Better search results

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "@ztimson/zim-utils",
-	"version": "0.3.8",
+	"version": "0.4.0",
 	"description": "Native, dependency-light ZIM archive reader/searcher and Kiwix catalog downloader for Node.js",
 	"author": "Zak Timson",
 	"license": "MIT",

src/manager.js

@@ -107,7 +107,7 @@ export class ZimManager {
 		const file = match.href + (match.href.endsWith('.zim') ? '' : '.zim');
 		await fs.promises.rm(path.join(this.#dir, file), {force: true});
 		await this.#ensureServer();
-		await this.#waitUntilVisible(file, {expect: false});
+		await this.#waitUntilVicsible(file, {expect: false});
 		return {file: match.file, status: 'deleted'};
 	}
 
@@ -154,9 +154,9 @@ export class ZimManager {
 	}
 
 	/** Two-pass fulltext search across every local ZIM, returns enriched results matching catalog/list shape. */
-	async search(terms, limit = 20) {
+	async search(terms, {limit = 20, sources = null} = {}) {
 		const server = await this.#ensureServer();
-		return server.search(terms, limit);
+		return server.search(terms, {limit, sources});
 	}
 
 	/** Checks all local ZIMs against the catalog and updates any that are outdated. */

src/reader.js

@@ -6,6 +6,8 @@ import {decompressPool} from './decompress.js';
 const HEADER_SIZE = 80;
 const NS_CONTENT = 'C';
 const NS_METADATA = 'M';
+const VOCAB_CACHE_LIMIT = 4;
+const vocabCache = new Map(); // zimPath -> {mtimeMs, size, words: Set<string>};
 
 async function readAt(fd, pos, length) {
 	const buf = Buffer.alloc(length);
@@ -33,7 +35,10 @@ async function readMimeTypes(fd, mimeListPos) {
 	for (;;) {
 		str += (await readAt(fd, pos, 1024)).toString('binary');
 		const end = str.indexOf('\0\0');
-		if (end !== -1) { str = str.slice(0, end + 1); break; }
+		if (end !== -1) {
+			str = str.slice(0, end + 1);
+			break;
+		}
 		pos += 1024;
 	}
 	return str.split('\0').filter(Boolean);
@@ -50,8 +55,15 @@ async function readDirent(fd, offset) {
 		o += 4; // revision, unused
 
 		let redirectIndex = null, cluster = null, blob = null;
-		if (mimetype === 0xffff) { redirectIndex = buf.readUInt32LE(o); o += 4; }
-		else { cluster = buf.readUInt32LE(o); o += 4; blob = buf.readUInt32LE(o); o += 4; }
+		if (mimetype === 0xffff) {
+			redirectIndex = buf.readUInt32LE(o);
+			o += 4;
+		} else {
+			cluster = buf.readUInt32LE(o);
+			o += 4;
+			blob = buf.readUInt32LE(o);
+			o += 4;
+		}
 
 		const urlEnd = buf.indexOf(0, o);
 		if (urlEnd === -1) continue;
@@ -73,7 +85,8 @@ async function findByUrl(fd, header, url, namespace) {
 		const dirKey = dirent.namespace + dirent.url;
 		const cmp = key < dirKey ? -1 : key > dirKey ? 1 : 0;
 		if (cmp === 0) return dirent;
-		if (cmp < 0) hi = mid - 1; else lo = mid + 1;
+		if (cmp < 0) hi = mid - 1;
+		else lo = mid + 1;
 	}
 	return null;
 }
@@ -136,3 +149,37 @@ export async function readZimMetadata(zimPath) {
 		author: creator, publisher,
 	};
 }
+
+/**
+ * Unique, lowercased words pulled from every article title in a ZIM.
+ * Only the deduped Set is cached (not the raw title list), and only for the
+ * last VOCAB_CACHE_LIMIT ZIMs touched (evicted least-recently-used), so memory scales with recent search activity rather than total library size.
+ * First call per ZIM does a full O(articleCount) directory walk; cached after that until the file's mtime/size changes.
+ */
+export async function titleVocabulary(zimPath) {
+	const stat = await fs.promises.stat(zimPath);
+	const cached = vocabCache.get(zimPath);
+	if (cached && cached.mtimeMs === stat.mtimeMs && cached.size === stat.size) {
+		vocabCache.delete(zimPath);
+		vocabCache.set(zimPath, cached); // bump to most-recently-used
+		return cached.words;
+	}
+
+	const fd = await fs.promises.open(zimPath, 'r');
+	let words;
+	try {
+		const header = await readHeader(fd);
+		words = new Set();
+		for (let i = 0; i < header.articleCount; i++) {
+			const dirent = await readDirent(fd, await ptr64(fd, header.urlPtrPos, i));
+			if (dirent.namespace !== NS_CONTENT || dirent.mimetype === 0xffff) continue; // skip redirects/non-content
+			for (const w of (dirent.title || dirent.url).toLowerCase().split(/\W+/)) if (w) words.add(w);
+		}
+	} finally {
+		await fd.close();
+	}
+
+	vocabCache.set(zimPath, {mtimeMs: stat.mtimeMs, size: stat.size, words});
+	if (vocabCache.size > VOCAB_CACHE_LIMIT) vocabCache.delete(vocabCache.keys().next().value);
+	return words;
+}

src/search.js

@@ -0,0 +1,225 @@
+'use strict';
+
+import {fuzzyMatch} from './utils.js';
+
+const RRF_K = 60;
+
+/** Merges independently-ranked result lists without comparing their raw Xapian scores. */
+export function rrfMerge(groups) {
+	const merged = new Map();
+
+	for(const group of groups) {
+		group.forEach((hit, rank) => {
+			const contribution = 1 / (RRF_K + rank + 1);
+			const entry = merged.get(hit.href);
+
+			if(entry) entry.score += contribution;
+			else merged.set(hit.href, {hit, score: contribution});
+		});
+	}
+
+	return [...merged.values()]
+		.sort((a, b) => b.score - a.score)
+		.map(({hit, score}) => ({...hit, rrf: score}));
+}
+
+/**
+ * Calculates field relevance from exact terms, phrase matches, proximity,
+ * match density and optionally fuzzy similarity.
+ */
+function fieldScore(text, terms, {fuzzy = false} = {}) {
+	const value = String(text || '').trim().toLowerCase();
+
+	if(!value || !terms.length) {
+		return {
+			exact: 0,
+			coverage: 0,
+			proximity: 0,
+			density: 0,
+			fuzzy: 0,
+			phrase: 0,
+			score: 0,
+		};
+	}
+
+	const words = value.split(/\W+/).filter(Boolean);
+	const normalizedTerms = terms.map(t => t.toLowerCase());
+	const phrase = normalizedTerms.join(' ');
+
+	const exactTerms = normalizedTerms.filter(t => words.includes(t));
+	const substringTerms = normalizedTerms.filter(t => value.includes(t));
+
+	const coverage = exactTerms.length / normalizedTerms.length;
+	const substringCoverage = substringTerms.length / normalizedTerms.length;
+	const exact = normalizedTerms.every(t => words.includes(t)) ? 1 : coverage;
+	const phraseScore = value.includes(phrase) ? 1 : 0;
+
+	let proximity = 0;
+
+	if(normalizedTerms.length > 1) {
+		const positions = [];
+
+		for(const term of normalizedTerms) {
+			const index = words.indexOf(term);
+			if(index !== -1) positions.push(index);
+		}
+
+		if(positions.length > 1) {
+			const span = Math.max(...positions) - Math.min(...positions);
+			proximity = 1 / Math.max(1, span);
+		}
+	}
+
+	const matchedChars = substringTerms.reduce((sum, term) => sum + term.length, 0);
+	const density = Math.min(1, matchedChars / Math.max(1, value.length * 0.25));
+	const fuzzyScore = fuzzy ? fuzzyMatch(value, ...normalizedTerms).avg : 0;
+
+	const score =
+		phraseScore * 1 +
+		exact * 0.8 +
+		proximity * 0.35 +
+		substringCoverage * 0.25 +
+		density * 0.15 +
+		fuzzyScore * 0.75;
+
+	return {
+		exact,
+		coverage,
+		proximity,
+		density,
+		fuzzy: fuzzyScore,
+		phrase: phraseScore,
+		score,
+	};
+}
+
+/** Reranks candidates using field-aware relevance while retaining RRF as the baseline. */
+export function rerank(hits, termList) {
+	if(!termList.length) return hits;
+
+	return hits.map(hit => {
+		const title = fieldScore(hit.title, termList, {fuzzy: true});
+		const summary = fieldScore(hit.summary, termList);
+		const titleLower = (hit.title || '').toLowerCase();
+		const summaryLower = (hit.summary || '').toLowerCase();
+		const phrase = termList.join(' ').toLowerCase();
+
+		const titleExactPhrase = titleLower.includes(phrase) ? 1 : 0;
+		const summaryExactPhrase = summaryLower.includes(phrase) ? 1 : 0;
+
+		const allTitleTerms = termList.every(term =>
+			titleLower.split(/\W+/).includes(term.toLowerCase())
+		) ? 1 : 0;
+
+		const allSummaryTerms = termList.every(term =>
+			summaryLower.includes(term.toLowerCase())
+		) ? 1 : 0;
+
+		const finalScore =
+			hit.rrf +
+			title.score * 1.25 +
+			summary.score * 0.35 +
+			titleExactPhrase * 1.5 +
+			allTitleTerms * 0.75 +
+			summaryExactPhrase * 0.2 +
+			allSummaryTerms * 0.15;
+
+		return {
+			...hit,
+			finalScore,
+			ranking: {
+				rrf: hit.rrf,
+				title: title.score,
+				summary: summary.score,
+				phrase: titleExactPhrase,
+				coverage: title.coverage,
+				proximity: title.proximity,
+				fuzzy: title.fuzzy,
+			},
+		};
+	}).sort((a, b) => b.finalScore - a.finalScore);
+}
+
+/** Round-robins results between source ZIMs so one archive cannot dominate the page. */
+export function diversify(hits, limit) {
+	const byBook = new Map();
+
+	for(const hit of hits)
+		(byBook.get(hit.name) ?? byBook.set(hit.name, []).get(hit.name)).push(hit);
+
+	for(const list of byBook.values())
+		list.sort((a, b) => b.finalScore - a.finalScore);
+
+	const queues = [...byBook.values()];
+	const out = [];
+
+	for(let i = 0; out.length < limit && queues.some(q => q.length); i++) {
+		const queue = queues[i % queues.length];
+		if(queue.length) out.push(queue.shift());
+	}
+
+	return out;
+}
+
+function bucketByFirstChar(words) {
+	const buckets = new Map();
+
+	for(const word of words) {
+		const key = word[0];
+		(buckets.get(key) ?? buckets.set(key, []).get(key)).push(word);
+	}
+
+	return buckets;
+}
+
+/** Finds the closest vocabulary term without comparing obviously unrelated word lengths. */
+export function bestFuzzyMatch(term, buckets) {
+	const lower = term.toLowerCase();
+	const maxDistance = Math.max(1, Math.ceil(lower.length * 0.34));
+	const candidates = new Set();
+
+	// Check every character so a typo in the first character doesn't eliminate the correct word.
+	for(const char of lower) {
+		const bucket = buckets.get(char);
+		if(bucket) for(const candidate of bucket) candidates.add(candidate);
+	}
+
+	let best = null;
+	let bestScore = 0;
+
+	for(const candidate of candidates) {
+		if(Math.abs(candidate.length - lower.length) > maxDistance) continue;
+
+		const score = fuzzyMatch(candidate, lower).max;
+
+		if(score > bestScore) {
+			bestScore = score;
+			best = candidate;
+		}
+	}
+
+	return best;
+}
+
+/** Suggests corrected terms from the supplied title vocabulary. */
+export function suggestCorrection(termList, vocabulary) {
+	if(!vocabulary.size) return null;
+
+	const buckets = bucketByFirstChar(vocabulary);
+	let changed = false;
+
+	const corrected = termList.map(term => {
+		if(vocabulary.has(term.toLowerCase())) return term;
+
+		const fix = bestFuzzyMatch(term, buckets);
+
+		if(fix && fix !== term.toLowerCase()) {
+			changed = true;
+			return fix;
+		}
+
+		return term;
+	});
+
+	return changed ? corrected : null;
+}

src/server.js

@@ -7,10 +7,12 @@ import fs from 'node:fs';
 import path from 'node:path';
 import {fileURLToPath} from 'node:url';
 import {fromXml, makeArray} from '@ztimson/utils';
+import {titleVocabulary} from './reader.js';
+import {diversify, rerank, rrfMerge, suggestCorrection} from './search.js';
 
 const execFileAsync = promisify(execFile);
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
-const DEFAULT_BIN_DIR = path.join(__dirname, '..', 'bin'); // npm package root/bin - where bin/install.js drops the kiwix-tools binaries
+const DEFAULT_BIN_DIR = path.join(__dirname, '..', 'bin');
 const READY_TIMEOUT = 10_000;
 const READY_POLL_INTERVAL = 100;
 const WATCH_DEBOUNCE = 300;
@@ -26,9 +28,10 @@ function findFreePort() {
 	});
 }
 
-/** Owns a kiwix-serve process's full lifecycle: library.xml, start/stop/reload, content + search access.
- * Watches its own directory for .zim files appearing/disappearing (from *any* writer - itself, a remote-attached
- * ZimManager, a script, whatever) and keeps library.xml + the running kiwix-serve process in sync automatically. */
+function tokenize(terms) {
+	return String(terms).split(/[,\s]+/).map(t => t.trim()).filter(Boolean);
+}
+
 export class KiwixServer {
 	static #empty = '<?xml version="1.0" encoding="UTF-8" ?>\n<library version="20110515"></library>\n';
 
@@ -38,7 +41,7 @@ export class KiwixServer {
 	#binDir;
 	#libraryPath;
 	#child = null;
-	#remote; // baseUrl string if attached to an externally-managed kiwix-serve, else null
+	#remote;
 	#watcher = null;
 	#watchTimer = null;
 
@@ -46,11 +49,6 @@ export class KiwixServer {
 	get running() { return !!this.#remote || !!this.#child; }
 	get baseUrl() { return this.#remote || (this.#child ? `http://${this.#host}:${this.#port}` : null); }
 
-	/** @param {{port?: number, host?: string, binDir?: string, url?: string}} [opts]
-	 * url: attach to an already-running kiwix-serve (e.g. one started elsewhere in your codebase) instead of
-	 * spawning/owning one - start/stop become no-ops, and library.xml is read over HTTP instead of disk.
-	 * Whichever instance *does* own the process is responsible for watching the shared directory; an attached
-	 * instance doesn't need its own watcher; it just reads whatever the owner already reloaded. */
 	constructor(dir, {port, host = '127.0.0.1', binDir = DEFAULT_BIN_DIR, url} = {}) {
 		this.#dir = dir;
 		this.#host = host;
@@ -58,25 +56,29 @@ export class KiwixServer {
 		this.#binDir = binDir;
 		this.#libraryPath = path.join(dir, 'library.xml');
 		this.#remote = url ? url.replace(/\/$/, '') : null;
-		if (!this.#remote) this.#ensureLocalStore();
+
+		if(!this.#remote) this.#ensureLocalStore();
 	}
 
 	#ensureLocalStore() {
 		fs.mkdirSync(this.#dir, {recursive: true});
-		if (!fs.existsSync(this.#libraryPath)) fs.writeFileSync(this.#libraryPath, KiwixServer.#empty);
+
+		if(!fs.existsSync(this.#libraryPath))
+			fs.writeFileSync(this.#libraryPath, KiwixServer.#empty);
 	}
 
 	#assertRunning() {
-		if (!this.running) throw new Error('KiwixServer is not running - call start() first');
+		if(!this.running) throw new Error('KiwixServer is not running - call start() first');
 	}
 
 	#bin(name) {
 		return path.join(this.#binDir, process.platform === 'win32' ? `${name}.exe` : name);
 	}
 
-	/** Reads library.xml from disk if we own the server, or over HTTP if attached to a remote one. */
 	async #fetchLibraryXml() {
-		if (!this.#remote) return fs.promises.readFile(this.#libraryPath, 'utf8').catch(() => '');
+		if(!this.#remote)
+			return fs.promises.readFile(this.#libraryPath, 'utf8').catch(() => '');
+
 		try {
 			const res = await fetch(`${this.#remote}/library.xml`);
 			return res.ok ? await res.text() : '';
@@ -85,44 +87,55 @@ export class KiwixServer {
 		}
 	}
 
-	/** Rebuilds library.xml from scratch by scanning `dir` for .zim files - no-op if attached to a remote server.
-	 * Rewriting the file bumps its mtime, which kiwix-serve (started with --monitorLibrary) picks up on its own
-	 * and hot-reloads without needing a restart. */
 	async #rebuildLibrary() {
-		if (this.#remote) return;
+		if(this.#remote) return;
+
 		await fs.promises.rm(this.#libraryPath, {force: true});
+
 		const files = await this.#zimFiles();
-		if (!files.length) return fs.promises.writeFile(this.#libraryPath, KiwixServer.#empty);
-		for (const f of files) await execFileAsync(this.#bin('kiwix-manage'), [this.#libraryPath, 'add', path.join(this.#dir, f)]);
+
+		if(!files.length)
+			return fs.promises.writeFile(this.#libraryPath, KiwixServer.#empty);
+
+		for(const file of files)
+			await execFileAsync(this.#bin('kiwix-manage'), [
+				this.#libraryPath,
+				'add',
+				path.join(this.#dir, file),
+			]);
 	}
 
 	async #waitUntilReady() {
 		const deadline = Date.now() + READY_TIMEOUT;
-		while (Date.now() < deadline) {
+
+		while(Date.now() < deadline) {
 			try {
 				await fetch(`http://${this.#host}:${this.#port}/`);
 				return;
 			} catch {}
+
 			await new Promise(r => setTimeout(r, READY_POLL_INTERVAL));
 		}
+
 		throw new Error('kiwix-serve did not become ready in time');
 	}
 
 	async #zimFiles() {
-		return (await fs.promises.readdir(this.#dir).catch(() => [])).filter(f => f.endsWith('.zim'));
+		return (await fs.promises.readdir(this.#dir).catch(() => []))
+			.filter(f => f.endsWith('.zim'));
 	}
 
-	/** Watches `dir` for .zim files being added/removed by anyone (this process, a remote-attached ZimManager,
-	 * a manual copy) and debounces a library rebuild so kiwix-serve's --monitorLibrary picks it up. Only runs
-	 * while we own the process - an attached instance has nothing local to watch on behalf of. */
 	#watchDir() {
 		this.#watcher?.close();
+
 		this.#watcher = fs.watch(this.#dir, (_event, filename) => {
-			if (!filename?.endsWith('.zim')) return;
+			if(!filename?.endsWith('.zim')) return;
+
 			clearTimeout(this.#watchTimer);
 			this.#watchTimer = setTimeout(() => this.#rebuildLibrary().catch(() => {}), WATCH_DEBOUNCE);
 		});
-		this.#watcher.on('error', () => {}); // e.g. dir removed out from under us - just stop watching, don't crash the process
+
+		this.#watcher.on('error', () => {});
 	}
 
 	#unwatchDir() {
@@ -132,23 +145,31 @@ export class KiwixServer {
 		this.#watcher = null;
 	}
 
-	/** Rebuilds library.xml and starts kiwix-serve. Resolves once the server is responding.
-	 * Starts with --monitorLibrary so the process reloads itself whenever library.xml's mtime changes -
-	 * no restart needed for updates after this. */
 	async start() {
-		if (this.#remote || this.#child) return;
+		if(this.#remote || this.#child) return;
+
 		await fs.promises.mkdir(this.#dir, {recursive: true});
 		await this.#rebuildLibrary();
 		this.#port ??= await findFreePort();
 
-		this.#child = spawn(this.#bin('kiwix-serve'),
-			['--library', '--monitorLibrary', '-i', this.#host, '-p', String(this.#port), this.#libraryPath],
-			{stdio: 'ignore'});
-		this.#child.on('exit', () => { this.#child = null; this.#unwatchDir(); });
+		this.#child = spawn(this.#bin('kiwix-serve'), [
+			'--library',
+			'--monitorLibrary',
+			'-i',
+			this.#host,
+			'-p',
+			String(this.#port),
+			this.#libraryPath,
+		], {stdio: 'ignore'});
+
+		this.#child.on('exit', () => {
+			this.#child = null;
+			this.#unwatchDir();
+		});
 
 		try {
 			await this.#waitUntilReady();
-		} catch (e) {
+		} catch(e) {
 			await this.stop();
 			throw e;
 		}
@@ -156,15 +177,18 @@ export class KiwixServer {
 		this.#watchDir();
 	}
 
-	/** Gracefully stops kiwix-serve, if we own it. No-op if attached to a remote instance. */
 	async stop() {
 		this.#unwatchDir();
-		if (this.#remote || !this.#child) return;
+
+		if(this.#remote || !this.#child) return;
+
 		const child = this.#child;
+
 		await new Promise(resolve => {
 			child.once('exit', resolve);
 			child.kill('SIGTERM');
 		});
+
 		this.#child = null;
 	}
 
@@ -173,24 +197,23 @@ export class KiwixServer {
 		await this.start();
 	}
 
-	/** Forces an immediate library rebuild rather than waiting for the directory watcher's debounce to fire.
-	 * Not required for correctness (the watcher does this automatically for any writer), just a manual way to
-	 * skip the ~300ms wait when you already know something changed. No-op if attached to a remote instance -
-	 * whoever owns that process already reloads itself. */
 	async reload() {
-		if (this.#remote || !this.#child) return;
+		if(this.#remote || !this.#child) return;
 		await this.#rebuildLibrary();
 	}
 
-	/** Local catalog listing - same flat shape as the online catalog (catalog.js), plus a `file` field. */
 	async list() {
 		this.#assertRunning();
+
 		const xml = await this.#fetchLibraryXml();
-		if (!xml) return [];
+		if(!xml) return [];
+
 		const entries = fromXml(xml);
+
 		return makeArray(entries?.library?.book || []).map(e => {
 			const tags = e.tags.split(';');
 			const name = e.path.replace('.zim', '');
+
 			return {
 				id: e.id,
 				title: e.title,
@@ -205,6 +228,7 @@ export class KiwixServer {
 				publisher: e.publisher,
 				articleCount: +e.articleCount || 0,
 				sizeMb: +(Number(e.size) / 1024).toFixed(1) || 0,
+				file: e.path,
 				href: name,
 				icon: `data:${e.faviconMimetype || 'image/png'};base64,${e.favicon}`,
 				viewer: `${this.baseUrl}/content/${name}`,
@@ -212,46 +236,63 @@ export class KiwixServer {
 		});
 	}
 
-	/** Splits a href ("zim/path/to/page") or a full content/viewer URL into {zim, path}. */
 	#splitHref(href) {
 		const clean = href.replace(`${this.baseUrl}/content/`, '').replace(/^\/+/, '');
 		const [zim, ...rest] = clean.split('/');
 		return {zim, path: rest.join('/')};
 	}
 
-	/** Builds a kiwix-serve content URL from a href (as returned by list()/search()), or from an already-built content/viewer URL. */
 	link(href) {
 		this.#assertRunning();
+
 		const {zim, path} = this.#splitHref(href);
+
 		return `${this.baseUrl}/content/${zim}${path ? '/' + path : ''}`;
 	}
 
-	/** Fetches a single asset's raw bytes straight from kiwix-serve. */
 	async raw(href) {
 		const res = await fetch(this.link(href));
+
 		if(!res.ok) return null;
-		return {mimetype: res.headers.get('content-type'), data: Buffer.from(await res.arrayBuffer())};
+
+		return {
+			mimetype: res.headers.get('content-type'),
+			data: Buffer.from(await res.arrayBuffer()),
+		};
 	}
 
-	/** Fulltext search across every local ZIM via kiwix-serve's own xapian index */
-	async search(terms, limit = 20) {
-		this.#assertRunning();
-		const termList = String(terms).split(/[,\s]+/).map(t => t.trim()).filter(Boolean);
-		if (!termList.length) return [];
+	async #rawSearch(termList, scoped, bookMap, limit) {
+		const groups = new Map();
+
+		for(const book of scoped) {
+			const lang = book.language || '';
+			(groups.get(lang) ?? groups.set(lang, []).get(lang)).push(book);
+		}
+
+		const perGroup = await Promise.all([...groups.values()].map(async group => {
+			const params = new URLSearchParams({
+				pattern: termList.join(' '),
+				format: 'xml',
+				pageLength: String(limit),
+			});
+
+			for(const book of group)
+				params.append('books.name', book.name);
 
-		const params = new URLSearchParams({pattern: termList.join(' '), format: 'xml', pageLength: String(limit)});
 			const res = await fetch(`${this.baseUrl}/search?${params}`);
-		if (!res.ok) return [];
+			if(!res.ok) return [];
 
 			const found = fromXml(await res.text())?.rss?.channel?.item || [];
-		const books = await this.list();
-		const bookMap = new Map(books.map(b => [b.title, b]));
 
 			return found.map(hit => {
 				const book = bookMap.get(hit.book.title);
-			if (!book) return null;
+				if(!book) return null;
+
 				const prefix = `/content/${book.href}/`;
-			const page = hit.link.startsWith(prefix) ? hit.link.slice(prefix.length) : hit.link.replace(/^\/+/, '');
+				const page = hit.link.startsWith(prefix)
+					? hit.link.slice(prefix.length)
+					: hit.link.replace(/^\/+/, '');
+
 				return {
 					id: book.id,
 					title: hit.title,
@@ -262,8 +303,66 @@ export class KiwixServer {
 					icon: book.icon,
 					viewer: this.baseUrl + hit.link,
 					summary: hit.description,
-				score: +hit.score || 0,
+					xapianScore: +hit.score || 0,
+				};
+			}).filter(Boolean).sort((a, b) => b.xapianScore - a.xapianScore);
+		}));
+
+		return rrfMerge(perGroup);
+	}
+
+	/** Fulltext search across local ZIMs with ranking, diversification and spelling correction. */
+	async search(terms, {limit = 20, sources = null} = {}) {
+		this.#assertRunning();
+
+		const termList = tokenize(terms);
+		if(!termList.length) return {results: [], spellcheck: null};
+
+		const books = await this.list();
+		const bookMap = new Map(books.map(b => [b.title, b]));
+		const scoped = sources?.length
+			? books.filter(b => sources.includes(b.name) || sources.includes(b.href))
+			: books;
+
+		if(!scoped.length) return {results: [], spellcheck: null};
+
+		let activeTerms = termList;
+		let hits = await this.#rawSearch(activeTerms, scoped, bookMap, limit);
+		let spellcheck = null;
+
+		if(!hits.length && !this.#remote) {
+			const vocabulary = new Set();
+
+			for(const book of scoped) {
+				if(!book.file) continue;
+
+				try {
+					for(const word of await titleVocabulary(path.join(this.#dir, book.file)))
+						vocabulary.add(word);
+				} catch {
+					// Unreadable ZIM - skip it, don't fail the whole search.
+				}
+			}
+
+			const corrected = suggestCorrection(termList, vocabulary);
+
+			if(corrected) {
+				const retry = await this.#rawSearch(corrected, scoped, bookMap, limit);
+
+				if(retry.length) {
+					hits = retry;
+					activeTerms = corrected;
+					spellcheck = {
+						from: termList.join(' '),
+						to: corrected.join(' '),
+					};
+				}
+			}
+		}
+
+		return {
+			results: diversify(rerank(hits, activeTerms), limit),
+			spellcheck,
 		};
-		}).filter(Boolean);
 	}
 }

src/utils.js

@@ -1,39 +1,36 @@
 export function levenshtein(a, b) {
 	const m = a.length, n = b.length;
-	if (!m) return n;
-	if (!n) return m;
+	if(!m) return n;
+	if(!n) return m;
 	const dp = Array.from({length: m + 1}, (_, i) => [i, ...Array(n).fill(0)]);
-	for (let j = 0; j <= n; j++) dp[0][j] = j;
-	for (let i = 1; i <= m; i++) {
-		for (let j = 1; j <= n; j++) {
-			dp[i][j] = a[i - 1] === b[j - 1]
-				? dp[i - 1][j - 1]
-				: 1 + Math.min(dp[i - 1][j - 1], dp[i - 1][j], dp[i][j - 1]);
+	for(let j = 0; j <= n; j++) dp[0][j] = j;
+	for(let i = 1; i <= m; i++) {
+		for(let j = 1; j <= n; j++) {
+			dp[i][j] = a[i - 1] === b[j - 1] ? dp[i - 1][j - 1] : 1 + Math.min(dp[i - 1][j - 1], dp[i - 1][j], dp[i][j - 1]);
 		}
 	}
 	return dp[m][n];
 }
 
 function scoreAgainst(text, term) {
-	if (text.includes(term)) return 1 - (text.length - term.length) / text.length * 0.3;
-	if (!text.length || !term.length || text[0] !== term[0]) return 0;
-	const dist = levenshtein(text, term);
+	if (!text.length || !term.length) return 0;
+	if (text === term) return 1;
+	if (text.includes(term)) return 0.8;
 	const maxAllowed = Math.max(1, Math.ceil(term.length * 0.34));
+	if (Math.abs(text.length - term.length) > maxAllowed) return 0;
+	const dist = levenshtein(text, term);
 	if (dist > maxAllowed) return 0;
 	return 1 - dist / Math.max(text.length, term.length);
 }
 
-/** Compares `target` against one or more search terms; returns avg/max/per-term similarity. */
 export function fuzzyMatch(target, ...terms) {
 	if (!terms.length) throw new Error('Requires at least 1 term to compare');
 	const lowerTarget = String(target).toLowerCase();
 	const words = lowerTarget.split(/\W+/).filter(Boolean);
-
 	const similarities = terms.map(term => {
-		const t = term.toLowerCase();
+		const t = String(term).toLowerCase();
 		return Math.max(scoreAgainst(lowerTarget, t), ...words.map(w => scoreAgainst(w, t)));
 	});
-
 	return {
 		avg: similarities.reduce((acc, s) => acc + s, 0) / similarities.length,
 		max: Math.max(...similarities),