lion/packages/form-core/src/InteractionStateMixin.js

import { dedupeMixin } from '@lion/core';
import { FormControlMixin } from './FormControlMixin.js';

/**
 * @typedef {import('../types/InteractionStateMixinTypes').InteractionStateMixin} InteractionStateMixin
 */

/**
 * @desc `InteractionStateMixin` adds meta information about touched and dirty states, that can
 * be read by other form components (ing-uic-input-error for instance, uses the touched state
 * to determine whether an error message needs to be shown).
 * Interaction states will be set when a user:
 * - leaves a form field(blur) -> 'touched' will be set to true. 'prefilled' when a
 *   field is left non-empty
 * - on keyup (actually, on the model-value-changed event) -> 'dirty' will be set to true
 *
 * @type {InteractionStateMixin}
 * @param {import('@open-wc/dedupe-mixin').Constructor<import('@lion/core').LitElement>} superclass
 */
const InteractionStateMixinImplementation = superclass =>
  class InteractionStateMixin extends FormControlMixin(superclass) {
    static get properties() {
      return {
        /**
         * True when user has focused and left(blurred) the field.
         */
        touched: {
          type: Boolean,
          reflect: true,
        },
        /**
         * True when user has changed the value of the field.
         */
        dirty: {
          type: Boolean,
          reflect: true,
        },
        /**
         * True when the modelValue is non-empty (see _isEmpty in FormControlMixin)
         */
        filled: {
          type: Boolean,
          reflect: true,
        },
        /**
         * True when user has left non-empty field or input is prefilled.
         * The name must be seen from the point of view of the input field:
         * once the user enters the input field, the value is non-empty.
         */
        prefilled: {
          attribute: false,
        },
        /**
         * True when user has attempted to submit the form, e.g. through a button
         * of type="submit"
         */
        submitted: {
          attribute: false,
        },
      };
    }

    /**
     *
     * @param {PropertyKey} name
     * @param {*} oldVal
     */
    requestUpdateInternal(name, oldVal) {
      super.requestUpdateInternal(name, oldVal);
      if (name === 'touched' && this.touched !== oldVal) {
        this._onTouchedChanged();
      }

      if (name === 'modelValue') {
        // We do this in requestUpdateInternal because we don't want to fire another re-render (e.g. when doing this in updated)
        // Furthermore, we cannot do it on model-value-changed event because it isn't fired initially.
        this.filled = !this._isEmpty();
      }

      if (name === 'dirty' && this.dirty !== oldVal) {
        this._onDirtyChanged();
      }
    }

    constructor() {
      super();
      this.touched = false;
      this.dirty = false;
      this.prefilled = false;
      this.filled = false;

      /** @type {string} */
      this._leaveEvent = 'blur';
      /** @type {string} */
      this._valueChangedEvent = 'model-value-changed';
      /** @type {EventHandlerNonNull} */
      this._iStateOnLeave = this._iStateOnLeave.bind(this);
      /** @type {EventHandlerNonNull} */
      this._iStateOnValueChange = this._iStateOnValueChange.bind(this);
    }

    /**
     * Register event handlers and validate prefilled inputs
     */
    connectedCallback() {
      super.connectedCallback();
      this.addEventListener(this._leaveEvent, this._iStateOnLeave);
      this.addEventListener(this._valueChangedEvent, this._iStateOnValueChange);
      this.initInteractionState();
    }

    disconnectedCallback() {
      super.disconnectedCallback();
      this.removeEventListener(this._leaveEvent, this._iStateOnLeave);
      this.removeEventListener(this._valueChangedEvent, this._iStateOnValueChange);
    }

    /**
     * Evaluations performed on connectedCallback. Since some components can be out of sync
     * (due to interdependence on light children that can only be processed
     * after connectedCallback and affect the initial value).
     * This method is exposed, so it can be called after they are initialized themselves.
     * Since this method will be called twice in last mentioned scenario, it must stay idempotent.
     */
    initInteractionState() {
      this.dirty = false;
      this.prefilled = !this._isEmpty();
    }

    /**
     * Sets touched value to true
     * Reevaluates prefilled state.
     * When false, on next interaction, user will start with a clean state.
     * @protected
     */
    _iStateOnLeave() {
      this.touched = true;
      this.prefilled = !this._isEmpty();
    }

    /**
     * Sets dirty value and validates when already touched or invalid
     * @protected
     */
    _iStateOnValueChange() {
      this.dirty = true;
    }

    /**
     * Resets touched and dirty, and recomputes prefilled
     */
    resetInteractionState() {
      this.touched = false;
      this.submitted = false;
      this.dirty = false;
      this.prefilled = !this._isEmpty();
    }

    _onTouchedChanged() {
      this.dispatchEvent(new CustomEvent('touched-changed', { bubbles: true, composed: true }));
    }

    _onDirtyChanged() {
      this.dispatchEvent(new CustomEvent('dirty-changed', { bubbles: true, composed: true }));
    }

    /**
     * Show the validity feedback when one of the following conditions is met:
     *
     * - submitted
     *   If the form is submitted, always show the error message.
     *
     * - prefilled
     *   the user already filled in something, or the value is prefilled
     *   when the form is initially rendered.
     *
     * - touched && dirty
     *   When a user starts typing for the first time in a field with for instance `required`
     *   validation, error message should not be shown until a field becomes `touched`
     *   (a user leaves(blurs) a field).
     *   When a user enters a field without altering the value(making it `dirty`),
     *   an error message shouldn't be shown either.
     */
    _showFeedbackConditionFor() {
      return (this.touched && this.dirty) || this.prefilled || this.submitted;
    }
  };

export const InteractionStateMixin = dedupeMixin(InteractionStateMixinImplementation);