Show filtered lists and their shared focus

A list may now be filtered (each t in tasks where !t.done), and several
filtered lists over one list share one focus: the focus view names an
item, so Vega asks Pure which row shows it and highlights it only in the
list that holds it; the other lists have no focus (null in the web
surface's JSON, and the spoken surface names the item where it is). A
click or point on a row points at the item that row shows, and the wheel
on a list without the focus focuses the row under it. Pure's rows now
take a mutable app.

examples/today.aup shows what is open and what is done; its CLI output
matches a model over random adds, moves, toggles and points into either
list, and the web surface leaves the other list without a focus.

8 files changed, 139 insertions, 19 deletions

diff --git a/docs/design/001-first-component.md b/docs/design/001-first-component.md
index df462e5..50a516d 100644
--- a/docs/design/001-first-component.md
+++ b/docs/design/001-first-component.md
@@ -40,6 +40,12 @@ view tasks_list_focus = at.position
 | NUI | `vega say app.pmod < script` | 문장. 이벤트마다 포커스 항목을 말하고(`Item 2 of 3: danger, milk, urgent.`), 실패하면 `Could not toggle.`, `show`에서 화면 전체 |
 | GUI | `vega web app.pmod [--listen 주소] [--port N]` | 웹 페이지. 제목·필드·목록(`listbox`)·표·키 목록·입력 칸. 키, 행 클릭, 휠, 입력을 받고 열린 페이지마다 변경을 알린다. 보이는 행만 계산한다 |
 
+목록은 걸러질 수 있다(`each t in tasks where !t.done`). 한 리스트에서 걸러진 목록 여럿이 포커스 하나를 나눠 쓴다.
+포커스 보기(`open_focus = at.position`)는 항목을 가리키므로 Vega는 Pure에게 그 항목의 행을 묻고
+(`pure_app_item_row`), 그 항목을 가진 목록에만 포커스를 보인다. 다른 목록에는 포커스가 없다(웹 JSON의 `focus`는
+null, 음성은 포커스를 가진 목록의 항목을 말한다). 행을 클릭하거나 가리키면 그 행의 항목을 가리킨다
+(`pure_app_row_item`). `examples/today.aup`가 열린 일과 끝난 일 두 목록을 이렇게 보인다.
+
 포커스는 표면에서도 옮긴다. TUI에서 목록·표의 행을 클릭하면 그 행이 포커스가 되고, 휠은 포커스를 한 행씩 옮긴다
 (SGR 마우스 보고). 스크립트는 `point 보기 행`(0부터)과 `click 줄 칸`(마지막으로 보인 프레임, 1부터)으로 같은 일을 한다.
 앱에 코드가 필요 없다. `<표>_focus` 보기가 `at.position`처럼 인덱스 상태의 위치 그대로이면 Vega는 Pure에게 그 상태를
@@ -130,6 +136,8 @@ CLI나 문장 표면이 그대로 이어받는다. Vega에도 앱에도 저장 �
 - aup와 Vega의 예제 11개를 세 표면에 무작위 입력으로 돌려 비정상 종료가 없다. sanitizer 빌드로도 같은 검사를 통과한다.
 - 규약을 여덟 가지로 어긴 명세에서 `vega check`가 아홉 곳을 모두 정확한 문장으로 알리고, 예제에서는 아무것도 알리지
   않는다.
+- 걸러진 두 목록(`examples/today.aup`)의 CLI 출력이 무작위 추가·이동·완료·양쪽 목록 가리키기 1,600단계에서 모델과
+  같다(포커스는 그 항목을 가진 목록에만 있다). 웹 JSON은 다른 목록의 포커스를 null로 준다.
 - 무작위 스크립트에 `point`(범위 밖 포함)와 TUI `click`을 섞어도 CLI·문장·프레임이 모델과 같다. 가상 터미널에서
   마우스로 행을 클릭하면 포커스가 옮겨지고, 저장소를 쓰는 다음 실행이 그 포커스에서 시작한다.
 
diff --git a/examples/today.aup b/examples/today.aup
new file mode 100644
index 0000000..e5db53b
--- /dev/null
+++ b/examples/today.aup
@@ -0,0 +1,39 @@
+# Two lists over one list state: what is open and what is done. Each shows
+# the items its where keeps; the focus (at) is one item, shown in whichever
+# list holds it, and a click in either list points at that item.
+use vega
+
+record Task {
+  title: text
+  done = 0
+}
+
+state tasks: list of Task
+state at: index of tasks
+
+input add = text
+input up = key ArrowUp
+input down = key ArrowDown
+input toggle = key Space
+
+on add {
+  tasks.append(Task { title: add })
+  at = tasks.last
+}
+on up.down { at = at - 1 }
+on down.down { at = at + 1 }
+on toggle.down { at.done = !at.done }
+
+view title = "Today"
+view left = "{count(t in tasks where !t.done)} open"
+
+view open = each t in tasks where !t.done {
+  label = t.title
+}
+view open_focus = at.position
+
+view done = each t in tasks where t.done {
+  label = t.title
+  tone = vega.muted
+}
+view done_focus = at.position
diff --git a/src/draw.c b/src/draw.c
index 738c2db..31188c7 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -138,6 +138,7 @@ static void say_focus(FILE *out, PureApp *app, const VegaPart *part) {
     size_t length, rows = vega_rows(app, part);
     if (!rows) { fprintf(out, "%s is empty.\n", m->view_names[part->view]); return; }
     size_t focus = vega_focus(app, part);
+    if (focus >= rows) { fprintf(out, "%s: none of %zu focused.\n", m->view_names[part->view], rows); return; }
     fprintf(out, "Item %zu of %zu: ", focus + 1, rows);
     VegaTone tone = vega_tone(app, part, focus);
     if (tone >= VEGA_ACCENT) fprintf(out, "%s, ", tone_names[tone]);
@@ -164,8 +165,15 @@ void vega_say(FILE *out, PureApp *app, const VegaScreen *screen, bool all) {
     char text[VEGA_TEXT];
     size_t length;
     if (!all) {
-        for (unsigned i = 0; i < screen->count; ++i)
-            if (screen->parts[i].kind != VEGA_FIELD) { say_focus(out, app, &screen->parts[i]); return; }
+        /* The focused item where a list shows it, else the first list. */
+        const VegaPart *first = NULL;
+        for (unsigned i = 0; i < screen->count; ++i) {
+            const VegaPart *part = &screen->parts[i];
+            if (part->kind == VEGA_FIELD) continue;
+            if (!first) first = part;
+            if (vega_focus(app, part) < vega_rows(app, part)) { say_focus(out, app, part); return; }
+        }
+        if (first) say_focus(out, app, first);
         return;
     }
     if (screen->title >= 0 && vega_text(app, (uint32_t)screen->title, 0, text, &length)) {
diff --git a/src/main.c b/src/main.c
index 46b672f..b9ea91e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -95,8 +95,10 @@ static bool mouse(unsigned button, unsigned line) {
     const VegaPart *part = &screen.parts[index];
     if (button == 64 || button == 65) {
         size_t focus = vega_focus(&app, part), rows = vega_rows(&app, part);
-        if (button == 64 ? !focus : focus + 1 >= rows) return false;
-        item = button == 64 ? focus - 1 : focus + 1;
+        if (focus < rows) { /* else the wheel focuses the row under it */
+            if (button == 64 ? !focus : focus + 1 >= rows) return false;
+            item = button == 64 ? focus - 1 : focus + 1;
+        }
     } else if (button) return false;
     return vega_point(&app, part, item);
 }
diff --git a/src/screen.c b/src/screen.c
index bb50de1..26b9fb0 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -146,20 +146,23 @@ bool vega_number(PureApp *app, uint32_t view, size_t row, double *out) {
     return app->module->view_table[view] ? pure_app_cell(app, view, row, out) : pure_app_view(app, view, out);
 }
 
-size_t vega_rows(const PureApp *app, const VegaPart *part) {
+size_t vega_rows(PureApp *app, const VegaPart *part) {
     return part->kind == VEGA_FIELD ? 0 : pure_app_rows(app, part->view);
 }
 
 size_t vega_focus(PureApp *app, const VegaPart *part) {
-    size_t rows = vega_rows(app, part);
+    size_t rows = vega_rows(app, part), row;
     double focus;
     if (part->focus < 0 || !rows || !vega_number(app, (uint32_t)part->focus, 0, &focus) || !(focus >= 0)) return 0;
-    return focus >= (double)(rows - 1) ? rows - 1 : (size_t)focus;
+    bool filtered = app->module->view_code[part->view].length > 0;
+    size_t item = focus < (double)SIZE_MAX ? (size_t)focus : SIZE_MAX;
+    if (pure_app_item_row(app, part->view, item, &row)) return row;
+    return filtered ? VEGA_NO_ROW : rows - 1;
 }
 
 size_t vega_scroll(size_t first, size_t focus, size_t visible, size_t rows) {
-    if (focus < first) first = focus;
-    if (visible && focus >= first + visible) first = focus - visible + 1;
+    if (focus < rows && focus < first) first = focus;
+    if (focus < rows && visible && focus >= first + visible) first = focus - visible + 1;
     if (first + visible > rows) first = rows > visible ? rows - visible : 0;
     return first;
 }
@@ -184,7 +187,9 @@ bool vega_commit(PureApp *app, const VegaScreen *screen, const char *text, size_
 }
 
 bool vega_point(PureApp *app, const VegaPart *part, size_t row) {
-    return part->pointer >= 0 && pure_app_point(app, (uint32_t)part->pointer, row) == PURE_OK;
+    size_t item; /* a filtered list's row shows some item of the list */
+    return part->pointer >= 0 && pure_app_row_item(app, part->view, row, &item) &&
+           pure_app_point(app, (uint32_t)part->pointer, item) == PURE_OK;
 }
 
 VegaTone vega_tone(PureApp *app, const VegaPart *part, size_t row) {
diff --git a/src/vega.h b/src/vega.h
index 98ed410..59a663e 100644
--- a/src/vega.h
+++ b/src/vega.h
@@ -45,14 +45,18 @@ unsigned vega_check(const PureModule *, void (*report)(void *, const char *name,
  * shortest form. false when it has no value (for example a missing item). */
 bool vega_text(PureApp *, uint32_t view, size_t row, char out[VEGA_TEXT], size_t *length);
 bool vega_number(PureApp *, uint32_t view, size_t row, double *out);
-size_t vega_rows(const PureApp *, const VegaPart *);
-/* The focused row, clamped to the rows; 0 without a focus view. */
+size_t vega_rows(PureApp *, const VegaPart *);
+/* The row of the focused item: the focus view names an item (an index's
+ * position), shown on the row that holds it; VEGA_NO_ROW when a filtered
+ * list leaves that item out. Clamped to the rows without a filter; 0
+ * without a focus view. */
+#define VEGA_NO_ROW SIZE_MAX
 size_t vega_focus(PureApp *, const VegaPart *);
 /* Focus a row, as a user pointing at it (a click); false when the part's
  * focus is not a plain index position or the row is not there. */
 bool vega_point(PureApp *, const VegaPart *, size_t row);
 /* The first row to show of `rows` when `visible` fit: the least scrolling
- * from first that keeps the focused row in view. */
+ * from first that keeps the focused row in view (any, without one). */
 size_t vega_scroll(size_t first, size_t focus, size_t visible, size_t rows);
 /* The key input answering a key name (Pure's names, as KeyboardEvent.code
  * spells them), or -1; press sends its press and release. */
diff --git a/src/web.c b/src/web.c
index 78da0ab..149e888 100644
--- a/src/web.c
+++ b/src/web.c
@@ -123,8 +123,10 @@ static void screen_json(Buffer *b, PureApp *app, const VegaScreen *screen, size_
         puts_(b, comma ? ",{\"part\":" : "{\"part\":");
         putf(b, "%u,\"name\":", i);
         json_name(b, m->view_names[part->view]);
-        putf(b, ",\"kind\":\"%s\",\"rows\":%zu,\"focus\":%zu,\"first\":%zu,\"pointable\":%s,\"columns\":[",
-             part->kind == VEGA_LIST ? "list" : "table", rows, rows ? focus : 0, first, part->pointer >= 0 ? "true" : "false");
+        putf(b, ",\"kind\":\"%s\",\"rows\":%zu,\"focus\":", part->kind == VEGA_LIST ? "list" : "table", rows);
+        if (focus < rows) putf(b, "%zu", focus);
+        else puts_(b, "null");
+        putf(b, ",\"first\":%zu,\"pointable\":%s,\"columns\":[", first, part->pointer >= 0 ? "true" : "false");
         if (part->kind == VEGA_TABLE)
             for (unsigned c = 0; c < part->column_count; ++c) {
                 if (c) puts_(b, ",");
@@ -224,12 +226,12 @@ static const char *const page_parts[] = {
 "el('span',{className:'label',textContent:it.label?\?''}),it.detail?el('span',{className:'detail',textContent:it.detail}):null,"
 "it.badge?el('span',{className:'badge',textContent:it.badge}):null);item.setAttribute('role','option');"
 "item.setAttribute('aria-selected',it.row===p.focus);list.append(item)}"
-"list.onwheel=e=>{e.preventDefault();pick(Math.max(0,Math.min(p.rows-1,p.focus+Math.sign(e.deltaY))))};"
+"list.onwheel=e=>{e.preventDefault();pick(Math.max(0,Math.min(p.rows-1,(p.focus?\?-1)+Math.sign(e.deltaY))))};"
 "return el('section',{},head,list)}"
 "const table=el('table',{},el('thead',{},el('tr',{},...p.columns.map(c=>el('th',{textContent:c})))));"
 "const body=el('tbody');for(const it of p.items){const tr=el('tr',{className:it.tone,onclick:()=>pick(it.row)},"
 "...it.cells.map(c=>el('td',{textContent:c?\?'-'})));tr.setAttribute('aria-selected',it.row===p.focus);body.append(tr)}"
-"table.append(body);table.onwheel=e=>{e.preventDefault();pick(Math.max(0,Math.min(p.rows-1,p.focus+Math.sign(e.deltaY))))};"
+"table.append(body);table.onwheel=e=>{e.preventDefault();pick(Math.max(0,Math.min(p.rows-1,(p.focus?\?-1)+Math.sign(e.deltaY))))};"
 "return el('section',{},head,table)}));"
 "$('prompt').hidden=!s.prompt;if(s.prompt)$('entry').placeholder=s.prompt;"
 "const symbols={ArrowUp:'\u2191',ArrowDown:'\u2193',ArrowLeft:'\u2190',ArrowRight:'\u2192',Backspace:'Bksp',"
diff --git a/tests/check.py b/tests/check.py
index 1e1289f..48487a3 100644
--- a/tests/check.py
+++ b/tests/check.py
@@ -431,7 +431,7 @@ def web(vega, module, work, seeds, steps=150, visible=4):
             if model.at >= first + visible: first = model.at - visible + 1
             if first + visible > n: first = max(n - visible, 0)
             assert screen['title'] == 'To do' and screen['fields'] == [{'name': 'left', 'text': model.left()}], screen
-            assert (listed['rows'], listed['focus'], listed['first']) == (n, model.at, first), (seed, listed, model.at)
+            assert (listed['rows'], listed['focus'], listed['first']) == (n, model.at if n else None, first), (seed, listed)
             window = tasks[first:first + visible]
             assert [(item['row'], item['label'], item['badge'], item['tone']) for item in listed['items']] == \
                 [(first + i, task['title'], Todo.badge(task), Todo.tone(task)) for i, task in enumerate(window)], seed
@@ -489,6 +489,57 @@ def browser(vega, module, work):
     return len(outcome['steps'])
 
 
+def split(vega, module, work, seeds, steps=200):
+    """examples/today.aup: two lists filtered from one list share one focus.
+    The CLI shows each list's items in order with the focus in whichever
+    list holds it; point takes a row of either list; the web surface gives
+    the other list no focus."""
+    compared = 0
+    for seed in seeds:
+        rng, tasks, at, script, expected = random.Random(seed + 700), [], 0, [], []
+        for _ in range(steps):
+            roll = rng.random()
+            opened = [i for i, t in enumerate(tasks) if not t['done']]
+            closed = [i for i, t in enumerate(tasks) if t['done']]
+            if roll < 0.3:
+                word = rng.choice(WORDS)
+                script.append('text ' + (word.encode().hex() or '-'))
+                tasks.append({'title': word, 'done': 0})
+                at = len(tasks) - 1
+            elif roll < 0.5:
+                name, rows = rng.choice([('open', opened), ('done', closed)])
+                row = rng.randrange(len(rows) + 1)
+                script.append(f'point {name} {row}')
+                if row < len(rows): at = rows[row]
+            else:
+                key = rng.choice(['ArrowUp', 'ArrowDown', 'Space'])
+                script.append(f'key {key}')
+                if key == 'ArrowUp': at = max(at - 1, 0)
+                elif key == 'ArrowDown': at = min(at + 1, max(len(tasks) - 1, 0))
+                elif tasks: tasks[at]['done'] = int(not tasks[at]['done'])
+            if rng.random() < 0.3:
+                script.append('show')
+                opened = [i for i, t in enumerate(tasks) if not t['done']]
+                closed = [i for i, t in enumerate(tasks) if t['done']]
+                expected += ['Today', f'left: {len(opened)} open', f'open ({len(opened)})']
+                expected += [('> ' if i == at else '  ') + pictures(tasks[i]['title']) for i in opened]
+                expected += [f'done ({len(closed)})']
+                expected += [('> ' if i == at else '  ') + pictures(tasks[i]['title']) + ' (muted)' for i in closed]
+        out = run(vega, 'cli', module, stdin='\n'.join(script) + '\n')
+        assert out.returncode == 0 and out.stdout.splitlines() == expected, \
+            (seed, [(a, b) for a, b in zip(out.stdout.splitlines(), expected) if a != b][:3])
+        compared += len(expected)
+    surface = WebSurface(vega, module)
+    try:
+        for word in ('a', 'b', 'c'): surface.call('POST', '/text', word)
+        surface.call('POST', '/key', 'Space')  # c is done: the focus moves to the done list
+        parts = json.loads(surface.call('GET', '/screen?rows=5')[1])['parts']
+    finally:
+        surface.stop()
+    assert [(p['name'], p['rows'], p['focus']) for p in parts] == [('open', 2, None), ('done', 1, 0)], parts
+    return compared
+
+
 def scores(vega, module):
     joins = ['ann', '범수', 'Zoë']
     script = [f'text {name.encode().hex()}' for name in joins]
@@ -680,7 +731,7 @@ def main():
         work = Path(directory)
         env = dict(os.environ, AUP_PATH=str(ROOT / 'lib'))
         modules = {}
-        for name in ('todo', 'scores'):
+        for name in ('todo', 'scores', 'today'):
             modules[name] = work / f'{name}.pmod'
             built = run(aup, 'build', ROOT / 'examples' / f'{name}.aup', '-o', modules[name], env=env)
             assert built.returncode == 0, built.stderr
@@ -688,6 +739,7 @@ def main():
             cli_and_say(vega, modules['todo'], range(args.seeds))
         report['tui_frames'] = tui(vega, modules['todo'], range(args.seeds), [(40, 12), (24, 9), (80, 30), (16, 6)])
         report['table_lines'] = scores(vega, modules['scores'])
+        report['split_list_lines'] = split(vega, modules['today'], work, range(args.seeds))
         report['painted_frames'], report['first_paint_bytes'], report['later_paint_bytes'] = \
             painting(vega, modules['todo'], range(args.seeds), [(40, 12), (24, 9), (80, 30)])
         report['web_screens'] = web(vega, modules['todo'], work, range(args.seeds))