site: decouple state from event handlers

Try to avoid directly setting state from event handlers and instead
provide utility functions that mutate state in a consistent way.

public/js/app.js

@@ -6,7 +6,7 @@ function mySplice(s, idx, del, n) {
   return s.substring(0, idx) + n + s.substring(idx + del);
 }
 
-function suggestionPosition(el) {
+function suggestionIndex(el) {
   // el.parentNode is ul#tags-suggestion, which include a template. That's why
   // a -1 is needed here.
   const idx = [...el.parentNode.children].indexOf(el);
@@ -52,50 +52,63 @@ document.addEventListener('alpine:init', () => {
       this.suggestions = await response.json();
     },
 
-    completeSuggestion(evt) {
+    completeSuggestion() {
       if (this.currentSuggestion === null)
         return;
 
       const value = this.$refs.tags.value;
-      const pos = this.inputCursor - this.query.length;
+      const pos = Math.max(this.inputCursor - this.query.length, 0);
       const tag = this.suggestions[this.currentSuggestion].display;
+      const newValue = mySplice(value, pos, this.query.length, tag + ' ');
 
-      this.$refs.tags.value = mySplice(value, pos, this.query.length,
-        tag + ' ');
       this.reset();
+
+      this.$refs.tags.value = newValue;
       this.inputCursor =
         this.$refs.tags.selectionStart =
         this.$refs.tags.selectionEnd =
         pos + tag.length + 1;
+
       this.$refs.tags.focus();
-
-      // Don't switch focus if we're completing after a Tab press.
-      if (evt.type === "keydown" && evt.keyCode === 9)
-        evt.preventDefault();
     },
 
-    selectCurrentSuggestion(evt) {
-      this.currentSuggestion = suggestionPosition(evt.currentTarget);
-      this.completeSuggestion(evt);
+    completeClickedSuggestion(evt) {
+      this.currentSuggestion = suggestionIndex(evt.currentTarget);
+      this.completeSuggestion();
     },
 
-    setCurrentSuggestion(evt, amount = 0) {
+    setCurrentSuggestion(idx) {
+      const len = this.suggestions.length;
+      if (len === 0)
+        return;
+
       currentSuggestionElement(this.currentSuggestion)
         ?.classList.remove("suggestion-hover");
 
-      if (evt.type === 'mouseenter')
-        this.currentSuggestion = suggestionPosition(evt.currentTarget);
-      else {
-        const len = this.suggestions.length;
-        let cur = this.currentSuggestion;
-
-        if (cur === null)
-          cur = amount > 0 ? -1 : amount < 0 ? len : 0;
-        this.currentSuggestion = (cur + amount + len) % len;
-      }
+      idx = idx % len;
+      if (idx < 0)
+        idx += len;
+      this.currentSuggestion = idx;
 
       currentSuggestionElement(this.currentSuggestion)
         ?.classList.add("suggestion-hover");
-    }
+    },
+
+    setPointerSuggestion(evt) {
+      this.setCurrentSuggestion(suggestionIndex(evt.currentTarget));
+    },
+
+    moveCurrentSuggestion(amount, defaultValue) {
+      this.setCurrentSuggestion(this.currentSuggestion === null ?
+        defaultValue : this.currentSuggestion + amount);
+    },
+
+    nextSuggestion(evt) {
+      this.moveCurrentSuggestion(1, 0);
+    },
+
+    previousSuggestion(evt) {
+      this.moveCurrentSuggestion(-1, -1);
+    },
   }));
 });

templates/_search.html.ep

@@ -11,16 +11,16 @@
       x-ref="tags"
       @focus="fetchSuggestions"
       @input.debounce="fetchSuggestions"
-      @keydown.tab="completeSuggestion"
-      @keydown.up.prevent="setCurrentSuggestion($event, -1)"
-      @keydown.down.prevent="setCurrentSuggestion($event, +1)"
+      @keydown.tab.prevent="completeSuggestion"
+      @keydown.up.prevent="previousSuggestion"
+      @keydown.down.prevent="nextSuggestion"
       @keydown.escape="reset">
     <ul id="tags-suggestions"
       x-cloak x-show="suggestions.length > 0">
       <template x-for="suggestion in suggestions">
         <li
-          @click="selectCurrentSuggestion"
-          @mouseenter="setCurrentSuggestion">
+          @click="completeClickedSuggestion"
+          @mouseenter="setPointerSuggestion">
           <span
             x-text="suggestion.display"
             :class="suggestion.kind_class">