replay-theater

1// Copyright 2026 Anthropic PBC
2// SPDX-License-Identifier: Apache-2.0
3//
4// Replay Theater: records the file edits Claude makes in a turn, then lets you
5// step through them in a pane, one diff at a time.
6//
7// Claude Code 2.1.280 function hooks. Load with --plugin-dir.
8//
9// Changed by Ben AI (2026-10): added the /mods switchboard support below
10// (turn off and hide via ~/.claude/mods/switches.json). The rest is Anthropic's original.
11
12const PANE_ID = "replay-theater";
13const MAX_DIFF_LINES = 12;
14const MAX_LCS_LINES = 400;
15const EDIT_TOOLS = new Set(["Edit", "Write", "MultiEdit"]);
16
17// Module state. `pending` fills during a turn; `replay` is the last finished
18// turn's steps, the ones the pane shows.
19const state = { pending: [], replay: [], index: 0, isOpen: false, inBand: false, turns: 0 };
20
21// The /mods switchboard turns this mod off in every chat with switches.json.
22// "replay-theater:hidden": true in the same file hides the hint band and closes the pane.
23const NAME = "replay-theater";
24const HIDE_KEY = `${NAME}:hidden`;
25const POLL_MS = 3000;
26const sw = { off: false, hidden: false, sid: "" };
27
28const homeOf = ($) => $.plugin.root.split("/.claude/")[0] || "";
29const switchesPath = ($) => `${homeOf($)}/.claude/mods/switches.json`;
30
31async function readSwitches($) {
32  const path = switchesPath($);
33  if (!(await $.fs.exists(path))) return {};
34  const json = JSON.parse(String(await $.fs.read(path)));
35  return json && typeof json === "object" && !Array.isArray(json) ? json : {};
36}
37
38async function readSwitch($) {
39  let nowOff = sw.off, nowHidden = sw.hidden;
40  try {
41    const json = await readSwitches($);
42    nowOff = json[NAME] === false;
43    nowHidden = json[HIDE_KEY] === true;
44  } catch { /* a broken or missing file changes nothing */ }
45  if (nowOff === sw.off && nowHidden === sw.hidden) return;
46  const closing = (nowOff && !sw.off) || (nowHidden && !sw.hidden);
47  sw.off = nowOff;
48  sw.hidden = nowHidden;
49  if (closing && state.isOpen) {
50    state.isOpen = false;
51    state.inBand = false;
52    await Promise.resolve($.ui.close({ id: PANE_ID })).catch(() => undefined);
53  }
54  $.ui.invalidate("ui.render");
55}
56
57// Read, change, write the whole file, so every chat sees the choice within 3 s.
58async function setHidden($, value) {
59  try {
60    const json = await readSwitches($).catch(() => ({}));
61    if (value) json[HIDE_KEY] = true;
62    else delete json[HIDE_KEY];
63    await $.process.run(["mkdir", "-p", `${homeOf($)}/.claude/mods`]);
64    await $.fs.write(switchesPath($), `${JSON.stringify(json, null, 2)}\n`);
65  } catch { /* the in-memory flag still changes */ }
66  sw.hidden = value;
67}
68
69// The /mods switchboard asks for the pane by leaving an empty file for this chat.
70async function checkOpen($) {
71  if (!sw.sid) return;
72  const path = `${homeOf($)}/.claude/mods/.open-${NAME}-${sw.sid}`;
73  try {
74    if (!(await $.fs.exists(path))) return;
75    await $.process.run(["rm", "-f", path]);
76    if (sw.off) return;
77    const opened = await openReplay($);
78    if (!opened) $.ui.toast("Replay Theater: no edits in the last turn yet.");
79  } catch { /* try again on the next poll */ }
80}
81
82async function poll($) {
83  await readSwitch($);
84  await checkOpen($);
85}
86
87function relPath(cwd, path) {
88  if (!path) return "(unknown file)";
89  if (cwd && path.startsWith(cwd + "/")) return path.slice(cwd.length + 1);
90  return path;
91}
92
93function splitLines(text) {
94  if (text === undefined || text === null || text === "") return [];
95  const lines = String(text).split("\n");
96  if (lines.length > 1 && lines[lines.length - 1] === "") lines.pop();
97  return lines;
98}
99
100// A line diff. Small inputs get an LCS diff, so unchanged lines show as
101// context; large ones fall back to all-removed then all-added.
102function diffLines(oldText, newText) {
103  const a = splitLines(oldText);
104  const b = splitLines(newText);
105  if (a.length > MAX_LCS_LINES || b.length > MAX_LCS_LINES) {
106    return [...a.map((t) => ({ op: "-", t })), ...b.map((t) => ({ op: "+", t }))];
107  }
108  const n = a.length, m = b.length;
109  const dp = Array.from({ length: n + 1 }, () => new Array(m + 1).fill(0));
110  for (let i = n - 1; i >= 0; i--)
111    for (let j = m - 1; j >= 0; j--)
112      dp[i][j] = a[i] === b[j] ? dp[i + 1][j + 1] + 1 : Math.max(dp[i + 1][j], dp[i][j + 1]);
113  const out = [];
114  let i = 0, j = 0;
115  while (i < n && j < m) {
116    if (a[i] === b[j]) { out.push({ op: " ", t: a[i] }); i++; j++; }
117    else if (dp[i + 1][j] >= dp[i][j + 1]) out.push({ op: "-", t: a[i++] });
118    else out.push({ op: "+", t: b[j++] });
119  }
120  while (i < n) out.push({ op: "-", t: a[i++] });
121  while (j < m) out.push({ op: "+", t: b[j++] });
122  return trimContext(out);
123}
124
125// Keep one line of context around each change, so a long file's Write shows
126// the changed lines, not the whole file.
127function trimContext(lines) {
128  if (!lines.some((l) => l.op !== " ")) return lines.slice(0, MAX_DIFF_LINES);
129  const keep = lines.map((l, k) =>
130    l.op !== " " || lines[k - 1]?.op && lines[k - 1].op !== " " || lines[k + 1]?.op && lines[k + 1].op !== " ");
131  const out = [];
132  let skipped = false;
133  lines.forEach((l, k) => {
134    if (keep[k]) { if (skipped && out.length) out.push({ op: "~", t: "⋯" }); out.push(l); skipped = false; }
135    else skipped = true;
136  });
137  return out;
138}
139
140function countChanges(diff) {
141  let add = 0, del = 0;
142  for (const l of diff) { if (l.op === "+") add++; else if (l.op === "-") del++; }
143  return { add, del };
144}
145
146// Turns one tool call into one or more steps.
147async function stepsFor($, e) {
148  let cwd = "";
149  try { cwd = await $.session.cwd(); } catch { /* keep the full path */ }
150  const file = relPath(cwd, e.file_path);
151  if (e.tool === "Edit") {
152    return [{ tool: "Edit", file, diff: diffLines(e.old_string, e.new_string), note: e.replace_all ? "replace all" : "" }];
153  }
154  if (e.tool === "MultiEdit" && Array.isArray(e.edits)) {
155    return e.edits.map((ed, k) => ({
156      tool: "MultiEdit", file, diff: diffLines(ed.old_string, ed.new_string), note: `edit ${k + 1} of ${e.edits.length}`,
157    }));
158  }
159  if (e.tool === "Write") {
160    let before = "";
161    let isNew = true;
162    try {
163      if (e.file_path && (await $.fs.exists(e.file_path))) {
164        before = await $.fs.read(e.file_path);
165        isNew = false;
166      }
167    } catch { /* unreadable: show it as a new file */ }
168    return [{ tool: "Write", file, diff: diffLines(before, e.content), note: isNew ? "new file" : "rewrite" }];
169  }
170  return [];
171}
172
173function hintText() {
174  const n = state.replay.length;
175  return `▶ Replay: ${n} edit${n === 1 ? "" : "s"} (press r)`;
176}
177
178async function openReplay($) {
179  if (!state.replay.length) return false;
180  state.index = 0;
181  state.isOpen = true;
182  // The pane only takes the keyboard while nothing else holds it. Hide the
183  // band first (it held the keys if its button was pressed), then open.
184  $.ui.invalidate("ui.render");
185  await $.clock.sleep(200);
186  const rows = Math.min(MAX_DIFF_LINES + 8, 22);
187  const placed = await $.ui.open({ id: PANE_ID, title: "Replay Theater", focus: true, closeOnEscape: true, rows, columns: 58 });
188  // No room for a pane (a narrow terminal): draw the replay in the band.
189  state.inBand = placed?.isPlaced === false;
190  $.ui.invalidate("ui.render");
191  return true;
192}
193
194// The replay view: one step at a time. Drawn in the Pane, or in the band
195// above the prompt when the surface can't place a pane.
196function replayView($, e, inBand) {
197    const { Box, Text, Button } = $.ui.resolve(e);
198    const maxDiff = inBand ? Math.max(3, Math.min(MAX_DIFF_LINES, (e.maxRows || 20) - 7)) : MAX_DIFF_LINES;
199    const total = state.replay.length;
200    if (!total) return Text({ dimColor: true, children: "No edits to replay." });
201    const k = Math.max(0, Math.min(state.index, total - 1));
202    const step = state.replay[k];
203    const width = Math.max(40, (e.bodyColumns || 100) - 4);
204    const { add, del } = countChanges(step.diff);
205    const shown = step.diff.slice(0, maxDiff);
206
207    const diffRows = shown.map((l, n) => {
208      const color = l.op === "+" ? "green" : l.op === "-" ? "red" : undefined;
209      const line = `${l.op === "~" ? " " : l.op} ${l.t}`.slice(0, width);
210      return Text({ key: `d${n}`, color, dimColor: l.op === " " || l.op === "~", wrap: "truncate-end", children: line });
211    });
212    if (step.diff.length > maxDiff) diffRows.push(Text({ key: "more", dimColor: true, children: `  … ${step.diff.length - maxDiff} more lines` }));
213    if (!shown.length) diffRows.push(Text({ key: "empty", dimColor: true, children: "  (no line changes)" }));
214
215    // The step list: one cell per step, the current one highlighted.
216    const strip = state.replay.map((s, n) =>
217      Text({ key: `s${n}`, inverse: n === k, color: n === k ? "cyan" : undefined, dimColor: n !== k, children: ` ${n + 1} ` }));
218
219    const go = (to) => { state.index = Math.max(0, Math.min(to, total - 1)); $.ui.invalidate("ui.render"); };
220    const close = () => {
221      state.isOpen = false;
222      if (!state.inBand) $.ui.close({ id: PANE_ID });
223      state.inBand = false;
224      $.ui.invalidate("ui.render");
225    };
226
227    return Box({
228      flexDirection: "column", borderStyle: "round", borderColor: "magenta", paddingX: 1,
229      children: [
230        Box({ flexDirection: "row", justifyContent: "space-between", children: [
231          Text({ bold: true, color: "magenta", children: "▶ Replay Theater" }),
232          Text({ bold: true, children: `step ${k + 1} of ${total}` }),
233        ] }),
234        Box({ flexDirection: "row", children: strip }),
235        Text({ bold: true, color: "cyan", wrap: "truncate-start", children: step.file }),
236        Box({ flexDirection: "row", gap: 2, children: [
237          Text({ dimColor: true, children: `${step.tool}${step.note ? " · " + step.note : ""}` }),
238          Text({ color: "green", children: `+${add}` }),
239          Text({ color: "red", children: `-${del}` }),
240        ] }),
241        Box({ flexDirection: "column", marginTop: 1, children: diffRows }),
242        Box({ flexDirection: "row", gap: 2, marginTop: 1, children: [
243          Button({ key: "prev", label: "◀ Prev", hotkey: "p", onPress: () => go(k - 1) }),
244          Button({ key: "next", label: "Next ▶", hotkey: "n", autoFocus: true, onPress: () => go(k + 1) }),
245          Button({ key: "close", label: "Close", hotkey: "c", onPress: close }),
246        ] }),
247      ],
248    });
249}
250
251export function register(on, options) {
252  // Slash command: /replay opens the pane.
253  on("session.start", async ($, e, next) => {
254    const r = await next(e);
255    try {
256      sw.sid = await $.session.id();
257      await $.command.register({ name: "replay", description: "Replay Theater: step through the last turn's file edits" });
258      await poll($).catch(() => undefined);
259      $.clock.every(POLL_MS, () => { void poll($).catch(() => undefined); });
260    } catch { /* the mod still records */ }
261    return r;
262  });
263
264  on("command.run", { command: "replay" }, async ($, e) => {
265    if (sw.off) return { text: "Replay Theater is off. Turn it on with /mods." };
266    if (sw.hidden) await setHidden($, false);
267    const opened = await openReplay($);
268    return { text: opened ? `Replay Theater: ${state.replay.length} edits` : "Replay Theater: no edits in the last turn." };
269  });
270
271  // Record each edit, then let it run. Never blocks the call.
272  on("tool.call", async ($, e, next) => {
273    if (!sw.off && EDIT_TOOLS.has(e.tool)) {
274      try {
275        const steps = await stepsFor($, e);
276        state.pending.push(...steps);
277      } catch { /* recording must never stop the edit */ }
278    }
279    return next(e);
280  });
281
282  on("turn.start", ($, e, next) => {
283    if (!e.agentId) state.pending = [];
284    return next(e);
285  });
286
287  // At the end of a main-loop turn, the pending edits become the replay.
288  on("turn.complete", async ($, e, next) => {
289    const r = await next(e);
290    if (sw.off || e.agentId || !state.pending.length) return r;
291    state.replay = state.pending;
292    state.pending = [];
293    state.index = 0;
294    state.turns++;
295    $.ui.invalidate("ui.render");
296    return r;
297  });
298
299  // The band above the prompt: the hint and a button that opens the pane.
300  // Local change (Ben AI, 2026-10-16): draw the other mods' bands first, so
301  // this band sits under them instead of replacing them.
302  on("ui.render", { component: "AbovePrompt" }, async ($, e, next) => {
303    if (sw.off || sw.hidden) return next(e);
304    if (state.isOpen && state.inBand) return replayView($, e, true);
305    if (!state.replay.length || state.isOpen) return next(e);
306    const rest = await next(e);
307    const { Box, Text, Button } = $.ui.resolve(e);
308    const band = Box({
309      key: "replay-band", flexDirection: "row", gap: 2, paddingX: 1,
310      children: [
311        Text({ color: "magenta", bold: true, children: hintText() }),
312        Button({ key: "open-replay", label: "Replay", hotkey: "r", onPress: () => openReplay($) }),
313      ],
314    });
315    return rest ? Box({ flexDirection: "column", children: [rest, band] }) : band;
316  });
317
318  // The pane.
319  on("ui.render", { component: "Pane" }, ($, e, next) => {
320    if (e.requestId !== PANE_ID || sw.off) return next(e);
321    return replayView($, e, false);
322  });
323
324  // The person closed the pane (Escape): keep our flag in step.
325  on("ui.close", ($, e, next) => {
326    if (e.id === PANE_ID || e.requestId === PANE_ID) state.isOpen = false;
327    $.ui.invalidate("ui.render");
328    return next(e);
329  });
330}
331