package app

func visibleSessionTree(children []*Child, focusID string) []*Child {
	rootID := activeRootID(children, focusID)
	if rootID == "" {
		return nil
	}
	out := make([]*Child, 0, len(children))
	for _, c := range children {
		if c.Status() != StatusRunning {
			continue
		}
		if c.ID == rootID || c.ParentID == rootID {
			out = append(out, c)
		}
	}
	return out
}

func activeRootID(children []*Child, focusID string) string {
	if focusID != "" {
		for _, c := range children {
			if c.ID != focusID {
				continue
			}
			if c.ParentID == "" {
				return c.ID
			}
			if parent := findChildInSnapshot(children, c.ParentID); parent != nil {
				return parent.ID
			}
			return ""
		}
	}
	for _, c := range children {
		if c.ParentID == "" && c.Status() == StatusRunning {
			return c.ID
		}
	}
	return ""
}

func findChildInSnapshot(children []*Child, id string) *Child {
	for _, c := range children {
		if c.ID == id {
			return c
		}
	}
	return nil
}

func firstRunningTopLevel(children []*Child) *Child {
	for _, c := range children {
		if c.ParentID == "" && c.Status() == StatusRunning {
			return c
		}
	}
	return nil
}