/*
 * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
 *
 * 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 cmd

import (
	"bufio"
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"io"
	"io/ioutil"
	"os"
	"path"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/minio/minio/cmd/config"
	"github.com/minio/minio/cmd/logger"
	"github.com/minio/minio/pkg/color"
	"github.com/minio/minio/pkg/env"
	"github.com/willf/bloom"
)

const (
	// Estimate bloom filter size. With this many items
	dataUpdateTrackerEstItems = 10000000
	// ... we want this false positive rate:
	dataUpdateTrackerFP        = 0.99
	dataUpdateTrackerQueueSize = 10000

	dataUpdateTrackerFilename     = dataUsageBucket + SlashSeparator + ".tracker.bin"
	dataUpdateTrackerVersion      = 4
	dataUpdateTrackerSaveInterval = 5 * time.Minute
)

var (
	objectUpdatedCh      chan<- string
	intDataUpdateTracker *dataUpdateTracker
)

func init() {
	intDataUpdateTracker = newDataUpdateTracker()
	objectUpdatedCh = intDataUpdateTracker.input
}

type dataUpdateTracker struct {
	mu         sync.Mutex
	input      chan string
	save       chan struct{}
	debug      bool
	saveExited chan struct{}
	dirty      bool

	Current dataUpdateFilter
	History dataUpdateTrackerHistory
	Saved   time.Time
}

// newDataUpdateTracker returns a dataUpdateTracker with default settings.
func newDataUpdateTracker() *dataUpdateTracker {
	d := &dataUpdateTracker{
		Current: dataUpdateFilter{
			idx: 1,
		},
		debug:      env.Get(envDataUsageCrawlDebug, config.EnableOff) == config.EnableOn,
		input:      make(chan string, dataUpdateTrackerQueueSize),
		save:       make(chan struct{}, 1),
		saveExited: make(chan struct{}),
	}
	d.Current.bf = d.newBloomFilter()
	d.dirty = true
	return d
}

type dataUpdateTrackerHistory []dataUpdateFilter

type dataUpdateFilter struct {
	idx uint64
	bf  bloomFilter
}

type bloomFilter struct {
	*bloom.BloomFilter
}

// emptyBloomFilter returns an empty bloom filter.
func emptyBloomFilter() bloomFilter {
	return bloomFilter{BloomFilter: &bloom.BloomFilter{}}
}

// containsDir returns whether the bloom filter contains a directory.
// Note that objects in XL mode are also considered directories.
func (b bloomFilter) containsDir(in string) bool {
	split := splitPathDeterministic(path.Clean(in))

	if len(split) == 0 {
		return false
	}
	return b.TestString(hashPath(path.Join(split...)).String())
}

// bytes returns the bloom filter serialized as a byte slice.
func (b *bloomFilter) bytes() []byte {
	if b == nil || b.BloomFilter == nil {
		return nil
	}
	var buf bytes.Buffer
	_, err := b.WriteTo(&buf)
	if err != nil {
		logger.LogIf(GlobalContext, err)
		return nil
	}
	return buf.Bytes()
}

// sort the dataUpdateTrackerHistory, newest first.
// Returns whether the history is complete.
func (d dataUpdateTrackerHistory) sort() bool {
	if len(d) == 0 {
		return true
	}
	sort.Slice(d, func(i, j int) bool {
		return d[i].idx > d[j].idx
	})
	return d[0].idx-d[len(d)-1].idx == uint64(len(d))
}

// removeOlderThan will remove entries older than index 'n'.
func (d *dataUpdateTrackerHistory) removeOlderThan(n uint64) {
	d.sort()
	dd := *d
	end := len(dd)
	for i := end - 1; i >= 0; i-- {
		if dd[i].idx < n {
			end = i
		}
	}
	dd = dd[:end]
	*d = dd
}

// newBloomFilter returns a new bloom filter with default settings.
func (d *dataUpdateTracker) newBloomFilter() bloomFilter {
	return bloomFilter{bloom.NewWithEstimates(dataUpdateTrackerEstItems, dataUpdateTrackerFP)}
}

// current returns the current index.
func (d *dataUpdateTracker) current() uint64 {
	d.mu.Lock()
	defer d.mu.Unlock()
	return d.Current.idx
}

// latestWithDir returns the highest index that contains the directory.
// This means that any cycle higher than this does NOT contain the entry.
func (d *dataUpdateTracker) latestWithDir(dir string) uint64 {
	bucket, _ := path2BucketObjectWithBasePath("", dir)
	if bucket == "" {
		if d.debug && len(dir) > 0 {
			logger.Info(color.Green("dataUpdateTracker:")+" no bucket (%s)", dir)
		}
		return d.current()
	}
	if isReservedOrInvalidBucket(bucket, false) {
		if d.debug {
			logger.Info(color.Green("dataUpdateTracker:")+" isReservedOrInvalidBucket: %v, entry: %v", bucket, dir)
		}
		return d.current()
	}

	d.mu.Lock()
	defer d.mu.Unlock()
	if d.Current.bf.containsDir(dir) || d.Current.idx == 0 {
		return d.Current.idx
	}
	if d.debug {
		logger.Info("current bloom does NOT contains dir %s", dir)
	}

	idx := d.Current.idx - 1
	for {
		f := d.History.find(idx)
		if f == nil || f.bf.containsDir(dir) || idx == 0 {
			break
		}
		idx--
	}
	return idx
}

// start will load the current data from the drives start collecting information and
// start a saver goroutine.
// All of these will exit when the context is canceled.
func (d *dataUpdateTracker) start(ctx context.Context, drives ...string) {
	if len(drives) <= 0 {
		logger.LogIf(ctx, errors.New("dataUpdateTracker.start: No drives specified"))
		return
	}
	d.load(ctx, drives...)
	go d.startCollector(ctx)
	// startSaver will unlock.
	d.mu.Lock()
	go d.startSaver(ctx, dataUpdateTrackerSaveInterval, drives)
}

// load will attempt to load data tracking information from the supplied drives.
// The data will only be loaded if d.Saved is older than the one found on disk.
// The newest working cache will be kept in d.
// If no valid data usage tracker can be found d will remain unchanged.
// If object is shared the caller should lock it.
func (d *dataUpdateTracker) load(ctx context.Context, drives ...string) {
	if len(drives) <= 0 {
		logger.LogIf(ctx, errors.New("dataUpdateTracker.load: No drives specified"))
		return
	}
	for _, drive := range drives {

		cacheFormatPath := pathJoin(drive, dataUpdateTrackerFilename)
		f, err := os.Open(cacheFormatPath)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}
			logger.LogIf(ctx, err)
			continue
		}
		err = d.deserialize(f, d.Saved)
		if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
			logger.LogIf(ctx, err)
		}
		f.Close()
	}
}

// startSaver will start a saver that will write d to all supplied drives at specific intervals.
// 'd' must be write locked when started and will be unlocked.
// The saver will save and exit when supplied context is closed.
func (d *dataUpdateTracker) startSaver(ctx context.Context, interval time.Duration, drives []string) {
	saveNow := d.save
	exited := make(chan struct{})
	d.saveExited = exited
	d.mu.Unlock()
	t := time.NewTicker(interval)
	defer t.Stop()
	defer close(exited)
	var buf bytes.Buffer
	for {
		var exit bool
		select {
		case <-ctx.Done():
			exit = true
		case <-t.C:
		case <-saveNow:
		}
		buf.Reset()
		d.mu.Lock()
		if !d.dirty {
			d.mu.Unlock()
			if exit {
				return
			}
			continue
		}
		d.Saved = UTCNow()
		err := d.serialize(&buf)
		if d.debug {
			logger.Info(color.Green("dataUpdateTracker:")+" Saving: %v bytes, Current idx: %v", buf.Len(), d.Current.idx)
		}
		d.dirty = false
		d.mu.Unlock()
		if err != nil {
			logger.LogIf(ctx, err, "Error serializing usage tracker data")
			if exit {
				return
			}
			continue
		}
		if buf.Len() == 0 {
			logger.LogIf(ctx, errors.New("zero sized output, skipping save"))
			continue
		}
		for _, drive := range drives {
			cacheFormatPath := pathJoin(drive, dataUpdateTrackerFilename)
			err := ioutil.WriteFile(cacheFormatPath, buf.Bytes(), os.ModePerm)
			if err != nil {
				if os.IsNotExist(err) {
					continue
				}
				logger.LogIf(ctx, err)
				continue
			}
		}
		if exit {
			return
		}
	}
}

// serialize all data in d to dst.
// Caller should hold lock if d is expected to be shared.
// If an error is returned, there will likely be partial data written to dst.
func (d *dataUpdateTracker) serialize(dst io.Writer) (err error) {
	ctx := GlobalContext
	var tmp [8]byte
	o := bufio.NewWriter(dst)
	defer func() {
		if err == nil {
			err = o.Flush()
		}
	}()

	// Version
	if err := o.WriteByte(dataUpdateTrackerVersion); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}
	// Timestamp.
	binary.LittleEndian.PutUint64(tmp[:], uint64(d.Saved.Unix()))
	if _, err := o.Write(tmp[:]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}

	// Current
	binary.LittleEndian.PutUint64(tmp[:], d.Current.idx)
	if _, err := o.Write(tmp[:]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}

	if _, err := d.Current.bf.WriteTo(o); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}

	// History
	binary.LittleEndian.PutUint64(tmp[:], uint64(len(d.History)))
	if _, err := o.Write(tmp[:]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}

	for _, bf := range d.History {
		// Current
		binary.LittleEndian.PutUint64(tmp[:], bf.idx)
		if _, err := o.Write(tmp[:]); err != nil {
			if d.debug {
				logger.LogIf(ctx, err)
			}
			return err
		}

		if _, err := bf.bf.WriteTo(o); err != nil {
			if d.debug {
				logger.LogIf(ctx, err)
			}
			return err
		}
	}
	return nil
}

// deserialize will deserialize the supplied input if the input is newer than the supplied time.
func (d *dataUpdateTracker) deserialize(src io.Reader, newerThan time.Time) error {
	ctx := GlobalContext
	var dst dataUpdateTracker
	var tmp [8]byte

	// Version
	if _, err := io.ReadFull(src, tmp[:1]); err != nil {
		if d.debug {
			if err != io.EOF {
				logger.LogIf(ctx, err)
			}
		}
		return err
	}
	switch tmp[0] {
	case 1, 2:
		logger.Info(color.Green("dataUpdateTracker: ") + "deprecated data version, updating.")
		return nil
	case dataUpdateTrackerVersion:
	default:
		return errors.New("dataUpdateTracker: Unknown data version")
	}
	// Timestamp.
	if _, err := io.ReadFull(src, tmp[:8]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}
	t := time.Unix(int64(binary.LittleEndian.Uint64(tmp[:])), 0)
	if !t.After(newerThan) {
		return nil
	}

	// Current
	if _, err := io.ReadFull(src, tmp[:8]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}
	dst.Current.idx = binary.LittleEndian.Uint64(tmp[:])
	dst.Current.bf = emptyBloomFilter()
	if _, err := dst.Current.bf.ReadFrom(src); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}

	// History
	if _, err := io.ReadFull(src, tmp[:8]); err != nil {
		if d.debug {
			logger.LogIf(ctx, err)
		}
		return err
	}
	n := binary.LittleEndian.Uint64(tmp[:])
	dst.History = make(dataUpdateTrackerHistory, int(n))
	for i, e := range dst.History {
		if _, err := io.ReadFull(src, tmp[:8]); err != nil {
			if d.debug {
				logger.LogIf(ctx, err)
			}
			return err
		}
		e.idx = binary.LittleEndian.Uint64(tmp[:])
		e.bf = emptyBloomFilter()
		if _, err := e.bf.ReadFrom(src); err != nil {
			if d.debug {
				logger.LogIf(ctx, err)
			}
			return err
		}
		dst.History[i] = e
	}
	// Ignore what remains on the stream.
	// Update d:
	d.mu.Lock()
	defer d.mu.Unlock()
	d.Current = dst.Current
	d.History = dst.History
	d.Saved = dst.Saved
	return nil
}

// start a collector that picks up entries from objectUpdatedCh
// and adds them  to the current bloom filter.
func (d *dataUpdateTracker) startCollector(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			return
		case in := <-d.input:
			if d.debug {
				logger.Info(color.Green("dataUpdateTracker:")+" got (%s)", in)
			}

			bucket, _ := path2BucketObjectWithBasePath("", in)
			if bucket == "" {
				if d.debug && len(in) > 0 {
					logger.Info(color.Green("dataUpdateTracker:")+" no bucket (%s)", in)
				}
				continue
			}

			if isReservedOrInvalidBucket(bucket, false) {
				if d.debug {
					logger.Info(color.Green("dataUpdateTracker:")+" isReservedOrInvalidBucket: %v, entry: %v", bucket, in)
				}
				continue
			}
			split := splitPathDeterministic(in)

			// Add all paths until done.
			d.mu.Lock()
			for i := range split {
				if d.debug {
					logger.Info(color.Green("dataUpdateTracker:") + " Marking path dirty: " + color.Blue(path.Join(split[:i+1]...)))
				}
				d.Current.bf.AddString(hashPath(path.Join(split[:i+1]...)).String())
			}
			d.dirty = d.dirty || len(split) > 0
			d.mu.Unlock()
		}
	}
}

// find entry with specified index.
// Returns nil if not found.
func (d dataUpdateTrackerHistory) find(idx uint64) *dataUpdateFilter {
	for _, f := range d {
		if f.idx == idx {
			return &f
		}
	}
	return nil
}

// filterFrom will return a combined bloom filter.
func (d *dataUpdateTracker) filterFrom(ctx context.Context, oldest, newest uint64) *bloomFilterResponse {
	bf := d.newBloomFilter()
	bfr := bloomFilterResponse{
		OldestIdx:  oldest,
		CurrentIdx: d.Current.idx,
		Complete:   true,
	}
	// Loop through each index requested.
	for idx := oldest; idx <= newest; idx++ {
		v := d.History.find(idx)
		if v == nil {
			if d.Current.idx == idx {
				// Merge current.
				err := bf.Merge(d.Current.bf.BloomFilter)
				logger.LogIf(ctx, err)
				if err != nil {
					bfr.Complete = false
				}
				continue
			}
			bfr.Complete = false
			bfr.OldestIdx = idx + 1
			continue
		}

		err := bf.Merge(v.bf.BloomFilter)
		if err != nil {
			bfr.Complete = false
			logger.LogIf(ctx, err)
			continue
		}
		bfr.NewestIdx = idx
	}
	var dst bytes.Buffer
	_, err := bf.WriteTo(&dst)
	if err != nil {
		logger.LogIf(ctx, err)
		return nil
	}
	bfr.Filter = dst.Bytes()

	return &bfr
}

// cycleFilter will cycle the bloom filter to start recording to index y if not already.
// The response will contain a bloom filter starting at index x up to, but not including index y.
// If y is 0, the response will not update y, but return the currently recorded information
// from the oldest (unless 0, then it will be all) until and including current y.
func (d *dataUpdateTracker) cycleFilter(ctx context.Context, req bloomFilterRequest) (*bloomFilterResponse, error) {
	if req.OldestClean != "" {
		return &bloomFilterResponse{OldestIdx: d.latestWithDir(req.OldestClean)}, nil
	}
	current := req.Current
	oldest := req.Oldest
	d.mu.Lock()
	defer d.mu.Unlock()
	if current == 0 {
		if len(d.History) == 0 {
			return d.filterFrom(ctx, d.Current.idx, d.Current.idx), nil
		}
		d.History.sort()
		if oldest == 0 {
			oldest = d.History[len(d.History)-1].idx
		}
		return d.filterFrom(ctx, oldest, d.Current.idx), nil
	}

	// Move current to history if new one requested
	if d.Current.idx != current {
		d.dirty = true
		if d.debug {
			logger.Info(color.Green("dataUpdateTracker:")+" cycle bloom filter: %v -> %v", d.Current.idx, current)
		}

		d.History = append(d.History, d.Current)
		d.Current.idx = current
		d.Current.bf = d.newBloomFilter()
		select {
		case d.save <- struct{}{}:
		default:
		}
	}
	d.History.removeOlderThan(oldest)
	return d.filterFrom(ctx, oldest, current), nil
}

// splitPathDeterministic will split the provided relative path
// deterministically and return up to the first 3 elements of the path.
// Slash and dot prefixes are removed.
// Trailing slashes are removed.
// Returns 0 length if no parts are found after trimming.
func splitPathDeterministic(in string) []string {
	split := strings.Split(in, SlashSeparator)

	// Trim empty start/end
	for len(split) > 0 {
		if len(split[0]) > 0 && split[0] != "." {
			break
		}
		split = split[1:]
	}
	for len(split) > 0 {
		if len(split[len(split)-1]) > 0 {
			break
		}
		split = split[:len(split)-1]
	}

	return split
}

// bloomFilterRequest request bloom filters.
// Current index will be updated to current and entries back to Oldest is returned.
type bloomFilterRequest struct {
	Oldest  uint64
	Current uint64
	// If set the oldest clean version will be returned in OldestIdx
	// and the rest of the request will be ignored.
	OldestClean string
}

type bloomFilterResponse struct {
	// Current index being written to.
	CurrentIdx uint64
	// Oldest index in the returned bloom filter.
	OldestIdx uint64
	// Newest Index in the returned bloom filter.
	NewestIdx uint64
	// Are all indexes between oldest and newest filled?
	Complete bool
	// Binary data of the bloom filter.
	Filter []byte
}

// ObjectPathUpdated indicates a path has been updated.
// The function will never block.
func ObjectPathUpdated(s string) {
	if strings.HasPrefix(s, minioMetaBucket) {
		return
	}
	select {
	case objectUpdatedCh <- s:
	default:
	}
}