/* =============================================================================
 * ui_template_sheet_header.ts
 * 여러 층 머리 짜기 — 열마다 `머리`(층 수만큼 글) → 층마다 칸(colspan · rowspan).
 *
 * `null` = 위 칸과 합침(세로) · 모자란 층도 `null` 로 채움(위 칸이 늘어남).
 * 옆 열과 그 층까지 앞머리가 모두 같고 아래 합침 모양도 같으면 가로로 합침.
 * ========================================================================== */

import type { SheetColumn } from "./ui_template_sheet_types";

export interface HeadCell {
  level: number;
  col: number;
  colspan: number;
  rowspan: number;
  label: string;
}

export function headDepth(cols: SheetColumn[], layers?: string[]): number {
  return Math.max(1, layers?.length ?? 0, ...cols.map((c) => c.머리.length));
}

/** 층마다 칸 목록 — 앞 층부터. */
export function layoutHead(cols: SheetColumn[], depth: number): HeadCell[][] {
  const paths = cols.map((c) =>
    Array.from({ length: depth }, (_, i) => (i === 0 ? (c.머리[0] ?? "") : (c.머리[i] ?? null))),
  );
  const span = (j: number, i: number): number => {
    let k = i + 1;
    while (k < depth && paths[j][k] === null) k += 1;
    return k - i;
  };
  const samePrefix = (a: number, b: number, i: number): boolean =>
    paths[a].slice(0, i + 1).every((label, lv) => label === paths[b][lv]);

  const levels: HeadCell[][] = [];
  for (let i = 0; i < depth; i += 1) {
    const cells: HeadCell[] = [];
    let j = 0;
    while (j < cols.length) {
      if (paths[j][i] === null) {
        j += 1;
        continue;
      }
      const rowspan = span(j, i);
      let colspan = 1;
      while (
        j + colspan < cols.length &&
        paths[j + colspan][i] !== null &&
        samePrefix(j, j + colspan, i) &&
        span(j + colspan, i) === rowspan
      ) {
        colspan += 1;
      }
      cells.push({ level: i, col: j, colspan, rowspan, label: paths[j][i] as string });
      j += colspan;
    }
    levels.push(cells);
  }
  return levels;
}