Add search to docs

Closes: #295

website/site/static/js/searchhelper.js

@@ -0,0 +1,130 @@
+// Taken from mdbook
+// The strategy is as follows:
+// First, assign a value to each word in the document:
+//  Words that correspond to search terms (stemmer aware): 40
+//  Normal words: 2
+//  First word in a sentence: 8
+// Then use a sliding window with a constant number of words and count the
+// sum of the values of the words within the window. Then use the window that got the
+// maximum sum. If there are multiple maximas, then get the last one.
+// Enclose the terms in *.
+function makeTeaser(body, terms) {
+  var TERM_WEIGHT = 40;
+  var NORMAL_WORD_WEIGHT = 2;
+  var FIRST_WORD_WEIGHT = 8;
+  var TEASER_MAX_WORDS = 30;
+
+  var stemmedTerms = terms.map(function (w) {
+    return elasticlunr.stemmer(w.toLowerCase());
+  });
+  var termFound = false;
+  var index = 0;
+  var weighted = []; // contains elements of ["word", weight, index_in_document]
+
+  // split in sentences, then words
+  var sentences = body.toLowerCase().split(". ");
+
+  for (var i in sentences) {
+    var words = sentences[i].split(" ");
+    var value = FIRST_WORD_WEIGHT;
+
+    for (var j in words) {
+      var word = words[j];
+
+      if (word.length > 0) {
+        for (var k in stemmedTerms) {
+          if (elasticlunr.stemmer(word).startsWith(stemmedTerms[k])) {
+            value = TERM_WEIGHT;
+            termFound = true;
+          }
+        }
+        weighted.push([word, value, index]);
+        value = NORMAL_WORD_WEIGHT;
+      }
+
+      index += word.length;
+      index += 1;  // ' ' or '.' if last word in sentence
+    }
+
+    index += 1;  // because we split at a two-char boundary '. '
+  }
+
+  if (weighted.length === 0) {
+    return body;
+  }
+
+  var windowWeights = [];
+  var windowSize = Math.min(weighted.length, TEASER_MAX_WORDS);
+  // We add a window with all the weights first
+  var curSum = 0;
+  for (var i = 0; i < windowSize; i++) {
+    curSum += weighted[i][1];
+  }
+  windowWeights.push(curSum);
+
+  for (var i = 0; i < weighted.length - windowSize; i++) {
+    curSum -= weighted[i][1];
+    curSum += weighted[i + windowSize][1];
+    windowWeights.push(curSum);
+  }
+
+  // If we didn't find the term, just pick the first window
+  var maxSumIndex = 0;
+  if (termFound) {
+    var maxFound = 0;
+    // backwards
+    for (var i = windowWeights.length - 1; i >= 0; i--) {
+      if (windowWeights[i] > maxFound) {
+        maxFound = windowWeights[i];
+        maxSumIndex = i;
+      }
+    }
+  }
+
+  var teaser = [];
+  var startIndex = weighted[maxSumIndex][2];
+  for (var i = maxSumIndex; i < maxSumIndex + windowSize; i++) {
+    var word = weighted[i];
+    if (startIndex < word[2]) {
+      // missing text from index to start of `word`
+      teaser.push(body.substring(startIndex, word[2]));
+      startIndex = word[2];
+    }
+
+    // add <em/> around search terms
+    if (word[1] === TERM_WEIGHT) {
+      teaser.push("**");
+    }
+    startIndex = word[2] + word[0].length;
+    teaser.push(body.substring(word[2], startIndex));
+
+    if (word[1] === TERM_WEIGHT) {
+      teaser.push("**");
+    }
+  }
+  teaser.push("…");
+  return teaser.join("");
+}
+
+var index = elasticlunr.Index.load(window.searchIndex);
+
+
+var initElmSearch = function(elmSearch) {
+    var options = {
+        bool: "AND",
+        fields: {
+            title: {boost: 2},
+            body: {boost: 1},
+        }
+    };
+
+    elmSearch.ports.doSearch.subscribe(function(str) {
+        var results = index.search(str, options);
+        for (var i = 0; i < results.length; i ++) {
+            var teaser = makeTeaser(results[i].doc.body, str.split(" "));
+            results[i].doc.body = teaser;
+        }
+        elmSearch.ports.receiveSearch.send(results);
+    });
+
+};