node_modules/lit-html/node/development/directives/cache.js

import { render, nothing } from '../lit-html.js';
import { directive, Directive } from '../directive.js';
import { isTemplateResult, getCommittedValue, setCommittedValue, insertPart, clearPart, isCompiledTemplateResult } from '../directive-helpers.js';

/**
 * @license
 * Copyright 2017 Google LLC
 * SPDX-License-Identifier: BSD-3-Clause
 */
/**
 * The template strings array contents are not compatible between the two
 * template result types as the compiled template contains a prepared string;
 * only use the returned template strings array as a cache key.
 */
const getStringsFromTemplateResult = (result) => isCompiledTemplateResult(result) ? result['_$litType$'].h : result.strings;
class CacheDirective extends Directive {
    constructor(partInfo) {
        super(partInfo);
        this._templateCache = new WeakMap();
    }
    render(v) {
        // Return an array of the value to induce lit-html to create a ChildPart
        // for the value that we can move into the cache.
        return [v];
    }
    update(containerPart, [v]) {
        const _valueKey = isTemplateResult(this._value)
            ? getStringsFromTemplateResult(this._value)
            : null;
        const vKey = isTemplateResult(v) ? getStringsFromTemplateResult(v) : null;
        // If the previous value is a TemplateResult and the new value is not,
        // or is a different Template as the previous value, move the child part
        // into the cache.
        if (_valueKey !== null && (vKey === null || _valueKey !== vKey)) {
            // This is always an array because we return [v] in render()
            const partValue = getCommittedValue(containerPart);
            const childPart = partValue.pop();
            let cachedContainerPart = this._templateCache.get(_valueKey);
            if (cachedContainerPart === undefined) {
                const fragment = document.createDocumentFragment();
                cachedContainerPart = render(nothing, fragment);
                cachedContainerPart.setConnected(false);
                this._templateCache.set(_valueKey, cachedContainerPart);
            }
            // Move into cache
            setCommittedValue(cachedContainerPart, [childPart]);
            insertPart(cachedContainerPart, undefined, childPart);
        }
        // If the new value is a TemplateResult and the previous value is not,
        // or is a different Template as the previous value, restore the child
        // part from the cache.
        if (vKey !== null) {
            if (_valueKey === null || _valueKey !== vKey) {
                const cachedContainerPart = this._templateCache.get(vKey);
                if (cachedContainerPart !== undefined) {
                    // Move the cached part back into the container part value
                    const partValue = getCommittedValue(cachedContainerPart);
                    const cachedPart = partValue.pop();
                    // Move cached part back into DOM
                    clearPart(containerPart);
                    insertPart(containerPart, undefined, cachedPart);
                    setCommittedValue(containerPart, [cachedPart]);
                }
            }
            // Because vKey is non null, v must be a TemplateResult.
            this._value = v;
        }
        else {
            this._value = undefined;
        }
        return this.render(v);
    }
}
/**
 * Enables fast switching between multiple templates by caching the DOM nodes
 * and TemplateInstances produced by the templates.
 *
 * Example:
 *
 * ```js
 * let checked = false;
 *
 * html`
 *   ${cache(checked ? html`input is checked` : html`input is not checked`)}
 * `
 * ```
 */
const cache = directive(CacheDirective);

export { cache };
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