// streamstore implements helpers to store large
// data streams in a repository
package streamstore

import (
	"bytes"
	"context"
	"encoding/json"
	"io"

	"github.com/pkg/errors"

	"github.com/alcionai/corso/src/internal/data"
	"github.com/alcionai/corso/src/internal/kopia"
	"github.com/alcionai/corso/src/internal/stats"
	"github.com/alcionai/corso/src/pkg/backup/details"
	"github.com/alcionai/corso/src/pkg/path"
)

type streamStore struct {
	kw      *kopia.Wrapper
	tenant  string
	service path.ServiceType
}

func New(
	kw *kopia.Wrapper,
	tenant string,
	service path.ServiceType,
) *streamStore {
	return &streamStore{kw: kw, tenant: tenant, service: service}
}

const (
	// detailsItemName is the name of the stream used to store
	// backup details
	detailsItemName = "details"
	// collectionPurposeDetails is used to indicate
	// what the collection is being used for
	collectionPurposeDetails = "details"
)

// WriteBackupDetails persists a `details.Details`
// object in the stream store
func (ss *streamStore) WriteBackupDetails(
	ctx context.Context,
	backupDetails *details.Details,
) (string, error) {
	// construct the path of the container for the `details` item
	p, err := path.Builder{}.
		ToStreamStorePath(
			ss.tenant,
			collectionPurposeDetails,
			ss.service,
			false,
		)
	if err != nil {
		return "", err
	}

	// TODO: We could use an io.Pipe here to avoid a double copy but that
	// makes error handling a bit complicated
	dbytes, err := json.Marshal(backupDetails)
	if err != nil {
		return "", errors.Wrap(err, "marshalling backup details")
	}

	dc := &streamCollection{
		folderPath: p,
		item: &streamItem{
			name: detailsItemName,
			data: dbytes,
		},
	}

	backupStats, _, err := ss.kw.BackupCollections(ctx, nil, []data.Collection{dc}, ss.service, nil)
	if err != nil {
		return "", nil
	}

	return backupStats.SnapshotID, nil
}

// ReadBackupDetails reads the specified details object
// from the kopia repository
func (ss *streamStore) ReadBackupDetails(
	ctx context.Context,
	detailsID string,
) (*details.Details, error) {
	// construct the path for the `details` item
	detailsPath, err := path.Builder{}.
		Append(detailsItemName).
		ToStreamStorePath(
			ss.tenant,
			collectionPurposeDetails,
			ss.service,
			true,
		)
	if err != nil {
		return nil, err
	}

	var bc stats.ByteCounter

	dcs, err := ss.kw.RestoreMultipleItems(ctx, detailsID, []path.Path{detailsPath}, &bc)
	if err != nil {
		return nil, errors.Wrap(err, "retrieving backup details data")
	}

	// Expect only 1 data collection
	if len(dcs) != 1 {
		return nil, errors.Errorf("expected 1 details data collection: %d", len(dcs))
	}

	dc := dcs[0]

	var d details.Details

	found := false
	items := dc.Items()

	for {
		select {
		case <-ctx.Done():
			return nil, errors.New("context cancelled waiting for backup details data")

		case itemData, ok := <-items:
			if !ok {
				if !found {
					return nil, errors.New("no backup details found")
				}

				return &d, nil
			}

			err := json.NewDecoder(itemData.ToReader()).Decode(&d)
			if err != nil {
				return nil, errors.Wrap(err, "failed to decode details data from repository")
			}

			found = true
		}
	}
}

// DeleteBackupDetails deletes the specified details object from the kopia repository
func (ss *streamStore) DeleteBackupDetails(
	ctx context.Context,
	detailsID string,
) error {
	err := ss.kw.DeleteSnapshot(ctx, detailsID)
	if err != nil {
		return errors.Wrap(err, "deleting backup details failed")
	}

	return nil
}

// streamCollection is a data.Collection used to persist
// a single data stream
type streamCollection struct {
	// folderPath indicates what level in the hierarchy this collection
	// represents
	folderPath path.Path
	item       *streamItem
}

func (dc *streamCollection) FullPath() path.Path {
	return dc.folderPath
}

func (dc *streamCollection) PreviousPath() path.Path {
	return nil
}

func (dc *streamCollection) State() data.CollectionState {
	return data.NewState
}

// Items() always returns a channel with a single data.Stream
// representing the object to be persisted
func (dc *streamCollection) Items() <-chan data.Stream {
	items := make(chan data.Stream, 1)
	defer close(items)
	items <- dc.item

	return items
}

type streamItem struct {
	name string
	data []byte
}

func (di *streamItem) UUID() string {
	return di.name
}

func (di *streamItem) ToReader() io.ReadCloser {
	return io.NopCloser(bytes.NewReader(di.data))
}

func (di *streamItem) Deleted() bool {
	return false
}