/*
Copyright (c) 2015-2017 VMware, Inc. All Rights Reserved.

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 object

import (
	"context"
	"errors"
	"fmt"
	"net"
	"path"

	"github.com/vmware/govmomi/nfc"
	"github.com/vmware/govmomi/property"
	"github.com/vmware/govmomi/vim25"
	"github.com/vmware/govmomi/vim25/methods"
	"github.com/vmware/govmomi/vim25/mo"
	"github.com/vmware/govmomi/vim25/types"
)

const (
	PropRuntimePowerState = "summary.runtime.powerState"
	PropConfigTemplate    = "summary.config.template"
)

type VirtualMachine struct {
	Common
}

func NewVirtualMachine(c *vim25.Client, ref types.ManagedObjectReference) *VirtualMachine {
	return &VirtualMachine{
		Common: NewCommon(c, ref),
	}
}

func (v VirtualMachine) PowerState(ctx context.Context) (types.VirtualMachinePowerState, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{PropRuntimePowerState}, &o)
	if err != nil {
		return "", err
	}

	return o.Summary.Runtime.PowerState, nil
}

func (v VirtualMachine) IsTemplate(ctx context.Context) (bool, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{PropConfigTemplate}, &o)
	if err != nil {
		return false, err
	}

	return o.Summary.Config.Template, nil
}

func (v VirtualMachine) PowerOn(ctx context.Context) (*Task, error) {
	req := types.PowerOnVM_Task{
		This: v.Reference(),
	}

	res, err := methods.PowerOnVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) PowerOff(ctx context.Context) (*Task, error) {
	req := types.PowerOffVM_Task{
		This: v.Reference(),
	}

	res, err := methods.PowerOffVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) PutUsbScanCodes(ctx context.Context, spec types.UsbScanCodeSpec) (int32, error) {
	req := types.PutUsbScanCodes{
		This: v.Reference(),
		Spec: spec,
	}

	res, err := methods.PutUsbScanCodes(ctx, v.c, &req)
	if err != nil {
		return 0, err
	}

	return res.Returnval, nil
}

func (v VirtualMachine) Reset(ctx context.Context) (*Task, error) {
	req := types.ResetVM_Task{
		This: v.Reference(),
	}

	res, err := methods.ResetVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Suspend(ctx context.Context) (*Task, error) {
	req := types.SuspendVM_Task{
		This: v.Reference(),
	}

	res, err := methods.SuspendVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) ShutdownGuest(ctx context.Context) error {
	req := types.ShutdownGuest{
		This: v.Reference(),
	}

	_, err := methods.ShutdownGuest(ctx, v.c, &req)
	return err
}

func (v VirtualMachine) RebootGuest(ctx context.Context) error {
	req := types.RebootGuest{
		This: v.Reference(),
	}

	_, err := methods.RebootGuest(ctx, v.c, &req)
	return err
}

func (v VirtualMachine) Destroy(ctx context.Context) (*Task, error) {
	req := types.Destroy_Task{
		This: v.Reference(),
	}

	res, err := methods.Destroy_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Clone(ctx context.Context, folder *Folder, name string, config types.VirtualMachineCloneSpec) (*Task, error) {
	req := types.CloneVM_Task{
		This:   v.Reference(),
		Folder: folder.Reference(),
		Name:   name,
		Spec:   config,
	}

	res, err := methods.CloneVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Customize(ctx context.Context, spec types.CustomizationSpec) (*Task, error) {
	req := types.CustomizeVM_Task{
		This: v.Reference(),
		Spec: spec,
	}

	res, err := methods.CustomizeVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Relocate(ctx context.Context, config types.VirtualMachineRelocateSpec, priority types.VirtualMachineMovePriority) (*Task, error) {
	req := types.RelocateVM_Task{
		This:     v.Reference(),
		Spec:     config,
		Priority: priority,
	}

	res, err := methods.RelocateVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Reconfigure(ctx context.Context, config types.VirtualMachineConfigSpec) (*Task, error) {
	req := types.ReconfigVM_Task{
		This: v.Reference(),
		Spec: config,
	}

	res, err := methods.ReconfigVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) RefreshStorageInfo(ctx context.Context) error {
	req := types.RefreshStorageInfo{
		This: v.Reference(),
	}

	_, err := methods.RefreshStorageInfo(ctx, v.c, &req)
	return err
}

// WaitForIP waits for the VM guest.ipAddress property to report an IP address.
// Waits for an IPv4 address if the v4 param is true.
func (v VirtualMachine) WaitForIP(ctx context.Context, v4 ...bool) (string, error) {
	var ip string

	p := property.DefaultCollector(v.c)
	err := property.Wait(ctx, p, v.Reference(), []string{"guest.ipAddress"}, func(pc []types.PropertyChange) bool {
		for _, c := range pc {
			if c.Name != "guest.ipAddress" {
				continue
			}
			if c.Op != types.PropertyChangeOpAssign {
				continue
			}
			if c.Val == nil {
				continue
			}

			ip = c.Val.(string)
			if len(v4) == 1 && v4[0] {
				if net.ParseIP(ip).To4() == nil {
					return false
				}
			}
			return true
		}

		return false
	})

	if err != nil {
		return "", err
	}

	return ip, nil
}

// WaitForNetIP waits for the VM guest.net property to report an IP address for all VM NICs.
// Only consider IPv4 addresses if the v4 param is true.
// By default, wait for all NICs to get an IP address, unless 1 or more device is given.
// A device can be specified by the MAC address or the device name, e.g. "ethernet-0".
// Returns a map with MAC address as the key and IP address list as the value.
func (v VirtualMachine) WaitForNetIP(ctx context.Context, v4 bool, device ...string) (map[string][]string, error) {
	macs := make(map[string][]string)
	eths := make(map[string]string)

	p := property.DefaultCollector(v.c)

	// Wait for all NICs to have a MacAddress, which may not be generated yet.
	err := property.Wait(ctx, p, v.Reference(), []string{"config.hardware.device"}, func(pc []types.PropertyChange) bool {
		for _, c := range pc {
			if c.Op != types.PropertyChangeOpAssign {
				continue
			}

			devices := VirtualDeviceList(c.Val.(types.ArrayOfVirtualDevice).VirtualDevice)
			for _, d := range devices {
				if nic, ok := d.(types.BaseVirtualEthernetCard); ok {
					mac := nic.GetVirtualEthernetCard().MacAddress
					if mac == "" {
						return false
					}
					macs[mac] = nil
					eths[devices.Name(d)] = mac
				}
			}
		}

		return true
	})

	if err != nil {
		return nil, err
	}

	if len(device) != 0 {
		// Only wait for specific NIC(s)
		macs = make(map[string][]string)
		for _, mac := range device {
			if eth, ok := eths[mac]; ok {
				mac = eth // device name, e.g. "ethernet-0"
			}
			macs[mac] = nil
		}
	}

	err = property.Wait(ctx, p, v.Reference(), []string{"guest.net"}, func(pc []types.PropertyChange) bool {
		for _, c := range pc {
			if c.Op != types.PropertyChangeOpAssign {
				continue
			}

			nics := c.Val.(types.ArrayOfGuestNicInfo).GuestNicInfo
			for _, nic := range nics {
				mac := nic.MacAddress
				if mac == "" || nic.IpConfig == nil {
					continue
				}

				for _, ip := range nic.IpConfig.IpAddress {
					if _, ok := macs[mac]; !ok {
						continue // Ignore any that don't correspond to a VM device
					}
					if v4 && net.ParseIP(ip.IpAddress).To4() == nil {
						continue // Ignore non IPv4 address
					}
					macs[mac] = append(macs[mac], ip.IpAddress)
				}
			}
		}

		for _, ips := range macs {
			if len(ips) == 0 {
				return false
			}
		}

		return true
	})

	if err != nil {
		return nil, err
	}

	return macs, nil
}

// Device returns the VirtualMachine's config.hardware.device property.
func (v VirtualMachine) Device(ctx context.Context) (VirtualDeviceList, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"config.hardware.device", "summary.runtime.connectionState"}, &o)
	if err != nil {
		return nil, err
	}

	// Quoting the SDK doc:
	//   The virtual machine configuration is not guaranteed to be available.
	//   For example, the configuration information would be unavailable if the server
	//   is unable to access the virtual machine files on disk, and is often also unavailable
	//   during the initial phases of virtual machine creation.
	if o.Config == nil {
		return nil, fmt.Errorf("%s Config is not available, connectionState=%s",
			v.Reference(), o.Summary.Runtime.ConnectionState)
	}

	return VirtualDeviceList(o.Config.Hardware.Device), nil
}

func (v VirtualMachine) HostSystem(ctx context.Context) (*HostSystem, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"summary.runtime.host"}, &o)
	if err != nil {
		return nil, err
	}

	host := o.Summary.Runtime.Host
	if host == nil {
		return nil, errors.New("VM doesn't have a HostSystem")
	}

	return NewHostSystem(v.c, *host), nil
}

func (v VirtualMachine) ResourcePool(ctx context.Context) (*ResourcePool, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"resourcePool"}, &o)
	if err != nil {
		return nil, err
	}

	rp := o.ResourcePool
	if rp == nil {
		return nil, errors.New("VM doesn't have a resourcePool")
	}

	return NewResourcePool(v.c, *rp), nil
}

func (v VirtualMachine) configureDevice(ctx context.Context, op types.VirtualDeviceConfigSpecOperation, fop types.VirtualDeviceConfigSpecFileOperation, devices ...types.BaseVirtualDevice) error {
	spec := types.VirtualMachineConfigSpec{}

	for _, device := range devices {
		config := &types.VirtualDeviceConfigSpec{
			Device:    device,
			Operation: op,
		}

		if disk, ok := device.(*types.VirtualDisk); ok {
			config.FileOperation = fop

			// Special case to attach an existing disk
			if op == types.VirtualDeviceConfigSpecOperationAdd && disk.CapacityInKB == 0 {
				childDisk := false
				if b, ok := disk.Backing.(*types.VirtualDiskFlatVer2BackingInfo); ok {
					childDisk = b.Parent != nil
				}

				if !childDisk {
					config.FileOperation = "" // existing disk
				}
			}
		}

		spec.DeviceChange = append(spec.DeviceChange, config)
	}

	task, err := v.Reconfigure(ctx, spec)
	if err != nil {
		return err
	}

	return task.Wait(ctx)
}

// AddDevice adds the given devices to the VirtualMachine
func (v VirtualMachine) AddDevice(ctx context.Context, device ...types.BaseVirtualDevice) error {
	return v.configureDevice(ctx, types.VirtualDeviceConfigSpecOperationAdd, types.VirtualDeviceConfigSpecFileOperationCreate, device...)
}

// EditDevice edits the given (existing) devices on the VirtualMachine
func (v VirtualMachine) EditDevice(ctx context.Context, device ...types.BaseVirtualDevice) error {
	return v.configureDevice(ctx, types.VirtualDeviceConfigSpecOperationEdit, types.VirtualDeviceConfigSpecFileOperationReplace, device...)
}

// RemoveDevice removes the given devices on the VirtualMachine
func (v VirtualMachine) RemoveDevice(ctx context.Context, keepFiles bool, device ...types.BaseVirtualDevice) error {
	fop := types.VirtualDeviceConfigSpecFileOperationDestroy
	if keepFiles {
		fop = ""
	}
	return v.configureDevice(ctx, types.VirtualDeviceConfigSpecOperationRemove, fop, device...)
}

// BootOptions returns the VirtualMachine's config.bootOptions property.
func (v VirtualMachine) BootOptions(ctx context.Context) (*types.VirtualMachineBootOptions, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"config.bootOptions"}, &o)
	if err != nil {
		return nil, err
	}

	return o.Config.BootOptions, nil
}

// SetBootOptions reconfigures the VirtualMachine with the given options.
func (v VirtualMachine) SetBootOptions(ctx context.Context, options *types.VirtualMachineBootOptions) error {
	spec := types.VirtualMachineConfigSpec{}

	spec.BootOptions = options

	task, err := v.Reconfigure(ctx, spec)
	if err != nil {
		return err
	}

	return task.Wait(ctx)
}

// Answer answers a pending question.
func (v VirtualMachine) Answer(ctx context.Context, id, answer string) error {
	req := types.AnswerVM{
		This:         v.Reference(),
		QuestionId:   id,
		AnswerChoice: answer,
	}

	_, err := methods.AnswerVM(ctx, v.c, &req)
	if err != nil {
		return err
	}

	return nil
}

func (v VirtualMachine) AcquireTicket(ctx context.Context, kind string) (*types.VirtualMachineTicket, error) {
	req := types.AcquireTicket{
		This:       v.Reference(),
		TicketType: kind,
	}

	res, err := methods.AcquireTicket(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return &res.Returnval, nil
}

// CreateSnapshot creates a new snapshot of a virtual machine.
func (v VirtualMachine) CreateSnapshot(ctx context.Context, name string, description string, memory bool, quiesce bool) (*Task, error) {
	req := types.CreateSnapshot_Task{
		This:        v.Reference(),
		Name:        name,
		Description: description,
		Memory:      memory,
		Quiesce:     quiesce,
	}

	res, err := methods.CreateSnapshot_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

// RemoveAllSnapshot removes all snapshots of a virtual machine
func (v VirtualMachine) RemoveAllSnapshot(ctx context.Context, consolidate *bool) (*Task, error) {
	req := types.RemoveAllSnapshots_Task{
		This:        v.Reference(),
		Consolidate: consolidate,
	}

	res, err := methods.RemoveAllSnapshots_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

type snapshotMap map[string][]types.ManagedObjectReference

func (m snapshotMap) add(parent string, tree []types.VirtualMachineSnapshotTree) {
	for i, st := range tree {
		sname := st.Name
		names := []string{sname, st.Snapshot.Value}

		if parent != "" {
			sname = path.Join(parent, sname)
			// Add full path as an option to resolve duplicate names
			names = append(names, sname)
		}

		for _, name := range names {
			m[name] = append(m[name], tree[i].Snapshot)
		}

		m.add(sname, st.ChildSnapshotList)
	}
}

// FindSnapshot supports snapshot lookup by name, where name can be:
// 1) snapshot ManagedObjectReference.Value (unique)
// 2) snapshot name (may not be unique)
// 3) snapshot tree path (may not be unique)
func (v VirtualMachine) FindSnapshot(ctx context.Context, name string) (*types.ManagedObjectReference, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"snapshot"}, &o)
	if err != nil {
		return nil, err
	}

	if o.Snapshot == nil || len(o.Snapshot.RootSnapshotList) == 0 {
		return nil, errors.New("no snapshots for this VM")
	}

	m := make(snapshotMap)
	m.add("", o.Snapshot.RootSnapshotList)

	s := m[name]
	switch len(s) {
	case 0:
		return nil, fmt.Errorf("snapshot %q not found", name)
	case 1:
		return &s[0], nil
	default:
		return nil, fmt.Errorf("%q resolves to %d snapshots", name, len(s))
	}
}

// RemoveSnapshot removes a named snapshot
func (v VirtualMachine) RemoveSnapshot(ctx context.Context, name string, removeChildren bool, consolidate *bool) (*Task, error) {
	snapshot, err := v.FindSnapshot(ctx, name)
	if err != nil {
		return nil, err
	}

	req := types.RemoveSnapshot_Task{
		This:           snapshot.Reference(),
		RemoveChildren: removeChildren,
		Consolidate:    consolidate,
	}

	res, err := methods.RemoveSnapshot_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

// RevertToCurrentSnapshot reverts to the current snapshot
func (v VirtualMachine) RevertToCurrentSnapshot(ctx context.Context, suppressPowerOn bool) (*Task, error) {
	req := types.RevertToCurrentSnapshot_Task{
		This:            v.Reference(),
		SuppressPowerOn: types.NewBool(suppressPowerOn),
	}

	res, err := methods.RevertToCurrentSnapshot_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

// RevertToSnapshot reverts to a named snapshot
func (v VirtualMachine) RevertToSnapshot(ctx context.Context, name string, suppressPowerOn bool) (*Task, error) {
	snapshot, err := v.FindSnapshot(ctx, name)
	if err != nil {
		return nil, err
	}

	req := types.RevertToSnapshot_Task{
		This:            snapshot.Reference(),
		SuppressPowerOn: types.NewBool(suppressPowerOn),
	}

	res, err := methods.RevertToSnapshot_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

// IsToolsRunning returns true if VMware Tools is currently running in the guest OS, and false otherwise.
func (v VirtualMachine) IsToolsRunning(ctx context.Context) (bool, error) {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"guest.toolsRunningStatus"}, &o)
	if err != nil {
		return false, err
	}

	return o.Guest.ToolsRunningStatus == string(types.VirtualMachineToolsRunningStatusGuestToolsRunning), nil
}

// Wait for the VirtualMachine to change to the desired power state.
func (v VirtualMachine) WaitForPowerState(ctx context.Context, state types.VirtualMachinePowerState) error {
	p := property.DefaultCollector(v.c)
	err := property.Wait(ctx, p, v.Reference(), []string{PropRuntimePowerState}, func(pc []types.PropertyChange) bool {
		for _, c := range pc {
			if c.Name != PropRuntimePowerState {
				continue
			}
			if c.Val == nil {
				continue
			}

			ps := c.Val.(types.VirtualMachinePowerState)
			if ps == state {
				return true
			}
		}
		return false
	})

	return err
}

func (v VirtualMachine) MarkAsTemplate(ctx context.Context) error {
	req := types.MarkAsTemplate{
		This: v.Reference(),
	}

	_, err := methods.MarkAsTemplate(ctx, v.c, &req)
	if err != nil {
		return err
	}

	return nil
}

func (v VirtualMachine) MarkAsVirtualMachine(ctx context.Context, pool ResourcePool, host *HostSystem) error {
	req := types.MarkAsVirtualMachine{
		This: v.Reference(),
		Pool: pool.Reference(),
	}

	if host != nil {
		ref := host.Reference()
		req.Host = &ref
	}

	_, err := methods.MarkAsVirtualMachine(ctx, v.c, &req)
	if err != nil {
		return err
	}

	return nil
}

func (v VirtualMachine) Migrate(ctx context.Context, pool *ResourcePool, host *HostSystem, priority types.VirtualMachineMovePriority, state types.VirtualMachinePowerState) (*Task, error) {
	req := types.MigrateVM_Task{
		This:     v.Reference(),
		Priority: priority,
		State:    state,
	}

	if pool != nil {
		ref := pool.Reference()
		req.Pool = &ref
	}

	if host != nil {
		ref := host.Reference()
		req.Host = &ref
	}

	res, err := methods.MigrateVM_Task(ctx, v.c, &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Unregister(ctx context.Context) error {
	req := types.UnregisterVM{
		This: v.Reference(),
	}

	_, err := methods.UnregisterVM(ctx, v.Client(), &req)
	return err
}

// QueryEnvironmentBrowser is a helper to get the environmentBrowser property.
func (v VirtualMachine) QueryConfigTarget(ctx context.Context) (*types.ConfigTarget, error) {
	var vm mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"environmentBrowser"}, &vm)
	if err != nil {
		return nil, err
	}

	req := types.QueryConfigTarget{
		This: vm.EnvironmentBrowser,
	}

	res, err := methods.QueryConfigTarget(ctx, v.Client(), &req)
	if err != nil {
		return nil, err
	}

	return res.Returnval, nil
}

func (v VirtualMachine) MountToolsInstaller(ctx context.Context) error {
	req := types.MountToolsInstaller{
		This: v.Reference(),
	}

	_, err := methods.MountToolsInstaller(ctx, v.Client(), &req)
	return err
}

func (v VirtualMachine) UnmountToolsInstaller(ctx context.Context) error {
	req := types.UnmountToolsInstaller{
		This: v.Reference(),
	}

	_, err := methods.UnmountToolsInstaller(ctx, v.Client(), &req)
	return err
}

func (v VirtualMachine) UpgradeTools(ctx context.Context, options string) (*Task, error) {
	req := types.UpgradeTools_Task{
		This:             v.Reference(),
		InstallerOptions: options,
	}

	res, err := methods.UpgradeTools_Task(ctx, v.Client(), &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

func (v VirtualMachine) Export(ctx context.Context) (*nfc.Lease, error) {
	req := types.ExportVm{
		This: v.Reference(),
	}

	res, err := methods.ExportVm(ctx, v.Client(), &req)
	if err != nil {
		return nil, err
	}

	return nfc.NewLease(v.c, res.Returnval), nil
}

func (v VirtualMachine) UpgradeVM(ctx context.Context, version string) (*Task, error) {
	req := types.UpgradeVM_Task{
		This:    v.Reference(),
		Version: version,
	}

	res, err := methods.UpgradeVM_Task(ctx, v.Client(), &req)
	if err != nil {
		return nil, err
	}

	return NewTask(v.c, res.Returnval), nil
}

// UUID is a helper to get the UUID of the VirtualMachine managed object.
// This method returns an empty string if an error occurs when retrieving UUID from the VirtualMachine object.
func (v VirtualMachine) UUID(ctx context.Context) string {
	var o mo.VirtualMachine

	err := v.Properties(ctx, v.Reference(), []string{"config.uuid"}, &o)
	if err != nil {
		return ""
	}

	return o.Config.Uuid
}

func (v VirtualMachine) QueryChangedDiskAreas(ctx context.Context, baseSnapshot, curSnapshot *types.ManagedObjectReference, disk *types.VirtualDisk, offset int64) (types.DiskChangeInfo, error) {
	var noChange types.DiskChangeInfo
	var err error

	if offset > disk.CapacityInBytes {
		return noChange, fmt.Errorf("offset is greater than the disk size (%#x and %#x)", offset, disk.CapacityInBytes)
	} else if offset == disk.CapacityInBytes {
		return types.DiskChangeInfo{StartOffset: offset, Length: 0}, nil
	}

	var b mo.VirtualMachineSnapshot
	err = v.Properties(ctx, baseSnapshot.Reference(), []string{"config.hardware"}, &b)
	if err != nil {
		return noChange, fmt.Errorf("failed to fetch config.hardware of snapshot %s: %s", baseSnapshot, err)
	}

	var changeId *string
	for _, vd := range b.Config.Hardware.Device {
		d := vd.GetVirtualDevice()
		if d.Key != disk.Key {
			continue
		}

		// As per VDDK programming guide, these are the four types of disks
		// that support CBT, see "Gathering Changed Block Information".
		if b, ok := d.Backing.(*types.VirtualDiskFlatVer2BackingInfo); ok {
			changeId = &b.ChangeId
			break
		}
		if b, ok := d.Backing.(*types.VirtualDiskSparseVer2BackingInfo); ok {
			changeId = &b.ChangeId
			break
		}
		if b, ok := d.Backing.(*types.VirtualDiskRawDiskMappingVer1BackingInfo); ok {
			changeId = &b.ChangeId
			break
		}
		if b, ok := d.Backing.(*types.VirtualDiskRawDiskVer2BackingInfo); ok {
			changeId = &b.ChangeId
			break
		}

		return noChange, fmt.Errorf("disk %d has backing info without .ChangeId: %t", disk.Key, d.Backing)
	}
	if changeId == nil || *changeId == "" {
		return noChange, fmt.Errorf("CBT is not enabled on disk %d", disk.Key)
	}

	req := types.QueryChangedDiskAreas{
		This:        v.Reference(),
		Snapshot:    curSnapshot,
		DeviceKey:   disk.Key,
		StartOffset: offset,
		ChangeId:    *changeId,
	}

	res, err := methods.QueryChangedDiskAreas(ctx, v.Client(), &req)
	if err != nil {
		return noChange, err
	}

	return res.Returnval, nil
}