Add plugin code for autocomplete

Author: WebCoder49

plugins/autocomplete.css

@@ -0,0 +1,10 @@
+code-input .code-input_autocomplete_popup {
+    display: block;
+    position: absolute;
+    margin-top: 1em; /* Popup shows under the caret */
+}
+
+
+code-input .code-input_autocomplete_testpos {
+    opacity: 0;
+}

plugins/autocomplete.js

@@ -0,0 +1,79 @@
+/**
+ *
+ */
+codeInput.plugins.Autocomplete = class extends codeInput.Plugin {
+    /**
+     * Pass in a function to display the popup that takes in (popup element, textarea, textarea.selectionEnd).
+     * @param {function} updatePopupCallback  
+     */
+    constructor(updatePopupCallback) {
+        super();
+        this.updatePopupCallback = updatePopupCallback;
+    }
+    /* When a key is pressed, or scrolling occurs, update the autocomplete */
+    updatePopup(codeInput, onlyScrolled) {
+        let textarea = codeInput.querySelector("textarea");
+        let caretCoords = this.getCaretCoordinates(codeInput, textarea, textarea.selectionEnd, onlyScrolled);
+        let popupElem = codeInput.querySelector(".code-input_autocomplete_popup");
+        popupElem.style.top = caretCoords.top + "px";
+        popupElem.style.left = caretCoords.left + "px";
+        
+        if(!onlyScrolled) {
+            this.updatePopupCallback(popupElem, textarea, textarea.selectionEnd);
+        }
+    }
+    /* Runs after elements are added into a `code-input` (useful for adding events to the textarea); Params: codeInput element) */
+    afterElementsAdded(codeInput) {
+        let popupElem = document.createElement("div");
+        popupElem.classList.add("code-input_autocomplete_popup");
+        codeInput.appendChild(popupElem);
+
+        let testPosElem = document.createElement("pre");
+        testPosElem.classList.add("code-input_autocomplete_testpos");
+        codeInput.appendChild(testPosElem); // Styled like first pre, but first pre found to update
+
+        let textarea = codeInput.querySelector("textarea");
+        textarea.addEventListener("keyup", this.updatePopup.bind(this, codeInput, false)); // Override this+args in bind - not just scrolling
+        document.addEventListener("click", this.updatePopup.bind(this, codeInput, false)); // Override this+args in bind - not just scrolling
+        textarea.addEventListener("scroll", this.updatePopup.bind(this, codeInput, true)); // Override this+args in bind - just scrolling
+    }
+    /**
+     * Return the coordinates of the caret in a code-input
+     * @param {codeInput.CodeInput} codeInput 
+     * @param {HTMLElement} textarea 
+     * @param {Number} charIndex 
+     * @param {boolean} onlyScrolled True if no edits have been made to the text and the caret hasn't been repositioned 
+     * @returns 
+     */
+    getCaretCoordinates(codeInput, textarea, charIndex, onlyScrolled) {
+        let afterSpan;
+        if(onlyScrolled) {
+            // No edits to text; don't update element - span at index 1 is after span
+            let spans = codeInput.querySelector(".code-input_autocomplete_testpos").querySelectorAll("span");
+            if(spans.length < 2) {
+                // Hasn't saved text in test pre to find pos
+                // Need to regenerate text in test pre
+                return this.getCaretCoordinates(codeInput, textarea, charIndex, false);
+            } 
+            afterSpan = spans[1];
+        } else {
+            /* Inspired by https://github.com/component/textarea-caret-position */
+            let testPosElem = codeInput.querySelector(".code-input_autocomplete_testpos");
+            
+            let beforeSpan = document.createElement("span");
+            beforeSpan.textContent = textarea.value.substring(0, charIndex);
+            afterSpan = document.createElement("span");
+            afterSpan.textContent = "."; // Placeholder
+
+            // Clear test pre - https://developer.mozilla.org/en-US/docs/Web/API/Node/removeChild
+            while (testPosElem.firstChild) {
+                testPosElem.removeChild(testPosElem.firstChild);
+            }
+            testPosElem.appendChild(beforeSpan);
+            testPosElem.appendChild(afterSpan);
+        }
+        return {"top": afterSpan.offsetTop - textarea.scrollTop, "left": afterSpan.offsetLeft - textarea.scrollLeft};
+    }
+    observedAttributes = [];
+    updatePopupCallback = function() {};
+}