/* =============================================================================
 * spreadsheet_commands.ts  (주인 A)
 * 명령 적용 — 문서를 그 자리에서 바꾸고 되돌림 짝 · 바뀐 칸 · 통째 다시 여부를 돌려줌.
 * 병합 규칙(엑셀): 병합 일부를 가르는 칸 쓰기 · 옮기기는 막음(오류 던짐 → 화면이 알림) ·
 * 병합 안에 행열을 넣으면 병합이 늘고 지우면 줆 · 병합하면 왼위 칸 값만 남김.
 * 서식 표는 같은 서식을 한 번만 둠(칸은 번호) · 안 쓰는 서식 정리는 저장 전에(`compactStyles`).
 * 행열 · 옮기기 · 시트 지우기는 바뀐 시트를 통째로 되돌림(`시트통째`) — 다른 시트 식 글까지 한 번에.
 * ========================================================================== */

import {
  colName,
  inRange,
  normRange,
  parseA1,
  parseRange,
  rangeInside,
  rangesOverlap,
  rangeToA1,
  toA1,
} from "./spreadsheet_address";
import {
  addSheet,
  moveSheet,
  removeSheet,
  renameSheet,
  replaceSheet,
} from "./spreadsheet_commands_sheet";
import { shiftForCommand, shiftSpan } from "./spreadsheet_refshift";
import { applyFilter, applySort, shiftFilter } from "./spreadsheet_sortfilter";
import { MAX_COLS, MAX_ROWS } from "./spreadsheet_types";
import type {
  Cell,
  CellRange,
  CellStyle,
  Command,
  CommandEffect,
  Sheet,
  SheetCellAddress,
  Workbook,
} from "./spreadsheet_types";

/** 막힌 명령(병합 가름 · 마지막 시트 지우기 · 같은 시트 이름 …) — 화면이 `message` 를 알림 */
export class CommandError extends Error {}

export type Of<K extends Command["종류"]> = Extract<Command, { 종류: K }>;

export const clone = <T>(x: T): T => structuredClone(x);

export function sheetOf(book: Workbook, id: string): Sheet {
  const s = book.시트.find((x) => x.id === id);
  if (!s) throw new CommandError(`없는 시트: ${id}`);
  return s;
}

const mergesOf = (s: Sheet): CellRange[] =>
  (s.병합 ?? []).map((t) => parseRange(t)).filter((r): r is CellRange => r !== null);

function setMerges(s: Sheet, list: CellRange[]) {
  if (list.length) s.병합 = list.map(rangeToA1);
  else delete s.병합;
}

/** 칸 열쇠 중 범위 안 것 */
function cellsIn(s: Sheet, ranges: CellRange[]): [string, number, number][] {
  const out: [string, number, number][] = [];
  for (const a1 of Object.keys(s.칸)) {
    const at = parseA1(a1);
    if (at && ranges.some((rg) => inRange(rg, at.r, at.c))) out.push([a1, at.r, at.c]);
  }
  return out;
}

const isFull = (rg: CellRange, rows: boolean) =>
  rows ? rg.c0 === 0 && rg.c1 === MAX_COLS - 1 : rg.r0 === 0 && rg.r1 === MAX_ROWS - 1;

function sortKeys(v: unknown): unknown {
  if (!v || typeof v !== "object" || Array.isArray(v)) return v;
  const o = v as Record<string, unknown>;
  return Object.fromEntries(
    Object.keys(o)
      .sort()
      .map((k) => [k, sortKeys(o[k])]),
  );
}
const styleKey = (s: CellStyle) => JSON.stringify(sortKeys(s));

function internStyle(book: Workbook, style: CellStyle): number {
  const key = styleKey(style);
  const i = book.서식.findIndex((s) => styleKey(s) === key);
  if (i >= 0) return i;
  book.서식.push(style);
  return book.서식.length - 1;
}

function setComments(s: Sheet, notes: Record<string, string>) {
  if (Object.keys(notes).length) s.comments = notes;
  else delete s.comments;
}

/** 시트 통째 서식 */
const sheetStyle = (s: Sheet) => s.기본?.서식 ?? 0;

/** 칸 자리에서 물려받는 서식(칸 서식 없을 때) — 행 · 열 · 시트 · 0 */
const inherited = (s: Sheet, r: number, c: number) =>
  s.행?.[r + 1]?.서식 ?? s.열?.[colName(c)]?.서식 ?? sheetStyle(s);

/** 시트 `기본` 한 칸 — undefined 면 지움 · 빈 `기본` 도 지움 */
function setSheetDefault(s: Sheet, key: "서식" | "열폭" | "행높이", value: number | undefined) {
  const d = (s.기본 ??= {});
  if (value === undefined) delete d[key];
  else d[key] = value;
  if (!Object.keys(d).length) delete s.기본;
}

const addr = (시트: string, r: number, c: number): SheetCellAddress => ({ 시트, r, c });

/** 바뀐 시트만 통째 되돌림 짝 */
export function restoreChanged(book: Workbook, old: Sheet[]): Command[] {
  const out: Command[] = [];
  for (const o of old) {
    const now = book.시트.find((x) => x.id === o.id);
    if (now && JSON.stringify(now) !== JSON.stringify(o)) out.push({ 종류: "시트통째", 시트: o });
  }
  return out;
}

/** 모든 식 글을 명령에 맞춰 고침 — 시트 이름을 바꾸기 전에 부름 */
export function rewriteAll(book: Workbook, command: Command) {
  for (const s of book.시트)
    for (const cell of Object.values(s.칸))
      if (cell.식 !== undefined) cell.식 = shiftForCommand(cell.식, s.id, command, book);
}

// ── 칸 ────────────────────────────────────────────────────────────────────

function setCells(book: Workbook, cmd: Of<"칸">): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const merges = mergesOf(s);
  const plan: [string, number, number, Cell | null][] = [];
  for (const [key, cell] of Object.entries(cmd.칸)) {
    const at = parseA1(key);
    if (!at) throw new CommandError(`칸 주소 틀림: ${key}`);
    if (cell && (cell.값 !== undefined || cell.식 !== undefined))
      if (merges.some((m) => inRange(m, at.r, at.c) && (m.r0 !== at.r || m.c0 !== at.c)))
        throw new CommandError("병합한 칸은 왼위 칸에만 값을 넣음");
    plan.push([toA1(at.r, at.c), at.r, at.c, cell]);
  }
  const prev: Record<string, Cell | null> = {};
  for (const [a1, , , cell] of plan) {
    prev[a1] = s.칸[a1] ? clone(s.칸[a1]) : null;
    if (cell) s.칸[a1] = clone(cell);
    else delete s.칸[a1];
  }
  return {
    undo: { 종류: "칸", 시트: s.id, 칸: prev },
    cells: plan.map(([, r, c]) => addr(s.id, r, c)),
    rebuild: false,
  };
}

function clearContents(book: Workbook, cmd: Of<"내용지움">): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const prev: Record<string, Cell | null> = {};
  const cells: SheetCellAddress[] = [];
  for (const [a1, r, c] of cellsIn(s, cmd.범위)) {
    const cell = s.칸[a1];
    if (cell.값 === undefined && cell.식 === undefined) continue;
    prev[a1] = clone(cell);
    if (cell.서식 === undefined) delete s.칸[a1];
    else s.칸[a1] = { 서식: cell.서식 };
    cells.push(addr(s.id, r, c));
  }
  return { undo: { 종류: "칸", 시트: s.id, 칸: prev }, cells, rebuild: false };
}

// ── 서식 ────────────────────────────────────────────────────────────────────

/** 범위 서식 바꿈 — `change(지금 번호) → 새 번호`. 행 · 열 전체는 행 · 열 서식 + 든 칸. */
function restyle(
  book: Workbook,
  sheet: string,
  ranges: CellRange[],
  change: (i: number) => number,
): CommandEffect {
  const s = sheetOf(book, sheet);
  const before = clone(s);
  const memo = new Map<number, number>();
  const f = (i: number) => {
    if (!memo.has(i)) memo.set(i, change(i));
    return memo.get(i)!;
  };
  const prev: Record<string, Cell | null> = {};
  const cells: SheetCellAddress[] = [];
  let whole = false;
  const setInfo = (axis: "행" | "열", key: string) => {
    const table = (s[axis] ??= {});
    const info = (table[key] ??= {});
    const idx = f(info.서식 ?? sheetStyle(s));
    if (idx !== sheetStyle(s)) info.서식 = idx;
    else delete info.서식;
    if (!Object.keys(info).length) delete table[key];
  };
  const touch = (r: number, c: number) => {
    const a1 = toA1(r, c);
    if (a1 in prev) return;
    const cell = s.칸[a1];
    prev[a1] = cell ? clone(cell) : null;
    const next: Cell = { ...cell };
    const idx = f(cell?.서식 ?? inherited(s, r, c));
    if (idx === inherited(s, r, c)) delete next.서식;
    else next.서식 = idx;
    if (Object.keys(next).length) s.칸[a1] = next;
    else delete s.칸[a1];
    cells.push(addr(s.id, r, c));
  };
  for (const rg of ranges) {
    const fullRows = isFull(rg, true);
    const fullCols = isFull(rg, false);
    if (fullRows && fullCols) {
      whole = true;
      const idx = f(sheetStyle(s));
      setSheetDefault(s, "서식", idx || undefined);
      for (const k of Object.keys(s.행 ?? {})) setInfo("행", k);
      for (const k of Object.keys(s.열 ?? {})) setInfo("열", k);
    } else if (fullRows || fullCols) {
      whole = true;
      for (let i = fullRows ? rg.r0 : rg.c0; i <= (fullRows ? rg.r1 : rg.c1); i++)
        setInfo(fullRows ? "행" : "열", fullRows ? String(i + 1) : colName(i));
    } else {
      if ((rg.r1 - rg.r0 + 1) * (rg.c1 - rg.c0 + 1) > 1_000_000)
        throw new CommandError("범위가 너무 큼");
      for (let r = rg.r0; r <= rg.r1; r++) for (let c = rg.c0; c <= rg.c1; c++) touch(r, c);
      continue;
    }
    for (const [, r, c] of cellsIn(s, [rg])) touch(r, c);
  }
  if (s.행 && !Object.keys(s.행).length) delete s.행;
  if (s.열 && !Object.keys(s.열).length) delete s.열;
  return whole
    ? { undo: { 종류: "시트통째", 시트: before }, cells, rebuild: true }
    : { undo: { 종류: "칸", 시트: s.id, 칸: prev }, cells, rebuild: false };
}

function patchStyle(book: Workbook, cmd: Of<"서식">): CommandEffect {
  return restyle(book, cmd.시트, cmd.범위, (i) => {
    const next: Record<string, unknown> = { ...book.서식[i] };
    for (const [k, v] of Object.entries(cmd.바꿀)) {
      if (v === null) delete next[k];
      else if (v !== undefined) next[k] = clone(v);
    }
    return internStyle(book, next as CellStyle);
  });
}

// ── 행열 넣기 · 지우기 ──────────────────────────────────────────────────────

function insertDelete(
  book: Workbook,
  cmd: Of<"행넣기" | "행지우기" | "열넣기" | "열지우기">,
): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const rows = cmd.종류.startsWith("행");
  const insert = cmd.종류.endsWith("넣기");
  const max = rows ? MAX_ROWS : MAX_COLS;
  const { at, 수: n } = cmd;
  if (n < 1 || at < 0 || at >= max || (!insert && at + n > max))
    throw new CommandError("넣기 · 지우기 자리가 틀림");
  const pos = (a1: string) => {
    const p = parseA1(a1)!;
    return rows ? p.r : p.c;
  };
  if (insert && Object.keys(s.칸).some((a1) => pos(a1) + n >= max))
    throw new CommandError("격자 끝 칸이 밀려 나감 — 끝 쪽 칸을 먼저 지움");
  const old = book.시트.map(clone);
  rewriteAll(book, cmd);
  const span = (i: number) => shiftSpan(i, i, insert, at, n, max)?.[0];

  const cells: Record<string, Cell> = {};
  for (const [a1, cell] of Object.entries(s.칸)) {
    const p = parseA1(a1)!;
    const i = span(rows ? p.r : p.c);
    if (i !== undefined) cells[rows ? toA1(i, p.c) : toA1(p.r, i)] = cell;
  }
  s.칸 = cells;
  if (s.comments) {
    const notes: Record<string, string> = {};
    for (const [a1, text] of Object.entries(s.comments)) {
      const p = parseA1(a1);
      const i = p && span(rows ? p.r : p.c);
      if (p && i !== undefined && i !== null) notes[rows ? toA1(i, p.c) : toA1(p.r, i)] = text;
    }
    setComments(s, notes);
  }

  const shiftRange = (m: CellRange) => {
    const sp = rows
      ? shiftSpan(m.r0, m.r1, insert, at, n, max)
      : shiftSpan(m.c0, m.c1, insert, at, n, max);
    return sp && (rows ? { ...m, r0: sp[0], r1: sp[1] } : { ...m, c0: sp[0], c1: sp[1] });
  };
  const merges: CellRange[] = [];
  for (const m of mergesOf(s)) {
    const next = shiftRange(m);
    if (next && (next.r0 !== next.r1 || next.c0 !== next.c1)) merges.push(next);
  }
  setMerges(s, merges);
  // 이름 범위도 따라감 · 범위가 통째로 지워진 이름은 뺌(엑셀은 `#REF!` 이름으로 남김 — 여기선 식이 `#NAME?`)
  if (s.이름정의)
    s.이름정의 = s.이름정의.flatMap((d) => {
      const 범위 = shiftRange(d.범위);
      return 범위 ? [{ ...d, 범위 }] : [];
    });

  const axis = rows ? "행" : "열";
  const table = s[axis];
  if (table) {
    const next: Record<string, (typeof table)[string]> = {};
    for (const [k, v] of Object.entries(table)) {
      const i = span(rows ? Number(k) - 1 : parseA1(`${k}1`)!.c);
      if (i !== undefined) next[rows ? String(i + 1) : colName(i)] = v;
    }
    if (Object.keys(next).length) s[axis] = next;
    else delete s[axis];
  }

  // 넣은 줄은 위(왼) 줄 서식 · 폭 · 높이를 따라감(엑셀 「위와 같은 서식」) — 첫 줄 앞 넣기는 안 따라감
  if (insert && at > 0) {
    for (const [a1, cell] of Object.entries(s.칸)) {
      const p = parseA1(a1)!;
      if ((rows ? p.r : p.c) !== at - 1 || cell.서식 === undefined) continue;
      for (let k = 0; k < n; k++)
        s.칸[rows ? toA1(at + k, p.c) : toA1(p.r, at + k)] = { 서식: cell.서식 };
    }
    const info = s[axis]?.[rows ? String(at) : colName(at - 1)];
    if (info) {
      const { 숨김: _hidden, ...look } = info;
      if (Object.keys(look).length)
        for (let k = 0; k < n; k++)
          s[axis]![rows ? String(at + k + 1) : colName(at + k)] = { ...look };
    }
  }

  shiftFilter(s, rows, insert, at, n);
  const key = rows ? "행" : "열";
  const frozen = s.틀고정?.[key];
  if (frozen && at < frozen)
    s.틀고정![key] = insert ? frozen + n : frozen - (Math.min(frozen, at + n) - at);

  return { undo: { 종류: "묶음", 명령: restoreChanged(book, old) }, cells: [], rebuild: true };
}

// ── 옮기기 (잘라 붙이기) ─────────────────────────────────────────────────────

function move(book: Workbook, cmd: Of<"옮기기">): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const t = sheetOf(book, cmd.대상시트);
  const src = normRange(cmd.범위.r0, cmd.범위.c0, cmd.범위.r1, cmd.범위.c1);
  const dr = cmd.r - src.r0;
  const dc = cmd.c - src.c0;
  const dst: CellRange = { r0: cmd.r, c0: cmd.c, r1: src.r1 + dr, c1: src.c1 + dc };
  if (dst.r0 < 0 || dst.c0 < 0 || dst.r1 >= MAX_ROWS || dst.c1 >= MAX_COLS)
    throw new CommandError("옮길 자리가 격자 밖");
  const cuts = (list: CellRange[], rg: CellRange) =>
    list.some((m) => rangesOverlap(m, rg) && !rangeInside(m, rg));
  if (cuts(mergesOf(s), src) || cuts(mergesOf(t), dst))
    throw new CommandError("병합 일부를 가르는 옮기기는 못 함");
  if (s === t && dr === 0 && dc === 0)
    return { undo: { 종류: "묶음", 명령: [] }, cells: [], rebuild: false };

  const old = book.시트.map(clone);
  const moved: [number, number, Cell][] = [];
  for (const [a1, r, c] of cellsIn(s, [src])) {
    const cell = s.칸[a1];
    if (cell.식 !== undefined) cell.식 = shiftForCommand(cell.식, s.id, cmd, book, t.id);
    moved.push([r + dr, c + dc, cell]);
    delete s.칸[a1];
  }
  rewriteAll(book, cmd);
  for (const [a1] of cellsIn(t, [dst])) delete t.칸[a1];
  for (const [r, c, cell] of moved) t.칸[toA1(r, c)] = cell;
  // 메모도 칸과 같이 — 덮은 자리 메모는 지움
  const carriedNotes: [string, string][] = [];
  const srcNotes = { ...s.comments };
  for (const [a1, text] of Object.entries(srcNotes)) {
    const p = parseA1(a1);
    if (p && inRange(src, p.r, p.c)) {
      carriedNotes.push([toA1(p.r + dr, p.c + dc), text]);
      delete srcNotes[a1];
    }
  }
  setComments(s, srcNotes);
  const dstNotes = { ...t.comments };
  for (const a1 of Object.keys(dstNotes)) {
    const p = parseA1(a1);
    if (p && inRange(dst, p.r, p.c)) delete dstNotes[a1];
  }
  setComments(t, { ...dstNotes, ...Object.fromEntries(carriedNotes) });

  const sm = mergesOf(s);
  const carried = sm.filter((m) => rangeInside(m, src));
  setMerges(
    s,
    sm.filter((m) => !rangeInside(m, src)),
  );
  setMerges(t, [
    ...mergesOf(t).filter((m) => !rangeInside(m, dst)),
    ...carried.map((m) => ({ r0: m.r0 + dr, c0: m.c0 + dc, r1: m.r1 + dr, c1: m.c1 + dc })),
  ]);
  return { undo: { 종류: "묶음", 명령: restoreChanged(book, old) }, cells: [], rebuild: true };
}

// ── 병합 ────────────────────────────────────────────────────────────────────

function merge(book: Workbook, cmd: Of<"병합">): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const rg = normRange(cmd.범위.r0, cmd.범위.c0, cmd.범위.r1, cmd.범위.c1);
  if (rg.r0 === rg.r1 && rg.c0 === rg.c1)
    return { undo: { 종류: "묶음", 명령: [] }, cells: [], rebuild: false };
  const list = mergesOf(s);
  if (list.some((m) => rangesOverlap(m, rg) && !rangeInside(m, rg)))
    throw new CommandError("다른 병합과 걸침");
  const absorbed = list.filter((m) => rangeInside(m, rg));
  const prev: Record<string, Cell | null> = {};
  const cells: SheetCellAddress[] = [];
  for (const [a1, r, c] of cellsIn(s, [rg])) {
    const cell = s.칸[a1];
    if ((r === rg.r0 && c === rg.c0) || (cell.값 === undefined && cell.식 === undefined)) continue;
    prev[a1] = clone(cell);
    if (cell.서식 === undefined) delete s.칸[a1];
    else s.칸[a1] = { 서식: cell.서식 };
    cells.push(addr(s.id, r, c));
  }
  setMerges(s, [...list.filter((m) => !rangeInside(m, rg)), rg]);
  const undo: Command[] = [
    { 종류: "병합풀기", 시트: s.id, 범위: rg },
    ...absorbed.map((m): Command => ({ 종류: "병합", 시트: s.id, 범위: m })),
    { 종류: "칸", 시트: s.id, 칸: prev },
  ];
  return { undo: { 종류: "묶음", 명령: undo }, cells, rebuild: false };
}

function unmerge(book: Workbook, cmd: Of<"병합풀기">): CommandEffect {
  const s = sheetOf(book, cmd.시트);
  const list = mergesOf(s);
  const gone = list.filter((m) => rangesOverlap(m, cmd.범위));
  setMerges(
    s,
    list.filter((m) => !rangesOverlap(m, cmd.범위)),
  );
  const undo = gone.map((m): Command => ({ 종류: "병합", 시트: s.id, 범위: m }));
  return { undo: { 종류: "묶음", 명령: undo }, cells: [], rebuild: false };
}

// ── 행 · 열 모양 ─────────────────────────────────────────────────────────────

/** 행 · 열 정보 한 속성 바꿈 → 원래 값끼리 묶은 되돌림 짝 */
function setAxis<V>(
  s: Sheet,
  axis: "행" | "열",
  idx: number[],
  prop: "폭" | "높이" | "숨김" | "묶음",
  value: V | null,
  undoOf: (idx: number[], prev: V | null) => Command,
): Command {
  const table = ((s as unknown as Record<string, Record<string, Record<string, unknown>>>)[axis] ??=
    {});
  const groups = new Map<string, number[]>();
  for (const i of idx) {
    const k = axis === "열" ? colName(i) : String(i + 1);
    const prev = table[k]?.[prop];
    const g = JSON.stringify(prev ?? null);
    groups.set(g, [...(groups.get(g) ?? []), i]);
    const info = (table[k] ??= {});
    if (value === null || value === false) delete info[prop];
    else info[prop] = value;
    if (!Object.keys(info).length) delete table[k];
  }
  if (!Object.keys(table).length) delete s[axis];
  return { 종류: "묶음", 명령: [...groups].map(([g, list]) => undoOf(list, JSON.parse(g))) };
}

/** 모두 고르기 폭 · 높이 — 시트 `기본` 에 두고 줄마다 값은 지움(엑셀 기본 폭 · 높이) */
function sheetSize(s: Sheet, axis: "행" | "열", value: number | null): CommandEffect {
  const before = clone(s);
  const prop = axis === "열" ? "폭" : "높이";
  setSheetDefault(s, axis === "열" ? "열폭" : "행높이", value ?? undefined);
  const table = s[axis] as Record<string, Record<string, unknown>> | undefined;
  for (const [k, info] of Object.entries(table ?? {})) {
    delete info[prop];
    if (!Object.keys(info).length) delete table![k];
  }
  if (table && !Object.keys(table).length) delete s[axis];
  return { undo: { 종류: "시트통째", 시트: before }, cells: [], rebuild: false };
}

function batch(book: Workbook, cmd: Of<"묶음">): CommandEffect {
  const done: CommandEffect[] = [];
  try {
    for (const c of cmd.명령) done.push(applyCommand(book, c));
  } catch (e) {
    for (const d of done.reverse()) applyCommand(book, d.undo);
    throw e;
  }
  return {
    undo: { 종류: "묶음", 명령: done.map((d) => d.undo).reverse() },
    cells: done.flatMap((d) => d.cells),
    rebuild: done.some((d) => d.rebuild),
  };
}

// ── 들머리 ──────────────────────────────────────────────────────────────────

export function applyCommand(book: Workbook, command: Command): CommandEffect {
  const plain = (undo: Command): CommandEffect => ({ undo, cells: [], rebuild: false });
  switch (command.종류) {
    case "칸":
      return setCells(book, command);
    case "내용지움":
      return clearContents(book, command);
    case "서식":
      return patchStyle(book, command);
    case "서식지움":
      return restyle(book, command.시트, command.범위, () => 0);
    case "행넣기":
    case "행지우기":
    case "열넣기":
    case "열지우기":
      return insertDelete(book, command);
    case "옮기기":
      return move(book, command);
    case "병합":
      return merge(book, command);
    case "병합풀기":
      return unmerge(book, command);
    case "열폭": {
      const s = sheetOf(book, command.시트);
      if (new Set(command.열).size >= MAX_COLS) return sheetSize(s, "열", command.폭);
      return plain(
        setAxis(s, "열", command.열, "폭", command.폭, (열, 폭) => ({
          종류: "열폭",
          시트: s.id,
          열,
          폭,
        })),
      );
    }
    case "행높이": {
      const s = sheetOf(book, command.시트);
      if (new Set(command.행).size >= MAX_ROWS) return sheetSize(s, "행", command.높이);
      return plain(
        setAxis(s, "행", command.행, "높이", command.높이, (행, 높이) => ({
          종류: "행높이",
          시트: s.id,
          행,
          높이,
        })),
      );
    }
    case "숨김": {
      const s = sheetOf(book, command.시트);
      const { 축 } = command;
      return plain(
        setAxis(s, 축, command.번호, "숨김", command.숨김, (번호, prev) => ({
          종류: "숨김",
          시트: s.id,
          축,
          번호,
          숨김: prev ?? false,
        })),
      );
    }
    case "묶음설정": {
      const s = sheetOf(book, command.시트);
      const { 축 } = command;
      return plain(
        setAxis(s, 축, command.번호, "묶음", command.묶음, (번호, prev) => ({
          종류: "묶음설정",
          시트: s.id,
          축,
          번호,
          묶음: prev,
        })),
      );
    }
    case "틀고정": {
      const s = sheetOf(book, command.시트);
      const prev = { 행: s.틀고정?.행 ?? 0, 열: s.틀고정?.열 ?? 0 };
      const next: Sheet["틀고정"] = {};
      if (command.행 > 0) next.행 = command.행;
      if (command.열 > 0) next.열 = command.열;
      if (Object.keys(next).length) s.틀고정 = next;
      else delete s.틀고정;
      return plain({ 종류: "틀고정", 시트: s.id, ...prev });
    }
    case "눈금선": {
      const s = sheetOf(book, command.시트);
      const prev = s.보기?.눈금선 ?? true;
      if (command.보임) {
        delete s.보기?.눈금선;
        if (s.보기 && !Object.keys(s.보기).length) delete s.보기;
      } else (s.보기 ??= {}).눈금선 = false;
      return plain({ 종류: "눈금선", 시트: s.id, 보임: prev });
    }
    case "시트더하기":
      return addSheet(book, command);
    case "시트지우기":
      return removeSheet(book, command);
    case "시트이름":
      return renameSheet(book, command);
    case "시트옮기기":
      return moveSheet(book, command);
    case "시트통째":
      return replaceSheet(book, command);
    case "정렬":
      return applySort(book, command);
    case "필터":
      return applyFilter(book, command);
    case "묶음":
      return batch(book, command);
  }
}

/** 빈 통합문서 — 시트 하나(`s1` · 이름은 부른 쪽) · 서식 [{}] */
export function emptyWorkbook(column: string, sheetName: string): Workbook {
  return {
    종류: "통합문서",
    판: 1,
    열: column,
    서식: [{}],
    시트: [emptySheet("s1", sheetName)],
    활성: "s1",
  };
}

export function emptySheet(id: string, name: string): Sheet {
  return { id, 이름: name, 칸: {} };
}

/** 안 쓰는 서식을 빼고 번호를 다시 매김 — 저장 직전(되돌리기 짝은 안 만듦) */
export function compactStyles(book: Workbook): void {
  const next: CellStyle[] = [];
  const byKey = new Map<string, number>();
  const remap = new Map<number, number>();
  const map = (i: number) => {
    let j = remap.get(i);
    if (j === undefined) {
      const style = book.서식[i] ?? {};
      const k = styleKey(style);
      j = byKey.get(k);
      if (j === undefined) {
        j = next.push(style) - 1;
        byKey.set(k, j);
      }
      remap.set(i, j);
    }
    return j;
  };
  map(0);
  for (const s of book.시트) {
    for (const cell of Object.values(s.칸)) if (cell.서식 !== undefined) cell.서식 = map(cell.서식);
    for (const info of [...Object.values(s.행 ?? {}), ...Object.values(s.열 ?? {}), s.기본 ?? {}])
      if (info.서식 !== undefined) info.서식 = map(info.서식);
  }
  book.서식 = next;
}