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import { TemplateRenderer } from '../renderer/renderTemplate.js';
import { DomPatcher } from '../renderer/domPatch.js';
import { unescapeTemplateMarkers } from '../utils/templateUtils.js';
/**
* Built-in component for high-performance virtualized list rendering.
* Only renders items currently visible within the viewport.
* Supports optional pagination mode with pageSize, current page tracking, and navigation controls.
*/
export class VirtualList extends AvenxComponent {
/**
* @param {object} [bridges] - External bridges.
* @param {object} [props] - Component properties (items, itemHeight, pageSize, page, totalItems, showControls).
*/
constructor(bridges, props = {}) {
super(
{},
{},
bridges,
`
<div class="virtual-list-container" style="display: flex; flex-direction: column; height: 100%; width: 100%;">
<div class="virtual-list-viewport" data-ax-ref="viewport" style="overflow-y: auto; position: relative; flex: 1 1 auto; height: 100%; width: 100%;">
<div class="virtual-list-spacer" data-ax-ref="spacer" data-ax-static style="box-sizing: border-box; width: 100%;">
<!-- Recycled item DOM elements will be injected here -->
</div>
</div>
<div class="virtual-list-pagination" data-ax-ref="pagination" style="display: none; box-sizing: border-box; padding: 8px 12px; align-items: center; justify-content: space-between; gap: 8px; border-top: 1px solid rgba(0,0,0,0.1); user-select: none;">
<div class="virtual-list-pagination-info" data-ax-ref="pageInfo" style="font-size: 13px; color: inherit;"></div>
<div class="virtual-list-pagination-controls" style="display: flex; align-items: center; gap: 4px;">
<button type="button" class="virtual-list-btn prev-btn" data-ax-ref="prevBtn" style="cursor: pointer; padding: 4px 10px; font-size: 13px;">« Prev</button>
<span class="virtual-list-page-number" data-ax-ref="pageNum" style="font-size: 13px; padding: 0 4px;">1</span>
<button type="button" class="virtual-list-btn next-btn" data-ax-ref="nextBtn" style="cursor: pointer; padding: 4px 10px; font-size: 13px;">Next »</button>
</div>
</div>
</div>
`,
{},
props
);
/** Measured actual heights of individual items. @type {number[]} */
this.measuredHeights = [];
/** The template node extracted from slot transclusion. @type {HTMLTemplateElement|null} */
this.templateNode = null;
/** Loop item variable name (e.g. 'item'). @type {string} */
this.itemVar = 'item';
/** Resize observer to monitor dynamic item size changes and viewport resizing. @type {ResizeObserver|null} */
this.resizeObserver = null;
/** Cached viewport height to prevent redundant layout loops. @type {number} */
this.lastViewportHeight = 0;
/** Animation frame request handle. @type {number|null} */
this.rafId = null;
/** Animation frame request handle for scroll throttling. @type {number|null} */
this.scrollRafId = null;
/** Currently active 1-based page index. @type {number} */
this.currentPage = Number(props.page || props['current-page'] || 1);
this.renderer = new TemplateRenderer();
this.patcher = new DomPatcher();
this.onScroll = this.onScroll.bind(this);
}
/**
* Lifecycle hook called after component is mounted.
* Sets up transcluded template slots, scroll listeners, and pagination handlers.
*/
onMount() {
const transcluded = this._getTranscludedGroups();
const defaultNodes = (transcluded && transcluded.default) || [];
// Extract template slot node from transcluded default contents
const templateEl = defaultNodes.find(
(node) => node.nodeType === 1 && node.tagName.toLowerCase() === 'template'
);
if (templateEl) {
this.templateNode = templateEl;
this.itemVar = templateEl.getAttribute('data-ax-as') || 'item';
} else {
// Fallback: If no template is provided, use the first element node as row template
const itemEl = defaultNodes.find((node) => node.nodeType === 1);
if (itemEl) {
const temp = document.createElement('template');
temp.appendChild(itemEl.cloneNode(true));
this.templateNode = temp;
}
}
if (this.$refs.viewport) {
this.$refs.viewport.addEventListener('scroll', this.onScroll);
}
if (this.$refs.prevBtn) {
this.$refs.prevBtn.addEventListener('click', () => this.prevPage());
}
if (this.$refs.nextBtn) {
this.$refs.nextBtn.addEventListener('click', () => this.nextPage());
}
if (this.$refs.spacer) {
this.$refs.spacer.innerHTML = '';
}
this.measuredHeights = [];
this.initResizeObserver();
this.layout();
}
/**
* Navigates to a specific page when pagination is enabled.
* @param {number} targetPage - 1-based target page index.
*/
goToPage(targetPage) {
const pageSize = Number(this.props.pageSize || this.props['page-size'] || 0);
if (pageSize <= 0) return;
const allItems = this.props.items || [];
const totalItems =
this.props.totalItems !== undefined
? Number(this.props.totalItems)
: this.props['total-items'] !== undefined
? Number(this.props['total-items'])
: allItems.length;
const totalPages = Math.max(1, Math.ceil(totalItems / pageSize));
const page = Math.min(totalPages, Math.max(1, Math.floor(targetPage)));
if (this.currentPage !== page) {
this.currentPage = page;
if (this.$refs.viewport) {
this.$refs.viewport.scrollTop = 0;
}
const eventDetail = {
page,
pageSize,
totalPages,
totalItems,
startIndex: (page - 1) * pageSize,
endIndex: Math.min(totalItems, page * pageSize),
};
this.$emit('page-change', eventDetail);
this.$emit('pageChange', eventDetail);
this.layout();
}
}
/**
* Navigates to the next page.
*/
nextPage() {
this.goToPage(this.currentPage + 1);
}
/**
* Navigates to the previous page.
*/
prevPage() {
this.goToPage(this.currentPage - 1);
}
/**
* Initializes unified ResizeObserver for viewport container and row items.
*/
initResizeObserver() {
if (this.resizeObserver || typeof ResizeObserver === 'undefined') return;
this.resizeObserver = new ResizeObserver((entries) => {
let layoutNeeded = false;
for (const entry of entries) {
if (this.$refs.viewport && entry.target === this.$refs.viewport) {
const newHeight = entry.target.clientHeight;
if (newHeight !== this.lastViewportHeight) {
this.lastViewportHeight = newHeight;
layoutNeeded = true;
}
} else if (entry.target && entry.target.hasAttribute && entry.target.hasAttribute('data-index')) {
const indexAttr = entry.target.getAttribute('data-index');
if (indexAttr !== null) {
const idx = parseInt(indexAttr, 10);
const newHeight = entry.target.offsetHeight;
if (newHeight && newHeight !== this.measuredHeights[idx]) {
this.measuredHeights[idx] = newHeight;
layoutNeeded = true;
}
}
}
}
if (layoutNeeded) {
this.scheduleLayout();
}
});
if (this.$refs.viewport) {
this.lastViewportHeight = this.$refs.viewport.clientHeight || 0;
this.resizeObserver.observe(this.$refs.viewport);
}
}
/**
* Schedules layout recalculation on the next animation frame to prevent layout thrashing.
*/
scheduleLayout() {
if (this.rafId) {
cancelAnimationFrame(this.rafId);
}
this.rafId = requestAnimationFrame(() => {
this.rafId = null;
this.layout();
});
}
/**
* Lifecycle hook called after component updates.
* Re-evaluates virtualization layouts when properties (e.g. items, page) change.
*/
onUpdate() {
const pageProp = this.props.page || this.props['current-page'];
if (pageProp !== undefined) {
this.currentPage = Number(pageProp);
}
this.layout();
}
/**
* Lifecycle hook called when component unmounts.
* Clean up event listeners and observers to prevent leaks.
*/
onUnmount() {
if (this.rafId) {
cancelAnimationFrame(this.rafId);
this.rafId = null;
}
if (this.scrollRafId) {
cancelAnimationFrame(this.scrollRafId);
this.scrollRafId = null;
}
if (this.$refs.viewport) {
this.$refs.viewport.removeEventListener('scroll', this.onScroll);
}
if (this.resizeObserver) {
this.resizeObserver.disconnect();
this.resizeObserver = null;
}
}
/**
* Viewport scroll event handler.
* Throttles scroll processing via requestAnimationFrame to align rendering with the screen refresh rate.
*/
onScroll() {
if (this.scrollRafId) return;
this.scrollRafId = requestAnimationFrame(() => {
this.scrollRafId = null;
this.layout();
});
}
/**
* Creates a fresh element structure from the template to populate recycled element pool.
* @returns {Element}
*/
createItemElement() {
const templateHTML = unescapeTemplateMarkers(this.templateNode.innerHTML);
const tempDiv = document.createElement('div');
const html = this.renderer.render(templateHTML, () => '').trim();
tempDiv.innerHTML = html;
let element = tempDiv.firstElementChild || document.createElement('div');
element = this.patcher.cleanElement(element);
return element;
}
/**
* Measures visible DOM nodes and updates layout variables (e.g., offsets/heights/scrollbars/pagination).
*/
layout() {
if (!this.templateNode) return;
const allItems = this.props.items || [];
const pageSize = Number(this.props.pageSize || this.props['page-size'] || 0);
const defaultHeight = Number(this.props.itemHeight || this.props['item-height']) || 40;
const viewport = this.$refs.viewport;
const spacer = this.$refs.spacer;
const pagination = this.$refs.pagination;
const pageInfo = this.$refs.pageInfo;
const pageNum = this.$refs.pageNum;
const prevBtn = this.$refs.prevBtn;
const nextBtn = this.$refs.nextBtn;
if (!viewport || !spacer) return;
const totalItems =
this.props.totalItems !== undefined
? Number(this.props.totalItems)
: this.props['total-items'] !== undefined
? Number(this.props['total-items'])
: allItems.length;
let displayedItems = allItems;
let pageOffset = 0;
if (pageSize > 0) {
const totalPages = Math.max(1, Math.ceil(totalItems / pageSize));
const pageProp = Number(this.props.page || this.props['current-page'] || this.currentPage || 1);
this.currentPage = Math.min(totalPages, Math.max(1, Math.floor(pageProp)));
if (allItems.length > pageSize) {
// Client-side pagination slicing
pageOffset = (this.currentPage - 1) * pageSize;
displayedItems = allItems.slice(pageOffset, pageOffset + pageSize);
} else {
// Server-side paginated items provided
displayedItems = allItems;
pageOffset = 0;
}
// Update Pagination Controls UI
const showControls =
this.props.showControls !== undefined
? Boolean(this.props.showControls)
: this.props['show-controls'] !== undefined
? Boolean(this.props['show-controls'])
: true;
if (pagination && showControls) {
pagination.style.display = 'flex';
if (pageInfo) {
pageInfo.textContent = `Page ${this.currentPage} of ${totalPages} (${totalItems} items)`;
}
if (pageNum) {
pageNum.textContent = String(this.currentPage);
}
if (prevBtn) {
prevBtn.disabled = this.currentPage <= 1;
}
if (nextBtn) {
nextBtn.disabled = this.currentPage >= totalPages;
}
} else if (pagination) {
pagination.style.display = 'none';
}
} else if (pagination) {
pagination.style.display = 'none';
}
const items = displayedItems;
const viewportHeight = viewport.clientHeight || 400;
this.lastViewportHeight = viewportHeight;
const scrollTop = viewport.scrollTop;
// 1. Calculate heights array
const heights = [];
for (let i = 0; i < items.length; i++) {
const globalIdx = pageOffset + i;
heights.push(this.measuredHeights[globalIdx] !== undefined ? this.measuredHeights[globalIdx] : defaultHeight);
}
// 2. Cumulative heights for fast offset/index resolution
const cumHeights = [0];
for (let i = 0; i < items.length; i++) {
cumHeights.push(cumHeights[i] + heights[i]);
}
const totalHeight = cumHeights[items.length];
// 3. Find visible item range with buffer
const buffer = 5;
let startIndex = 0;
while (startIndex < items.length && cumHeights[startIndex + 1] <= scrollTop) {
startIndex++;
}
startIndex = Math.max(0, startIndex - buffer);
let endIndex = startIndex;
while (endIndex < items.length && cumHeights[endIndex] < scrollTop + viewportHeight) {
endIndex++;
}
endIndex = Math.min(items.length, endIndex + buffer);
const visibleCount = endIndex - startIndex;
// 4. Update spacer paddings and min-height
const paddingTop = cumHeights[startIndex];
const paddingBottom = totalHeight - cumHeights[endIndex];
spacer.style.paddingTop = `${paddingTop}px`;
spacer.style.paddingBottom = `${paddingBottom}px`;
spacer.style.minHeight = `${totalHeight}px`;
// 5. Sync spacer's child node count with visibleCount to manage recycled elements pool
while (spacer.childNodes.length > visibleCount) {
const lastChild = spacer.lastChild;
if (this.resizeObserver && lastChild.nodeType === 1) {
this.resizeObserver.unobserve(lastChild);
}
spacer.removeChild(lastChild);
}
while (spacer.childNodes.length < visibleCount) {
const itemEl = this.createItemElement();
spacer.appendChild(itemEl);
}
// 6. Ensure unified ResizeObserver is initialized
this.initResizeObserver();
// 7. Dynamic patching and recycling of row elements
const templateHTML = unescapeTemplateMarkers(this.templateNode.innerHTML);
for (let i = 0; i < visibleCount; i++) {
const itemIndex = startIndex + i;
const globalIndex = pageOffset + itemIndex;
const item = items[itemIndex];
const domNode = spacer.childNodes[i];
domNode.setAttribute('data-index', String(globalIndex));
if (this.resizeObserver && domNode.nodeType === 1) {
this.resizeObserver.observe(domNode);
}
// Resolver using parent context or component scope
const resolver = (expr) => {
const extraScope = {
[this.itemVar]: item,
index: globalIndex,
};
return this.$parent ? this.$parent._evaluate(expr, extraScope) : this._evaluate(expr, extraScope);
};
const renderedHTML = this.renderer.render(templateHTML, resolver).trim();
const tempDiv = document.createElement('div');
tempDiv.innerHTML = renderedHTML;
let newElement = tempDiv.firstElementChild;
if (newElement) {
newElement = this.patcher.cleanElement(newElement);
newElement.setAttribute('data-index', String(globalIndex));
this.patcher.patchElement(domNode, newElement, resolver, this.$app);
}
}
}
}
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