oko-server/server/server.go

package server

import (
	"archive/zip"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"sync/atomic"
	"time"

	"cernobor.cz/oko-server/errs"
	"cernobor.cz/oko-server/models"
	mbsh "github.com/consbio/mbtileserver/handlers"
	"github.com/coreos/go-semver/semver"
	geojson "github.com/paulmach/go.geojson"
	"github.com/sirupsen/logrus"
	"zombiezen.com/go/sqlite"
	"zombiezen.com/go/sqlite/sqlitemigration"
	"zombiezen.com/go/sqlite/sqlitex"
)

type Server struct {
	config           ServerConfig
	dbpool           *sqlitemigration.Pool
	dbAvailable      atomic.Bool
	checkpointNotice chan struct{}
	log              *logrus.Logger
	ctx              context.Context
	tileserverSvSet  *mbsh.ServiceSet
	mapPackSize      int64
}

type ServerConfig struct {
	VersionHash   string
	BuildTime     *time.Time
	Port          int
	DbPath        string
	TilepackPath  string
	MinZoom       int
	DefaultCenter models.Coords
	MaxPhotoX     int
	MaxPhotoY     int
	PhotoQuality  int
	Debug         bool
}

func New(config ServerConfig) *Server {
	return &Server{
		config: config,
	}
}

func (s *Server) Run(ctx context.Context) {
	s.log = logrus.New()
	if s.config.Debug {
		s.log.SetLevel(logrus.DebugLevel)
	}

	s.dbAvailable.Store(false)

	s.ctx = ctx
	err := s.setupDB()
	if err != nil {
		panic(err)
	}
	defer s.cleanupDb()

	s.setupTiles()

	router := s.setupRouter()

	server := &http.Server{
		Addr:    fmt.Sprintf(":%d", s.config.Port),
		Handler: router,
	}
	s.log.Infof("Running on %s", server.Addr)
	go func() {
		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			s.log.Infof("listen: %s\n", err)
		}
	}()

	<-s.ctx.Done()
	s.log.Info("Shutting down server...")
	defer s.log.Info("Server exitting.")

	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
	defer cancel()
	if err := server.Shutdown(ctx); err != nil {
		s.log.WithError(err).Fatal("Server forced to shutdown.")
	}
}

func (s *Server) setupTiles() {
	tsRootURL, err := url.Parse(URITileserverRoot)
	if err != nil {
		s.log.WithError(err).Fatal("Failed to parse tileserver root URL.")
	}
	svs, err := mbsh.New(&mbsh.ServiceSetConfig{
		EnableServiceList: true,
		EnableTileJSON:    true,
		EnablePreview:     false,
		EnableArcGIS:      false,
		RootURL:           tsRootURL,
	})
	if err != nil {
		s.log.WithError(err).Fatal("Failed to create tileserver service set.")
	}
	err = svs.AddTileset(s.config.TilepackPath, "map")
	if err != nil {
		s.log.WithError(err).Fatal("Failed to register tileset.")
	}
	s.tileserverSvSet = svs

	info, err := os.Stat(s.config.TilepackPath)
	if err != nil {
		s.log.WithError(err).Fatal("Failed to get info about tile pack file.")
	}
	s.mapPackSize = info.Size()
}

func (s *Server) getLatestVersion(v *semver.Version) (*models.AppVersionInfo, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	var latest *models.AppVersionInfo
	versions, err := s.getAppVersions()
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve app versions from db: %w", err)
	}

	for _, ver := range versions {
		if (v == nil || v.LessThan(ver.Version)) && (latest == nil || latest.Version.LessThan(ver.Version)) {
			latest = ver
		}
	}

	return latest, nil
}

func (s *Server) getAppVersions() ([]*models.AppVersionInfo, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	versions := []*models.AppVersionInfo{}
	err := sqlitex.Execute(conn, "select version, address from app_versions", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			verStr := stmt.ColumnText(0)
			addr := stmt.ColumnText(1)

			ver, err := semver.NewVersion(verStr)
			if err != nil {
				return fmt.Errorf("failed to parse version: %w", err)
			}

			versions = append(versions, &models.AppVersionInfo{
				Version: *ver,
				Address: addr,
			})
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to insert/retrieve user from db: %w", err)
	}

	return versions, nil
}

func (s *Server) putAppVersion(versionInfo *models.AppVersionInfo) error {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	err := sqlitex.Execute(conn, "insert into app_versions(version, address) values(?, ?) on conflict(version) do update set address = excluded.address", &sqlitex.ExecOptions{
		Args: []interface{}{versionInfo.Version.String(), versionInfo.Address},
	})
	if err != nil {
		return fmt.Errorf("failed to insert app version into db: %w", err)
	}

	return nil
}

func (s *Server) getAppVersion(version string) (*models.AppVersionInfo, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	var v *models.AppVersionInfo
	err := sqlitex.Execute(conn, "select version, address from app_versions where version = ?", &sqlitex.ExecOptions{
		Args: []interface{}{version},
		ResultFunc: func(stmt *sqlite.Stmt) error {
			verStr := stmt.ColumnText(0)
			ver, err := semver.NewVersion(verStr)
			if err != nil {
				return fmt.Errorf("failed to parse version string %s from db: %w", verStr, err)
			}
			addr := stmt.ColumnText(1)
			v = &models.AppVersionInfo{
				Version: *ver,
				Address: addr,
			}
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve app version %s from db: %w", version, err)
	}

	return v, nil
}

func (s *Server) deleteAppVersion(version string) (bool, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	err := sqlitex.Execute(conn, "delete from app_versions where version = ?", &sqlitex.ExecOptions{
		Args: []interface{}{version},
	})
	if err != nil {
		return false, fmt.Errorf("failed to delete app version %s from db: %w", version, err)
	}
	n := conn.Changes()

	return n > 0, nil
}

func (s *Server) handshake(hc models.HandshakeChallenge) (models.UserID, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	userID, err := func() (uid int64, err error) {
		defer sqlitex.Save(conn)(&err)

		var id *int64
		if hc.Exists {
			err = sqlitex.Execute(conn, "select id from users where name = ?", &sqlitex.ExecOptions{
				Args: []interface{}{hc.Name},
				ResultFunc: func(stmt *sqlite.Stmt) error {
					id = ptr(stmt.ColumnInt64(0))
					return nil
				},
			})
			if sqlite.ErrCode(err) != sqlite.ResultOK {
				return 0, err
			}
			if id == nil {
				return 0, errs.ErrUserNotExists
			}
			if *id == 0 {
				return 0, errs.ErrAttemptedSystemUser
			}
		} else {
			err = sqlitex.Execute(conn, "insert into users(name) values(?)", &sqlitex.ExecOptions{
				Args: []interface{}{hc.Name},
				ResultFunc: func(stmt *sqlite.Stmt) error {
					id = ptr(stmt.ColumnInt64(0))
					return nil
				},
			})
			if sqlite.ErrCode(err) == sqlite.ResultConstraintUnique {
				return 0, errs.ErrUserAlreadyExists
			}
			if sqlite.ErrCode(err) != sqlite.ResultOK {
				return 0, err
			}
			id = ptr(conn.LastInsertRowID())
			s.requestCheckpoint()
		}
		return *id, nil
	}()

	if err != nil {
		return 0, fmt.Errorf("failed to insert/retrieve user from db: %w", err)
	}
	return models.UserID(userID), nil
}

func (s *Server) getData(conn *sqlite.Conn) (data models.Data, err error) {
	err = s.deleteExpiredFeatures(conn)
	if err != nil {
		return models.Data{}, fmt.Errorf("failed to delete expired featured: %w", err)
	}
	people, err := s.getPeople(conn)
	if err != nil {
		return models.Data{}, fmt.Errorf("failed to retreive people: %w", err)
	}
	features, err := s.getFeatures(conn)
	if err != nil {
		return models.Data{}, fmt.Errorf("failed to retreive features: %w", err)
	}

	return models.Data{
		Users:    people,
		Features: features,
	}, nil
}

func (s *Server) getDataOnly() (data models.Data, err error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)
	defer sqlitex.Save(conn)(&err)

	data, err = s.getData(conn)
	if err != nil {
		return models.Data{}, fmt.Errorf("failed to get json data: %w", err)
	}
	return data, err
}

func (s *Server) getDataWithPhotos() (file *os.File, err error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	defer sqlitex.Save(conn)(&err)

	makePhotoFilename := func(id models.FeaturePhotoID) string {
		return fmt.Sprintf("img%d", id)
	}
	makeThumbnailFilename := func(id models.FeaturePhotoID) string {
		return fmt.Sprintf("thumb_%s", makePhotoFilename(id))
	}

	data, err := s.getData(conn)
	if err != nil {
		return nil, fmt.Errorf("failed to get json data: %w", err)
	}

	data.PhotoMetadata = make(map[string]models.PhotoMetadata, 100)
	err = sqlitex.Execute(conn, "select id, content_type, length(contents) from feature_photos", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			id := models.FeaturePhotoID(stmt.ColumnInt64(0))
			contentType := stmt.ColumnText(1)
			fileSize := stmt.ColumnInt64(2)
			data.PhotoMetadata[makePhotoFilename(id)] = models.PhotoMetadata{
				ContentType:       contentType,
				Size:              fileSize,
				ID:                id,
				ThumbnailFilename: makeThumbnailFilename(id),
			}
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to collect photo metadata: %w", err)
	}

	dataBytes, err := json.MarshalIndent(&data, "", "  ")
	if err != nil {
		return nil, fmt.Errorf("failed to marshal json data: %w", err)
	}

	f, err := os.CreateTemp("", "")
	if err != nil {
		return nil, fmt.Errorf("failed to create temporary file: %w", err)
	}

	zw := zip.NewWriter(f)
	defer zw.Close()
	w, err := zw.Create("data.json")
	if err != nil {
		return nil, fmt.Errorf("failed to create data zip entry: %w", err)
	}
	_, err = w.Write(dataBytes)
	if err != nil {
		return nil, fmt.Errorf("failed to write data zip entry: %w", err)
	}

	err = sqlitex.Execute(conn, "select id from feature_photos fp where exists (select 1 from features f where f.id = fp.feature_id)", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			id := stmt.ColumnInt64(0)

			blob, err := conn.OpenBlob("", "feature_photos", "thumbnail_contents", id, false)
			if err != nil {
				return fmt.Errorf("failed to open photo ID %d thumbnail content blob: %w", id, err)
			}
			err = func() error {
				defer blob.Close()
				w, err := zw.Create(makeThumbnailFilename(models.FeaturePhotoID(id)))
				if err != nil {
					return fmt.Errorf("failed to create zip entry: %w", err)
				}
				_, err = io.Copy(w, blob)
				if err != nil {
					return fmt.Errorf("failed to write zip entry: %w", err)
				}
				return nil
			}()
			if err != nil {
				return fmt.Errorf("failed to write photo ID %d thumbnail: %w", id, err)
			}

			blob, err = conn.OpenBlob("", "feature_photos", "contents", id, false)
			if err != nil {
				return fmt.Errorf("failed to open photo ID %d photo content blob: %w", id, err)
			}
			err = func() error {
				defer blob.Close()
				w, err := zw.Create(makePhotoFilename(models.FeaturePhotoID(id)))
				if err != nil {
					return fmt.Errorf("failed to create zip entry: %w", err)
				}
				_, err = io.Copy(w, blob)
				if err != nil {
					return fmt.Errorf("failed to write zip entry: %w", err)
				}
				return nil
			}()
			if err != nil {
				return fmt.Errorf("failed to write photo ID %d photo: %w", id, err)
			}

			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to collect photo files: %w", err)
	}

	return f, nil
}

func (s *Server) update(data models.Update, photos map[string]models.Photo) error {
	s.log.Debugf("Updating data: %d created, %d created photos, %d updated, %d deleted, %d deleted photos, %d photo files, %d proposals", len(data.Create), len(data.CreatedPhotos), len(data.Update), len(data.Delete), len(data.DeletePhotos), len(photos), len(data.Proposals))
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	return func() (err error) {
		defer sqlitex.Transaction(conn)(&err)

		var createdIDMapping map[models.FeatureID]models.FeatureID
		if data.Create != nil {
			createdIDMapping, err = s.addFeatures(conn, data.Create)
			if err != nil {
				err = fmt.Errorf("failed to add features: %w", err)
				return
			}
		}
		if data.CreatedPhotos != nil || data.AddPhotos != nil {
			if photos == nil {
				err = fmt.Errorf("photo assignment present but no photos provided")
				return
			}
			err = s.addPhotos(conn, data.CreatedPhotos, data.AddPhotos, createdIDMapping, photos)
			if err != nil {
				err = fmt.Errorf("failed to add photos: %w", err)
				return
			}
		}
		if data.Update != nil {
			err = s.updateFeatures(conn, data.Update)
			if err != nil {
				err = fmt.Errorf("failed to update features: %w", err)
				return
			}
		}
		if data.Delete != nil {
			err = s.deleteFeatures(conn, data.Delete)
			if err != nil {
				err = fmt.Errorf("failed to delete features: %w", err)
				return
			}
		}
		if data.DeletePhotos != nil {
			err = s.deletePhotos(conn, data.DeletePhotos)
			if err != nil {
				err = fmt.Errorf("failed to delete photos: %w", err)
				return
			}
		}
		if data.Proposals != nil {
			err = s.addProposals(conn, data.Proposals)
			if err != nil {
				err = fmt.Errorf("failed to add proposals: %w", err)
				return
			}
		}

		return nil
	}()
}

func (s *Server) deleteExpiredFeatures(conn *sqlite.Conn) error {
	now := time.Now().Unix()
	err := sqlitex.Execute(conn, "delete from features where deadline < ?", &sqlitex.ExecOptions{
		Args: []interface{}{now},
	})
	if err != nil {
		return fmt.Errorf("failed to delete expired features: %w", err)
	}
	s.requestCheckpoint()
	return nil
}

func (s *Server) getPeople(conn *sqlite.Conn) ([]models.User, error) {
	if conn == nil {
		conn = s.getDbConn()
		defer s.returnDbConn(conn)
	}

	users := make([]models.User, 0, 50)
	err := sqlitex.Execute(conn, "select id, name from users", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			users = append(users, models.User{
				ID:   models.UserID(stmt.ColumnInt(0)),
				Name: stmt.ColumnText(1),
			})
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to get users from db: %w", err)
	}
	return users, nil
}

func (s *Server) getFeatures(conn *sqlite.Conn) ([]models.Feature, error) {
	if conn == nil {
		conn = s.getDbConn()
		defer s.dbpool.Put(conn)
	}

	features := make([]models.Feature, 0, 100)
	err := sqlitex.Execute(conn, `select f.id, f.owner_id, f.name, f.deadline, f.properties, f.geom, '[' || coalesce(group_concat(p.id, ', '), '') || ']'
		from features f
		left join feature_photos p on f.id = p.feature_id
		group by f.id, f.owner_id, f.name, f.properties, f.geom`, &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {

			id := stmt.ColumnInt64(0)

			ownerID := stmt.ColumnInt64(1)

			name := stmt.ColumnText(2)

			var deadline *time.Time
			if stmt.ColumnType(3) != sqlite.TypeNull {
				dl := time.Unix(stmt.ColumnInt64(3), 0)
				deadline = &dl
			}

			propertiesRaw := stmt.ColumnText(4)
			var properties map[string]interface{}
			err := json.Unmarshal([]byte(propertiesRaw), &properties)
			if err != nil {
				return fmt.Errorf("failed to parse properties for feature id=%d: %w", id, err)
			}

			geomRaw := stmt.ColumnText(5)
			var geom geojson.Geometry
			err = json.Unmarshal([]byte(geomRaw), &geom)
			if err != nil {
				return fmt.Errorf("failed to parse geometry for feature id=%d: %w", id, err)
			}

			photosRaw := stmt.ColumnText(6)
			var photos []models.FeaturePhotoID
			err = json.Unmarshal([]byte(photosRaw), &photos)
			if err != nil {
				return fmt.Errorf("failed to parse list of photo IDs: %w", err)
			}

			feature := models.Feature{
				ID:         models.FeatureID(id),
				OwnerID:    models.UserID(ownerID),
				Name:       name,
				Deadline:   deadline,
				Properties: properties,
				Geometry:   geom,
				PhotoIDs:   photos,
			}

			features = append(features, feature)
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to get users from db: %w", err)
	}
	return features, nil
}

func (s *Server) addFeatures(conn *sqlite.Conn, features []models.Feature) (map[models.FeatureID]models.FeatureID, error) {
	stmt, err := conn.Prepare("insert into features(owner_id, name, deadline, properties, geom) values(?, ?, ?, ?, ?)")
	if err != nil {
		return nil, fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	localIDMapping := make(map[models.FeatureID]models.FeatureID, len(features))
	for _, feature := range features {
		if _, ok := localIDMapping[feature.ID]; ok {
			return nil, errs.ErrNonUniqueCreatedFeatureIDs
		}
		err := stmt.Reset()
		if err != nil {
			return nil, fmt.Errorf("failed to reset prepared statement: %w", err)
		}
		err = stmt.ClearBindings()
		if err != nil {
			return nil, fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
		}

		stmt.BindInt64(1, int64(feature.OwnerID))

		stmt.BindText(2, feature.Name)

		if feature.Deadline == nil {
			stmt.BindNull(3)
		} else {
			stmt.BindInt64(3, feature.Deadline.Unix())
		}

		if feature.Properties == nil {
			stmt.BindText(4, "{}")
		} else {
			propertiesBytes, err := json.Marshal(feature.Properties)
			if err != nil {
				return nil, fmt.Errorf("failed to marshal properties of feature id=%d: %w", feature.ID, err)
			}
			stmt.BindText(4, string(propertiesBytes))
		}

		geomBytes, err := json.Marshal(feature.Geometry)
		if err != nil {
			return nil, fmt.Errorf("failed to marshal geometry of feature id=%d: %w", feature.ID, err)
		}
		stmt.BindText(5, string(geomBytes))

		_, err = stmt.Step()
		if err != nil {
			return nil, fmt.Errorf("failed to evaluate prepared statement: %w", err)
		}

		localIDMapping[feature.ID] = models.FeatureID(conn.LastInsertRowID())
	}
	s.requestCheckpoint()
	return localIDMapping, nil
}

func (s *Server) addPhotos(conn *sqlite.Conn, createdFeatureMapping, addedFeatureMapping map[models.FeatureID][]string, createdIDMapping map[models.FeatureID]models.FeatureID, photos map[string]models.Photo) error {
	stmt, err := conn.Prepare("insert into feature_photos(feature_id, thumbnail_content_type, content_type, thumbnail_contents, contents) values(?, ?, ?, ?, ?)")
	if err != nil {
		return fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	uploadPhotos := func(featureID models.FeatureID, photoNames []string) error {
		for _, photoName := range photoNames {
			photo, ok := photos[photoName]
			if !ok {
				return errs.NewErrPhotoNotProvided(photoName)
			}
			thumbnail, ok := photos[fmt.Sprintf("thumb_%s", photoName)]
			if !ok {
				return errs.NewErrPhotoThumbnailNotProvided(photoName)
			}
			if !checkImageContentType(photo.ContentType) {
				return errs.NewErrUnsupportedContentType(photoName)
			}

			err := stmt.Reset()
			if err != nil {
				return fmt.Errorf("failed to reset prepared statement: %w", err)
			}
			err = stmt.ClearBindings()
			if err != nil {
				return fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
			}

			resizedPhoto, err := func() ([]byte, error) {
				defer photo.File.Close()

				resized, err := resizePhoto(s.config.MaxPhotoX, s.config.MaxPhotoY, s.config.PhotoQuality, photo.File)
				if err != nil {
					return nil, err
				}

				return resized, nil
			}()

			stmt.BindInt64(1, int64(featureID))
			stmt.BindText(2, thumbnail.ContentType)
			stmt.BindText(3, "image/jpeg")
			stmt.BindZeroBlob(4, thumbnail.Size)
			stmt.BindZeroBlob(5, int64(len(resizedPhoto)))

			_, err = stmt.Step()
			if err != nil {
				return fmt.Errorf("failed to evaluate prepared statement: %w", err)
			}

			blob, err := conn.OpenBlob("", "feature_photos", "thumbnail_contents", conn.LastInsertRowID(), true)
			if err != nil {
				return fmt.Errorf("failed to open thumbnail content blob: %w", err)
			}
			err = func() error {
				defer blob.Close()
				defer thumbnail.File.Close()

				_, err := io.Copy(blob, thumbnail.File)
				return err
			}()
			if err != nil {
				return fmt.Errorf("failed to write to thumbnail content blob: %w", err)
			}

			blob, err = conn.OpenBlob("", "feature_photos", "contents", conn.LastInsertRowID(), true)
			if err != nil {
				return fmt.Errorf("failed to open photo content blob: %w", err)
			}
			err = func() error {
				defer blob.Close()

				_, err = io.Copy(blob, bytes.NewBuffer(resizedPhoto))
				return err
			}()
			if err != nil {
				return fmt.Errorf("failed to write to photo content blob: %w", err)
			}
		}
		return nil
	}

	changed := false
	defer func() {
		if changed {
			s.requestCheckpoint()
		}
	}()
	for localFeatureID, photoNames := range createdFeatureMapping {
		featureID, ok := createdIDMapping[localFeatureID]
		if !ok {
			return errs.NewErrFeatureForPhotoNotExists(int64(localFeatureID))
		}
		err = uploadPhotos(featureID, photoNames)
		changed = true
		if err != nil {
			return fmt.Errorf("failed to upload photos for created features: %w", err)
		}
	}
	for featureID, photoNames := range addedFeatureMapping {
		err = uploadPhotos(featureID, photoNames)
		changed = true
		if err != nil {
			return fmt.Errorf("failed to upload photos for existing features: %w", err)
		}
	}
	return nil
}

func (s *Server) updateFeatures(conn *sqlite.Conn, features []models.Feature) error {
	stmt, err := conn.Prepare("update features set owner_id = ?, name = ?, deadline = ?, properties = ?, geom = ? where id = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	for _, feature := range features {
		err := stmt.Reset()
		if err != nil {
			return fmt.Errorf("failed to reset prepared statement: %w", err)
		}
		err = stmt.ClearBindings()
		if err != nil {
			return fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
		}

		stmt.BindInt64(1, int64(feature.OwnerID))

		stmt.BindText(2, feature.Name)

		if feature.Deadline == nil {
			stmt.BindNull(3)
		} else {
			stmt.BindInt64(3, feature.Deadline.Unix())
		}

		if feature.Properties == nil {
			stmt.BindText(4, "{}")
		} else {
			propertiesBytes, err := json.Marshal(feature.Properties)
			if err != nil {
				return fmt.Errorf("failed to marshal properties of feature id=%d: %w", feature.ID, err)
			}
			stmt.BindText(4, string(propertiesBytes))
		}

		geomBytes, err := json.Marshal(feature.Geometry)
		if err != nil {
			return fmt.Errorf("failed to marshal geometry of feature ID %d: %w", feature.ID, err)
		}
		stmt.BindText(5, string(geomBytes))

		stmt.BindInt64(6, int64(feature.ID))

		_, err = stmt.Step()
		if err != nil {
			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
		}
	}
	s.requestCheckpoint()
	return nil
}

func (s *Server) deleteFeatures(conn *sqlite.Conn, featureIDs []models.FeatureID) error {
	stmt, err := conn.Prepare("delete from features where id = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	for _, featureID := range featureIDs {
		err := stmt.Reset()
		if err != nil {
			return fmt.Errorf("failed to reset prepared statement: %w", err)
		}
		err = stmt.ClearBindings()
		if err != nil {
			return fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
		}

		stmt.BindInt64(1, int64(featureID))

		_, err = stmt.Step()
		if err != nil {
			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
		}
	}
	s.requestCheckpoint()
	return nil
}

func (s *Server) deletePhotos(conn *sqlite.Conn, photoIDs []models.FeaturePhotoID) error {
	stmt, err := conn.Prepare("delete from feature_photos where id = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	for _, photoID := range photoIDs {
		err := stmt.Reset()
		if err != nil {
			return fmt.Errorf("failed to reset prepared statement: %w", err)
		}
		err = stmt.ClearBindings()
		if err != nil {
			return fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
		}

		stmt.BindInt64(1, int64(photoID))

		_, err = stmt.Step()
		if err != nil {
			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
		}
	}
	s.requestCheckpoint()
	return nil
}

func (s *Server) getPhoto(featureID models.FeatureID, photoID models.FeaturePhotoID) ([]byte, string, error) {
	conn := s.getDbConn()
	defer s.dbpool.Put(conn)

	var contentType *string = nil
	var data []byte = nil
	found := false
	err := sqlitex.Execute(conn, "select content_type, contents from feature_photos where id = ? and feature_id = ?", &sqlitex.ExecOptions{
		Args: []interface{}{photoID, featureID},
		ResultFunc: func(stmt *sqlite.Stmt) error {
			if found {
				return fmt.Errorf("multiple photos returned for feature id %d, photo id %d", featureID, photoID)
			}
			contentType = ptr(stmt.ColumnText(0))
			data = make([]byte, stmt.ColumnLen(1))
			stmt.ColumnBytes(1, data)
			found = true
			return nil
		},
	})
	if err != nil {
		return nil, "", fmt.Errorf("photo db query failed: %w", err)
	}

	if !found {
		return nil, "", errs.ErrPhotoNotExists
	}

	return data, *contentType, nil
}

func (s *Server) addProposals(conn *sqlite.Conn, proposals []models.Proposal) error {
	stmt, err := conn.Prepare("insert into proposals(owner_id, description, how) values(?, ?, ?)")
	if err != nil {
		return fmt.Errorf("failed to prepare statement: %w", err)
	}
	defer stmt.Finalize()

	for _, proposal := range proposals {
		err := stmt.Reset()
		if err != nil {
			return fmt.Errorf("failed to reset prepared statement: %w", err)
		}
		err = stmt.ClearBindings()
		if err != nil {
			return fmt.Errorf("failed to clear bindings of prepared statement: %w", err)
		}

		stmt.BindInt64(1, int64(proposal.OwnerID))
		stmt.BindText(2, proposal.Description)
		stmt.BindText(3, proposal.How)

		_, err = stmt.Step()
		if err != nil {
			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
		}
	}
	s.requestCheckpoint()
	return nil
}

func (s *Server) getProposals(conn *sqlite.Conn) ([]models.Proposal, error) {
	if conn == nil {
		conn = s.getDbConn()
		defer s.dbpool.Put(conn)
	}

	proposals := make([]models.Proposal, 0, 100)
	err := sqlitex.Execute(conn, "select owner_id, description, how from proposals", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			proposals = append(proposals, models.Proposal{
				OwnerID:     models.UserID(stmt.ColumnInt(0)),
				Description: stmt.ColumnText(1),
				How:         stmt.ColumnText(2),
			})
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to get proposals from db: %w", err)
	}
	return proposals, nil
}

func (s *Server) getUsageInfo(conn *sqlite.Conn) ([]models.UserInfo, error) {
	if conn == nil {
		conn = s.getDbConn()
		defer s.returnDbConn(conn)
	}

	users := make([]models.UserInfo, 0, 50)
	err := sqlitex.Execute(conn, "select id, name, app_version, last_seen_time, last_upload_time, last_download_time from users", &sqlitex.ExecOptions{
		ResultFunc: func(stmt *sqlite.Stmt) error {
			ver, _ := semver.NewVersion(stmt.ColumnText(2))
			var lstp, lutp, ldtp *time.Time
			if stmt.ColumnType(3) != sqlite.TypeNull {
				lstp = ptr(time.Unix(stmt.ColumnInt64(3), 0))
			}
			if stmt.ColumnType(4) != sqlite.TypeNull {
				lutp = ptr(time.Unix(stmt.ColumnInt64(3), 0))
			}
			if stmt.ColumnType(5) != sqlite.TypeNull {
				ldtp = ptr(time.Unix(stmt.ColumnInt64(3), 0))
			}
			users = append(users, models.UserInfo{
				User: models.User{
					ID:   models.UserID(stmt.ColumnInt(0)),
					Name: stmt.ColumnText(1),
				},
				AppVersion:       ver,
				LastSeenTime:     lstp,
				LastUploadTime:   lutp,
				LastDownloadTime: ldtp,
			})
			return nil
		},
	})
	if err != nil {
		return nil, fmt.Errorf("failed to get users from db: %w", err)
	}
	return users, nil
}