/*
 * 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 (
	"bytes"
	"crypto/sha256"
	"errors"
	"hash"
	"io"

	"github.com/minio/highwayhash"
	"github.com/minio/minio/cmd/logger"
	"golang.org/x/crypto/blake2b"
)

// magic HH-256 key as HH-256 hash of the first 100 decimals of π as utf-8 string with a zero key.
var magicHighwayHash256Key = []byte("\x4b\xe7\x34\xfa\x8e\x23\x8a\xcd\x26\x3e\x83\xe6\xbb\x96\x85\x52\x04\x0f\x93\x5d\xa3\x9f\x44\x14\x97\xe0\x9d\x13\x22\xde\x36\xa0")

var bitrotAlgorithms = map[BitrotAlgorithm]string{
	SHA256:          "sha256",
	BLAKE2b512:      "blake2b",
	HighwayHash256:  "highwayhash256",
	HighwayHash256S: "highwayhash256S",
}

// New returns a new hash.Hash calculating the given bitrot algorithm.
func (a BitrotAlgorithm) New() hash.Hash {
	switch a {
	case SHA256:
		return sha256.New()
	case BLAKE2b512:
		b2, _ := blake2b.New512(nil) // New512 never returns an error if the key is nil
		return b2
	case HighwayHash256:
		hh, _ := highwayhash.New(magicHighwayHash256Key) // New will never return error since key is 256 bit
		return hh
	case HighwayHash256S:
		hh, _ := highwayhash.New(magicHighwayHash256Key) // New will never return error since key is 256 bit
		return hh
	default:
		logger.CriticalIf(GlobalContext, errors.New("Unsupported bitrot algorithm"))
		return nil
	}
}

// Available reports whether the given algorithm is available.
func (a BitrotAlgorithm) Available() bool {
	_, ok := bitrotAlgorithms[a]
	return ok
}

// String returns the string identifier for a given bitrot algorithm.
// If the algorithm is not supported String panics.
func (a BitrotAlgorithm) String() string {
	name, ok := bitrotAlgorithms[a]
	if !ok {
		logger.CriticalIf(GlobalContext, errors.New("Unsupported bitrot algorithm"))
	}
	return name
}

// NewBitrotVerifier returns a new BitrotVerifier implementing the given algorithm.
func NewBitrotVerifier(algorithm BitrotAlgorithm, checksum []byte) *BitrotVerifier {
	return &BitrotVerifier{algorithm, checksum}
}

// BitrotVerifier can be used to verify protected data.
type BitrotVerifier struct {
	algorithm BitrotAlgorithm
	sum       []byte
}

// BitrotAlgorithmFromString returns a bitrot algorithm from the given string representation.
// It returns 0 if the string representation does not match any supported algorithm.
// The zero value of a bitrot algorithm is never supported.
func BitrotAlgorithmFromString(s string) (a BitrotAlgorithm) {
	for alg, name := range bitrotAlgorithms {
		if name == s {
			return alg
		}
	}
	return
}

func newBitrotWriter(disk StorageAPI, volume, filePath string, length int64, algo BitrotAlgorithm, shardSize int64, heal bool) io.Writer {
	if algo == HighwayHash256S {
		return newStreamingBitrotWriter(disk, volume, filePath, length, algo, shardSize, heal)
	}
	return newWholeBitrotWriter(disk, volume, filePath, algo, shardSize)
}

func newBitrotReader(disk StorageAPI, data []byte, bucket string, filePath string, tillOffset int64, algo BitrotAlgorithm, sum []byte, shardSize int64) io.ReaderAt {
	if algo == HighwayHash256S {
		return newStreamingBitrotReader(disk, data, bucket, filePath, tillOffset, algo, shardSize)
	}
	return newWholeBitrotReader(disk, bucket, filePath, algo, tillOffset, sum)
}

// Close all the readers.
func closeBitrotReaders(rs []io.ReaderAt) {
	for _, r := range rs {
		if br, ok := r.(io.Closer); ok {
			br.Close()
		}
	}
}

// Close all the writers.
func closeBitrotWriters(ws []io.Writer) {
	for _, w := range ws {
		if bw, ok := w.(io.Closer); ok {
			bw.Close()
		}
	}
}

// Returns hash sum for whole-bitrot, nil for streaming-bitrot.
func bitrotWriterSum(w io.Writer) []byte {
	if bw, ok := w.(*wholeBitrotWriter); ok {
		return bw.Sum(nil)
	}
	return nil
}

// Returns the size of the file with bitrot protection
func bitrotShardFileSize(size int64, shardSize int64, algo BitrotAlgorithm) int64 {
	if algo != HighwayHash256S {
		return size
	}
	return ceilFrac(size, shardSize)*int64(algo.New().Size()) + size
}

// bitrotVerify a single stream of data.
func bitrotVerify(r io.Reader, wantSize, partSize int64, algo BitrotAlgorithm, want []byte, shardSize int64) error {
	if algo != HighwayHash256S {
		h := algo.New()
		if n, err := io.Copy(h, r); err != nil || n != wantSize {
			// Premature failure in reading the object, file is corrupt.
			return errFileCorrupt
		}
		if !bytes.Equal(h.Sum(nil), want) {
			return errFileCorrupt
		}
		return nil
	}

	h := algo.New()
	hashBuf := make([]byte, h.Size())
	buf := make([]byte, shardSize)
	left := wantSize

	// Calculate the size of the bitrot file and compare
	// it with the actual file size.
	if left != bitrotShardFileSize(partSize, shardSize, algo) {
		return errFileCorrupt
	}

	for left > 0 {
		// Read expected hash...
		h.Reset()
		n, err := io.ReadFull(r, hashBuf)
		if err != nil {
			// Read's failed for object with right size, file is corrupt.
			return err
		}
		// Subtract hash length..
		left -= int64(n)
		if left < shardSize {
			shardSize = left
		}
		read, err := io.CopyBuffer(h, io.LimitReader(r, shardSize), buf)
		if err != nil {
			// Read's failed for object with right size, at different offsets.
			return err
		}
		left -= read
		if !bytes.Equal(h.Sum(nil), hashBuf) {
			return errFileCorrupt
		}
	}
	return nil
}