/*
 * Minio Cloud Storage, (C) 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 (
	"bytes"
	"errors"
	"hash"
	"io"
	"sync"

	"github.com/klauspost/reedsolomon"
	"github.com/minio/sha256-simd"
	"golang.org/x/crypto/blake2b"
)

// newHashWriters - inititialize a slice of hashes for the disk count.
func newHashWriters(diskCount int, algo HashAlgo) []hash.Hash {
	hashWriters := make([]hash.Hash, diskCount)
	for index := range hashWriters {
		hashWriters[index] = newHash(algo)
	}
	return hashWriters
}

// newHash - gives you a newly allocated hash depending on the input algorithm.
func newHash(algo HashAlgo) (h hash.Hash) {
	switch algo {
	case HashSha256:
		// sha256 checksum specially on ARM64 platforms or whenever
		// requested as dictated by `xl.json` entry.
		h = sha256.New()
	case HashBlake2b:
		// ignore the error, because New512 without a key never fails
		// New512 only returns a non-nil error, if the length of the passed
		// key > 64 bytes - but we use blake2b as hash function (no key)
		h, _ = blake2b.New512(nil)
	// Add new hashes here.
	default:
		// Default to blake2b.
		// ignore the error, because New512 without a key never fails
		// New512 only returns a non-nil error, if the length of the passed
		// key > 64 bytes - but we use blake2b as hash function (no key)
		h, _ = blake2b.New512(nil)
	}
	return h
}

// Hash buffer pool is a pool of reusable
// buffers used while checksumming a stream.
var hashBufferPool = sync.Pool{
	New: func() interface{} {
		b := make([]byte, readSizeV1)
		return &b
	},
}

// hashSum calculates the hash of the entire path and returns.
func hashSum(disk StorageAPI, volume, path string, writer hash.Hash) ([]byte, error) {
	// Fetch a new staging buffer from the pool.
	bufp := hashBufferPool.Get().(*[]byte)
	defer hashBufferPool.Put(bufp)

	// Copy entire buffer to writer.
	if err := copyBuffer(writer, disk, volume, path, *bufp); err != nil {
		return nil, err
	}

	// Return the final hash sum.
	return writer.Sum(nil), nil
}

// getDataBlockLen - get length of data blocks from encoded blocks.
func getDataBlockLen(enBlocks [][]byte, dataBlocks int) int {
	size := 0
	// Figure out the data block length.
	for _, block := range enBlocks[:dataBlocks] {
		size += len(block)
	}
	return size
}

// Writes all the data blocks from encoded blocks until requested
// outSize length. Provides a way to skip bytes until the offset.
func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, offset int64, length int64) (int64, error) {
	// Offset and out size cannot be negative.
	if offset < 0 || length < 0 {
		return 0, traceError(errUnexpected)
	}

	// Do we have enough blocks?
	if len(enBlocks) < dataBlocks {
		return 0, traceError(reedsolomon.ErrTooFewShards)
	}

	// Do we have enough data?
	if int64(getDataBlockLen(enBlocks, dataBlocks)) < length {
		return 0, traceError(reedsolomon.ErrShortData)
	}

	// Counter to decrement total left to write.
	write := length

	// Counter to increment total written.
	var totalWritten int64

	// Write all data blocks to dst.
	for _, block := range enBlocks[:dataBlocks] {
		// Skip blocks until we have reached our offset.
		if offset >= int64(len(block)) {
			// Decrement offset.
			offset -= int64(len(block))
			continue
		} else {
			// Skip until offset.
			block = block[offset:]

			// Reset the offset for next iteration to read everything
			// from subsequent blocks.
			offset = 0
		}
		// We have written all the blocks, write the last remaining block.
		if write < int64(len(block)) {
			n, err := io.Copy(dst, bytes.NewReader(block[:write]))
			if err != nil {
				return 0, traceError(err)
			}
			totalWritten += n
			break
		}
		// Copy the block.
		n, err := io.Copy(dst, bytes.NewReader(block))
		if err != nil {
			return 0, traceError(err)
		}

		// Decrement output size.
		write -= n

		// Increment written.
		totalWritten += n
	}

	// Success.
	return totalWritten, nil
}

// chunkSize is roughly BlockSize/DataBlocks.
// chunkSize is calculated such that chunkSize*DataBlocks accommodates BlockSize bytes.
// So chunkSize*DataBlocks can be slightly larger than BlockSize if BlockSize is not divisible by
// DataBlocks. The extra space will have 0-padding.
func getChunkSize(blockSize int64, dataBlocks int) int64 {
	return (blockSize + int64(dataBlocks) - 1) / int64(dataBlocks)
}

// copyBuffer - copies from disk, volume, path to input writer until either EOF
// is reached at volume, path or an error occurs. A success copyBuffer returns
// err == nil, not err == EOF. Because copyBuffer is defined to read from path
// until EOF. It does not treat an EOF from ReadFile an error to be reported.
// Additionally copyBuffer stages through the provided buffer; otherwise if it
// has zero length, returns error.
func copyBuffer(writer io.Writer, disk StorageAPI, volume string, path string, buf []byte) error {
	// Error condition of zero length buffer.
	if buf != nil && len(buf) == 0 {
		return errors.New("empty buffer in readBuffer")
	}

	// Starting offset for Reading the file.
	var startOffset int64

	// Read until io.EOF.
	for {
		n, err := disk.ReadFile(volume, path, startOffset, buf)
		if n > 0 {
			m, wErr := writer.Write(buf[:n])
			if wErr != nil {
				return wErr
			}
			if int64(m) != n {
				return io.ErrShortWrite
			}
		}
		if err != nil {
			if err == io.EOF || err == io.ErrUnexpectedEOF {
				break
			}
			return err
		}
		// Progress the offset.
		startOffset += n
	}

	// Success.
	return nil
}

// bitRotVerifier - type representing bit-rot verification process for
// a single under-lying object (currently whole files)
type bitRotVerifier struct {
	// has the bit-rot verification been done?
	isVerified bool
	// is the data free of bit-rot?
	hasBitRot bool
	// hashing algorithm
	algo HashAlgo
	// hex-encoded expected raw-hash value
	checkSum string
}
