styledTextRange

/**
 * Slice styled text while preserving style ranges.
 *
 * Idea:
 * - Slice the raw text normally.
 * - For each style range, keep only the part that overlaps [start, end).
 * - Shift kept ranges left by `start` so offsets are relative to new text.
 *
 * @param {{
 *   text: string,
 *   ranges: { start: number, end: number, style: string }[],
 * }} node
 * @param {number} start
 * @param {number} end
 * @returns {{
 *   text: string,
 *   ranges: { start: number, end: number, style: string }[],
 * }}
 */
export default function sliceStyledText(node, start, end) {
  if (start === end) {
    return {
      text: '',
      ranges: [],
    };
  }

  const ranges = [];

  for (const range of node.ranges) {
    const overlapStart = Math.max(range.start, start);
    const overlapEnd = Math.min(range.end, end);

    // Positive overlap only.
    if (overlapStart < overlapEnd) {
      ranges.push({
        start: overlapStart - start,
        end: overlapEnd - start,
        style: range.style,
      });
    }
  }

  return {
    text: node.text.slice(start, end),
    ranges,
  };
}