internal/playback/playlist_navigation.go

@@ -23,6 +23,7 @@ type PlaylistState struct {
 var (
 	ErrPlaylistEmpty           = errors.New("playlist is empty")
 	ErrPlaylistIndexOutOfRange = errors.New("playlist index is out of range")
+	ErrPlaylistNoSelection     = errors.New("playlist has no selected entry")
 	ErrUnknownPlaylistCommand  = errors.New("unknown playlist command")
 )
 
@@ -91,3 +92,39 @@ func (s PlaylistState) Entry(playlist Playlist) (PlaylistEntry, bool) {
 	}
 	return playlist.Entries[s.CurrentIndex], true
 }
+
+func ApplyPlaylistSelection(
+	playlist Playlist,
+	current PlaylistState,
+	command PlaylistCommand,
+	retry RetryPolicy,
+) (
+	next PlaylistState,
+	sessionCommand SessionCommand,
+	apply bool,
+	err error,
+) {
+	next, err = ApplyPlaylistCommand(playlist, current, command)
+	if err != nil {
+		return current, SessionCommand{}, false, err
+	}
+
+	apply = command.Kind == PlaylistSelect || next != current
+	if !apply {
+		return next, SessionCommand{}, false, nil
+	}
+
+	entry, ok := next.Entry(playlist)
+	if !ok {
+		return current, SessionCommand{}, false, ErrPlaylistNoSelection
+	}
+	session := entry.SessionConfig(retry)
+	if err := session.Validate(); err != nil {
+		return current, SessionCommand{}, false, err
+	}
+
+	return next, SessionCommand{
+		Kind:    CommandSetSession,
+		Session: session,
+	}, true, nil
+}

internal/playback/playlist_selection_test.go

@@ -0,0 +1,189 @@
+package playback
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestApplyPlaylistSelectionFirstNext(t *testing.T) {
+	retry := validPlaylistRetryPolicy()
+
+	next, command, apply, err := ApplyPlaylistSelection(
+		navigationPlaylist(false),
+		PlaylistState{},
+		PlaylistCommand{Kind: PlaylistNext},
+		retry,
+	)
+	if err != nil {
+		t.Fatalf("ApplyPlaylistSelection() error = %v", err)
+	}
+	if !apply {
+		t.Fatal("ApplyPlaylistSelection() apply = false, want true")
+	}
+	wantState := PlaylistState{CurrentIndex: 0, HasSelection: true}
+	if next != wantState {
+		t.Fatalf("ApplyPlaylistSelection() state = %#v, want %#v", next, wantState)
+	}
+	wantCommand := SessionCommand{
+		Kind: CommandSetSession,
+		Session: SessionConfig{
+			Video: FeedConfig{Domain: "domain", UUID: "video-1", Active: true},
+			Retry: retry,
+		},
+	}
+	if command != wantCommand {
+		t.Fatalf("ApplyPlaylistSelection() command = %#v, want %#v", command, wantCommand)
+	}
+}
+
+func TestApplyPlaylistSelectionUsesCompleteEntrySession(t *testing.T) {
+	retry := validPlaylistRetryPolicy()
+	playlist := Playlist{Entries: []PlaylistEntry{
+		{
+			Video:         PlaylistFeed{Domain: "video-domain", UUID: "video"},
+			Audio:         PlaylistFeed{Domain: "audio-domain", UUID: "audio"},
+			SyncRequested: true,
+		},
+		{Video: PlaylistFeed{Domain: "next-domain", UUID: "next-video"}},
+	}}
+
+	_, command, apply, err := ApplyPlaylistSelection(
+		playlist,
+		PlaylistState{CurrentIndex: 1, HasSelection: true},
+		PlaylistCommand{Kind: PlaylistSelect, Index: 0},
+		retry,
+	)
+	if err != nil {
+		t.Fatalf("ApplyPlaylistSelection() error = %v", err)
+	}
+	if !apply {
+		t.Fatal("ApplyPlaylistSelection() apply = false, want true")
+	}
+	want := SessionConfig{
+		Video:         FeedConfig{Domain: "video-domain", UUID: "video", Active: true},
+		Audio:         FeedConfig{Domain: "audio-domain", UUID: "audio", Active: true},
+		SyncRequested: true,
+		Retry:         retry,
+	}
+	if command.Kind != CommandSetSession || command.Session != want {
+		t.Fatalf("ApplyPlaylistSelection() command = %#v, want session %#v", command, want)
+	}
+}
+
+func TestApplyPlaylistSelectionVideoOnlyClearsAudio(t *testing.T) {
+	_, command, apply, err := ApplyPlaylistSelection(
+		navigationPlaylist(false),
+		PlaylistState{CurrentIndex: 1, HasSelection: true},
+		PlaylistCommand{Kind: PlaylistSelect, Index: 0},
+		validPlaylistRetryPolicy(),
+	)
+	if err != nil {
+		t.Fatalf("ApplyPlaylistSelection() error = %v", err)
+	}
+	if !apply {
+		t.Fatal("ApplyPlaylistSelection() apply = false, want true")
+	}
+	if command.Session.Audio != (FeedConfig{}) {
+		t.Fatalf("ApplyPlaylistSelection() audio = %#v, want zero value", command.Session.Audio)
+	}
+}
+
+func TestApplyPlaylistSelectionApplicationDecision(t *testing.T) {
+	tests := []struct {
+		name    string
+		loop    bool
+		current int
+		command PlaylistCommand
+		want    int
+		apply   bool
+	}{
+		{name: "reselect current", current: 1, command: PlaylistCommand{Kind: PlaylistSelect, Index: 1}, want: 1, apply: true},
+		{name: "move next", current: 1, command: PlaylistCommand{Kind: PlaylistNext}, want: 2, apply: true},
+		{name: "next stops at end", current: 2, command: PlaylistCommand{Kind: PlaylistNext}, want: 2},
+		{name: "previous stops at beginning", current: 0, command: PlaylistCommand{Kind: PlaylistPrevious}, want: 0},
+		{name: "next wraps", loop: true, current: 2, command: PlaylistCommand{Kind: PlaylistNext}, want: 0, apply: true},
+		{name: "previous wraps", loop: true, current: 0, command: PlaylistCommand{Kind: PlaylistPrevious}, want: 2, apply: true},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			next, command, apply, err := ApplyPlaylistSelection(
+				navigationPlaylist(test.loop),
+				PlaylistState{CurrentIndex: test.current, HasSelection: true},
+				test.command,
+				validPlaylistRetryPolicy(),
+			)
+			if err != nil {
+				t.Fatalf("ApplyPlaylistSelection() error = %v", err)
+			}
+			wantState := PlaylistState{CurrentIndex: test.want, HasSelection: true}
+			if next != wantState {
+				t.Fatalf("ApplyPlaylistSelection() state = %#v, want %#v", next, wantState)
+			}
+			if apply != test.apply {
+				t.Fatalf("ApplyPlaylistSelection() apply = %v, want %v", apply, test.apply)
+			}
+			if apply && command.Kind != CommandSetSession {
+				t.Fatalf("ApplyPlaylistSelection() command kind = %v, want %v", command.Kind, CommandSetSession)
+			}
+			if !apply && command != (SessionCommand{}) {
+				t.Fatalf("ApplyPlaylistSelection() command = %#v, want zero value", command)
+			}
+		})
+	}
+}
+
+func TestApplyPlaylistSelectionErrorsDoNotApply(t *testing.T) {
+	current := PlaylistState{CurrentIndex: 1, HasSelection: true}
+	tests := []struct {
+		name    string
+		command PlaylistCommand
+		retry   RetryPolicy
+		wantErr error
+	}{
+		{
+			name:    "invalid command",
+			command: PlaylistCommand{},
+			retry:   validPlaylistRetryPolicy(),
+			wantErr: ErrUnknownPlaylistCommand,
+		},
+		{
+			name:    "invalid retry",
+			command: PlaylistCommand{Kind: PlaylistNext},
+			retry:   RetryPolicy{},
+			wantErr: ErrInvalidRetryDelay,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			next, command, apply, err := ApplyPlaylistSelection(
+				navigationPlaylist(false),
+				current,
+				test.command,
+				test.retry,
+			)
+			if !errors.Is(err, test.wantErr) {
+				t.Fatalf("ApplyPlaylistSelection() error = %v, want %v", err, test.wantErr)
+			}
+			if next != current {
+				t.Fatalf("ApplyPlaylistSelection() state = %#v, want unchanged %#v", next, current)
+			}
+			if apply {
+				t.Fatal("ApplyPlaylistSelection() apply = true, want false")
+			}
+			if command != (SessionCommand{}) {
+				t.Fatalf("ApplyPlaylistSelection() command = %#v, want zero value", command)
+			}
+		})
+	}
+}
+
+func validPlaylistRetryPolicy() RetryPolicy {
+	return RetryPolicy{
+		MaxAttempts:  3,
+		InitialDelay: time.Millisecond,
+		MaxDelay:     time.Second,
+	}
+}