Implement "backends" command

backends/interfaces.go

@@ -25,6 +25,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"strings"
 	"time"
 
 	"github.com/spf13/viper"
@@ -55,35 +56,105 @@ type ImportResult struct {
 	LastTimestamp time.Time
 }
 
-func resolveBackend(config *viper.Viper) (string, Backend, error) {
-	backendName := config.GetString("backend")
-	// fmt.Printf("requested backend %s\n", backendName)
-	backendType := knownBackends[backendName]
-	if backendType == nil {
-		return backendName, nil, errors.New(fmt.Sprintf("Unknown backend %s", backendName))
-	}
-	return backendName, backendType().FromConfig(config), nil
+type BackendInfo struct {
+	Name               string
+	ExportCapabilities []Capability
+	ImportCapabilities []Capability
 }
 
+type Capability = string
+
 func ResolveBackend[T interface{}](config *viper.Viper) (T, error) {
-	expectedInterface := reflect.TypeOf((*T)(nil)).Elem()
 	backendName, backend, err := resolveBackend(config)
 	var result T
 	if err != nil {
 		return result, err
 	}
-	if backend != nil && reflect.TypeOf(backend).Implements(expectedInterface) {
+	implements, interfaceName := implementsInterface[T](backend)
+	if implements {
 		result = backend.(T)
 	} else {
 		err = errors.New(
-			fmt.Sprintf("Backend %s does not implement %s", backendName, expectedInterface.String()))
+			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() Backend{
 	"dump":             func() Backend { return &DumpBackend{} },
 	"listenbrainz-api": func() Backend { return &ListenBrainzApiBackend{} },
 	"maloja-api":       func() Backend { return &MalojaApiBackend{} },
 	"scrobbler-log":    func() Backend { return &ScrobblerLogBackend{} },
 }
+
+func resolveBackend(config *viper.Viper) (string, 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 Backend) (bool, string) {
+	expectedInterface := reflect.TypeOf((*T)(nil)).Elem()
+	implements := backend != nil && reflect.TypeOf(backend).Implements(expectedInterface)
+	return implements, expectedInterface.Name()
+}
+
+func getExportCapabilities(backend Backend) []string {
+	caps := make([]Capability, 0)
+	var name string
+	var found bool
+	name, found = checkCapability[ListenExport](backend, "export")
+	if found {
+		caps = append(caps, name)
+	}
+	name, found = checkCapability[LovesExport](backend, "export")
+	if found {
+		caps = append(caps, name)
+	}
+	return caps
+}
+
+func getImportCapabilities(backend Backend) []Capability {
+	caps := make([]Capability, 0)
+	var name string
+	var found bool
+	name, found = checkCapability[ListenImport](backend, "import")
+	if found {
+		caps = append(caps, name)
+	}
+	name, found = checkCapability[LovesImport](backend, "import")
+	if found {
+		caps = append(caps, name)
+	}
+	return caps
+}
+
+func checkCapability[T interface{}](backend 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
+}

backends/interfaces_test.go

@@ -0,0 +1,88 @@
+/*
+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_test
+
+import (
+	"reflect"
+	"slices"
+	"testing"
+
+	"github.com/spf13/viper"
+	"go.uploadedlobster.com/scotty/backends"
+)
+
+func TestResolveBackend(t *testing.T) {
+	config := viper.New()
+	config.Set("backend", "dump")
+	backend, err := backends.ResolveBackend[backends.ListenImport](config)
+	if err != nil {
+		t.Errorf("ResolveBackend failed unexpected: %v", err)
+	}
+	realType := reflect.TypeOf(backend)
+	if realType.Name() != "DumpBackend" {
+		t.Errorf("ResolveBackend did not return a DumpBackend, unexpected type %v", realType)
+	}
+}
+
+func TestResolveBackendUnknown(t *testing.T) {
+	config := viper.New()
+	config.Set("backend", "foo")
+	_, err := backends.ResolveBackend[backends.ListenImport](config)
+	if err == nil {
+		t.Error("Expected ResolveBackend to fail", err)
+	} else if err.Error() != "Unknown backend foo" {
+		t.Errorf("Expected \"Unknown backend foo\", got \"%s\"", err)
+	}
+}
+
+func TestResolveBackendInvalidInterface(t *testing.T) {
+	config := viper.New()
+	config.Set("backend", "dump")
+	_, err := backends.ResolveBackend[backends.ListenExport](config)
+	if err == nil {
+		t.Error("Expected ResolveBackend to fail", err)
+	} else if err.Error() != "Backend dump does not implement ListenExport" {
+		t.Errorf("Expected \"Backend dump does not implement ListenExport\", got \"%s\"", err)
+	}
+}
+
+func TestGetBackends(t *testing.T) {
+	backends := backends.GetBackends()
+	for _, info := range backends {
+		if info.Name == "dump" {
+			if !slices.Contains[[]string](info.ImportCapabilities, "listen") {
+				t.Error("Backend \"dump\" is expected to provide listen import capability")
+			}
+			if len(info.ExportCapabilities) > 0 {
+				t.Errorf(
+					"Backend \"dump\" is not expected to provide any export capabilities, provides %s",
+					info.ExportCapabilities,
+				)
+			}
+			return // Finish the test
+		}
+	}
+
+	// If we got here the "dump" backend was not included
+	t.Errorf("GetBackends() did not return expected bacend \"dump\"")
+}

cmd/backends.go

@@ -0,0 +1,59 @@
+/*
+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 cmd
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"go.uploadedlobster.com/scotty/backends"
+)
+
+// backendsCmd represents the backends command
+var backendsCmd = &cobra.Command{
+	Use:   "backends",
+	Short: "List available backends",
+	Long:  `List the names and supported capabilities of all available backends.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		backends := backends.GetBackends()
+		for _, info := range backends {
+			fmt.Printf("%s:\n", info.Name)
+			fmt.Printf("\texport: %s\n", strings.Join(info.ExportCapabilities, ", "))
+			fmt.Printf("\timport: %s\n\n", strings.Join(info.ImportCapabilities, ", "))
+		}
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(backendsCmd)
+
+	// Here you will define your flags and configuration settings.
+
+	// Cobra supports Persistent Flags which will work for this command
+	// and all subcommands, e.g.:
+	// backendsCmd.PersistentFlags().String("foo", "", "A help for foo")
+
+	// Cobra supports local flags which will only run when this command
+	// is called directly, e.g.:
+	// backendsCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+}