Add a WooCommerce attribute (minimum quantity) to a Contact Form 7 form. Can be easily adapted to other attributes, as well as product meta, terms, etc

functions.php

// Save product_quantity_field.php in your active theme directory, then
// add this line  to your functions.php file to include it in the theme
include( get_stylesheet_directory() . '/product_quantity_field.php' );

product_quantity_field.php

<?php
/**
** A base module for the following types of tags:
** 	[quantity] and [quantity*]		# Quantity
**/

/* Shortcode handler */

add_action( 'wpcf7_init', 'wpcf7_add_shortcode_quantity' );

function wpcf7_add_shortcode_quantity() {
	wpcf7_add_shortcode( array( 'quantity', 'quantity*' ),
		'wpcf7_quantity_shortcode_handler', true );
}

function wpcf7_quantity_shortcode_handler( $tag ) {
	$tag = new WPCF7_Shortcode( $tag );

	if ( empty( $tag->name ) )
		return '';

	$validation_error = wpcf7_get_validation_error( $tag->name );

	$class = wpcf7_form_controls_class( $tag->type );

	$class .= ' wpcf7-validates-as-number';

	if ( $validation_error )
		$class .= ' wpcf7-not-valid';

	$atts = array();
	
	global $product;
	$words = explode( ' ', $product->get_attribute( 'minimum-quantity' ) );
	$min = ( $words ? $words[0] : 1 );

	$atts['class'] = $tag->get_class_option( $class );
	$atts['id'] = $tag->get_id_option();
	$atts['tabindex'] = $tag->get_option( 'tabindex', 'int', true );
	$atts['value'] = $min;
	$atts['min'] = $min;
	$atts['max'] = $min * 50;
	$atts['step'] = $min;

	if ( $tag->has_option( 'readonly' ) )
		$atts['readonly'] = 'readonly';

	if ( $tag->is_required() )
		$atts['aria-required'] = 'true';

	$atts['aria-invalid'] = $validation_error ? 'true' : 'false';

	if ( wpcf7_support_html5() ) {
		$atts['type'] = 'number';
	} else {
		$atts['type'] = 'text';
	}

	$atts['name'] = $tag->name;

	$atts = wpcf7_format_atts( $atts );

	$html = sprintf(
		'<span class="wpcf7-form-control-wrap %1$s"><input %2$s />%3$s</span>',
		sanitize_html_class( $tag->name ), $atts, $validation_error );

	return $html;
}

add_filter( 'wpcf7_validate_quantity', 'wpcf7_number_validation_filter', 10, 2 );
add_filter( 'wpcf7_validate_quantity*', 'wpcf7_number_validation_filter', 10, 2 );

/* Tag generator */

if ( is_admin() ) {
	add_action( 'admin_init', 'wpcf7_add_tag_generator_quantity', 18 );
}

function wpcf7_add_tag_generator_quantity() {
	$tag_generator = WPCF7_TagGenerator::get_instance();
	$tag_generator->add( 'quantity', __( 'quantity', 'contact-form-7' ),
		'wpcf7_tag_generator_quantity' );
}

function wpcf7_tag_generator_quantity( $contact_form, $args = '' ) {
	$args = wp_parse_args( $args, array() );
	$type = 'quantity';

	$description = __( "Generate a form-tag for a field for numeric value input. For more details, see %s.", 'contact-form-7' );

	$desc_link = wpcf7_link( __( 'http://contactform7.com/number-fields/', 'contact-form-7' ), __( 'Number Fields', 'contact-form-7' ) );

?>
<div class="control-box">
<fieldset>
<legend><?php echo sprintf( esc_html( $description ), $desc_link ); ?></legend>

<table class="form-table">
<tbody>
	<tr>
	<th scope="row"><?php echo esc_html( __( 'Field type', 'contact-form-7' ) ); ?></th>
	<td>
		<fieldset>
		<legend class="screen-reader-text"><?php echo esc_html( __( 'Field type', 'contact-form-7' ) ); ?></legend>
		<input type="hidden" name="tagtype" value="quantity">
		<label><input type="checkbox" name="required" /> <?php echo esc_html( __( 'Required field', 'contact-form-7' ) ); ?></label>
		</fieldset>
	</td>
	</tr>

	<tr>
	<th scope="row"><label for="<?php echo esc_attr( $args['content'] . '-name' ); ?>"><?php echo esc_html( __( 'Name', 'contact-form-7' ) ); ?></label></th>
	<td><input type="text" name="name" class="tg-name oneline" id="<?php echo esc_attr( $args['content'] . '-name' ); ?>" /></td>
	</tr>

	<tr>
	<th scope="row"><label for="<?php echo esc_attr( $args['content'] . '-values' ); ?>"><?php echo esc_html( __( 'Default value', 'contact-form-7' ) ); ?></label></th>
	<td><input type="text" name="values" class="oneline" id="<?php echo esc_attr( $args['content'] . '-values' ); ?>" /><br />
	<label><input type="checkbox" name="placeholder" class="option" /> <?php echo esc_html( __( 'Use this text as the placeholder of the field', 'contact-form-7' ) ); ?></label></td>
	</tr>

	<tr>
	<th scope="row"><label for="<?php echo esc_attr( $args['content'] . '-id' ); ?>"><?php echo esc_html( __( 'Id attribute', 'contact-form-7' ) ); ?></label></th>
	<td><input type="text" name="id" class="idvalue oneline option" id="<?php echo esc_attr( $args['content'] . '-id' ); ?>" /></td>
	</tr>

	<tr>
	<th scope="row"><label for="<?php echo esc_attr( $args['content'] . '-class' ); ?>"><?php echo esc_html( __( 'Class attribute', 'contact-form-7' ) ); ?></label></th>
	<td><input type="text" name="class" class="classvalue oneline option" id="<?php echo esc_attr( $args['content'] . '-class' ); ?>" /></td>
	</tr>
</tbody>
</table>
</fieldset>
</div>

<div class="insert-box">
	<input type="text" name="<?php echo $type; ?>" class="tag code" readonly="readonly" onfocus="this.select()" />

	<div class="submitbox">
	<input type="button" class="button button-primary insert-tag" value="<?php echo esc_attr( __( 'Insert Tag', 'contact-form-7' ) ); ?>" />
	</div>

	<br class="clear" />

	<p class="description mail-tag"><label for="<?php echo esc_attr( $args['content'] . '-mailtag' ); ?>"><?php echo sprintf( esc_html( __( "To use the value input through this field in a mail field, you need to insert the corresponding mail-tag (%s) into the field on the Mail tab.", 'contact-form-7' ) ), '<strong><span class="mail-tag"></span></strong>' ); ?><input type="text" class="mail-tag code hidden" readonly="readonly" id="<?php echo esc_attr( $args['content'] . '-mailtag' ); ?>" /></label></p>
</div>
<?php
}