textSearch

/**
 * Find all case-insensitive, non-overlapping matches of query in content
 * and wrap matched regions in <b>...</b>. Adjacent matches are merged into
 * one bold block.
 *
 * @param {string} content
 * @param {string} query
 * @returns {string}
 */
export default function textSearch(content, query) {
	if (query.length === 0 || content.length === 0 || query.length > content.length) {
		return content;
	}

	const contentLower = content.toLowerCase();
	const queryLower = query.toLowerCase();
	const qLen = query.length;
	const rawRanges = [];

	// Left-to-right greedy scan so earlier characters get priority.
	let i = 0;
	while (i <= content.length - qLen) {
		if (contentLower.slice(i, i + qLen) === queryLower) {
			rawRanges.push([i, i + qLen]);
			i += qLen;
		} else {
			i++;
		}
	}

	if (rawRanges.length === 0) {
		return content;
	}

	// Merge touching ranges: e.g. [0,2] + [2,4] becomes [0,4].
	const mergedRanges = [rawRanges[0]];
	for (let j = 1; j < rawRanges.length; j++) {
		const [start, end] = rawRanges[j];
		const last = mergedRanges[mergedRanges.length - 1];

		if (start <= last[1]) {
			last[1] = Math.max(last[1], end);
		} else {
			mergedRanges.push([start, end]);
		}
	}

	let result = '';
	let cursor = 0;

	for (const [start, end] of mergedRanges) {
		result += content.slice(cursor, start);
		result += `<b>${content.slice(start, end)}</b>`;
		cursor = end;
	}

	result += content.slice(cursor);
	return result;
}

// Examples:
// textSearch('The Quick Brown Fox Jumps Over The Lazy Dog', 'fox')
// => 'The Quick Brown <b>Fox</b> Jumps Over The Lazy Dog'
//
// textSearch('The hardworking Dog overtakes the lazy dog', 'dog')
// => 'The hardworking <b>Dog</b> overtakes the lazy <b>dog</b>'
//
// textSearch('aaa', 'aa')
// => '<b>aa</b>a'
//
// textSearch('aaaa', 'aa')
// => '<b>aaaa</b>'