/*
 * 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 main

import (
	"crypto/sha512"
	"hash"
	"io"

	"github.com/klauspost/reedsolomon"
)

// newHashWriters - inititialize a slice of hashes for the disk count.
func newHashWriters(diskCount int) []hash.Hash {
	hashWriters := make([]hash.Hash, diskCount)
	for index := range hashWriters {
		hashWriters[index] = newHash("sha512")
	}
	return hashWriters
}

// newHash - gives you a newly allocated hash depending on the input algorithm.
func newHash(algo string) hash.Hash {
	switch algo {
	case "sha512":
		return sha512.New()
	// Add new hashes here.
	default:
		return sha512.New()
	}
}

func hashSum(disk StorageAPI, volume, path string, writer hash.Hash) ([]byte, error) {
	startOffset := int64(0)
	// Read until io.EOF.
	for {
		buf := make([]byte, blockSizeV1)
		n, err := disk.ReadFile(volume, path, startOffset, buf)
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, err
		}
		writer.Write(buf[:n])
		startOffset += n
	}
	return writer.Sum(nil), nil
}

// getDataBlocks - fetches the data block only part of the input encoded blocks.
func getDataBlocks(enBlocks [][]byte, dataBlocks int, curBlockSize int) (data []byte, err error) {
	if len(enBlocks) < dataBlocks {
		return nil, reedsolomon.ErrTooFewShards
	}
	size := 0
	blocks := enBlocks[:dataBlocks]
	for _, block := range blocks {
		size += len(block)
	}
	if size < curBlockSize {
		return nil, reedsolomon.ErrShortData
	}

	write := curBlockSize
	for _, block := range blocks {
		if write < len(block) {
			data = append(data, block[:write]...)
			return data, nil
		}
		data = append(data, block...)
		write -= len(block)
	}
	return data, nil
}

// getBlockInfo - find start/end block and bytes to skip for given offset, length and block size.
func getBlockInfo(offset, length, blockSize int64) (startBlock, bytesToSkip, endBlock int64) {
	// Calculate start block for given offset and how many bytes to skip to get the offset.
	startBlock = offset / blockSize
	bytesToSkip = offset % blockSize

	// Calculate end block for given size to read
	endBlock = (offset + length) / blockSize
	if endBlock > 0 && (offset+length)%blockSize == 0 {
		endBlock--
	}

	return
}