// Copyright (c) 2017 Intel Corporation
//
// SPDX-License-Identifier: Apache-2.0
//

package utils

import (
	"crypto/rand"
	"fmt"
	"os"
	"os/exec"
)

const cpBinaryName = "cp"

const fileMode0755 = os.FileMode(0755)

// FileCopy copys files from srcPath to dstPath
func FileCopy(srcPath, dstPath string) error {
	if srcPath == "" {
		return fmt.Errorf("Source path cannot be empty")
	}

	if dstPath == "" {
		return fmt.Errorf("Destination path cannot be empty")
	}

	binPath, err := exec.LookPath(cpBinaryName)
	if err != nil {
		return err
	}

	cmd := exec.Command(binPath, srcPath, dstPath)

	return cmd.Run()
}

// GenerateRandomBytes generate n random bytes
func GenerateRandomBytes(n int) ([]byte, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)

	if err != nil {
		return nil, err
	}

	return b, nil
}

// ReverseString reverses whole string
func ReverseString(s string) string {
	r := []rune(s)

	length := len(r)
	for i, j := 0, length-1; i < length/2; i, j = i+1, j-1 {
		r[i], r[j] = r[j], r[i]
	}

	return string(r)
}

// CleanupFds closed bundles of open fds in batch
func CleanupFds(fds []*os.File, numFds int) {
	maxFds := len(fds)

	if numFds < maxFds {
		maxFds = numFds
	}

	for i := 0; i < maxFds; i++ {
		_ = fds[i].Close()
	}
}

// WriteToFile opens a file in write only mode and writes bytes to it
func WriteToFile(path string, data []byte) error {
	f, err := os.OpenFile(path, os.O_WRONLY, fileMode0755)
	if err != nil {
		return err
	}

	defer f.Close()

	if _, err := f.Write(data); err != nil {
		return err
	}

	return nil
}

// ConstraintsToVCPUs converts CPU quota and period to vCPUs
func ConstraintsToVCPUs(quota int64, period uint64) uint {
	if quota != 0 && period != 0 {
		// Use some math magic to round up to the nearest whole vCPU
		// (that is, a partial part of a quota request ends up assigning
		// a whole vCPU, for instance, a request of 1.5 'cpu quotas'
		// will give 2 vCPUs).
		// This also has the side effect that we will always allocate
		// at least 1 vCPU.
		return uint((uint64(quota) + (period - 1)) / period)
	}

	return 0
}

// GetVirtDriveName returns the disk name format for virtio-blk
// Reference: https://github.com/torvalds/linux/blob/master/drivers/block/virtio_blk.c @c0aa3e0916d7e531e69b02e426f7162dfb1c6c0
func GetVirtDriveName(index int) (string, error) {
	if index < 0 {
		return "", fmt.Errorf("Index cannot be negative for drive")
	}

	// Prefix used for virtio-block devices
	const prefix = "vd"

	//Refer to DISK_NAME_LEN: https://github.com/torvalds/linux/blob/08c521a2011ff492490aa9ed6cc574be4235ce2b/include/linux/genhd.h#L61
	diskNameLen := 32
	base := 26

	suffLen := diskNameLen - len(prefix)
	diskLetters := make([]byte, suffLen)

	var i int

	for i = 0; i < suffLen && index >= 0; i++ {
		letter := byte('a' + (index % base))
		diskLetters[i] = letter
		index = index/base - 1
	}

	if index >= 0 {
		return "", fmt.Errorf("Index not supported")
	}

	diskName := prefix + ReverseString(string(diskLetters[:i]))
	return diskName, nil
}

const maxSCSIDevices = 65535

// GetSCSIIdLun gets the SCSI id and lun, based on the index of the drive being inserted.
// qemu code suggests that scsi-id can take values from 0 to 255 inclusive, while lun can
// take values from 0 to 16383 inclusive. But lun values over 255 do not seem to follow
// consistent SCSI addressing. Hence we limit to 255.
func GetSCSIIdLun(index int) (int, int, error) {
	if index < 0 {
		return -1, -1, fmt.Errorf("Index cannot be negative")
	}

	if index > maxSCSIDevices {
		return -1, -1, fmt.Errorf("Index cannot be greater than %d, maximum of %d devices are supported", maxSCSIDevices, maxSCSIDevices)
	}

	return index / 256, index % 256, nil
}

// GetSCSIAddress gets scsiID and lun from index, and combined them into a scsi ID
func GetSCSIAddress(index int) (string, error) {
	scsiID, lun, err := GetSCSIIdLun(index)
	if err != nil {
		return "", err
	}

	return fmt.Sprintf("%d:%d", scsiID, lun), nil
}