/*
 * Minio Cloud Storage, (C) 2015, 2016 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/hex"
	"fmt"
	"io"
	"math/rand"
	"path"
	"runtime"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"github.com/minio/minio/cmd/logger"
	"github.com/minio/minio/pkg/dns"
	"github.com/skyrings/skyring-common/tools/uuid"
)

const (
	// Minio meta bucket.
	minioMetaBucket = ".minio.sys"
	// Multipart meta prefix.
	mpartMetaPrefix = "multipart"
	// Minio Multipart meta prefix.
	minioMetaMultipartBucket = minioMetaBucket + "/" + mpartMetaPrefix
	// Minio Tmp meta prefix.
	minioMetaTmpBucket = minioMetaBucket + "/tmp"
	// DNS separator (period), used for bucket name validation.
	dnsDelimiter = "."
)

// isMinioBucket returns true if given bucket is a Minio internal
// bucket and false otherwise.
func isMinioMetaBucketName(bucket string) bool {
	return bucket == minioMetaBucket ||
		bucket == minioMetaMultipartBucket ||
		bucket == minioMetaTmpBucket
}

// IsValidBucketName verifies that a bucket name is in accordance with
// Amazon's requirements (i.e. DNS naming conventions). It must be 3-63
// characters long, and it must be a sequence of one or more labels
// separated by periods. Each label can contain lowercase ascii
// letters, decimal digits and hyphens, but must not begin or end with
// a hyphen. See:
// http://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html
func IsValidBucketName(bucket string) bool {
	// Special case when bucket is equal to one of the meta buckets.
	if isMinioMetaBucketName(bucket) {
		return true
	}
	if len(bucket) < 3 || len(bucket) > 63 {
		return false
	}

	// Split on dot and check each piece conforms to rules.
	allNumbers := true
	pieces := strings.Split(bucket, dnsDelimiter)
	for _, piece := range pieces {
		if len(piece) == 0 || piece[0] == '-' ||
			piece[len(piece)-1] == '-' {
			// Current piece has 0-length or starts or
			// ends with a hyphen.
			return false
		}
		// Now only need to check if each piece is a valid
		// 'label' in AWS terminology and if the bucket looks
		// like an IP address.
		isNotNumber := false
		for i := 0; i < len(piece); i++ {
			switch {
			case (piece[i] >= 'a' && piece[i] <= 'z' ||
				piece[i] == '-'):
				// Found a non-digit character, so
				// this piece is not a number.
				isNotNumber = true
			case piece[i] >= '0' && piece[i] <= '9':
				// Nothing to do.
			default:
				// Found invalid character.
				return false
			}
		}
		allNumbers = allNumbers && !isNotNumber
	}
	// Does the bucket name look like an IP address?
	return !(len(pieces) == 4 && allNumbers)
}

// IsValidObjectName verifies an object name in accordance with Amazon's
// requirements. It cannot exceed 1024 characters and must be a valid UTF8
// string.
//
// See:
// http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadata.html
//
// You should avoid the following characters in a key name because of
// significant special handling for consistency across all
// applications.
//
// Rejects strings with following characters.
//
// - Backslash ("\")
//
// additionally minio does not support object names with trailing "/".
func IsValidObjectName(object string) bool {
	if len(object) == 0 {
		return false
	}
	if hasSuffix(object, slashSeparator) || hasPrefix(object, slashSeparator) {
		return false
	}
	return IsValidObjectPrefix(object)
}

// IsValidObjectPrefix verifies whether the prefix is a valid object name.
// Its valid to have a empty prefix.
func IsValidObjectPrefix(object string) bool {
	if hasBadPathComponent(object) {
		return false
	}
	if len(object) > 1024 {
		return false
	}
	if !utf8.ValidString(object) {
		return false
	}
	// Reject unsupported characters in object name.
	if strings.ContainsAny(object, "\\") {
		return false
	}
	return true
}

// Slash separator.
const slashSeparator = "/"

// retainSlash - retains slash from a path.
func retainSlash(s string) string {
	return strings.TrimSuffix(s, slashSeparator) + slashSeparator
}

// pathJoin - like path.Join() but retains trailing "/" of the last element
func pathJoin(elem ...string) string {
	trailingSlash := ""
	if len(elem) > 0 {
		if hasSuffix(elem[len(elem)-1], slashSeparator) {
			trailingSlash = "/"
		}
	}
	return path.Join(elem...) + trailingSlash
}

// mustGetUUID - get a random UUID.
func mustGetUUID() string {
	uuid, err := uuid.New()
	if err != nil {
		logger.CriticalIf(context.Background(), err)
	}

	return uuid.String()
}

// Create an s3 compatible MD5sum for complete multipart transaction.
func getCompleteMultipartMD5(ctx context.Context, parts []CompletePart) (string, error) {
	var finalMD5Bytes []byte
	for _, part := range parts {
		md5Bytes, err := hex.DecodeString(part.ETag)
		if err != nil {
			logger.LogIf(ctx, err)
			return "", err
		}
		finalMD5Bytes = append(finalMD5Bytes, md5Bytes...)
	}
	s3MD5 := fmt.Sprintf("%s-%d", getMD5Hash(finalMD5Bytes), len(parts))
	return s3MD5, nil
}

// Clean unwanted fields from metadata
func cleanMetadata(metadata map[string]string) map[string]string {
	// Remove STANDARD StorageClass
	metadata = removeStandardStorageClass(metadata)
	// Clean meta etag keys 'md5Sum', 'etag'.
	return cleanMetadataKeys(metadata, "md5Sum", "etag")
}

// Filter X-Amz-Storage-Class field only if it is set to STANDARD.
// This is done since AWS S3 doesn't return STANDARD Storage class as response header.
func removeStandardStorageClass(metadata map[string]string) map[string]string {
	if metadata[amzStorageClass] == standardStorageClass {
		delete(metadata, amzStorageClass)
	}
	return metadata
}

// cleanMetadataKeys takes keyNames to be filtered
// and returns a new map with all the entries with keyNames removed.
func cleanMetadataKeys(metadata map[string]string, keyNames ...string) map[string]string {
	var newMeta = make(map[string]string)
	for k, v := range metadata {
		if contains(keyNames, k) {
			continue
		}
		newMeta[k] = v
	}
	return newMeta
}

// Extracts etag value from the metadata.
func extractETag(metadata map[string]string) string {
	// md5Sum tag is kept for backward compatibility.
	etag, ok := metadata["md5Sum"]
	if !ok {
		etag = metadata["etag"]
	}
	// Success.
	return etag
}

// Prefix matcher string matches prefix in a platform specific way.
// For example on windows since its case insensitive we are supposed
// to do case insensitive checks.
func hasPrefix(s string, prefix string) bool {
	if runtime.GOOS == globalWindowsOSName {
		return strings.HasPrefix(strings.ToLower(s), strings.ToLower(prefix))
	}
	return strings.HasPrefix(s, prefix)
}

// Suffix matcher string matches suffix in a platform specific way.
// For example on windows since its case insensitive we are supposed
// to do case insensitive checks.
func hasSuffix(s string, suffix string) bool {
	if runtime.GOOS == globalWindowsOSName {
		return strings.HasSuffix(strings.ToLower(s), strings.ToLower(suffix))
	}
	return strings.HasSuffix(s, suffix)
}

// Validates if two strings are equal.
func isStringEqual(s1 string, s2 string) bool {
	if runtime.GOOS == globalWindowsOSName {
		return strings.EqualFold(s1, s2)
	}
	return s1 == s2
}

// Ignores all reserved bucket names or invalid bucket names.
func isReservedOrInvalidBucket(bucketEntry string) bool {
	bucketEntry = strings.TrimSuffix(bucketEntry, slashSeparator)
	if !IsValidBucketName(bucketEntry) {
		return true
	}
	return isMinioMetaBucket(bucketEntry) || isMinioReservedBucket(bucketEntry)
}

// Returns true if input bucket is a reserved minio meta bucket '.minio.sys'.
func isMinioMetaBucket(bucketName string) bool {
	return bucketName == minioMetaBucket
}

// Returns true if input bucket is a reserved minio bucket 'minio'.
func isMinioReservedBucket(bucketName string) bool {
	return bucketName == minioReservedBucket
}

// returns a slice of hosts by reading a slice of DNS records
func getHostsSlice(records []dns.SrvRecord) []string {
	var hosts []string
	for _, r := range records {
		hosts = append(hosts, r.Host)
	}
	return hosts
}

// returns a random host (and corresponding port) from a slice of DNS records
func getRandomHostPort(records []dns.SrvRecord) (string, int) {
	rand.Seed(time.Now().Unix())
	srvRecord := records[rand.Intn(len(records))]
	return srvRecord.Host, srvRecord.Port
}

// byBucketName is a collection satisfying sort.Interface.
type byBucketName []BucketInfo

func (d byBucketName) Len() int           { return len(d) }
func (d byBucketName) Swap(i, j int)      { d[i], d[j] = d[j], d[i] }
func (d byBucketName) Less(i, j int) bool { return d[i].Name < d[j].Name }

// GetObjectReader is a type that wraps a reader with a lock to
// provide a ReadCloser interface that unlocks on Close()
type GetObjectReader struct {
	lock RWLocker
	pr   io.Reader

	// register any clean up actions (happens before unlocking)
	cleanUp func()

	once sync.Once
}

// NewGetObjectReader creates a new GetObjectReader. The cleanUp
// action is called on Close() before the lock is unlocked.
func NewGetObjectReader(reader io.Reader, lock RWLocker, cleanUp func()) io.ReadCloser {
	return &GetObjectReader{
		lock:    lock,
		pr:      reader,
		cleanUp: cleanUp,
	}
}

// Close - calls the cleanup action if provided, and *then* unlocks
// the object. Calling Close multiple times is safe.
func (g *GetObjectReader) Close() error {
	// sync.Once is used here to ensure that Close() is
	// idempotent.
	g.once.Do(func() {
		// Unlocking is defer-red - this ensures that
		// unlocking happens even if cleanUp panics.
		defer func() {
			if g.lock != nil {
				g.lock.RUnlock()
			}
		}()
		if g.cleanUp != nil {
			g.cleanUp()
		}
	})
	return nil
}

// Read - to implement Reader interface.
func (g *GetObjectReader) Read(p []byte) (n int, err error) {
	n, err = g.pr.Read(p)
	if err != nil {
		// Calling code may not Close() in case of error, so
		// we ensure it.
		g.Close()
	}
	return
}