feat(engine): add topological sort and descendants for module DAG

internal/engine/dag_test.go

@@ -0,0 +1,79 @@
+package engine
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+)
+
+func TestTopoSort(t *testing.T) {
+	cases := []struct {
+		name  string
+		metas []module.Meta
+		want  []string
+		err   bool
+	}{
+		{
+			name:  "linear chain",
+			metas: []module.Meta{{ID: "a"}, {ID: "b", Deps: []string{"a"}}, {ID: "c", Deps: []string{"b"}}},
+			want:  []string{"a", "b", "c"},
+		},
+		{
+			name:  "independent modules sorted alphabetically",
+			metas: []module.Meta{{ID: "c"}, {ID: "a"}, {ID: "b"}},
+			want:  []string{"a", "b", "c"},
+		},
+		{
+			name:  "diamond",
+			metas: []module.Meta{{ID: "a"}, {ID: "b", Deps: []string{"a"}}, {ID: "c", Deps: []string{"a"}}, {ID: "d", Deps: []string{"b", "c"}}},
+			want:  []string{"a", "b", "c", "d"},
+		},
+		{
+			name:  "unknown dep",
+			metas: []module.Meta{{ID: "a", Deps: []string{"missing"}}},
+			err:   true,
+		},
+		{
+			name:  "cycle",
+			metas: []module.Meta{{ID: "a", Deps: []string{"b"}}, {ID: "b", Deps: []string{"a"}}},
+			err:   true,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := TopoSort(tc.metas)
+			if tc.err {
+				if err == nil {
+					t.Fatalf("want error, got nil (order=%v)", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Fatalf("order = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestDescendants(t *testing.T) {
+	metas := []module.Meta{
+		{ID: "a"},
+		{ID: "b", Deps: []string{"a"}},
+		{ID: "c", Deps: []string{"a"}},
+		{ID: "d", Deps: []string{"b"}},
+		{ID: "e"}, // independent
+	}
+	got := Descendants(metas, "a")
+	want := map[string]bool{"b": true, "c": true, "d": true}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("descendants(a) = %v, want %v", got, want)
+	}
+
+	if len(Descendants(metas, "e")) != 0 {
+		t.Fatalf("descendants(e) should be empty")
+	}
+}