Moved specifc backends into separate packages

backends/backends.go

@@ -0,0 +1,141 @@
+/*
+Copyright © 2023 Philipp Wolfer <phw@uploadedlobster.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+package backends
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/spf13/viper"
+	"go.uploadedlobster.com/scotty/backends/dump"
+	"go.uploadedlobster.com/scotty/backends/funkwhale"
+	"go.uploadedlobster.com/scotty/backends/listenbrainz"
+	"go.uploadedlobster.com/scotty/backends/maloja"
+	"go.uploadedlobster.com/scotty/backends/scrobblerlog"
+	"go.uploadedlobster.com/scotty/models"
+)
+
+type BackendInfo struct {
+	Name               string
+	ExportCapabilities []Capability
+	ImportCapabilities []Capability
+}
+
+type Capability = string
+
+func ResolveBackend[T interface{}](config *viper.Viper) (T, error) {
+	backendName, backend, err := resolveBackend(config)
+	var result T
+	if err != nil {
+		return result, err
+	}
+	implements, interfaceName := implementsInterface[T](backend)
+	if implements {
+		result = backend.(T)
+	} else {
+		err = errors.New(
+			fmt.Sprintf("Backend %s does not implement %s", backendName, interfaceName))
+	}
+	return result, err
+}
+
+func GetBackends() []BackendInfo {
+	backends := make([]BackendInfo, 0)
+	for name, backendFunc := range knownBackends {
+		backend := backendFunc()
+		info := BackendInfo{
+			Name:               name,
+			ExportCapabilities: getExportCapabilities(backend),
+			ImportCapabilities: getImportCapabilities(backend),
+		}
+		backends = append(backends, info)
+	}
+
+	return backends
+}
+
+var knownBackends = map[string]func() models.Backend{
+	"dump":             func() models.Backend { return &dump.DumpBackend{} },
+	"funkwhale-api":    func() models.Backend { return &funkwhale.FunkwhaleApiBackend{} },
+	"listenbrainz-api": func() models.Backend { return &listenbrainz.ListenBrainzApiBackend{} },
+	"maloja-api":       func() models.Backend { return &maloja.MalojaApiBackend{} },
+	"scrobbler-log":    func() models.Backend { return &scrobblerlog.ScrobblerLogBackend{} },
+}
+
+func resolveBackend(config *viper.Viper) (string, models.Backend, error) {
+	backendName := config.GetString("backend")
+	backendType := knownBackends[backendName]
+	if backendType == nil {
+		return backendName, nil, errors.New(fmt.Sprintf("Unknown backend %s", backendName))
+	}
+	return backendName, backendType().FromConfig(config), nil
+}
+
+func implementsInterface[T interface{}](backend models.Backend) (bool, string) {
+	expectedInterface := reflect.TypeOf((*T)(nil)).Elem()
+	implements := backend != nil && reflect.TypeOf(backend).Implements(expectedInterface)
+	return implements, expectedInterface.Name()
+}
+
+func getExportCapabilities(backend models.Backend) []string {
+	caps := make([]Capability, 0)
+	var name string
+	var found bool
+	name, found = checkCapability[models.ListenExport](backend, "export")
+	if found {
+		caps = append(caps, name)
+	}
+	name, found = checkCapability[models.LovesExport](backend, "export")
+	if found {
+		caps = append(caps, name)
+	}
+	return caps
+}
+
+func getImportCapabilities(backend models.Backend) []Capability {
+	caps := make([]Capability, 0)
+	var name string
+	var found bool
+	name, found = checkCapability[models.ListenImport](backend, "import")
+	if found {
+		caps = append(caps, name)
+	}
+	name, found = checkCapability[models.LovesImport](backend, "import")
+	if found {
+		caps = append(caps, name)
+	}
+	return caps
+}
+
+func checkCapability[T interface{}](backend models.Backend, suffix string) (string, bool) {
+	implements, name := implementsInterface[T](backend)
+	if implements {
+		cap, found := strings.CutSuffix(strings.ToLower(name), suffix)
+		if found {
+			return cap, found
+		}
+	}
+
+	return "", false
+}