// 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"

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

// DiskBlock handles reads against a Block of time series data.
type DiskBlock interface {
	// Directory where block data is stored.
	Dir() string

	// Stats returns statistics about the block.
	Meta() BlockMeta

	// Index returns an IndexReader over the block's data.
	Index() IndexReader

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

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

	// Delete deletes data from the block.
	Delete(mint, maxt int64, ms ...labels.Matcher) error

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

// Block is an interface to a DiskBlock that can also be queried.
type Block interface {
	DiskBlock
	Queryable
	Snapshottable
}

// headBlock is a regular block that can still be appended to.
type headBlock interface {
	Block
	Appendable
}

// Snapshottable defines an entity that can be backedup online.
type Snapshottable interface {
	Snapshot(dir string) 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

	// Busy returns whether there are any currently active appenders.
	Busy() bool
}

// Queryable defines an entity which provides a Querier.
type Queryable interface {
	Querier(mint, maxt int64) Querier
}

// 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 struct {
		NumSamples    uint64 `json:"numSamples,omitempty"`
		NumSeries     uint64 `json:"numSeries,omitempty"`
		NumChunks     uint64 `json:"numChunks,omitempty"`
		NumTombstones uint64 `json:"numTombstones,omitempty"`
	} `json:"stats,omitempty"`

	// Information on compactions the block was created from.
	Compaction struct {
		Generation int `json:"generation"`
	} `json:"compaction"`
}

const (
	flagNone = 0
	flagStd  = 1
)

type blockMeta struct {
	Version int `json:"version"`

	*BlockMeta
}

const metaFilename = "meta.json"

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 {
		return nil, errors.Errorf("unexpected meta file version %d", m.Version)
	}

	return m.BlockMeta, 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
	if merr.Add(enc.Encode(&blockMeta{Version: 1, BlockMeta: meta})); merr.Err() != nil {
		merr.Add(f.Close())
		return merr
	}
	if err := f.Close(); err != nil {
		return err
	}
	return renameFile(tmp, path)
}

type persistedBlock struct {
	dir  string
	meta BlockMeta

	chunkr *chunkReader
	indexr *indexReader

	tombstones tombstoneReader
}

func newPersistedBlock(dir string) (*persistedBlock, error) {
	meta, err := readMetaFile(dir)
	if err != nil {
		return nil, err
	}

	cr, err := newChunkReader(chunkDir(dir))
	if err != nil {
		return nil, err
	}
	ir, err := newIndexReader(dir)
	if err != nil {
		return nil, err
	}

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

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

func (pb *persistedBlock) Close() error {
	var merr MultiError

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

	return merr.Err()
}

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

func (pb *persistedBlock) Querier(mint, maxt int64) Querier {
	return &blockQuerier{
		mint:       mint,
		maxt:       maxt,
		index:      pb.Index(),
		chunks:     pb.Chunks(),
		tombstones: pb.Tombstones(),
	}
}

func (pb *persistedBlock) Dir() string         { return pb.dir }
func (pb *persistedBlock) Index() IndexReader  { return pb.indexr }
func (pb *persistedBlock) Chunks() ChunkReader { return pb.chunkr }
func (pb *persistedBlock) Tombstones() TombstoneReader {
	return pb.tombstones
}
func (pb *persistedBlock) Meta() BlockMeta { return pb.meta }

func (pb *persistedBlock) Delete(mint, maxt int64, ms ...labels.Matcher) error {
	pr := newPostingsReader(pb.indexr)
	p, absent := pr.Select(ms...)

	ir := pb.indexr

	// Choose only valid postings which have chunks in the time-range.
	stones := map[uint32]intervals{}

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

		for _, abs := range absent {
			if lset.Get(abs) != "" {
				continue Outer
			}
		}

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

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

	// Merge the current and new tombstones.
	for k, v := range stones {
		pb.tombstones.add(k, v[0])
	}

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

	pb.meta.Stats.NumTombstones = uint64(len(pb.tombstones))
	return writeMetaFile(pb.dir, &pb.meta)
}

func (pb *persistedBlock) 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
	filenames := []string{metaFilename, indexFilename, tombstoneFilename}
	for _, fname := range filenames {
		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 chunkDir(dir string) string { return filepath.Join(dir, "chunks") }
func walDir(dir string) string   { return filepath.Join(dir, "wal") }

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

	return a, b
}

type mmapFile struct {
	f *os.File
	b []byte
}

func openMmapFile(path string) (*mmapFile, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, errors.Wrap(err, "try lock file")
	}
	info, err := f.Stat()
	if err != nil {
		return nil, errors.Wrap(err, "stat")
	}

	b, err := mmap(f, int(info.Size()))
	if err != nil {
		return nil, errors.Wrap(err, "mmap")
	}

	return &mmapFile{f: f, b: b}, nil
}

func (f *mmapFile) Close() error {
	err0 := munmap(f.b)
	err1 := f.f.Close()

	if err0 != nil {
		return err0
	}
	return err1
}