Any-amount donation form

<?php
/**
 * Donation amount form + amount parser.
 *
 * @package Acme_Theme
 */

defined( 'ABSPATH' ) || exit;

/**
 * Turn user input like "25", "25.5" or "1,250.00" into minor units (cents).
 * Returns 0 when the value is outside the allowed range.
 */
function acme_parse_donation( string $raw, int $min = 100, int $max = 500000 ): int {
	$clean = preg_replace( '/[^0-9.]/', '', str_replace( ',', '', $raw ) );
	if ( '' === $clean || ! is_numeric( $clean ) ) {
		return 0;
	}
	$minor = (int) round( (float) $clean * 100 );
	return ( $minor >= $min && $minor <= $max ) ? $minor : 0;
}

function acme_donation_form(): string {
	$presets = array( 10, 25, 50, 100 );
	ob_start();
	?>
	<form class="acme-donate" method="post" action="<?php echo esc_url( admin_url( 'admin-post.php' ) ); ?>">
		<input type="hidden" name="action" value="acme_donate">
		<?php wp_nonce_field( 'acme_donate', 'acme_nonce' ); ?>
		<fieldset>
			<legend><?php esc_html_e( 'Choose an amount', 'acme-theme' ); ?></legend>
			<?php foreach ( $presets as $amount ) : ?>
				<label class="acme-chip">
					<input type="radio" name="preset" value="<?php echo esc_attr( (string) $amount ); ?>">
					<span><?php echo esc_html( '$' . $amount ); ?></span>
				</label>
			<?php endforeach; ?>
			<label class="acme-custom">
				<?php esc_html_e( 'Other amount', 'acme-theme' ); ?>
				<input type="text" name="custom" inputmode="decimal" autocomplete="off" placeholder="0.00">
			</label>
		</fieldset>
		<button type="submit"><?php esc_html_e( 'Continue', 'acme-theme' ); ?></button>
	</form>
	<?php
	return (string) ob_get_clean();
}
add_shortcode( 'acme_donate', 'acme_donation_form' );

function acme_donate_handle(): void {
	check_admin_referer( 'acme_donate', 'acme_nonce' );

	$raw    = sanitize_text_field( wp_unslash( $_POST['custom'] ?? '' ) );
	$raw    = '' !== $raw ? $raw : sanitize_text_field( wp_unslash( $_POST['preset'] ?? '' ) );
	$amount = acme_parse_donation( $raw );

	if ( 0 === $amount ) {
		wp_safe_redirect( add_query_arg( 'donate_error', '1', wp_get_referer() ?: home_url( '/' ) ) );
		exit;
	}

	// Hand the validated amount to your payment step.
	wp_safe_redirect( add_query_arg( 'amount', $amount, home_url( '/give/confirm/' ) ) );
	exit;
}
add_action( 'admin_post_nopriv_acme_donate', 'acme_donate_handle' );
add_action( 'admin_post_acme_donate', 'acme_donate_handle' );

document.querySelectorAll('.acme-donate').forEach((form) => {
	const custom = form.querySelector('input[name="custom"]');
	const presets = form.querySelectorAll('input[name="preset"]');

	// Typing a custom amount clears the preset; picking a preset clears the text.
	custom.addEventListener('input', () => presets.forEach((r) => { r.checked = false; }));
	presets.forEach((r) => r.addEventListener('change', () => { custom.value = ''; }));
});