/*
 * 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 (
	"bytes"
	"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
}

// 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, outOffset int64, outSize int64) (int64, error) {
	// Do we have enough blocks?
	if len(enBlocks) < dataBlocks {
		return 0, reedsolomon.ErrTooFewShards
	}

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

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

	// Counter to increment total written.
	totalWritten := int64(0)

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

			// Reset the offset for next iteration to read everything
			// from subsequent blocks.
			outOffset = 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, err
			}
			totalWritten += n
			break
		}
		// Copy the block.
		n, err := io.Copy(dst, bytes.NewReader(block))
		if err != nil {
			return 0, err
		}

		// Decrement output size.
		write -= n

		// Increment written.
		totalWritten += n
	}

	// Success.
	return totalWritten, nil
}

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

// calculate the blockSize based on input length and total number of
// data blocks.
func getEncodedBlockLen(inputLen int64, dataBlocks int) (curEncBlockSize int64) {
	curEncBlockSize = (inputLen + int64(dataBlocks) - 1) / int64(dataBlocks)
	return curEncBlockSize
}