Implement weight-based topological sort for timeline blocks

cmd/qrunproxy/show.go

@@ -19,6 +19,8 @@ type Block struct {
 	Track string `json:"track,omitempty"`
 	Name  string `json:"name"`
 	Loop  bool   `json:"loop,omitempty"`
+
+	weight uint64
 }
 
 type Trigger struct {

cmd/qrunproxy/timeline.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"cmp"
 	"fmt"
 	"slices"
 )
@@ -35,11 +36,11 @@ const (
 )
 
 type TimelineCell struct {
-	Type     CellType       `json:"type"`
-	BlockID  string         `json:"block_id,omitempty"`
-	Event    string         `json:"event,omitempty"`
-	row      int            `json:"-"`
-	track    *TimelineTrack `json:"-"`
+	Type    CellType       `json:"type"`
+	BlockID string         `json:"block_id,omitempty"`
+	Event   string         `json:"event,omitempty"`
+	row     int            `json:"-"`
+	track   *TimelineTrack `json:"-"`
 }
 
 func (t *TimelineTrack) cellTypeAt(index int, types ...CellType) bool {
@@ -150,6 +151,8 @@ func BuildTimeline(show *Show) (Timeline, error) {
 		tl.Blocks[block.ID] = block
 	}
 
+	sortedBlocks := tl.sortBlocks()
+
 	endChains := map[string]bool{}
 	for _, trigger := range show.Triggers {
 		if trigger.Source.Signal != "END" {
@@ -163,7 +166,7 @@ func BuildTimeline(show *Show) (Timeline, error) {
 		}
 	}
 
-	tl.buildCells(endChains)
+	tl.buildCells(endChains, sortedBlocks)
 	tl.buildConstraints()
 	if err := tl.assignRows(); err != nil {
 		return Timeline{}, err
@@ -172,6 +175,33 @@ func BuildTimeline(show *Show) (Timeline, error) {
 	return tl, nil
 }
 
+func (tl *Timeline) sortBlocks() []*Block {
+	for i, b := range tl.show.Blocks {
+		b.weight = uint64(i) << 32
+	}
+
+	changed := true
+	for changed {
+		changed = false
+		for _, t := range tl.show.Triggers {
+			src := tl.Blocks[t.Source.Block]
+			for _, target := range t.Targets {
+				dst := tl.Blocks[target.Block]
+				if dst.weight <= src.weight {
+					dst.weight = src.weight + 1
+					changed = true
+				}
+			}
+		}
+	}
+
+	sorted := slices.Clone(tl.show.Blocks)
+	slices.SortFunc(sorted, func(a, b *Block) int {
+		return cmp.Compare(a.weight, b.weight)
+	})
+	return sorted
+}
+
 func (tl *Timeline) addConstraint(kind constraintKind, a, b *TimelineCell) {
 	tl.constraints = append(tl.constraints, constraint{kind: kind, a: a, b: b})
 }
@@ -208,13 +238,13 @@ func (tl *Timeline) findCell(blockID, event string) *TimelineCell {
 	panic("cell not found: " + blockID + " " + event)
 }
 
-func (tl *Timeline) buildCells(endChains map[string]bool) {
+func (tl *Timeline) buildCells(endChains map[string]bool, sortedBlocks []*Block) {
 	lastOnTrack := map[string]*Block{}
-	for _, block := range tl.show.Blocks {
+	for _, block := range sortedBlocks {
 		lastOnTrack[block.Track] = block
 	}
 
-	for _, block := range tl.show.Blocks {
+	for _, block := range sortedBlocks {
 		track := tl.trackIdx[block.Track]
 		var cells []*TimelineCell
 		switch block.Type {

cmd/qrunproxy/timeline_test.go

@@ -35,3 +35,41 @@ func BenchmarkBuildTimeline(b *testing.B) {
 		BuildTimeline(show)
 	}
 }
+
+func TestTimelineOrderDependency(t *testing.T) {
+	show := &Show{
+		Tracks: []*Track{
+			{ID: "T1", Name: "Track 1"},
+			{ID: "T2", Name: "Track 2"},
+		},
+		Blocks: []*Block{
+			{ID: "B", Type: "media", Track: "T1", Name: "Block B"},
+			{ID: "A", Type: "media", Track: "T1", Name: "Block A"},
+			{ID: "C", Type: "media", Track: "T2", Name: "Block C"},
+			{ID: "C1", Type: "cue", Name: "Cue 1"},
+		},
+		Triggers: []*Trigger{
+			{
+				Source: TriggerSource{Block: "C1", Signal: "GO"},
+				Targets: []TriggerTarget{{Block: "A", Hook: "START"}},
+			},
+			{
+				Source: TriggerSource{Block: "A", Signal: "END"},
+				Targets: []TriggerTarget{{Block: "C", Hook: "START"}},
+			},
+			{
+				Source: TriggerSource{Block: "C", Signal: "END"},
+				Targets: []TriggerTarget{{Block: "B", Hook: "START"}},
+			},
+		},
+	}
+
+	if err := show.Validate(); err != nil {
+		t.Fatalf("Validate failed: %v", err)
+	}
+
+	_, err := BuildTimeline(show)
+	if err != nil {
+		t.Fatalf("BuildTimeline failed: %v", err)
+	}
+}