<?php
/**
 * Date format conversion between PHP and JavaScript.
 *
 * @package Postlinkly
 * @since   1.0.0
 */

declare(strict_types=1);

namespace Postlinkly\Text;

/**
 * Converts WordPress's PHP date format strings into the format expected
 * by JavaScript date pickers (moment.js / day.js style).
 *
 * The conversion is character-by-character and preserves any character not
 * in the mapping table (typically separators like `-`, `/`, `:`, ` `).
 * Unknown format characters pass through untouched, which is the expected
 * behaviour for arbitrary literals.
 *
 * @since 1.0.0
 */
final class DateFormat {

	/**
	 * Mapping from PHP format characters to moment.js tokens.
	 *
	 * Covers the characters WordPress's default formats use. Add more
	 * entries here as we encounter PHP-side formats that need translating.
	 *
	 * @var array<string, string>
	 */
	private const PHP_TO_MOMENT = array(
		'Y' => 'YYYY',
		'y' => 'YY',
		'F' => 'MMMM',
		'M' => 'MMM',
		'm' => 'MM',
		'n' => 'M',
		'd' => 'DD',
		'j' => 'D',
		'l' => 'dddd',
		'D' => 'ddd',
		'H' => 'HH',
		'G' => 'H',
		'h' => 'hh',
		'g' => 'h',
		'i' => 'mm',
		's' => 'ss',
		'a' => 'a',
		'A' => 'A',
	);

	/**
	 * Converts a PHP date format string to a moment.js-compatible one.
	 *
	 * @since 1.0.0
	 *
	 * @param string $php_format PHP date format string.
	 *
	 * @return string Moment.js format string.
	 */
	public static function to_javascript( string $php_format ): string {
		$out    = '';
		$length = strlen( $php_format );
		for ( $i = 0; $i < $length; $i++ ) {
			$char = $php_format[ $i ];
			// Backslash escapes the next character — pass it through as a literal.
			if ( '\\' === $char && $i + 1 < $length ) {
				$out .= '[' . $php_format[ $i + 1 ] . ']';
				++$i;
				continue;
			}
			$out .= self::PHP_TO_MOMENT[ $char ] ?? $char;
		}
		return $out;
	}
}