| 1 | // Fetch the search index only when the user wants to search. Then cache it thereafter.
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| 2 | //
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| 3 | // We also have to avoid race conditions. On very slow networks, multiple calls to getIndex can be
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| 4 | // made before the fetch completes. To remedy this, we store the promise returning the index in
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| 5 | // _index. Then any calls to await getIndex() implicitly wait on this single promise.
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| 6 | let _index;
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| 7 | function getIndex() {
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| 8 | if (!_index) {
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| 9 | _index = (async () => {
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| 10 | const res = await fetch(`${window.basePath}/index.json`);
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| 11 | _index = await res.json();
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| 12 | return _index;
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| 13 | })();
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| 14 | }
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| 15 |
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| 16 | return _index;
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| 17 | }
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| 18 |
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| 19 | /**
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| 20 | * True Damerau–Levenshtein distance (allows multiple transpositions).
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| 21 | * Adapted from [0] with help from ChatGPT 5.2.
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| 22 | *
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| 23 | * Computes the DL distance between textA and textB. This is the number of edits between A and B. The possible edits are:
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| 24 | * - Insertion (adding a single char)
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| 25 | * - Deletion (removing a single char)
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| 26 | * - Substitution (changing a single char)
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| 27 | * - Transposition (swapping the locations of 2 chars)
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| 28 | *
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| 29 | * [0] https://en.wikipedia.org/wiki/Damerau%E2%80%93Levenshtein_distance#Distance_with_adjacent_transpositions
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| 30 | */
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| 31 | function damerauLevenshteinDistance(textA, textB) {
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| 32 | const lenA = textA.length;
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| 33 | const lenB = textB.length;
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| 34 |
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| 35 | const INF = lenA + lenB;
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| 36 |
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| 37 | // lastRowByChar == da in the pseudocode:
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| 38 | // maps a character -> last row index (1..lenA) where it appeared in textA
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| 39 | const lastRowByChar = new Map();
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| 40 |
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| 41 | // dist is the shifted version of d. Size: (lenA+2) x (lenB+2)
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| 42 | const dist = Array.from({ length: lenA + 2 }, () => new Array(lenB + 2).fill(0));
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| 43 |
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| 44 | // Initialize sentinel borders
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| 45 | dist[0][0] = INF;
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| 46 | for (let i = 0; i <= lenA; i++) {
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| 47 | dist[i + 1][0] = INF; // d[i, -1]
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| 48 | dist[i + 1][1] = i; // d[i, 0]
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| 49 | }
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| 50 | for (let j = 0; j <= lenB; j++) {
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| 51 | dist[0][j + 1] = INF; // d[-1, j]
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| 52 | dist[1][j + 1] = j; // d[ 0, j]
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| 53 | }
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| 54 |
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| 55 | // Main dynamic programming algorithm
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| 56 | for (let i = 1; i <= lenA; i++) {
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| 57 | let lastMatchingColInB = 0; // db in the pseudocode (last column j where a[i] matched)
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| 58 | const charA = textA[i - 1];
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| 59 |
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| 60 | for (let j = 1; j <= lenB; j++) {
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| 61 | const charB = textB[j - 1];
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| 62 |
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| 63 | const lastRowWithCharBInA = lastRowByChar.get(charB) ?? 0; // k := da[b[j]]
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| 64 | const lastMatchingColForThisRow = lastMatchingColInB; // ℓ := db
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| 65 |
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| 66 | const cost = (charA === charB) ? 0 : 1;
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| 67 | if (cost === 0) lastMatchingColInB = j;
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| 68 |
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| 69 | // Shifted accesses:
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| 70 | // d[i-1, j-1] -> dist[i][j]
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| 71 | // d[i, j-1] -> dist[i+1][j]
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| 72 | // d[i-1, j ] -> dist[i][j+1]
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| 73 | const substitution = dist[i][j] + cost;
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| 74 | const insertion = dist[i + 1][j] + 1;
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| 75 | const deletion = dist[i][j + 1] + 1;
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| 76 |
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| 77 | // Transposition term (shifted):
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| 78 | // d[k-1, ℓ-1] in pseudocode -> dist[k][ℓ]
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| 79 | const transposition =
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| 80 | dist[lastRowWithCharBInA][lastMatchingColForThisRow] +
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| 81 | (i - lastRowWithCharBInA - 1) +
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| 82 | cost +
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| 83 | (j - lastMatchingColForThisRow - 1);
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| 84 |
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| 85 | dist[i + 1][j + 1] = Math.min(substitution, insertion, deletion, transposition);
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| 86 | }
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| 87 |
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| 88 | // da[a[i]] := i
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| 89 | lastRowByChar.set(charA, i);
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| 90 | }
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| 91 |
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| 92 | // return d[lenA, lenB] -> dist[lenA+1][lenB+1]
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| 93 | return dist[lenA + 1][lenB + 1];
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| 94 | }
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| 95 |
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| 96 | /**
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| 97 | * Compute a match rank for a single label against query.
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| 98 | * Lower is better. 0 = exact substring match, 1..5 = fuzzy, Infinity = no match.
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| 99 | *
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| 100 | * Expects both symbol and query to be all lowercase.
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| 101 | */
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| 102 | function rankSymbol(symbol, query) {
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| 103 | // Exact match
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| 104 | if (symbol.includes(query)) return 0;
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| 105 |
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| 106 | const d = damerauLevenshteinDistance(query, symbol);
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| 107 | return d <= 5 ? d : Infinity;
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| 108 | }
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| 109 |
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| 110 | /**
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| 111 | * Recursively filter the index to only branches containing matches.
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| 112 | *
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| 113 | * `query` must be a lowercase string.
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| 114 | */
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| 115 | function filterAndRank(index, query) {
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| 116 | const kept = [];
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| 117 | for (const node of index) {
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| 118 | const symbol = node.symbol.toLowerCase();
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| 119 | const anchor = node.anchor;
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| 120 | const children = node.children ?? []; // We omit the children in the index when empty
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| 121 |
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| 122 | const selfRank = rankSymbol(symbol, query);
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| 123 | const keptChildren = filterAndRank(children, query);
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| 124 |
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| 125 | // Best descendant rank (if any)
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| 126 | let bestChildRank = Infinity;
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| 127 | for (const c of keptChildren) {
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| 128 | if (c._rank < bestChildRank) bestChildRank = c._rank;
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| 129 | }
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| 130 |
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| 131 | // Keep node if it matches or has matching descendants
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| 132 | const bestRank = Math.min(selfRank, bestChildRank);
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| 133 | if (bestRank !== Infinity) {
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| 134 | const copy = { symbol: node.symbol, anchor, children: keptChildren };
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| 135 |
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| 136 | // Store rank for sorting
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| 137 | copy._rank = bestRank;
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| 138 |
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| 139 | kept.push(copy);
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| 140 | }
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| 141 | }
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| 142 |
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| 143 | kept.sort((a, b) => (a._rank ?? Infinity) - (b._rank ?? Infinity));
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| 144 | return kept;
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| 145 | }
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| 146 |
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| 147 | /**
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| 148 | * Trim the pruned tree to at most `limit` total rendered links (nodes).
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| 149 | * Keeps structure (parents) only as needed to show kept children.
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| 150 | *
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| 151 | * This way searching 'a' doesn't fill the entire page with junk.
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| 152 | * TODO: pagination / a next button
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| 153 | */
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| 154 | function trimResults(results, limit) {
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| 155 | let count = 0;
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| 156 |
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| 157 | function walk(list) {
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| 158 | const out = [];
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| 159 | for (const node of list) {
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| 160 | if (count >= limit) break;
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| 161 |
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| 162 | // Count this node as one rendered link
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| 163 | count += 1;
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| 164 |
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| 165 | const trimmedChildren = walk(node.children);
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| 166 |
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| 167 | out.push({
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| 168 | symbol: node.symbol,
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| 169 | anchor: node.anchor,
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| 170 | children: trimmedChildren,
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| 171 | });
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| 172 | }
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| 173 | return out;
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| 174 | }
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| 175 |
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| 176 | return walk(results);
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| 177 | }
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| 178 |
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| 179 | /**
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| 180 | * Search across the website using the global search index.
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| 181 | * Returns a pruned tree (array of nodes) ready to render (see renderResults).
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| 182 | *
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| 183 | * Matching algorithm:
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| 184 | * - Exact substring match: rank 0
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| 185 | * - DL distance <= 5: rank 1..5
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| 186 | * - Otherwise excluded
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| 187 | *
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| 188 | * Only the top `limit` rendered nodes are returned (default 25).
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| 189 | */
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| 190 | async function search(query) {
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| 191 | if (!query) return [];
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| 192 |
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| 193 | const index = await getIndex();
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| 194 | const pruned = filterAndRank(index, query.toLowerCase());
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| 195 | return trimResults(pruned, /* limit */ 25);
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| 196 | }
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| 197 |
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| 198 | /**
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| 199 | * Render as nested <ul>/<li> where *every* item is a link.
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| 200 | */
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| 201 | function renderResults(nodes) {
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| 202 | const ul = document.createElement("ul");
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| 203 |
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| 204 | for (const node of nodes) {
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| 205 | const li = document.createElement("li");
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| 206 |
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| 207 | const a = document.createElement("a");
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| 208 | a.textContent = String(node.symbol ?? "");
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| 209 | a.href = (typeof node.anchor === "string")
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| 210 | ? window.basePath + "/" + node.anchor
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| 211 | : "#";
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| 212 | li.appendChild(a);
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| 213 |
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| 214 | const children = Array.isArray(node.children) ? node.children : [];
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| 215 | if (children.length) {
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| 216 | li.appendChild(renderResults(children));
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| 217 | }
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| 218 |
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| 219 | ul.appendChild(li);
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| 220 | }
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| 221 |
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| 222 | return ul;
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| 223 | }
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| 224 |
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| 225 | function searchbar() {
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| 226 | const searchDiv = document.getElementById("search");
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| 227 |
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| 228 | // Create the searchbar dynamically so that users without JS enabled don't get
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| 229 | // a broken searchbar
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| 230 | const searchbar = document.createElement("input");
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| 231 | searchbar.id = "searchbar";
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| 232 | searchbar.setAttribute("placeholder", "Search");
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| 233 | searchbar.setAttribute("title", "Search");
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| 234 | searchbar.setAttribute("autocapitalize", "none");
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| 235 | searchbar.setAttribute("enterkeyhint", "search");
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| 236 | searchDiv.appendChild(searchbar);
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| 237 |
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| 238 | // We show a loading bar on the first fetch.
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| 239 | const loading = document.createElement("p");
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| 240 | loading.innerText = "Loading...";
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| 241 | const showLoading = () => (loading.style.display = "block");
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| 242 | const hideLoading = () => (loading.style.display = "none");
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| 243 | hideLoading();
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| 244 | searchDiv.appendChild(loading);
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| 245 |
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| 246 | let resultsList = null;
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| 247 | searchbar.addEventListener("input", async (event) => {
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| 248 | showLoading();
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| 249 | const query = event.target.value;
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| 250 |
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| 251 | const prunedTree = await search(query);
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| 252 |
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| 253 | hideLoading();
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| 254 |
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| 255 | // We have to clear the previous results, if present
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| 256 | if (resultsList) {
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| 257 | resultsList.remove();
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| 258 | }
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| 259 |
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| 260 | resultsList = renderResults(prunedTree);
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| 261 | searchDiv.appendChild(resultsList);
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| 262 | });
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| 263 | }
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| 264 |
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| 265 | searchbar();
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