Filter dialog: only offer options that yield results

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ui/library_test.go

@@ -1,6 +1,7 @@
 package ui
 
 import (
+	"slices"
 	"strings"
 	"testing"
 
@@ -156,3 +157,55 @@ func TestMovieItemAttrs(t *testing.T) {
 		t.Error("series with files must fetch its attributes")
 	}
 }
+
+func TestListedValues(t *testing.T) {
+	uhd := arr.FileAttrs{Resolution: 2160, Codec: arr.CodecX265, HDR: true, Audio: []string{"Atmos"}, Languages: []string{"English"}}
+	hd := arr.FileAttrs{Resolution: 1080, Codec: arr.CodecX264, Audio: []string{"DD"}, Languages: []string{"German"}}
+	pool := filterPool{files: [][]arr.FileAttrs{{uhd}, {hd}, nil}}
+	byLabel := func(label string) facet {
+		for _, f := range facetDefs {
+			if f.label == label {
+				return f
+			}
+		}
+		t.Fatalf("no facet %q", label)
+		return facet{}
+	}
+	list := func(label string, state attrFilter, p filterPool) []string {
+		return listedValues(byLabel(label), state, p)
+	}
+
+	// Without other criteria only options present in the pool are offered.
+	if got := list("Quality", attrFilter{}, pool); !slices.Equal(got, []string{"", "2160p", "1080p"}) {
+		t.Errorf("quality = %v", got)
+	}
+	if got := list("Audio", attrFilter{}, pool); !slices.Equal(got, []string{"", "Atmos", "DD"}) {
+		t.Errorf("audio = %v", got)
+	}
+	if got := list("Language", attrFilter{}, pool); !slices.Equal(got, []string{"", "English", "German"}) {
+		t.Errorf("language = %v", got)
+	}
+	// Other criteria narrow the options: nothing in 2160p is x264.
+	if got := list("Codec", attrFilter{res: "2160p"}, pool); !slices.Equal(got, []string{"", "x265"}) {
+		t.Errorf("codec given 2160p = %v", got)
+	}
+	// A facet is not narrowed by its own choice.
+	if got := list("Quality", attrFilter{res: "2160p"}, pool); !slices.Equal(got, []string{"", "2160p", "1080p"}) {
+		t.Errorf("quality given 2160p = %v", got)
+	}
+	// The current choice stays listed even when it matches nothing.
+	if got := list("Audio", attrFilter{res: "1080p", audio: "Atmos"}, pool); !slices.Equal(got, []string{"", "Atmos", "DD"}) {
+		t.Errorf("audio = %v", got)
+	}
+	if got := list("Language", attrFilter{lang: "Swahili"}, pool); got[1] != "Swahili" {
+		t.Errorf("a language not in the pool must stay listed: %v", got)
+	}
+	// While files are unknown nothing is ruled out.
+	if got := list("Quality", attrFilter{}, filterPool{unknown: true}); len(got) != 1+len(resOptions) {
+		t.Errorf("unknown pool: %v", got)
+	}
+	// An empty pool offers nothing but "any".
+	if got := list("Codec", attrFilter{}, filterPool{}); !slices.Equal(got, []string{""}) {
+		t.Errorf("empty pool: %v", got)
+	}
+}