replay-theater

1// Copyright 2026 Anthropic PBC
2// SPDX-License-Identifier: Apache-2.0
3// Modified 2026 by suhoon (Windows port / display changes). Original: https://github.com/anthropics/claude-code-playground — see NOTICE.
4//
5// Replay Theater: records the file edits Claude makes in a turn, then lets you
6// step through them in a pane, one diff at a time.
7//
8// Claude Code 2.1.280 function hooks. Load with --plugin-dir.
9
10const PANE_ID = "replay-theater";
11const MAX_DIFF_LINES = 12;
12const MAX_LCS_LINES = 400;
13const EDIT_TOOLS = new Set(["Edit", "Write", "MultiEdit"]);
14
15// Module state. `pending` fills during a turn; `replay` is the last finished
16// turn's steps, the ones the pane shows.
17const state = { pending: [], replay: [], index: 0, isOpen: false, inBand: false, turns: 0 };
18
19function relPath(cwd, path) {
20  if (!path) return "(unknown file)";
21  const normalized = String(path).replaceAll("\\", "/");
22  const base = String(cwd || "").replaceAll("\\", "/").replace(/\/$/, "");
23  const isWindows = /^[a-z]:\//i.test(base);
24  const candidate = isWindows ? normalized.toLowerCase() : normalized;
25  const prefix = isWindows ? base.toLowerCase() : base;
26  if (base && candidate.startsWith(prefix + "/")) return normalized.slice(base.length + 1);
27  return normalized;
28}
29
30function splitLines(text) {
31  if (text === undefined || text === null || text === "") return [];
32  const lines = String(text).split(/\r?\n/);
33  if (lines.length > 1 && lines[lines.length - 1] === "") lines.pop();
34  return lines;
35}
36
37// A line diff. Small inputs get an LCS diff, so unchanged lines show as
38// context; large ones fall back to all-removed then all-added.
39function diffLines(oldText, newText) {
40  const a = splitLines(oldText);
41  const b = splitLines(newText);
42  if (a.length > MAX_LCS_LINES || b.length > MAX_LCS_LINES) {
43    return [...a.map((t) => ({ op: "-", t })), ...b.map((t) => ({ op: "+", t }))];
44  }
45  const n = a.length, m = b.length;
46  const dp = Array.from({ length: n + 1 }, () => new Array(m + 1).fill(0));
47  for (let i = n - 1; i >= 0; i--)
48    for (let j = m - 1; j >= 0; j--)
49      dp[i][j] = a[i] === b[j] ? dp[i + 1][j + 1] + 1 : Math.max(dp[i + 1][j], dp[i][j + 1]);
50  const out = [];
51  let i = 0, j = 0;
52  while (i < n && j < m) {
53    if (a[i] === b[j]) { out.push({ op: " ", t: a[i] }); i++; j++; }
54    else if (dp[i + 1][j] >= dp[i][j + 1]) out.push({ op: "-", t: a[i++] });
55    else out.push({ op: "+", t: b[j++] });
56  }
57  while (i < n) out.push({ op: "-", t: a[i++] });
58  while (j < m) out.push({ op: "+", t: b[j++] });
59  return trimContext(out);
60}
61
62// Keep one line of context around each change, so a long file's Write shows
63// the changed lines, not the whole file.
64function trimContext(lines) {
65  if (!lines.some((l) => l.op !== " ")) return lines.slice(0, MAX_DIFF_LINES);
66  const keep = lines.map((l, k) =>
67    l.op !== " " || lines[k - 1]?.op && lines[k - 1].op !== " " || lines[k + 1]?.op && lines[k + 1].op !== " ");
68  const out = [];
69  let skipped = false;
70  lines.forEach((l, k) => {
71    if (keep[k]) { if (skipped && out.length) out.push({ op: "~", t: "⋯" }); out.push(l); skipped = false; }
72    else skipped = true;
73  });
74  return out;
75}
76
77function countChanges(diff) {
78  let add = 0, del = 0;
79  for (const l of diff) { if (l.op === "+") add++; else if (l.op === "-") del++; }
80  return { add, del };
81}
82
83// Turns one tool call into one or more steps.
84async function stepsFor($, e) {
85  let cwd = "";
86  try { cwd = await $.session.cwd(); } catch { /* keep the full path */ }
87  const file = relPath(cwd, e.file_path);
88  if (e.tool === "Edit") {
89    return [{ tool: "Edit", file, diff: diffLines(e.old_string, e.new_string), note: e.replace_all ? "replace all" : "" }];
90  }
91  if (e.tool === "MultiEdit" && Array.isArray(e.edits)) {
92    return e.edits.map((ed, k) => ({
93      tool: "MultiEdit", file, diff: diffLines(ed.old_string, ed.new_string), note: `edit ${k + 1} of ${e.edits.length}`,
94    }));
95  }
96  if (e.tool === "Write") {
97    let before = "";
98    let isNew = true;
99    try {
100      if (e.file_path && (await $.fs.exists(e.file_path))) {
101        before = await $.fs.read(e.file_path);
102        isNew = false;
103      }
104    } catch { /* unreadable: show it as a new file */ }
105    return [{ tool: "Write", file, diff: diffLines(before, e.content), note: isNew ? "new file" : "rewrite" }];
106  }
107  return [];
108}
109
110function hintText() {
111  const n = state.replay.length;
112  return `▶ Replay: ${n} edit${n === 1 ? "" : "s"} (press r)`;
113}
114
115async function openReplay($) {
116  if (!state.replay.length) return false;
117  state.index = 0;
118  state.isOpen = true;
119  // The pane only takes the keyboard while nothing else holds it. Hide the
120  // band first (it held the keys if its button was pressed), then open.
121  $.ui.invalidate("ui.render");
122  await $.clock.sleep(200);
123  const rows = Math.min(MAX_DIFF_LINES + 8, 22);
124  const placed = await $.ui.open({ id: PANE_ID, title: "Replay Theater", focus: true, closeOnEscape: true, rows, columns: 58 });
125  // No room for a pane (a narrow terminal): draw the replay in the band.
126  state.inBand = placed?.isPlaced === false;
127  $.ui.invalidate("ui.render");
128  return true;
129}
130
131// The replay view: one step at a time. Drawn in the Pane, or in the band
132// above the prompt when the surface can't place a pane.
133function replayView($, e, inBand) {
134    const { Box, Text, Button } = $.ui.resolve(e);
135    const maxDiff = inBand ? Math.max(3, Math.min(MAX_DIFF_LINES, (e.maxRows || 20) - 7)) : MAX_DIFF_LINES;
136    const total = state.replay.length;
137    if (!total) return Text({ dimColor: true, children: "No edits to replay." });
138    const k = Math.max(0, Math.min(state.index, total - 1));
139    const step = state.replay[k];
140    const width = Math.max(40, (e.bodyColumns || 100) - 4);
141    const { add, del } = countChanges(step.diff);
142    const shown = step.diff.slice(0, maxDiff);
143
144    const diffRows = shown.map((l, n) => {
145      const color = l.op === "+" ? "green" : l.op === "-" ? "red" : undefined;
146      const line = `${l.op === "~" ? " " : l.op} ${l.t}`.slice(0, width);
147      return Text({ key: `d${n}`, color, dimColor: l.op === " " || l.op === "~", wrap: "truncate-end", children: line });
148    });
149    if (step.diff.length > maxDiff) diffRows.push(Text({ key: "more", dimColor: true, children: `  … ${step.diff.length - maxDiff} more lines` }));
150    if (!shown.length) diffRows.push(Text({ key: "empty", dimColor: true, children: "  (no line changes)" }));
151
152    // The step list: one cell per step, the current one highlighted.
153    const strip = state.replay.map((s, n) =>
154      Text({ key: `s${n}`, inverse: n === k, color: n === k ? "cyan" : undefined, dimColor: n !== k, children: ` ${n + 1} ` }));
155
156    const go = (to) => { state.index = Math.max(0, Math.min(to, total - 1)); $.ui.invalidate("ui.render"); };
157    const close = () => {
158      state.isOpen = false;
159      if (!state.inBand) $.ui.close({ id: PANE_ID });
160      state.inBand = false;
161      $.ui.invalidate("ui.render");
162    };
163
164    return Box({
165      flexDirection: "column", borderStyle: "round", borderColor: "magenta", paddingX: 1,
166      children: [
167        Box({ flexDirection: "row", justifyContent: "space-between", children: [
168          Text({ bold: true, color: "magenta", children: "▶ Replay Theater" }),
169          Text({ bold: true, children: `step ${k + 1} of ${total}` }),
170        ] }),
171        Box({ flexDirection: "row", children: strip }),
172        Text({ bold: true, color: "cyan", wrap: "truncate-start", children: step.file }),
173        Box({ flexDirection: "row", gap: 2, children: [
174          Text({ dimColor: true, children: `${step.tool}${step.note ? " · " + step.note : ""}` }),
175          Text({ color: "green", children: `+${add}` }),
176          Text({ color: "red", children: `-${del}` }),
177        ] }),
178        Box({ flexDirection: "column", marginTop: 1, children: diffRows }),
179        Box({ flexDirection: "row", gap: 2, marginTop: 1, children: [
180          Button({ key: "prev", label: "◀ Prev", hotkey: "p", onPress: () => go(k - 1) }),
181          Button({ key: "next", label: "Next ▶", hotkey: "n", autoFocus: true, onPress: () => go(k + 1) }),
182          Button({ key: "close", label: "Close", hotkey: "c", onPress: close }),
183        ] }),
184      ],
185    });
186}
187
188export function register(on, options) {
189  // Slash command: /replay opens the pane.
190  on("session.start", async ($, e, next) => {
191    const r = await next(e);
192    await $.command.register({ name: "replay", description: "Replay Theater: step through the last turn's file edits" });
193    return r;
194  });
195
196  on("command.run", { command: "replay" }, async ($, e) => {
197    const opened = await openReplay($);
198    return { text: opened ? `Replay Theater: ${state.replay.length} edits` : "Replay Theater: no edits in the last turn." };
199  });
200
201  // Record each edit, then let it run. Never blocks the call.
202  on("tool.call", async ($, e, next) => {
203    if (EDIT_TOOLS.has(e.tool)) {
204      try {
205        const steps = await stepsFor($, e);
206        state.pending.push(...steps);
207      } catch { /* recording must never stop the edit */ }
208    }
209    return next(e);
210  });
211
212  on("turn.start", ($, e, next) => {
213    if (!e.agentId) state.pending = [];
214    return next(e);
215  });
216
217  // At the end of a main-loop turn, the pending edits become the replay.
218  on("turn.complete", async ($, e, next) => {
219    const r = await next(e);
220    if (e.agentId || !state.pending.length) return r;
221    state.replay = state.pending;
222    state.pending = [];
223    state.index = 0;
224    state.turns++;
225    $.ui.invalidate("ui.render");
226    return r;
227  });
228
229  // The band above the prompt: the hint and a button that opens the pane,
230  // stacked over what the plugins beneath draw (token-weather's light) so the
231  // hint never hides another mod's row.
232  on("ui.render", { component: "AbovePrompt" }, async ($, e, next) => {
233    if (state.isOpen && state.inBand) return replayView($, e, true);
234    if (!state.replay.length || state.isOpen) return next(e);
235    const { Box, Text, Button } = $.ui.resolve(e);
236    const below = await next(e);
237    const hint = Box({
238      flexDirection: "row", gap: 2, paddingX: 1,
239      children: [
240        Text({ color: "magenta", bold: true, children: hintText() }),
241        Button({ key: "open-replay", label: "Replay", hotkey: "r", onPress: () => openReplay($) }),
242      ],
243    });
244    return below ? Box({ flexDirection: "column", children: [hint, below] }) : hint;
245  });
246
247  // The pane.
248  on("ui.render", { component: "Pane" }, ($, e, next) => {
249    if (e.requestId !== PANE_ID) return next(e);
250    return replayView($, e, false);
251  });
252
253  // The person closed the pane (Escape): keep our flag in step.
254  on("ui.close", ($, e, next) => {
255    if (e.id === PANE_ID || e.requestId === PANE_ID) state.isOpen = false;
256    $.ui.invalidate("ui.render");
257    return next(e);
258  });
259}
260