Type: selected type shows its in and out ports, and the in port threads backwards

Squashed from #3817 onto main.

crates/engine/src/cmd/threads.rs

@@ -28,7 +28,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Thread Text",
             [],
             None,
-            "{from, to?, rect?: [x, y, width, height], at?: [x, y]} thread area type or type on a path `from` (a click on its out port) into one more frame, put after it in its thread: closed path, area type or type on a path `to`, a new rectangle `rect`, or a new frame of `from`'s kind, shape and size with its top-left at `at` (give one of the three) → {id}; the two frames are selected",
+            "{from, to?, rect?: [x, y, width, height], at?: [x, y], before?} thread area type or type on a path `from` (a click on its out port) into one more frame, put after it in its thread, or before it with `before: true` (a click on its in port: the story starts there and flows on into `from`): closed path, area type or type on a path `to`, a new rectangle `rect`, or a new frame of `from`'s kind, shape and size with its top-left at `at` (give one of the three) → {id}; the two frames are selected",
             has_doc,
             add
         ),
@@ -263,11 +263,12 @@ fn create(s: &mut Session, _: &Value) -> Result<Value> {
     Ok(json!({ "ids": out.iter().map(|i| i.0).collect::<Vec<_>>() }))
 }
 
-/// `text.thread.add`: the out port's loaded text, placed.
+/// `text.thread.add`: the loaded text of a port, placed.
 fn add(s: &mut Session, p: &Value) -> Result<Value> {
     const C: &str = "text.thread.add";
     let given = |k: &str| p.get(k).filter(|v| !v.is_null());
     let from = checked_id(s, given("from").unwrap_or(&Value::Null), C)?;
+    let before = switch_or(p, "before", false, C)?;
     let d = &s.doc()?.doc;
     let src = text_of(d, from).ok_or_else(|| bad(C, "`from` must be area type or type on a path"))?;
     let style = src.first_style();
@@ -330,9 +331,10 @@ fn add(s: &mut Session, p: &Value) -> Result<Value> {
         };
         match d.text_threads.iter_mut().find(|t| t.contains(&from)) {
             Some(t) => {
-                let at = t.iter().position(|x| *x == from).map_or(t.len(), |i| i + 1);
+                let at = t.iter().position(|x| *x == from).map_or(t.len(), |i| if before { i } else { i + 1 });
                 t.insert(at, to);
             }
+            None if before => d.text_threads.push(vec![to, from]),
             None => d.text_threads.push(vec![from, to]),
         }
         // Force a re-flow of the thread on this edit: the edit leaves existing area type `to`
@@ -618,6 +620,35 @@ mod tests {
         assert_eq!(threads(&s), [[a, c, d]]);
     }
 
+    /// #2572: the text loaded from an in port threads back: the new frame or the path clicked comes
+    /// before the frame it was loaded from, so the story starts there and flows on into it; in the
+    /// middle of a thread the new frame goes in between, each in one undo step.
+    #[test]
+    fn add_before_threads_the_story_from_the_new_frame_into_the_clicked_one() {
+        let (mut s, a, b) = setup();
+        let c = new_id(s.execute("text.thread.add", &json!({"from": a, "at": [400, 200], "before": true})).unwrap());
+        assert_eq!(threads(&s), [[c, a]]);
+        assert_eq!(frame_box(&s, c), vectorcraft_geom::Rect::new(400.0, 200.0, 550.0, 260.0), "the clicked frame's size at the click");
+        assert!(TEXT.repeat(4).starts_with(&text(&s, c)) && !text(&s, c).is_empty(), "the story starts in the new frame: {:?}", text(&s, c));
+        assert_eq!(format!("{}{}", text(&s, c), text(&s, a)), TEXT.repeat(4));
+        assert_eq!(s.doc().unwrap().selection.objects, [NodeId(a), NodeId(c)]);
+        // In between the frame and the one before it.
+        let d = new_id(s.execute("text.thread.add", &json!({"from": a, "rect": [10, 100, 300, 150], "before": true})).unwrap());
+        assert_eq!(threads(&s), [[c, d, a]]);
+        assert_eq!(format!("{}{}{}", text(&s, c), text(&s, d), text(&s, a)), TEXT.repeat(4));
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(threads(&s), [[c, a]]);
+        // A closed path clicked with the in port's text comes first, with the start of the story.
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(new_id(s.execute("text.thread.add", &json!({"from": a, "to": b, "before": true})).unwrap()), b);
+        assert_eq!(threads(&s), [[b, a]]);
+        assert!(TEXT.repeat(4).starts_with(&text(&s, b)) && !text(&s, b).is_empty());
+        assert_eq!(format!("{}{}", text(&s, b), text(&s, a)), TEXT.repeat(4));
+        // `before: false` is the out port's.
+        let e = new_id(s.execute("text.thread.add", &json!({"from": a, "at": [0, 0], "before": false})).unwrap());
+        assert_eq!(threads(&s), [[b, a, e]]);
+    }
+
     /// Type on a path along a line beside the area type of [`setup`].
     fn type_on_a_line(s: &mut Session) -> u64 {
         let line = new_id(s.execute("shape.line", &json!({"x1": 10, "y1": 250, "x2": 110, "y2": 250})).unwrap());
@@ -692,6 +723,8 @@ mod tests {
             json!({"from": a, "rect": [0, 0, 10, 0]}),
             json!({"from": a, "rect": [0, 0, 10]}),
             json!({"from": a, "rect": "big"}),
+            json!({"from": a, "at": [0, 0], "before": "yes"}),
+            json!({"from": a, "at": [0, 0], "before": 1}),
         ] {
             assert!(s.execute("text.thread.add", &p).is_err(), "{p} was accepted");
             assert!(std::sync::Arc::ptr_eq(&s.doc().unwrap().doc, &before), "{p} changed the document");