import { type Worksheet } from "exceljs";


/**
 * Converts an Excel column label to a 1-based number.
 * Example: A -> 1, Z -> 26, AA -> 27
 */
function columnToNumber(label: string): number {
  let n = 0;

  for (let i = 0; i < label.length; i++) {
    n = n * 26 + label.charCodeAt(i) - 64;
  }

  return n;
}

/**
 * Generates merge ranges like:
 * C8:G10, I8:M10, ...
 * then C14:G16, I14:M16, ...
 */
type MergeRangePattern = {
  startColumns: readonly string[];
  firstStartRow: number;
  mergeWidthInColumns: number;
  mergeHeightInRows: number;
  mergeBlockCount: number;
  rowStepBetweenBlocks: number;
};

export function applyMergePattern(sheet: Worksheet, config: MergeRangePattern) {

  const {
    startColumns,
    firstStartRow,
    mergeWidthInColumns,
    mergeHeightInRows,
    mergeBlockCount,
    rowStepBetweenBlocks
  } = config;

  for (let block = 0; block < mergeBlockCount; block++) {

    const rowStart = firstStartRow + block * rowStepBetweenBlocks;
    const rowEnd = rowStart + mergeHeightInRows - 1;

    for (const column of startColumns) {

      const colStart = columnToNumber(column);
      const colEnd = colStart + mergeWidthInColumns - 1;

      sheet.mergeCells(rowStart, colStart, rowEnd, colEnd);

    }
  }
}