/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

import {
  Directive,
  noChange,
  nothing,
  directive,
} from "chrome://global/content/vendor/lit.all.mjs";

import { MozLitElement } from "chrome://global/content/lit-utils.mjs";

/**
 * A Lit directive that applies all properties of an object to a DOM element.
 *
 * This directive interprets keys in the provided props object as follows:
 * - Keys starting with `?` set or remove boolean attributes using `toggleAttribute`.
 * - Keys starting with `.` set properties directly on the element.
 * - Keys starting with `@` are currently not supported and will throw an error.
 * - All other keys are applied as regular attributes using `setAttribute`.
 *
 * It avoids reapplying values that have not changed, but does not currently
 * remove properties that were previously set and are no longer present in the new input.
 *
 * This directive is useful to "spread" an object of attributes/properties declaratively onto an
 * element in a Lit template.
 */
class SpreadDirective extends Directive {
  /**
   * A record of previously applied properties to avoid redundant updates.
   *
   * @type {Record<string, unknown>}
   */
  #prevProps = {};

  /**
   * Render nothing by default as all changes are made in update using DOM APIs
   * on the element directly.
   *
   * @returns {typeof nothing}
   */
  render() {
    return nothing;
  }

  /**
   * Apply props to the element using DOM APIs, updating only changed values.
   *
   * @param {AttributePart} part - The part of the template this directive is bound to.
   * @param {[Record<string, unknown>]} propsArray - An array with a single object containing props to apply.
   * @returns {typeof noChange} - Indicates to Lit that no re-render is needed.
   */
  update(part, [props]) {
    // TODO: This doesn't clear any values that were set in previous calls if
    // they are no longer present.
    // It isn't entirely clear to me (mstriemer) what we should do if a prop is
    // removed, or if the prop has changed from say ?foo to foo. By not
    // implementing the auto-clearing hopefully the consumer will do something
    // that fits their use case.

    /** @type {HTMLElement} */
    let el = part.element;

    for (let [key, value] of Object.entries(props)) {
      // Skip if the value hasn't changed since the last update.
      if (value === this.#prevProps[key]) {
        continue;
      }

      // Update the element based on the property key matching Lit's templates:
      //   ?key -> el.toggleAttribute(key, value)
      //   .key -> el.key = value
      //   key -> el.setAttribute(key, value)
      if (key.startsWith("?")) {
        el.toggleAttribute(key.slice(1), Boolean(value));
      } else if (key.startsWith(".")) {
        el[key.slice(1)] = value;
      } else if (key.startsWith("@")) {
        throw new Error(
          `Event listeners are not yet supported with spread (${key})`
        );
      } else {
        el.setAttribute(key, String(value));
      }
    }

    // Save current props for comparison in the next update.
    this.#prevProps = props;

    return noChange;
  }
}

export const spread = directive(SpreadDirective);

export class SettingElement extends MozLitElement {
  /**
   * The default properties that the setting element accepts.
   *
   * @param {PreferencesSettingsConfig} config
   * @returns {Record<string, any>}
   */
  getCommonPropertyMapping(config) {
    /**
     * @type {Record<string, any>}
     */
    const result = {
      id: config.id,
      "data-l10n-args": config.l10nArgs
        ? JSON.stringify(config.l10nArgs)
        : undefined,
      ".iconSrc": config.iconSrc,
      "data-subcategory": config.subcategory,
      ...config.controlAttrs,
    };
    if (config.supportPage) {
      result[".supportPage"] = config.supportPage;
    }
    if (config.l10nId) {
      result["data-l10n-id"] = config.l10nId;
    }
    return result;
  }
}