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// make sure JS file is enqueued and localized

function wpstagecoach_import() {

  // verify nonce
  
  // grab the latest finished row from the database
  
  // do the import
  
  // save the latest finished row to the database
  
  if( everything_went_smoothly() && we_still_have_more_to_do() ) {
    $result = intval( latest finished row );
  } elseif( everything_went_smoothly() && we_are_all_done() ) {
    $result = 'finished';
  } else {
    $result = 'error';
  }
  
  die( $result );

}

add_action( 'stagecoach_ajax_wpstagecoach_import', 'wpstagecoach_import' );

// The plugin JS file

$(document).ready(function() {

		$( "#wpsc-import" ).submit(function( event ) {

			event.preventDefault();

			$( '#wpsc-import' ).hide();

			do_the_import();

		});

});
	
function do_the_import() {
		var url = wpsc_ajax.ajaxurl;
		var nonce = $( 'NONCE NAME' ).val();
		var data = {
			'action': 'wpstagecoach_import',
			'nonce': nonce,
		};

		$.post(url, data, function (response) {
			if( response ) {
				if( 'error' == response ) {
					$("#import_results").html('We encountered an error. Please contact support');
				} else if( 'finished' == response ) {
					var success = 'All done';
					$("#import_results").html(success);
				} else {
					console.log('continue');
					var total = 'Updating ' + response + ' of ' + $('#working-on').val() + ' database rows';
					$("#import_results").html(total);
					do_the_import();
				}
			}

		});
	}	
	

/**
* The import page in the plugin
**/


// Form passes data about the last step finished, as well as whatever else you need
<form id="wpsc-import" action="<?php admin_url( 'THIS PAGE' ); ?>" method="post">
			<?php wp_nonce_field( 'NONCE ACTION', 'NONCE NAME' ); ?>

			<?php $current_step = $this->options['wpstagecoach_import_last_step'];
			if( !isset( $current_step ) || '0' == $current_step ) {
				$working_on = '1-100'; // or whatever interval you want
			} else {
				$next_step = intval( $current_step ) + 100;
				$working_on = $current_step . '-' . $next_step;
			} ?>
			<input type="hidden" name="working-on" id="working-on" value="<?php echo $working_on; ?>">

			<p class="submit">
				<input type="submit" class="button-primary" value="<?php _e( 'Import Now' ) ?>" name="wpsc-import-button" />
			</p>
		</form>

		<p id="import_results"></p>