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/* global define */
/* eslint-disable */
/**
* This file contains a reusable, and dependency-free JavaScript class,
* providing a contrast checker. This class allows you to assess the readability
* of the given background and text colors against the WCAG 2.0 AA standard.
*
* Example Usage:
*
* // Create an instance of the plugin with custom settings.
* const contrastChecker = new WPFormsColorContrastChecker({
* textColor: '#de8e8e', // Replace with your actual text color.
* bgColor: '#ffffff', // Replace with your actual background color.
* message: {
* contrastPass: '',
* contrastFail: 'Insufficient contrast. Please choose a darker text color or a lighter background color.',
* },
* });
*
* // Perform the contrast check.
* const contrastFailed = contrastChecker.checkContrast();
*
* // Display the result or handle the error, if any.
* if (contrastFailed) {
* console.error(contrastFailed);
* }
*/
/* eslint-enable */
( function( root, factory ) {
const pluginName = 'WPFormsColorContrastChecker';
if ( typeof define === 'function' && define.amd ) {
define( [], factory( pluginName ) );
} else if ( typeof exports === 'object' ) {
module.exports = factory( pluginName );
} else {
root[ pluginName ] = factory( pluginName );
}
// eslint-disable-next-line max-lines-per-function
}( this, function( pluginName ) {
// eslint-disable-next-line strict
'use strict';
/**
* Plugin Error Object.
*
* @since 1.8.6
*
* @class PluginError
*
* @augments Error
*/
class PluginError extends Error {
/**
* Constructor.
*
* @since 1.8.6
*
* @param {string} message The error message.
*/
constructor( message ) {
super( message );
this.name = pluginName;
}
}
/**
* Log the error message.
* This function can be replaced with a custom error logging logic.
*
* @since 1.8.6
*
* @param {string} error The error message.
*/
function logError( error ) {
// Custom error logging logic.
// Display the error message in a specific format or send it to a logging service
// eslint-disable-next-line no-console
console.error( error );
}
/**
* Plugin Object.
*
* @since 1.8.6
*
* @class Plugin
*/
class Plugin {
// Default settings.
static defaults = {
textColor: '',
bgColor: '',
contrastThreshold: 4.5, // W3C recommended minimum contrast ratio for normal text
message: {
contrastPass: 'The contrast ratio between the text and background color is sufficient.',
contrastFail: 'The contrast ratio between the text and background color is insufficient. Please choose a darker text color or a lighter background color.',
},
};
/**
* Constructor.
*
* @since 1.8.6
*
* @param {Object} args The argument object.
*/
constructor( args ) {
// Merge the default settings with the provided settings.
this.args = Object.assign( {}, Plugin.defaults, args );
}
/**
* Convert hex color code to an RGB array.
*
* @since 1.8.6
*
* @param {string} hexColor The hex color code.
*
* @return {number[]|null} The RGB array or null if the conversion failed.
*/
hexToRgb( hexColor ) {
const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec( hexColor );
if ( shorthandRegex.test( hexColor ) ) {
return result ? [
parseInt( result[ 1 ], 16 ) * 17,
parseInt( result[ 2 ], 16 ) * 17,
parseInt( result[ 3 ], 16 ) * 17,
] : null;
}
return result ? [
parseInt( result[ 1 ], 16 ),
parseInt( result[ 2 ], 16 ),
parseInt( result[ 3 ], 16 ),
] : null;
}
/**
* Calculate relative luminance for a color.
*
* The calculated relative luminance is a value between 0 and 1,
* where 0 represents black and 1 represents white.
*
* @since 1.8.6
*
* @param {string} rgb The RGB color code.
*
* @return {number} The relative luminance.
*/
calculateRelativeLuminance( rgb ) {
for ( let i = 0; i < rgb.length; i++ ) {
rgb[ i ] /= 255;
rgb[ i ] = rgb[ i ] <= 0.03928 ? rgb[ i ] / 12.92 : Math.pow( ( rgb[ i ] + 0.055 ) / 1.055, 2.4 );
}
// As Stated in WCAG the relative luminance of a color is defined as:
// L = 0.2126 * R + 0.7152 * G + 0.0722 * B
// where R, G and B are the color values normalized to the range [0, 1].
// @see https://www.w3.org/WAI/GL/wiki/Relative_luminance
// eslint-disable-next-line no-mixed-operators
return 0.2126 * rgb[ 0 ] + 0.7152 * rgb[ 1 ] + 0.0722 * rgb[ 2 ];
}
/**
* Get the contrast ratio between two colors.
*
* @since 1.8.6
*
* @return {number|null} The contrast ratio or an error if the calculation failed.
*/
getContrastRatio() {
try {
const rgbText = this.hexToRgb( this.args.textColor );
const rgbBg = this.hexToRgb( this.args.bgColor );
// Check for invalid color format
if ( ! rgbText || ! rgbBg ) {
throw new PluginError( 'Invalid color format. Provide valid hex color codes.' );
}
const [ l1, l2 ] = [ this.calculateRelativeLuminance( rgbText ), this.calculateRelativeLuminance( rgbBg ) ];
// The purpose of adding 0.05 to both the maximum and minimum relative luminance
// is to ensure that even if one of the luminance values is zero (which would cause division by zero),
// the result won't be infinite. This kind of adjustment is common in contrast ratio calculations
// to handle extreme cases and avoid mathematical errors.
return ( Math.max( l1, l2 ) + 0.05 ) / ( Math.min( l1, l2 ) + 0.05 );
} catch ( error ) {
logError( error.message );
return null;
}
}
/**
* Check the contrast and provide a warning if it's below the threshold.
*
* @since 1.8.6
*
* @return {string|null} The contrast check result or boolean false if the check failed.
*/
checkContrast() {
try {
const contrastRatio = this.getContrastRatio();
// Return early if invalid color format
if ( contrastRatio === null ) {
throw new PluginError( 'Invalid contrast ratio. Provide valid contrast ratio between two colors.' );
}
// Warn if the contrast is below the threshold.
if ( contrastRatio < this.args.contrastThreshold ) {
return this.args.message.contrastFail;
}
return this.args.message.contrastPass;
} catch ( error ) {
logError( error.message );
return null;
}
}
}
return Plugin;
} ) );