import stringWidth from 'string-width';

const graphemeSegmenter = new Intl.Segmenter(undefined, { granularity: 'grapheme' });

/** The number of terminal cells occupied by a string. */
export function terminalCellWidth(value: string): number {
  return stringWidth(value);
}

/**
 * Truncate without splitting emoji, combining marks, or other grapheme
 * clusters. The ellipsis itself is included in the cell budget.
 */
export function truncateTerminalText(value: string, maxWidth: number): string {
  const width = Number.isFinite(maxWidth) ? Math.max(0, Math.floor(maxWidth)) : 0;
  if (width === 0 || value.length === 0) return '';
  if (terminalCellWidth(value) <= width) return value;

  const ellipsis = '…';
  if (width <= terminalCellWidth(ellipsis)) return ellipsis;

  const budget = width - terminalCellWidth(ellipsis);
  let used = 0;
  let result = '';
  for (const { segment } of graphemeSegmenter.segment(value)) {
    const segmentWidth = terminalCellWidth(segment);
    if (used + segmentWidth > budget) break;
    result += segment;
    used += segmentWidth;
  }
  return `${result}${ellipsis}`;
}

/** Truncate and right-pad a string to an exact terminal-cell width. */
export function fitTerminalText(value: string, width: number): string {
  const target = Number.isFinite(width) ? Math.max(0, Math.floor(width)) : 0;
  const truncated = truncateTerminalText(value, target);
  return `${truncated}${' '.repeat(Math.max(0, target - terminalCellWidth(truncated)))}`;
}

/** Remove one user-perceived character without splitting an emoji cluster. */
export function removeLastGrapheme(value: string): string {
  const segments = Array.from(graphemeSegmenter.segment(value));
  const last = segments.at(-1);
  return last ? value.slice(0, last.index) : '';
}

/** Keep at most `limit` grapheme clusters without adding display punctuation. */
export function limitGraphemes(value: string, limit: number): string {
  const maximum = Number.isFinite(limit) ? Math.max(0, Math.floor(limit)) : 0;
  if (maximum === 0) return '';
  let result = '';
  let count = 0;
  for (const { segment } of graphemeSegmenter.segment(value)) {
    if (count >= maximum) break;
    result += segment;
    count++;
  }
  return result;
}