/*
 * MinIO Cloud Storage, (C) 2018 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 (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"reflect"
	"strings"

	"github.com/minio/minio/cmd/logger"
)

const (
	// Represents Cache format json holding details on all other cache drives in use.
	formatCache = "cache"

	// formatCacheV1.Cache.Version
	formatCacheVersionV1 = "1"
	formatCacheVersionV2 = "2"

	formatMetaVersion1 = "1"

	formatCacheV1DistributionAlgo = "CRCMOD"
)

// Represents the current cache structure with list of
// disks comprising the disk cache
// formatCacheV1 - structure holds format config version '1'.
type formatCacheV1 struct {
	formatMetaV1
	Cache struct {
		Version string `json:"version"` // Version of 'cache' format.
		This    string `json:"this"`    // This field carries assigned disk uuid.
		// Disks field carries the input disk order generated the first
		// time when fresh disks were supplied.
		Disks []string `json:"disks"`
		// Distribution algorithm represents the hashing algorithm
		// to pick the right set index for an object.
		DistributionAlgo string `json:"distributionAlgo"`
	} `json:"cache"` // Cache field holds cache format.
}

// formatCacheV2 is same as formatCacheV1
type formatCacheV2 = formatCacheV1

// Used to detect the version of "cache" format.
type formatCacheVersionDetect struct {
	Cache struct {
		Version string `json:"version"`
	} `json:"cache"`
}

// Return a slice of format, to be used to format uninitialized disks.
func newFormatCacheV2(drives []string) []*formatCacheV2 {
	diskCount := len(drives)
	var disks = make([]string, diskCount)

	var formats = make([]*formatCacheV2, diskCount)

	for i := 0; i < diskCount; i++ {
		format := &formatCacheV2{}
		format.Version = formatMetaVersion1
		format.Format = formatCache
		format.Cache.Version = formatCacheVersionV2
		format.Cache.DistributionAlgo = formatCacheV1DistributionAlgo
		format.Cache.This = mustGetUUID()
		formats[i] = format
		disks[i] = formats[i].Cache.This
	}
	for i := 0; i < diskCount; i++ {
		format := formats[i]
		format.Cache.Disks = disks
	}
	return formats
}

// Returns formatCache.Cache.Version
func formatCacheGetVersion(r io.ReadSeeker) (string, error) {
	format := &formatCacheVersionDetect{}
	if err := jsonLoad(r, format); err != nil {
		return "", err
	}
	return format.Cache.Version, nil
}

// Creates a new cache format.json if unformatted.
func createFormatCache(fsFormatPath string, format *formatCacheV1) error {
	// open file using READ & WRITE permission
	var file, err = os.OpenFile(fsFormatPath, os.O_RDWR|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	// Close the locked file upon return.
	defer file.Close()

	fi, err := file.Stat()
	if err != nil {
		return err
	}
	if fi.Size() != 0 {
		// format.json already got created because of another minio process's createFormatCache()
		return nil
	}
	return jsonSave(file, format)
}

// This function creates a cache format file on disk and returns a slice
// of format cache config
func initFormatCache(ctx context.Context, drives []string) (formats []*formatCacheV2, err error) {
	nformats := newFormatCacheV2(drives)
	for _, drive := range drives {
		_, err = os.Stat(drive)
		if err == nil {
			continue
		}
		if !os.IsNotExist(err) {
			logger.GetReqInfo(ctx).AppendTags("drive", drive)
			logger.LogIf(ctx, err)
			return nil, err
		}
		if err = os.Mkdir(drive, 0777); err != nil {
			logger.GetReqInfo(ctx).AppendTags("drive", drive)
			logger.LogIf(ctx, err)
			return nil, err
		}
	}
	for i, drive := range drives {
		if err = os.Mkdir(pathJoin(drive, minioMetaBucket), 0777); err != nil {
			if !os.IsExist(err) {
				logger.GetReqInfo(ctx).AppendTags("drive", drive)
				logger.LogIf(ctx, err)
				return nil, err
			}
		}
		cacheFormatPath := pathJoin(drive, minioMetaBucket, formatConfigFile)
		// Fresh disk - create format.json for this cfs
		if err = createFormatCache(cacheFormatPath, nformats[i]); err != nil {
			logger.GetReqInfo(ctx).AppendTags("drive", drive)
			logger.LogIf(ctx, err)
			return nil, err
		}
	}
	return nformats, nil
}

func loadFormatCache(ctx context.Context, drives []string) ([]*formatCacheV2, bool, error) {
	formats := make([]*formatCacheV2, len(drives))
	var formatV2 *formatCacheV2
	migrating := false
	for i, drive := range drives {
		cacheFormatPath := pathJoin(drive, minioMetaBucket, formatConfigFile)
		f, err := os.OpenFile(cacheFormatPath, os.O_RDWR, 0)

		if err != nil {
			if os.IsNotExist(err) {
				continue
			}
			logger.LogIf(ctx, err)
			return nil, migrating, err
		}
		defer f.Close()
		format, err := formatMetaCacheV1(f)
		if err != nil {
			continue
		}
		formatV2 = format
		if format.Cache.Version != formatCacheVersionV2 {
			migrating = true
		}
		formats[i] = formatV2
	}
	return formats, migrating, nil
}

// unmarshalls the cache format.json into formatCacheV1
func formatMetaCacheV1(r io.ReadSeeker) (*formatCacheV1, error) {
	format := &formatCacheV1{}
	if err := jsonLoad(r, format); err != nil {
		return nil, err
	}
	return format, nil
}

func checkFormatCacheValue(format *formatCacheV2, migrating bool) error {
	if format.Format != formatCache {
		return fmt.Errorf("Unsupported cache format [%s] found", format.Format)
	}

	// during migration one or more cache drive(s) formats can be out of sync
	if migrating {
		// Validate format version and format type.
		if format.Version != formatMetaVersion1 {
			return fmt.Errorf("Unsupported version of cache format [%s] found", format.Version)
		}
		if format.Cache.Version != formatCacheVersionV2 && format.Cache.Version != formatCacheVersionV1 {
			return fmt.Errorf("Unsupported Cache backend format found [%s]", format.Cache.Version)
		}
		return nil
	}
	// Validate format version and format type.
	if format.Version != formatMetaVersion1 {
		return fmt.Errorf("Unsupported version of cache format [%s] found", format.Version)
	}
	if format.Cache.Version != formatCacheVersionV2 {
		return fmt.Errorf("Unsupported Cache backend format found [%s]", format.Cache.Version)
	}
	return nil
}

func checkFormatCacheValues(migrating bool, formats []*formatCacheV2) (int, error) {
	for i, formatCache := range formats {
		if formatCache == nil {
			continue
		}
		if err := checkFormatCacheValue(formatCache, migrating); err != nil {
			return i, err
		}
		if len(formats) != len(formatCache.Cache.Disks) {
			return i, fmt.Errorf("Expected number of cache drives %d , got  %d",
				len(formatCache.Cache.Disks), len(formats))
		}
	}
	return -1, nil
}

// checkCacheDisksConsistency - checks if "This" disk uuid on each disk is consistent with all "Disks" slices
// across disks.
func checkCacheDiskConsistency(formats []*formatCacheV2) error {
	var disks = make([]string, len(formats))
	// Collect currently available disk uuids.
	for index, format := range formats {
		if format == nil {
			disks[index] = ""
			continue
		}
		disks[index] = format.Cache.This
	}
	for i, format := range formats {
		if format == nil {
			continue
		}
		j := findCacheDiskIndex(disks[i], format.Cache.Disks)
		if j == -1 {
			return fmt.Errorf("UUID on positions %d:%d do not match with , expected %s", i, j, disks[i])
		}
		if i != j {
			return fmt.Errorf("UUID on positions %d:%d do not match with , expected %s got %s", i, j, disks[i], format.Cache.Disks[j])
		}
	}
	return nil
}

// checkCacheDisksSliceConsistency - validate cache Disks order if they are consistent.
func checkCacheDisksSliceConsistency(formats []*formatCacheV2) error {
	var sentinelDisks []string
	// Extract first valid Disks slice.
	for _, format := range formats {
		if format == nil {
			continue
		}
		sentinelDisks = format.Cache.Disks
		break
	}
	for _, format := range formats {
		if format == nil {
			continue
		}
		currentDisks := format.Cache.Disks
		if !reflect.DeepEqual(sentinelDisks, currentDisks) {
			return errors.New("inconsistent cache drives found")
		}
	}
	return nil
}

// findCacheDiskIndex returns position of cache disk in JBOD.
func findCacheDiskIndex(disk string, disks []string) int {
	for index, uuid := range disks {
		if uuid == disk {
			return index
		}
	}
	return -1
}

// validate whether cache drives order has changed
func validateCacheFormats(ctx context.Context, migrating bool, formats []*formatCacheV2) error {
	count := 0
	for _, format := range formats {
		if format == nil {
			count++
		}
	}
	if count == len(formats) {
		return errors.New("Cache format files missing on all drives")
	}
	if _, err := checkFormatCacheValues(migrating, formats); err != nil {
		logger.LogIf(ctx, err)
		return err
	}
	if err := checkCacheDisksSliceConsistency(formats); err != nil {
		logger.LogIf(ctx, err)
		return err
	}
	err := checkCacheDiskConsistency(formats)
	logger.LogIf(ctx, err)
	return err
}

// return true if all of the list of cache drives are
// fresh disks
func cacheDrivesUnformatted(drives []string) bool {
	count := 0
	for _, drive := range drives {
		cacheFormatPath := pathJoin(drive, minioMetaBucket, formatConfigFile)
		if _, err := os.Stat(cacheFormatPath); os.IsNotExist(err) {
			count++
		}
	}
	return count == len(drives)
}

// create format.json for each cache drive if fresh disk or load format from disk
// Then validate the format for all drives in the cache to ensure order
// of cache drives has not changed.
func loadAndValidateCacheFormat(ctx context.Context, drives []string) (formats []*formatCacheV2, migrating bool, err error) {
	if cacheDrivesUnformatted(drives) {
		formats, err = initFormatCache(ctx, drives)
	} else {
		formats, migrating, err = loadFormatCache(ctx, drives)
	}
	if err != nil {
		return nil, false, err
	}
	if err = validateCacheFormats(ctx, migrating, formats); err != nil {
		return nil, false, err
	}
	return formats, migrating, nil
}

// reads cached object on disk and writes it back after adding bitrot
// hashsum per block as per the new disk cache format.
func migrateData(ctx context.Context, c *diskCache, oldfile, destDir string) error {
	st, err := os.Stat(oldfile)
	if err != nil {
		err = osErrToFSFileErr(err)
		return err
	}
	readCloser, err := readCacheFileStream(oldfile, 0, st.Size())
	if err != nil {
		return err
	}
	_, err = c.bitrotWriteToCache(ctx, destDir, readCloser, st.Size())
	return err
}

// migrate cache contents from old cacheFS format to new backend format
// new format is flat
//  sha(bucket,object)/  <== dir name
//      - part.1         <== data
//      - cache.json     <== metadata
func migrateOldCache(ctx context.Context, c *diskCache) error {
	oldCacheBucketsPath := path.Join(c.dir, minioMetaBucket, "buckets")
	cacheFormatPath := pathJoin(c.dir, minioMetaBucket, formatConfigFile)

	if _, err := os.Stat(oldCacheBucketsPath); err != nil {
		// remove .minio.sys sub directories
		removeAll(path.Join(c.dir, minioMetaBucket, "multipart"))
		removeAll(path.Join(c.dir, minioMetaBucket, "tmp"))
		removeAll(path.Join(c.dir, minioMetaBucket, "trash"))
		removeAll(path.Join(c.dir, minioMetaBucket, "buckets"))
		// just migrate cache format
		return migrateCacheFormatJSON(cacheFormatPath)
	}

	buckets, err := readDir(oldCacheBucketsPath)
	if err != nil {
		return err
	}

	for _, bucket := range buckets {
		var objMetaPaths []string
		root := path.Join(oldCacheBucketsPath, bucket)
		err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
			if strings.HasSuffix(path, cacheMetaJSONFile) {
				objMetaPaths = append(objMetaPaths, path)
			}
			return nil
		})
		if err != nil {
			return err
		}
		for _, oMeta := range objMetaPaths {
			objSlice := strings.SplitN(oMeta, cacheMetaJSONFile, 2)
			object := strings.TrimPrefix(objSlice[0], path.Join(oldCacheBucketsPath, bucket))
			object = strings.TrimSuffix(object, "/")

			destdir := getCacheSHADir(c.dir, bucket, object)
			if err := os.MkdirAll(destdir, 0777); err != nil {
				return err
			}
			prevCachedPath := path.Join(c.dir, bucket, object)
			// move cached object to new cache directory path
			// migrate cache data and add bit-rot protection hash sum
			// at the start of each block
			if err := migrateData(ctx, c, prevCachedPath, destdir); err != nil {
				continue
			}
			stat, err := os.Stat(prevCachedPath)
			if err != nil {
				if err == errFileNotFound {
					continue
				}
				logger.LogIf(ctx, err)
				return err
			}
			// old cached file can now be removed
			if err := os.Remove(prevCachedPath); err != nil {
				return err
			}

			// move cached metadata after changing cache metadata version
			oldMetaPath := pathJoin(oldCacheBucketsPath, bucket, object, cacheMetaJSONFile)
			metaPath := pathJoin(destdir, cacheMetaJSONFile)
			metaBytes, err := ioutil.ReadFile(oldMetaPath)
			if err != nil {
				return err
			}
			// marshal cache metadata after adding version and stat info
			meta := &cacheMeta{}
			if err = json.Unmarshal(metaBytes, &meta); err != nil {
				return err
			}
			meta.Checksum = CacheChecksumInfoV1{Algorithm: HighwayHash256S.String(), Blocksize: cacheBlkSize}
			meta.Version = cacheMetaVersion
			meta.Stat.Size = stat.Size()
			meta.Stat.ModTime = stat.ModTime()
			jsonData, err := json.Marshal(meta)
			if err != nil {
				return err
			}

			if err = ioutil.WriteFile(metaPath, jsonData, 0644); err != nil {
				return err
			}
		}

		// delete old bucket from cache, now that all contents are cleared
		removeAll(path.Join(c.dir, bucket))
	}

	// remove .minio.sys sub directories
	removeAll(path.Join(c.dir, minioMetaBucket, "multipart"))
	removeAll(path.Join(c.dir, minioMetaBucket, "tmp"))
	removeAll(path.Join(c.dir, minioMetaBucket, "trash"))
	removeAll(path.Join(c.dir, minioMetaBucket, "buckets"))

	return migrateCacheFormatJSON(cacheFormatPath)

}

func migrateCacheFormatJSON(cacheFormatPath string) error {
	// now migrate format.json
	f, err := os.OpenFile(cacheFormatPath, os.O_RDWR, 0)
	if err != nil {
		return err
	}
	defer f.Close()
	formatV1 := formatCacheV1{}
	if err := jsonLoad(f, &formatV1); err != nil {
		return err
	}

	formatV2 := &formatCacheV2{}
	formatV2.formatMetaV1 = formatV1.formatMetaV1
	formatV2.Version = formatMetaVersion1
	formatV2.Cache = formatV1.Cache
	formatV2.Cache.Version = formatCacheVersionV2
	if err := jsonSave(f, formatV2); err != nil {
		return err
	}
	return nil
}