style-map.ts

/**
 * @license
 * Copyright 2018 Google LLC
 * SPDX-License-Identifier: BSD-3-Clause
 */

import {AttributePart, noChange} from '../lit-html.js';
import {
  directive,
  Directive,
  DirectiveParameters,
  PartInfo,
  PartType,
} from '../directive.js';

/**
 * A key-value set of CSS properties and values.
 *
 * The key should be either a valid CSS property name string, like
 * `'background-color'`, or a valid JavaScript camel case property name
 * for CSSStyleDeclaration like `backgroundColor`.
 */
export interface StyleInfo {
  [name: string]: string | undefined | null;
}

const important = 'important';
// The leading space is important
const importantFlag = ' !' + important;
// How many characters to remove from a value, as a negative number
const flagTrim = 0 - importantFlag.length;

class StyleMapDirective extends Directive {
  _previousStyleProperties?: Set<string>;

  constructor(partInfo: PartInfo) {
    super(partInfo);
    if (
      partInfo.type !== PartType.ATTRIBUTE ||
      partInfo.name !== 'style' ||
      (partInfo.strings?.length as number) > 2
    ) {
      throw new Error(
        'The `styleMap` directive must be used in the `style` attribute ' +
          'and must be the only part in the attribute.'
      );
    }
  }

  render(styleInfo: Readonly<StyleInfo>) {
    return Object.keys(styleInfo).reduce((style, prop) => {
      const value = styleInfo[prop];
      if (value == null) {
        return style;
      }
      // Convert property names from camel-case to dash-case, i.e.:
      //  `backgroundColor` -> `background-color`
      // Vendor-prefixed names need an extra `-` appended to front:
      //  `webkitAppearance` -> `-webkit-appearance`
      // Exception is any property name containing a dash, including
      // custom properties; we assume these are already dash-cased i.e.:
      //  `--my-button-color` --> `--my-button-color`
      prop = prop
        .replace(/(?:^(webkit|moz|ms|o)|)(?=[A-Z])/g, '-$&')
        .toLowerCase();
      return style + `${prop}:${value};`;
    }, '');
  }

  override update(part: AttributePart, [styleInfo]: DirectiveParameters<this>) {
    const {style} = part.element as HTMLElement;

    if (this._previousStyleProperties === undefined) {
      this._previousStyleProperties = new Set();
      for (const name in styleInfo) {
        this._previousStyleProperties.add(name);
      }
      return this.render(styleInfo);
    }

    // Remove old properties that no longer exist in styleInfo
    // We use forEach() instead of for-of so that re don't require down-level
    // iteration.
    this._previousStyleProperties!.forEach((name) => {
      // If the name isn't in styleInfo or it's null/undefined
      if (styleInfo[name] == null) {
        this._previousStyleProperties!.delete(name);
        if (name.includes('-')) {
          style.removeProperty(name);
        } else {
          // Note reset using empty string (vs null) as IE11 does not always
          // reset via null (https://developer.mozilla.org/en-US/docs/Web/API/ElementCSSInlineStyle/style#setting_styles)
          // eslint-disable-next-line @typescript-eslint/no-explicit-any
          (style as any)[name] = '';
        }
      }
    });

    // Add or update properties
    for (const name in styleInfo) {
      const value = styleInfo[name];
      if (value != null) {
        this._previousStyleProperties.add(name);
        const isImportant = value.endsWith(importantFlag);
        if (name.includes('-') || isImportant) {
          style.setProperty(
            name,
            isImportant ? value.slice(0, flagTrim) : value,
            isImportant ? important : ''
          );
        } else {
          // eslint-disable-next-line @typescript-eslint/no-explicit-any
          (style as any)[name] = value;
        }
      }
    }
    return noChange;
  }
}

/**
 * A directive that applies CSS properties to an element.
 *
 * `styleMap` can only be used in the `style` attribute and must be the only
 * expression in the attribute. It takes the property names in the
 * {@link StyleInfo styleInfo} object and adds the property values as CSS
 * properties. Property names with dashes (`-`) are assumed to be valid CSS
 * property names and set on the element's style object using `setProperty()`.
 * Names without dashes are assumed to be camelCased JavaScript property names
 * and set on the element's style object using property assignment, allowing the
 * style object to translate JavaScript-style names to CSS property names.
 *
 * For example `styleMap({backgroundColor: 'red', 'border-top': '5px', '--size':
 * '0'})` sets the `background-color`, `border-top` and `--size` properties.
 *
 * @param styleInfo
 * @see {@link https://lit.dev/docs/templates/directives/#stylemap styleMap code samples on Lit.dev}
 */
export const styleMap = directive(StyleMapDirective);

/**
 * The type of the class that powers this directive. Necessary for naming the
 * directive's return type.
 */
export type {StyleMapDirective};