf2.len())

	w.buf2.putHash(w.crc32)

	err = w.write(w.buf1.get(), w.buf2.get())
	return errors.Wrap(err, "write label index")
}

// writeOffsetTable writes a sequence of readable hash entries.
func (w *indexWriter) writeOffsetTable(entries []hashEntry) error {
	w.buf1.reset()
	w.buf1.putBE32int(len(entries))

	w.buf2.reset()

	for _, e := range entries {
		w.buf2.putUvarint(len(e.keys))
		for _, k := range e.keys {
			w.buf2.putUvarintStr(k)
		}
		w.buf2.putUvarint64(e.offset)
	}

	w.buf1.putBE32int(w.buf2.len())
	w.buf2.putHash(w.crc32)

	return w.write(w.buf1.get(), w.buf2.get())
}

const indexTOCLen = 6*8 + 4

func (w *indexWriter) writeTOC() error {
	w.buf1.reset()

	w.buf1.putBE64(w.toc.symbols)
	w.buf1.putBE64(w.toc.series)
	w.buf1.putBE64(w.toc.labelIndices)
	w.buf1.putBE64(w.toc.labelIndicesTable)
	w.buf1.putBE64(w.toc.postings)
	w.buf1.putBE64(w.toc.postingsTable)

	w.buf1.putHash(w.crc32)

	return w.write(w.buf1.get())
}

func (w *indexWriter) WritePostings(name, value string, it Postings) error {
	if err := w.ensureStage(idxStagePostings); err != nil {
		return errors.Wrap(err, "ensure stage")
	}

	w.postings = append(w.postings, hashEntry{
		keys:   []string{name, value},
		offset: w.pos,
	})

	// Order of the references in the postings list does not imply order
	// of the series references within the persisted block they are mapped to.
	// We have to sort the new references again.
	refs := w.uint32s[:0]

	for it.Next() {
		s, ok := w.series[it.At()]
		if !ok {
			return errors.Errorf("series for reference %d not found", it.At())
		}
		refs = append(refs, s.offset)
	}
	if err := it.Err(); err != nil {
		return err
	}

	sort.Sort(uint32slice(refs))

	w.buf2.reset()
	for _, r := range refs {
		w.buf2.putBE32(r)
	}

	w.buf1.reset()
	w.buf1.putUvarint(w.buf2.len())

	w.buf2.putHash(w.crc32)

	err := w.write(w.buf1.get(), w.buf2.get())
	return errors.Wrap(err, "write postings")
}

type uint32slice []uint32

func (s uint32slice) Len() int           { return len(s) }
func (s uint32slice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s uint32slice) Less(i, j int) bool { return s[i] < s[j] }

type hashEntry struct {
	keys   []string
	offset uint64
}

func (w *indexWriter) Close() error {
	if err := w.ensureStage(idxStageDone); err != nil {
		return err
	}
	if err := w.fbuf.Flush(); err != nil {
		return err
	}
	if err := fileutil.Fsync(w.f); err != nil {
		return err
	}
	return w.f.Close()
}

// IndexReader provides reading access of serialized index data.
type IndexReader interface {
	// LabelValues returns the possible label values
	LabelValues(names ...string) (StringTuples, error)

	// Postings returns the postings list iterator for the label pair.
	// The Postings here contain the offsets to the series inside the index.
	Postings(name, value string) (Postings, error)

	// Series returns the series for the given reference.
	Series(ref uint32) (labels.Labels, []*ChunkMeta, error)

	// LabelIndices returns the label pairs for which indices exist.
	LabelIndices() ([][]string, error)

	// Close released the underlying resources of the reader.
	Close() error
}

// StringTuples provides access to a sorted list of string tuples.
type StringTuples interface {
	// Total number of tuples in the list.
	Len() int
	// At returns the tuple at position i.
	At(i int) ([]string, error)
}

type indexReader struct {
	// The underlying byte slice holding the encoded series data.
	b   []byte
	toc indexTOC

	// Close that releases the underlying resources of the byte slice.
	c io.Closer

	// Cached hashmaps of section offsets.
	labels   map[string]uint32
	postings map[string]uint32
}

var (
	errInvalidSize = fmt.Errorf("invalid size")
	errInvalidFlag = fmt.Errorf("invalid flag")
)

// newIndexReader returns a new indexReader on the given directory.
func newIndexReader(dir string) (*indexReader, error) {
	f, err := openMmapFile(filepath.Join(dir, "index"))
	if err != nil {
		return nil, err
	}
	r := &indexReader{b: f.b, c: f}

	// Verify magic number.
	if len(f.b) < 4 {
		return nil, errors.Wrap(errInvalidSize, "index header")
	}
	if m := binary.BigEndian.Uint32(r.b[:4]); m != MagicIndex {
		return nil, errors.Errorf("invalid magic number %x", m)
	}

	if err := r.readTOC(); err != nil {
		return nil, errors.Wrap(err, "read TOC")
	}

	r.labels, err = r.readOffsetTable(r.toc.labelIndicesTable)
	if err != nil {
		return nil, errors.Wrap(err, "read label index table")
	}
	r.postings, err = r.readOffsetTable(r.toc.postingsTable)
	if err != nil {
		return nil, errors.Wrap(err, "read postings table")
	}

	return r, nil
}

func (r *indexReader) readTOC() error {
	if len(r.b) < indexTOCLen {
		return errInvalidSize
	}
	b := r.b[len(r.b)-indexTOCLen:]

	r.toc.symbols = binary.BigEndian.Uint64(b[0:8])
	r.toc.series = binary.BigEndian.Uint64(b[8:16])
	r.toc.labelIndices = binary.BigEndian.Uint64(b[16:24])
	r.toc.labelIndicesTable = binary.BigEndian.Uint64(b[24:32])
	r.toc.postings = binary.BigEndian.Uint64(b[32:40])
	r.toc.postingsTable = binary.BigEndian.Uint64(b[40:48])

	// TODO(fabxc): validate checksum.

	return nil
}

func (r *indexReader) decbufAt(off int) decbuf {
	if len(r.b) < off {
		return decbuf{e: errInvalidSize}
	}
	return decbuf{b: r.b[off:]}
}

// readOffsetTable reads an offset table at the given position and returns a map
// with the key strings concatenated by the 0xff unicode non-character.
func (r *indexReader) readOffsetTable(off uint64) (map[string]uint32, error) {
	// A table might not have been written at all, in which case the position
	// is zeroed out.
	if off == 0 {
		return nil, nil
	}

	const sep = "\xff"

	var (
		d1  = r.decbufAt(int(off))
		cnt = d1.readBE32()
		el  = d1.readBE32()
		d2  = d1.get(int(el))
	)

	res := make(map[string]uint32, 512)

	for d2.err() == nil && d2.len() > 0 && cnt > 0 {
		keyCount := int(d2.readUvarint())
		keys := make([]string, 0, keyCount)

		for i := 0; i < keyCount; i++ {
			keys = append(keys, d2.readUvarintStr())
		}
		res[strings.Join(keys, sep)] = uint32(d2.readUvarint())

		cnt--
	}

	// TODO(fabxc): verify checksum from remainer of d1.
	return res, d2.err()
}

func (r *indexReader) Close() error {
	return r.c.Close()
}

func (r *indexReader) section(o uint32) (byte, []byte, error) {
	b := r.b[o:]

	if len(b) < 5 {
		return 0, nil, errors.Wrap(errInvalidSize, "read header")
	}

	flag := b[0]
	l := binary.BigEndian.Uint32(b[1:5])

	b = b[5:]

	// b must have the given length plus 4 bytes for the CRC32 checksum.
	if len(b) < int(l)+4 {
		return 0, nil, errors.Wrap(errInvalidSize, "section content")
	}
	return flag, b[:l], nil
}

func (r *indexReader) lookupSymbol(o uint32) (string, error) {
	if int(o) > len(r.b) {
		return "", errors.Errorf("invalid symbol offset %d", o)
	}
	l, n := binary.Uvarint(r.b[o:])
	if n < 0 {
		return "", errors.New("reading symbol length failed")
	}

	end := int(o) + n + int(l)
	if end > len(r.b) {
		return "", errors.Errorf("invalid length %d", l)
	}
	b := r.b[int(o)+n : end]

	return yoloString(b), nil
}

func (r *indexReader) getSized(off uint32) ([]byte, error) {
	if int(off) > len(r.b) {
		return nil, errInvalidSize
	}
	b := r.b[off:]
	l, n := binary.Uvarint(b)
	if n < 1 {
		return nil, errInvalidSize
	}
	if int(l) > len(b[n:]) {
		return nil, errInvalidSize
	}
	return b[n : n+int(l)], nil
}

func (r *indexReader) LabelValues(names ...string) (StringTuples, error) {
	const sep = "\xff"

	key := strings.Join(names, sep)
	off, ok := r.labels[key]
	if !ok {
		// XXX(fabxc): hot fix. Should return a partial data error and handle cases
		// where the entire block has no data gracefully.
		return emptyStringTuples{}, nil
		//return nil, fmt.Errorf("label index doesn't exist")
	}

	b, err := r.getSized(off)
	if err != nil {
		return nil, errors.Wrapf(err, "get sized region at %d", off)
	}

	c, n := binary.Uvarint(b)
	if n < 1 {
		return nil, errors.Wrap(errInvalidSize, "read label index size")
	}

	st := &serializedStringTuples{
		l:      int(c),
		b:      b[n:],
		lookup: r.lookupSymbol,
	}
	return st, nil
}

type emptyStringTuples struct{}

func (emptyStringTuples) At(i int) ([]string, error) { return nil, nil }
func (emptyStringTuples) Len() int                   { return 0 }

func (r *indexReader) LabelIndices() ([][]string, error) {
	const sep = "\xff"

	res := [][]string{}

	for s := range r.labels {
		res = append(res, strings.Split(s, string(sep)))
	}
	return res, nil
}

func (r *indexReader) Series(ref uint32) (labels.Labels, []*ChunkMeta, error) {
	// Read away length of series data.
	_, n := binary.Uvarint(r.b[ref:])
	b := r.b[int(ref)+n:]

	k, n := binary.Uvarint(b)
	if n < 1 {
		return nil, nil, errors.Wrap(errInvalidSize, "number of labels")
	}

	b = b[n:]
	lbls := make(labels.Labels, 0, k)

	for i := 0; i < 2*int(k); i += 2 {
		o, m := binary.Uvarint(b)
		if m < 1 {
			return nil, nil, errors.Wrap(errInvalidSize, "symbol offset")
		}
		n, err := r.lookupSymbol(uint32(o))
		if err != nil {
			return nil, nil, errors.Wrap(err, "symbol lookup")
		}
		b = b[m:]

		o, m = binary.Uvarint(b)
		if m < 1 {
			return nil, nil, errors.Wrap(errInvalidSize, "symbol offset")
		}
		v, err := r.lookupSymbol(uint32(o))
		if err != nil {
			return nil, nil, errors.Wrap(err, "symbol lookup")
		}
		b = b[m:]

		lbls = append(lbls, labels.Label{
			Name:  n,
			Value: v,
		})
	}

	// Read the chunks meta data.
	k, n = binary.Uvarint(b)
	if n < 1 {
		return nil, nil, errors.Wrap(errInvalidSize, "number of chunks")
	}

	b = b[n:]
	chunks := make([]*ChunkMeta, 0, k)

	for i := 0; i < int(k); i++ {
		firstTime, n := binary.Varint(b)
		if n < 1 {
			return nil, nil, errors.Wrap(errInvalidSize, "first time")
		}
		b = b[n:]

		lastTime, n := binary.Varint(b)
		if n < 1 {
			return nil, nil, errors.Wrap(errInvalidSize, "last time")
		}
		b = b[n:]

		o, n := binary.Uvarint(b)
		if n < 1 {
			return nil, nil, errors.Wrap(errInvalidSize, "chunk offset")
		}
		b = b[n:]

		// TODO(fabxc): read and potentially verify checksum.
		b = b[4:]

		chunks = append(chunks, &ChunkMeta{
			Ref:     o,
			MinTime: firstTime,
			MaxTime: lastTime,
		})
	}

	// TODO(fabxc): read and potentially verify checksum.

	return lbls, chunks, nil
}

func (r *indexReader) Postings(name, value string) (Postings, error) {
	const sep = "\xff"

	key := name + string(sep) + value

	off, ok := r.postings[key]
	if !ok {
		return emptyPostings, nil
	}

	b, err := r.getSized(off)
	if err != nil {
		return nil, errors.Wrapf(err, "get sized region at %d", off)
	}
	// Add iterator over the bytes.
	if len(b)%4 != 0 {
		return nil, errors.Wrap(errInvalidSize, "plain postings entry")
	}

	return newBigEndianPostings(b), nil
}

type stringTuples struct {
	l int      // tuple length
	s []string // flattened tuple entries
}

func newStringTuples(s []string, l int) (*stringTuples, error) {
	if len(s)%l != 0 {
		return nil, errors.Wrap(errInvalidSize, "string tuple list")
	}
	return &stringTuples{s: s, l: l}, nil
}

func (t *stringTuples) Len() int                   { return len(t.s) / t.l }
func (t *stringTuples) At(i int) ([]string, error) { return t.s[i : i+t.l], nil }

func (t *stringTuples) Swap(i, j int) {
	c := make([]string, t.l)
	copy(c, t.s[i:i+t.l])

	for k := 0; k < t.l; k++ {
		t.s[i+k] = t.s[j+k]
		t.s[j+k] = c[k]
	}
}

func (t *stringTuples) Less(i, j int) bool {
	for k := 0; k < t.l; k++ {
		d := strings.Compare(t.s[i+k], t.s[j+k])

		if d < 0 {
			return true
		}
		if d > 0 {
			return false
		}
	}
	return false
}

type serializedStringTuples struct {
	l      int
	b      []byte
	lookup func(uint32) (string, error)
}

func (t *serializedStringTuples) Len() int {
	// TODO(fabxc): Cache this?
	return len(t.b) / (4 * t.l)
}

func (t *serializedStringTuples) At(i int) ([]string, error) {
	if len(t.b) < (i+t.l)*4 {
		return nil, errInvalidSize
	}
	res := make([]string, 0, t.l)

	for k := 0; k < t.l; k++ {
		offset := binary.BigEndian.Uint32(t.b[(i+k)*4:])

		s, err := t.lookup(offset)
		if err != nil {
			return nil, errors.Wrap(err, "symbol lookup")
		}
		res = append(res, s)
	}

	return res, nil
}

// enbuf is a helper type to populate a byte slice with various types.
type encbuf struct {
	b []byte
	c [binary.MaxVarintLen64]byte
}

func (e *encbuf) reset()      { e.b = e.b[:0] }
func (e *encbuf) get() []byte { return e.b }
func (e *encbuf) len() int    { return len(e.b) }

func (e *encbuf) putString(s string) { e.b = append(e.b, s...) }
func (e *encbuf) putBytes(b []byte)  { e.b = append(e.b, b...) }
func (e *encbuf) putByte(c byte)     { e.b = append(e.b, c) }

func (e *encbuf) putBE32int(x int)      { e.putBE32(uint32(x)) }
func (e *encbuf) putBE64int(x int)      { e.putBE64(uint64(x)) }
func (e *encbuf) putUvarint32(x uint32) { e.putUvarint64(uint64(x)) }
func (e *encbuf) putUvarint(x int)      { e.putUvarint64(uint64(x)) }

func (e *encbuf) putBE32(x uint32) {
	binary.BigEndian.PutUint32(e.c[:], x)
	e.b = append(e.b, e.c[:4]...)
}

func (e *encbuf) putBE64(x uint64) {
	binary.BigEndian.PutUint64(e.c[:], x)
	e.b = append(e.b, e.c[:8]...)
}

func (e *encbuf) putUvarint64(x uint64) {
	n := binary.PutUvarint(e.c[:], x)
	e.b = append(e.b, e.c[:n]...)
}

func (e *encbuf) putVarint64(x int64) {
	n := binary.PutVarint(e.c[:], x)
	e.b = append(e.b, e.c[:n]...)
}

// putVarintStr writes a string to the buffer prefixed by its varint length (in bytes!).
func (e *encbuf) putUvarintStr(s string) {
	b := *(*[]byte)(unsafe.Pointer(&s))
	e.putUvarint(len(b))
	e.putString(s)
}

// putHash appends a hash over the buffers current contents to the buffer.
func (e *encbuf) putHash(h hash.Hash) {
	h.Reset()
	_, err := h.Write(e.b)
	if err != nil {
		panic(err) // The CRC32 implementation does not error
	}
	e.b = h.Sum(e.b)
}

type decbuf struct {
	b []byte
	e error
}

func (d *decbuf) readUvarintStr() string {
	l := d.readUvarint()
	if d.e != nil {
		return ""
	}
	if len(d.b) < int(l) {
		d.e = errInvalidSize
		return ""
	}
	s := string(d.b[:l])
	d.b = d.b[l:]
	return s
}

func (d *decbuf) readUvarint() uint64 {
	if d.e != nil {
		return 0
	}
	x, n := binary.Uvarint(d.b)
	if n < 1 {
		d.e = errInvalidSize
		return 0
	}
	d.b = d.b[n:]
	return x
}

func (d *decbuf) readBE32() uint32 {
	if d.e != nil {
		return 0
	}
	if len(d.b) < 4 {
		d.e = errInvalidSize
		return 0
	}
	x := binary.BigEndian.Uint32(d.b)
	d.b = d.b[4:]
	return x
}

func (d *decbuf) get(l int) decbuf {
	if d.e != nil {
		return decbuf{e: d.e}
	}
	if l > len(d.b) {
		return decbuf{e: errInvalidSize}
	}
	r := decbuf{b: d.b[:l]}
	d.b = d.b[l:]
	return r
}

func (d *decbuf) err() error {
	return d.e
}

func (d *decbuf) len() int {
	return len(d.b)
}