func createFilesystemDetails(
	st storageAccess, f state.Filesystem, attachments []state.FilesystemAttachment,
) (*params.FilesystemDetails, error) {

	details := &params.FilesystemDetails{
		FilesystemTag: f.FilesystemTag().String(),
	}

	if volumeTag, err := f.Volume(); err == nil {
		details.VolumeTag = volumeTag.String()
	}

	if info, err := f.Info(); err == nil {
		details.Info = storagecommon.FilesystemInfoFromState(info)
	}

	if len(attachments) > 0 {
		details.MachineAttachments = make(map[string]params.FilesystemAttachmentInfo, len(attachments))
		for _, attachment := range attachments {
			stateInfo, err := attachment.Info()
			var info params.FilesystemAttachmentInfo
			if err == nil {
				info = storagecommon.FilesystemAttachmentInfoFromState(stateInfo)
			}
			details.MachineAttachments[attachment.Machine().String()] = info
		}
	}

	status, err := f.Status()
	if err != nil {
		return nil, errors.Trace(err)
	}
	details.Status = common.EntityStatusFromState(status)

	if storageTag, err := f.Storage(); err == nil {
		storageInstance, err := st.StorageInstance(storageTag)
		if err != nil {
			return nil, errors.Trace(err)
		}
		storageDetails, err := createStorageDetails(st, storageInstance)
		if err != nil {
			return nil, errors.Trace(err)
		}
		details.Storage = storageDetails
	}

	return details, nil
}

// FilesystemParams returns the parameters for creating or destroying the
// given filesystem.
func FilesystemParams(
	f state.Filesystem,
	storageInstance state.StorageInstance,
	modelUUID, controllerUUID string,
	environConfig *config.Config,
	poolManager poolmanager.PoolManager,
	registry storage.ProviderRegistry,
) (params.FilesystemParams, error) {

	var pool string
	var size uint64
	if stateFilesystemParams, ok := f.Params(); ok {
		pool = stateFilesystemParams.Pool
		size = stateFilesystemParams.Size
	} else {
		filesystemInfo, err := f.Info()
		if err != nil {
			return params.FilesystemParams{}, errors.Trace(err)
		}
		pool = filesystemInfo.Pool
		size = filesystemInfo.Size
	}

	filesystemTags, err := storageTags(storageInstance, modelUUID, controllerUUID, environConfig)
	if err != nil {
		return params.FilesystemParams{}, errors.Annotate(err, "computing storage tags")
	}

	providerType, cfg, err := StoragePoolConfig(pool, poolManager, registry)
	if err != nil {
		return params.FilesystemParams{}, errors.Trace(err)
	}
	result := params.FilesystemParams{
		f.Tag().String(),
		"", // volume tag
		size,
		string(providerType),
		cfg.Attrs(),
		filesystemTags,
		nil, // attachment params set by the caller
	}

	volumeTag, err := f.Volume()
	if err == nil {
		result.VolumeTag = volumeTag.String()
	} else if err != state.ErrNoBackingVolume {
		return params.FilesystemParams{}, errors.Trace(err)
	}

	return result, nil
}

// FilesystemFromState converts a state.Filesystem to params.Filesystem.
func FilesystemFromState(f state.Filesystem) (params.Filesystem, error) {
	info, err := f.Info()
	if err != nil {
		return params.Filesystem{}, errors.Trace(err)
	}
	result := params.Filesystem{
		f.FilesystemTag().String(),
		"",
		FilesystemInfoFromState(info),
	}
	volumeTag, err := f.Volume()
	if err == nil {
		result.VolumeTag = volumeTag.String()
	} else if err != state.ErrNoBackingVolume {
		return params.Filesystem{}, errors.Trace(err)
	}
	return result, nil
}