search: pick snippet window that covers the most distinct query terms

scripts/smoke.mjs

@@ -154,4 +154,18 @@ check('search matches an author name', () => {
   assert.ok(hits[0].matched.includes('nirodbaran'));
 });
 
+check('snippet centres on the window covering the most distinct terms', () => {
+  // 'silence' appears early (isolated) and again near 'integral' much later.
+  // A window centred on the early occurrence captures only 'silence'; a window
+  // centred near 'integral' captures both.  The improved snippet picks the latter.
+  const filler = 'The way unfolds gradually. '.repeat(4);
+  const s = snippet(
+    { body: `Silence rests here. ${filler}In integral yoga, silence is paramount.` },
+    ['integral', 'silence'],
+    { contextChars: 80 },
+  );
+  assert.ok(s.toLowerCase().includes('integral'), `expected 'integral' in: ${s}`);
+  assert.ok(s.toLowerCase().includes('silence'), `expected 'silence' in: ${s}`);
+});
+
 console.log(`\n${passed} checks passed.`);

src/search.js

@@ -107,9 +107,15 @@ export function tokenize(text) {
 }
 
 /**
- * Build a short contextual snippet around the first matched term, for display
- * beneath a search result. Looks in the summary first, then the body; if no
- * term is found, falls back to the start of the text.
+ * Build a short contextual snippet around the best window for the matched
+ * terms, for display beneath a search result. Looks in the summary first, then
+ * the body; if no term is found, falls back to the start of the text.
+ *
+ * "Best window" means the position (among all occurrences of all terms) that
+ * maximises the number of distinct terms visible within the context window.
+ * For single-term queries this is identical to the previous behaviour; for
+ * multi-term queries it avoids returning a snippet that shows only one term
+ * when the terms cluster together elsewhere in the text.
  *
  * @param {{summary?: string, body?: string}} article
  * @param {string[]} terms lowercased query terms (as returned in `matched`)
@@ -121,14 +127,37 @@ export function snippet(article, terms = [], { contextChars = 120 } = {}) {
   for (const text of [article.summary, article.body]) {
     if (!text) continue;
     const lower = text.toLowerCase();
-    let idx = -1;
+
+    // Collect every occurrence position of every term.
+    const occurrences = [];
     for (const t of terms) {
-      const at = lower.indexOf(t);
-      if (at !== -1 && (idx === -1 || at < idx)) idx = at;
+      let at = lower.indexOf(t);
+      while (at !== -1) {
+        occurrences.push({ pos: at, term: t });
+        at = lower.indexOf(t, at + 1);
+      }
+    }
+    if (!occurrences.length) continue;
+
+    // Pick the position whose window covers the most distinct terms.
+    // Ties go to the earlier position (natural iteration order).
+    let bestPos = occurrences[0].pos;
+    let bestCoverage = 0;
+    for (const { pos } of occurrences) {
+      const lo = pos - half;
+      const hi = pos + half;
+      const seen = new Set();
+      for (const o of occurrences) {
+        if (o.pos >= lo && o.pos <= hi) seen.add(o.term);
+      }
+      if (seen.size > bestCoverage) {
+        bestCoverage = seen.size;
+        bestPos = pos;
+      }
     }
-    if (idx === -1) continue;
-    const start = Math.max(0, idx - half);
-    const end = Math.min(text.length, idx + half);
+
+    const start = Math.max(0, bestPos - half);
+    const end = Math.min(text.length, bestPos + half);
     let s = text.slice(start, end).trim();
     if (start > 0) s = `… ${s}`;
     if (end < text.length) s = `${s} …`;