vimhelp: Add offline tag search ability using tags.json

Add back the search box when using static page generation. This works by
querying tags.json and then performing a local search instead of relying
on the server code in tagsearch.py. The matching logic is ported over to
be the same though. Because we only have ~10k tags, linear search is
fast enough that we don't need to implement a binary search (since JS
doesn't come with a native binary search algorithm). Otherwise, for
performance, a indexed array using the initial character of the tag may
work better than implementing a binary search.

Author: ychin

vimhelp/static/vimhelp-v5.js

@@ -2,7 +2,6 @@
 
 // "Go to keyword" entry
 
-/*
 new TomSelect("#vh-select-tag", {
     maxItems: 1,
     loadThrottle: 250,
@@ -15,17 +14,97 @@ new TomSelect("#vh-select-tag", {
     },
     shouldLoad: (query) => query.length >= 1,
     load: async (query, callback) => {
+        /*
+         * Online dynamic server route. Not used.
+         *
         const url = "/api/tagsearch?q=" + encodeURIComponent(query);
         const resp = await fetch(url);
         callback((await resp.json()).results);
+        */
+
+        // Offline mode
+        if (!window.vimtags) {
+            // Only download this file on demand as it's not tiny.
+            const tags_url = "tags.json";
+            const tags_resp = await fetch(tags_url);
+            window.vimtags = await tags_resp.json();
+            window.sortedVimtags = Object.keys(window.vimtags).sort();
+        }
+        // Use logic from tagsearch.py
+        const MAX_RESULT = 30;
+
+        let results = [];
+        let results_set = {};
+        function addResult(tag) {
+            if (tag in results_set)
+                return false;
+            const link = window.vimtags[tag];
+            results.push({href: link, id: tag, text: tag});
+            results_set[tag] = null;
+            return results.length >= MAX_RESULT;
+        }
+
+        // Find all tags beginning with query.
+        for (let found = false, i = 0; i < sortedVimtags.length; i++) {
+            let tag = sortedVimtags[i];
+            if (tag.startsWith(query)) {
+                found = true;
+                if (addResult(tag)) {
+                    callback(results);
+                    return;
+                }
+            }
+            else if (found) {
+                break;
+            }
+        }
+        // If we didn't find enough, and the query is all-lowercase, add all
+        // case-insensitive matches.
+        const queryLower = query.toLowerCase();
+        if (queryLower == query) {
+            for (let i = 0; i < sortedVimtags.length; i++) {
+                let tag = sortedVimtags[i];
+                if (tag.toLowerCase().startsWith(queryLower)) {
+                    if (addResult(tag)) {
+                        callback(results);
+                        return;
+                    }
+                }
+            }
+        }
+        // If we still didn't find enough, additionally find all tags that contain query as a
+        // substring.
+        for (let i = 0; i < sortedVimtags.length; i++) {
+            let tag = sortedVimtags[i];
+            if (tag.includes(query)) {
+                if (addResult(tag)) {
+                    callback(results);
+                    return;
+                }
+            }
+        }
+
+        // If we still didn't find enough, and the query is all-lowercase, additionally find
+        // all tags that contain query as a substring case-insensitively.
+        if (queryLower == query) {
+            for (let i = 0; i < sortedVimtags.length; i++) {
+                let tag = sortedVimtags[i];
+                if (tag.toLowerCase().includes(queryLower)) {
+                    if (addResult(tag)) {
+                        callback(results);
+                        return;
+                    }
+                }
+            }
+        }
+        callback(results);
     },
     onChange: (value) => {
         if (value) {
             window.location = value;
         }
     }
 });
-*/
 
 // Theme switcher
 

vimhelp/templates/page.html

@@ -19,12 +19,10 @@
 <!-- {{project.favicon_notice}} -->
 
 {% if mode != "offline" %}
-{% if project.name != 'MacVim' %}
 {# MacVim does not host this on a server and cannot do dynamic queries #}
 <link rel="stylesheet" href="{{static_dir}}tom-select-2.2.2.min.css">
 <script defer src="{{static_dir}}tom-select-2.2.2.base.min.js"></script>
 {% endif %}
-{% endif %}
 
 <link rel="stylesheet" href="{{static_dir}}vimhelp-v5.css" type="text/css">
 <noscript><link rel="stylesheet" href="{{static_dir}}noscript.css" type="text/css"></noscript>
@@ -92,10 +90,10 @@ <h1>{{project.name}} help files</h1>
 {% if mode != "offline" %}
 <div class="bar">
   <div class="ql">{{sitenavi}}</div>
-  {% if project.name != "MacVim" %}
   <div class="srch" id="go-to-tag">
     <select id="vh-select-tag"></select>
   </div>
+  {% if project.name != "MacVim" %}
   <form class="srch" action="https://duckduckgo.com" method="get" target="_blank" rel="noopener noreferrer">
     <input type="hidden" name="sites" value="{{project.vimdoc_site}}">
     <input type="search" name="q" id="vh-srch-input" placeholder="Site search">