switch.ts

/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import '../../focus/md-focus-ring.js';
import '../../ripple/ripple.js';

import {html, isServer, LitElement, nothing, TemplateResult} from 'lit';
import {property, query} from 'lit/decorators.js';
import {ClassInfo, classMap} from 'lit/directives/class-map.js';

import {mixinDelegatesAria} from '../../internal/aria/delegate.js';
import {
  afterDispatch,
  setupDispatchHooks,
} from '../../internal/events/dispatch-hooks.js';
import {
  dispatchActivationClick,
  isActivationClick,
} from '../../internal/events/form-label-activation.js';
import {redispatchEvent} from '../../internal/events/redispatch-event.js';
import {
  createValidator,
  getValidityAnchor,
  mixinConstraintValidation,
} from '../../labs/behaviors/constraint-validation.js';
import {mixinElementInternals} from '../../labs/behaviors/element-internals.js';
import {
  getFormState,
  getFormValue,
  mixinFormAssociated,
} from '../../labs/behaviors/form-associated.js';
import {CheckboxValidator} from '../../labs/behaviors/validators/checkbox-validator.js';

// Separate variable needed for closure.
const switchBaseClass = mixinDelegatesAria(
  mixinConstraintValidation(
    mixinFormAssociated(mixinElementInternals(LitElement)),
  ),
);

/**
 * @fires input {InputEvent} Fired whenever `selected` changes due to user
 * interaction (bubbles and composed).
 * @fires change {Event} Fired whenever `selected` changes due to user
 * interaction (bubbles).
 */
export class Switch extends switchBaseClass {
  /** @nocollapse */
  static override shadowRootOptions: ShadowRootInit = {
    mode: 'open',
    delegatesFocus: true,
  };

  /**
   * Puts the switch in the selected state and sets the form submission value to
   * the `value` property.
   */
  @property({type: Boolean}) selected = false;

  /**
   * Shows both the selected and deselected icons.
   */
  @property({type: Boolean}) icons = false;

  /**
   * Shows only the selected icon, and not the deselected icon. If `true`,
   * overrides the behavior of the `icons` property.
   */
  @property({type: Boolean, attribute: 'show-only-selected-icon'})
  showOnlySelectedIcon = false;

  /**
   * When true, require the switch to be selected when participating in
   * form submission.
   *
   * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox#validation
   */
  @property({type: Boolean}) required = false;

  /**
   * The value associated with this switch on form submission. `null` is
   * submitted when `selected` is `false`.
   */
  @property() value = 'on';

  @query('input') private readonly input!: HTMLInputElement | null;

  constructor() {
    super();
    if (isServer) {
      return;
    }

    // This click listener does not currently need dispatch hooks since it does
    // not check `event.defaultPrevented`.
    this.addEventListener('click', (event: MouseEvent) => {
      if (!isActivationClick(event) || !this.input) {
        return;
      }
      this.focus();
      dispatchActivationClick(this.input);
    });

    // Add the aria keyboard interaction pattern for switch and the Enter key.
    // See https://www.w3.org/WAI/ARIA/apg/patterns/switch/.
    setupDispatchHooks(this, 'keydown');
    this.addEventListener('keydown', (event: KeyboardEvent) => {
      afterDispatch(event, () => {
        const ignoreEvent = event.defaultPrevented || event.key !== 'Enter';
        if (ignoreEvent || this.disabled || !this.input) {
          return;
        }

        this.input.click();
      });
    });
  }

  protected override render(): TemplateResult {
    return html`
      <div class="switch ${classMap(this.getRenderClasses())}">
        <input
          id="switch"
          class="touch"
          type="checkbox"
          role="switch"
          aria-label=${(this as ARIAMixin).ariaLabel || nothing}
          ?checked=${this.selected}
          ?disabled=${this.disabled}
          ?required=${this.required}
          @input=${this.handleInput}
          @change=${this.handleChange} />

        <md-focus-ring part="focus-ring" for="switch"></md-focus-ring>
        <span class="track"> ${this.renderHandle()} </span>
      </div>
    `;
  }

  private getRenderClasses(): ClassInfo {
    return {
      'selected': this.selected,
      'unselected': !this.selected,
      'disabled': this.disabled,
    };
  }

  private renderHandle() {
    const classes = {
      'with-icon': this.showOnlySelectedIcon ? this.selected : this.icons,
    };
    return html`
      ${this.renderTouchTarget()}
      <span class="handle-container">
        <md-ripple for="switch" ?disabled="${this.disabled}"></md-ripple>
        <span class="handle ${classMap(classes)}">
          ${this.shouldShowIcons() ? this.renderIcons() : html``}
        </span>
      </span>
    `;
  }

  private renderIcons() {
    return html`
      <div class="icons">
        ${this.renderOnIcon()}
        ${this.showOnlySelectedIcon ? html`` : this.renderOffIcon()}
      </div>
    `;
  }

  /**
   * https://fonts.google.com/icons?selected=Material%20Symbols%20Outlined%3Acheck%3AFILL%400%3Bwght%40500%3BGRAD%400%3Bopsz%4024
   */
  private renderOnIcon() {
    return html`
      <slot class="icon icon--on" name="on-icon">
        <svg viewBox="0 0 24 24">
          <path
            d="M9.55 18.2 3.65 12.3 5.275 10.675 9.55 14.95 18.725 5.775 20.35 7.4Z" />
        </svg>
      </slot>
    `;
  }

  /**
   * https://fonts.google.com/icons?selected=Material%20Symbols%20Outlined%3Aclose%3AFILL%400%3Bwght%40500%3BGRAD%400%3Bopsz%4024
   */
  private renderOffIcon() {
    return html`
      <slot class="icon icon--off" name="off-icon">
        <svg viewBox="0 0 24 24">
          <path
            d="M6.4 19.2 4.8 17.6 10.4 12 4.8 6.4 6.4 4.8 12 10.4 17.6 4.8 19.2 6.4 13.6 12 19.2 17.6 17.6 19.2 12 13.6Z" />
        </svg>
      </slot>
    `;
  }

  private renderTouchTarget() {
    return html`<span class="touch"></span>`;
  }

  private shouldShowIcons(): boolean {
    return this.icons || this.showOnlySelectedIcon;
  }

  private handleInput(event: Event) {
    const target = event.target as HTMLInputElement;
    this.selected = target.checked;
    // <input> 'input' event bubbles and is composed, don't re-dispatch it.
  }

  private handleChange(event: Event) {
    // <input> 'change' event is not composed, re-dispatch it.
    redispatchEvent(this, event);
  }

  // Writable mixin properties for lit-html binding, needed for lit-analyzer
  declare disabled: boolean;
  declare name: string;

  override [getFormValue]() {
    return this.selected ? this.value : null;
  }

  override [getFormState]() {
    return String(this.selected);
  }

  override formResetCallback() {
    // The selected property does not reflect, so the original attribute set by
    // the user is used to determine the default value.
    this.selected = this.hasAttribute('selected');
  }

  override formStateRestoreCallback(state: string) {
    this.selected = state === 'true';
  }

  [createValidator]() {
    return new CheckboxValidator(() => ({
      checked: this.selected,
      required: this.required,
    }));
  }

  [getValidityAnchor]() {
    return this.input;
  }
}