// 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 (
	"encoding/json"
	"io/ioutil"
	"os"
	"path/filepath"
	"sync"

	"github.com/oklog/ulid"
	"github.com/pkg/errors"
	"github.com/prometheus/tsdb/chunkenc"
	"github.com/prometheus/tsdb/chunks"
	"github.com/prometheus/tsdb/index"
	"github.com/prometheus/tsdb/labels"
)

// IndexWriter serializes the index for a block of series data.
// The methods must be called in the order they are specified in.
type IndexWriter interface {
	// AddSymbols registers all string symbols that are encountered in series
	// and other indices.
	AddSymbols(sym map[string]struct{}) error

	// AddSeries populates the index writer with a series and its offsets
	// of chunks that the index can reference.
	// Implementations may require series to be insert in increasing order by
	// their labels.
	// The reference numbers are used to resolve entries in postings lists that
	// are added later.
	AddSeries(ref uint64, l labels.Labels, chunks ...chunks.Meta) 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 index.Postings) error

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

// IndexReader provides reading access of serialized index data.
type IndexReader interface {
	// Symbols returns a set of string symbols that may occur in series' labels
	// and indices.
	Symbols() (map[string]struct{}, error)

	// LabelValues returns the possible label values.
	LabelValues(names ...string) (index.StringTuples, error)

	// Postings returns the postings list iterator for the label pair.
	// The Postings here contain the offsets to the series inside the index.
	// Found IDs are not strictly required to point to a valid Series, e.g. during
	// background garbage collections.
	Postings(name, value string) (index.Postings, error)

	// SortedPostings returns a postings list that is reordered to be sorted
	// by the label set of the underlying series.
	SortedPostings(index.Postings) index.Postings

	// Series populates the given labels and chunk metas for the series identified
	// by the reference.
	// Returns ErrNotFound if the ref does not resolve to a known series.
	Series(ref uint64, lset *labels.Labels, chks *[]chunks.Meta) error

	// LabelIndices returns a list of string tuples for which a label value index exists.
	LabelIndices() ([][]string, error)

	// Close releases 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)
}

// ChunkWriter serializes a time block of chunked series data.
type ChunkWriter interface {
	// WriteChunks writes several chunks. The Chunk field of the ChunkMetas
	// must be populated.
	// After returning successfully, the Ref fields in the ChunkMetas
	// are set and can be used to retrieve the chunks from the written data.
	WriteChunks(chunks ...chunks.Meta) error

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

// ChunkReader provides reading access of serialized time series data.
type ChunkReader interface {
	// Chunk returns the series data chunk with the given reference.
	Chunk(ref uint64) (chunkenc.Chunk, error)

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

// BlockReader provides reading access to a data block.
type BlockReader interface {
	// Index returns an IndexReader over the block's data.
	Index() (IndexReader, error)

	// Chunks returns a ChunkReader over the block's data.
	Chunks() (ChunkReader, error)

	// Tombstones returns a TombstoneReader over the block's deleted data.
	Tombstones() (TombstoneReader, error)
}

// Appendable defines an entity to which data can be appended.
type Appendable interface {
	// Appender returns a new Appender against an underlying store.
	Appender() Appender
}

// BlockMeta provides meta information about a block.
type BlockMeta struct {
	// Unique identifier for the block and its contents. Changes on compaction.
	ULID ulid.ULID `json:"ulid"`

	// MinTime and MaxTime specify the time range all samples
	// in the block are in.
	MinTime int64 `json:"minTime"`
	MaxTime int64 `json:"maxTime"`

	// Stats about the contents of the block.
	Stats BlockStats `json:"stats,omitempty"`

	// Information on compactions the block was created from.
	Compaction BlockMetaCompaction `json:"compaction"`

	// Version of the index format
	Version int `json:"version"`
}

// BlockStats contains stats about contents of a block.
type BlockStats struct {
	NumSamples    uint64 `json:"numSamples,omitempty"`
	NumSeries     uint64 `json:"numSeries,omitempty"`
	NumChunks     uint64 `json:"numChunks,omitempty"`
	NumTombstones uint64 `json:"numTombstones,omitempty"`
}

// BlockMetaCompaction holds information about compactions a block went through.
type BlockMetaCompaction struct {
	// Maximum number of compaction cycles any source block has
	// gone through.
	Level int `json:"level"`
	// ULIDs of all source head blocks that went into the block.
	Sources []ulid.ULID `json:"sources,omitempty"`
	Failed  bool        `json:"failed,omitempty"`
}

const (
	flagNone = 0
	flagStd  = 1
)

const indexFilename = "index"
const metaFilename = "meta.json"

func chunkDir(dir string) string { return filepath.Join(dir, "chunks") }
func walDir(dir string) string   { return filepath.Join(dir, "wal") }

func readMetaFile(dir string) (*BlockMeta, error) {
	b, err := ioutil.ReadFile(filepath.Join(dir, metaFilename))
	if err != nil {
		return nil, err
	}
	var m BlockMeta

	if err := json.Unmarshal(b, &m); err != nil {
		return nil, err
	}
	if m.Version != 1 && m.Version != 2 {
		return nil, errors.Errorf("unexpected meta file version %d", m.Version)
	}

	return &m, nil
}

func writeMetaFile(dir string, meta *BlockMeta) error {
	// Make any changes to the file appear atomic.
	path := filepath.Join(dir, metaFilename)
	tmp := path + ".tmp"

	f, err := os.Create(tmp)
	if err != nil {
		return err
	}

	enc := json.NewEncoder(f)
	enc.SetIndent("", "\t")

	var merr MultiError
	meta.Version = 2
	if merr.Add(enc.Encode(meta)); merr.Err() != nil {
		merr.Add(f.Close())
		return merr.Err()
	}
	if err := f.Close(); err != nil {
		return err
	}
	return renameFile(tmp, path)
}

// Block represents a directory of time series data covering a continuous time range.
type Block struct {
	mtx            sync.RWMutex
	closing        bool
	pendingReaders sync.WaitGroup

	dir  string
	meta BlockMeta

	chunkr     ChunkReader
	indexr     IndexReader
	tombstones TombstoneReader
}

// OpenBlock opens the block in the directory. It can be passed a chunk pool, which is used
// to instantiate chunk structs.
func OpenBlock(dir string, pool chunkenc.Pool) (*Block, error) {
	meta, err := readMetaFile(dir)
	if err != nil {
		return nil, err
	}

	cr, err := chunks.NewDirReader(chunkDir(dir), pool)
	if err != nil {
		return nil, err
	}
	ir, err := index.NewFileReader(filepath.Join(dir, "index"))
	if err != nil {
		return nil, err
	}

	tr, err := readTombstones(dir)
	if err != nil {
		return nil, err
	}

	pb := &Block{
		dir:        dir,
		meta:       *meta,
		chunkr:     cr,
		indexr:     ir,
		tombstones: tr,
	}
	return pb, nil
}

// Close closes the on-disk block. It blocks as long as there are readers reading from the block.
func (pb *Block) Close() error {
	pb.mtx.Lock()
	pb.closing = true
	pb.mtx.Unlock()

	pb.pendingReaders.Wait()

	var merr MultiError

	merr.Add(pb.chunkr.Close())
	merr.Add(pb.indexr.Close())
	merr.Add(pb.tombstones.Close())

	return merr.Err()
}

func (pb *Block) String() string {
	return pb.meta.ULID.String()
}

// Dir returns the directory of the block.
func (pb *Block) Dir() string { return pb.dir }

// Meta returns meta information about the block.
func (pb *Block) Meta() BlockMeta { return pb.meta }

// ErrClosing is returned when a block is in the process of being closed.
var ErrClosing = errors.New("block is closing")

func (pb *Block) startRead() error {
	pb.mtx.RLock()
	defer pb.mtx.RUnlock()

	if pb.closing {
		return ErrClosing
	}
	pb.pendingReaders.Add(1)
	return nil
}

// Index returns a new IndexReader against the block data.
func (pb *Block) Index() (IndexReader, error) {
	if err := pb.startRead(); err != nil {
		return nil, err
	}
	return blockIndexReader{IndexReader: pb.indexr, b: pb}, nil
}

// Chunks returns a new ChunkReader against the block data.
func (pb *Block) Chunks() (ChunkReader, error) {
	if err := pb.startRead(); err != nil {
		return nil, err
	}
	return blockChunkReader{ChunkReader: pb.chunkr, b: pb}, nil
}

// Tombstones returns a new TombstoneReader against the block data.
func (pb *Block) Tombstones() (TombstoneReader, error) {
	if err := pb.startRead(); err != nil {
		return nil, err
	}
	return blockTombstoneReader{TombstoneReader: pb.tombstones, b: pb}, nil
}

func (pb *Block) setCompactionFailed() error {
	pb.meta.Compaction.Failed = true
	return writeMetaFile(pb.dir, &pb.meta)
}

type blockIndexReader struct {
	IndexReader
	b *Block
}

func (r blockIndexReader) Close() error {
	r.b.pendingReaders.Done()
	return nil
}

type blockTombstoneReader struct {
	TombstoneReader
	b *Block
}

func (r blockTombstoneReader) Close() error {
	r.b.pendingReaders.Done()
	return nil
}

type blockChunkReader struct {
	ChunkReader
	b *Block
}

func (r blockChunkReader) Close() error {
	r.b.pendingReaders.Done()
	return nil
}

// Delete matching series between mint and maxt in the block.
func (pb *Block) Delete(mint, maxt int64, ms ...labels.Matcher) error {
	pb.mtx.Lock()
	defer pb.mtx.Unlock()

	if pb.closing {
		return ErrClosing
	}

	p, err := PostingsForMatchers(pb.indexr, ms...)
	if err != nil {
		return errors.Wrap(err, "select series")
	}

	ir := pb.indexr

	// Choose only valid postings which have chunks in the time-range.
	stones := memTombstones{}

	var lset labels.Labels
	var chks []chunks.Meta

Outer:
	for p.Next() {
		err := ir.Series(p.At(), &lset, &chks)
		if err != nil {
			return err
		}

		for _, chk := range chks {
			if intervalOverlap(mint, maxt, chk.MinTime, chk.MaxTime) {
				// Delete only until the current vlaues and not beyond.
				tmin, tmax := clampInterval(mint, maxt, chks[0].MinTime, chks[len(chks)-1].MaxTime)
				stones[p.At()] = Intervals{{tmin, tmax}}
				continue Outer
			}
		}
	}

	if p.Err() != nil {
		return p.Err()
	}

	err = pb.tombstones.Iter(func(id uint64, ivs Intervals) error {
		for _, iv := range ivs {
			stones.add(id, iv)
			pb.meta.Stats.NumTombstones++
		}
		return nil
	})
	if err != nil {
		return err
	}
	pb.tombstones = stones

	if err := writeTombstoneFile(pb.dir, pb.tombstones); err != nil {
		return err
	}
	return writeMetaFile(pb.dir, &pb.meta)
}

// CleanTombstones will rewrite the block if there any tombstones to remove them
// and returns if there was a re-write.
func (pb *Block) CleanTombstones(dest string, c Compactor) (bool, error) {
	numStones := 0

	pb.tombstones.Iter(func(id uint64, ivs Intervals) error {
		for _ = range ivs {
			numStones++
		}

		return nil
	})

	if numStones == 0 {
		return false, nil
	}

	if _, err := c.Write(dest, pb, pb.meta.MinTime, pb.meta.MaxTime); err != nil {
		return false, err
	}

	return true, nil
}

// Snapshot creates snapshot of the block into dir.
func (pb *Block) Snapshot(dir string) error {
	blockDir := filepath.Join(dir, pb.meta.ULID.String())
	if err := os.MkdirAll(blockDir, 0777); err != nil {
		return errors.Wrap(err, "create snapshot block dir")
	}

	chunksDir := chunkDir(blockDir)
	if err := os.MkdirAll(chunksDir, 0777); err != nil {
		return errors.Wrap(err, "create snapshot chunk dir")
	}

	// Hardlink meta, index and tombstones
	for _, fname := range []string{
		metaFilename,
		indexFilename,
		tombstoneFilename,
	} {
		if err := os.Link(filepath.Join(pb.dir, fname), filepath.Join(blockDir, fname)); err != nil {
			return errors.Wrapf(err, "create snapshot %s", fname)
		}
	}

	// Hardlink the chunks
	curChunkDir := chunkDir(pb.dir)
	files, err := ioutil.ReadDir(curChunkDir)
	if err != nil {
		return errors.Wrap(err, "ReadDir the current chunk dir")
	}

	for _, f := range files {
		err := os.Link(filepath.Join(curChunkDir, f.Name()), filepath.Join(chunksDir, f.Name()))
		if err != nil {
			return errors.Wrap(err, "hardlink a chunk")
		}
	}

	return nil
}

func clampInterval(a, b, mint, maxt int64) (int64, int64) {
	if a < mint {
		a = mint
	}
	if b > maxt {
		b = maxt
	}
	return a, b
}