[WordPress] Import a CSV file, break it into parts, and then import the data all the while providing the user with feedback.

1-separate-csv-file.php

<?php

/**
 * Note that this file is for demonstration purposes only. It should be treated
 * more like pseudo-code than code ready for production.
 *
 * The idea of the code below is how to break up a large CSV file into parts
 * and then write the individual files to disk.
 */

// Read the contents of the file
$csv = file_get_contents( $file );

/* Separate each file into an index of an array and store the total
 * number of rows that exist in the array. This assumes that
 * each row of the CSV file is on a new line.
 */
$csv_rows = explode( "\n", $csv );
$total_rows = count( $csv_rows );

// Store the title row. This will be written at the top of every file.
$title_row = $csv_rows[ 0 ];

/* Calculate the number of rows that will consist of 10, and then calculate
 * the number of rows for the final file.
 *
 * We use floor() so we don't round up by one.
 */
$rows_of_ten = floor( $total_rows / 10 );
$remaining_row = ( $rows_of_ten % 10 );

// Prepare to write out the files. This could just as easily be a for loop.
$file_counter = 0;
while( 0 < $rows_of_ten ) {

	/* Create the output file that will contain a title row and a set of ten rows.
	 * The filename is generated based on which file we're importing.
	 */
	$output_file = fopen( dirname( __FILE__ ). '/acme_csv_' . $file_counter . '.csv', 'w' );

	// Write out the title and then a batch of 10 rows into a string.
	for( $i = 0; $i <= 10; $i++ ) {

		/* Read the value from the array and then remove it from
		 * the array so it's not read again.
		 */
		$csv_data .= $csv_rows[ $i ] . "\n";
		unset( $csv_rows[ $i ] );

	}

	/* Write out the file and then close the handle since we'll be opening
	 * a new one on the next iteration.
	 */
	fwrite( $output_file, $csv_data );
	fclose( $output_file );

	/* Increase the file counter by one and decrement the rows of 10,
	 * reset the keys for the rows of the array, and then reset the
	 * string of data to the title row
	 */
	$file_counter++;
	$rows_of_ten--;
	$csv_rows = array_values( $csv_rows );
	$csv_data = $title_row;

}

2-add-number-of-files.php

<?php

/* $number_of_files can be calculated during the import process
 * previously discussed.
 */
update_option( 'acme-number-of-files', $number_of_files );

/* An alternative way to do this is to read all of the CSV files
 * that have been created after the process of creating the files
 * has completed.
 */
$files = glob( dirname( __FILE__ ) . '/acme_csv_*.csv' );
update_option( 'acme-number-of-files', count( $files ) );

3-start-the-machine.php

<?php

/* Setup the hook for the Ajax request.
 * This may be done in the constructor or somewhere else in your
 * plugin.
 */
add_action( 'wp_ajax_import_files', array( $this, 'import_files' ) );

/**
 * Begins importing the files. Only comments below because the
 * way in which you go about retrieving your files will vary
 * based on your overall implementation.
 */
public function import_files() {
  
  /*
   * 1. Read the most recent file that has not been read
   * 2. Insert the information from the file into the database
   * 3. Delete (or unlink()) the file that was just created
   * 4. Update the option of how many files have been processed.
   */
   
  // Step 4 may look something like this:
  if ( NULL === ( $parsed_files = get_option( 'acme-parsed-files' ) ) ) {
    $parsed_files = 0;
  }
  update_option( 'acme-parsed-files', $parsed_files );
  
}

4-making-progress.php

<?php

// Define the hook for getting the status somewhere in your plugin
add_action( 'wp_ajax_get_import_status', array( $this, 'get_import_status' ) );

public function get_import_status() {

  /* Notice that in the above code that we use die() with
   * a value - this is how the value is returned to
   * the client requesting a value from this function.
   *
   * $progress indicates how far we are during the import,
   * -1 indicates that we're done and we can eventually stop
   * the timer.
   */
   
   if ( FALSE !== get_option( 'acme-parsed-files' ) ) {
   	
   	$parsed_files = floatval( get_option( 'acme-parsed-files' ) );
	$total_files =  floatval( get_option( 'acme-number-of-files' ) );

	$progress =  $parsed_files / $total_files;

	die( $progress );
   	
   } else {
	die( '-1' );
   }

}

5-request.js

(function( $ ) {
	'use strict';

	$(function() {

		/* Use the global WordPress 'ajaxurl' to send the request to WordPress
		 * and tell it to fire the import_files function.
		 *
		 * Use the response returned from the server for how to update the display
		 * when the operation has completely finished.
		 */
		$.post( ajaxurl, {

			action: 'import_files'

		}, function( response ) {

			/* You can control the response from the server. In this case,
			 * I'm sending a '0' whenever all of the files have been imported.
			 */
			if ( '0' === response ) {
				
				// Update the progress to 100%, display an 'import complete' message
				
			}

		});

	});
	
})( jQuery );

6-request.js

(function( $ ) {
  'use strict';

	$(function() {
	
	var importTimer;
		
	/* Every second, we're going to poll the server to request for the
	 * value of the progress being made. This is using the get_import_status
	 * function on the server-side.
	 *
	 * If the response is -1, then the operation is done and we can stop the
	 * timer; otherwise, we can update the progressbar.
	 */
	importTimer = setInterval(function() {

		// Get the current status of the update
		$.get( ajaxurl, {
			action:    'get_import_status'
		}, function( response ) {

			if ( '-1' === response ) {

				// Set the progress bar equal to 100 and clear the timer

			} else {

				// Update the progress bar with (100 * response)

			}


		});

	}, 1000 );

  });
	
})( jQuery );

7-request.js

(function( $ ) {
  'use strict';

	$(function() {
	
	var importTimer;
		
	/* Every second, we're going to poll the server to request for the
	 * value of the progress being made. This is using the get_import_status
	 * function on the server-side.
	 *
	 * If the response is -1, then the operation is done and we can stop the
	 * timer; otherwise, we can update the progressbar.
	 */
	importTimer = setInterval(function() {

		// Get the current status of the update
		$.get( ajaxurl, {
			action:    'get_import_status'
		}, function( response ) {

			if ( '-1' === response ) {

				// Set the progress bar equal to 100 and clear the timer

			} else {

				// Update the progress bar with (100 * response)

			}


		});

	}, 1000 );
		
	/* Use the global WordPress 'ajaxurl' to send the request to WordPress
	 * and tell it to fire the import_files function.
	 *
	 * Use the response returned from the server for how to update the display
	 * when the operation has completely finished.
	 */
	$.post( ajaxurl, {

		action: 'import_files'

	}, function( response ) {

		/* You can control the response from the server. In this case,
		 * I'm sending a '0' whenever all of the files have been imported.
		 */
		  if ( '0' === response ) {
				
			  // Update the progress to 100%, display an 'import complete' message
				
		  }

	  });

  });
	
})( jQuery );

It seems you did not treat $remaining_row in 1/ :D

for "$remaining_row" i did:
if($remaining_row){
$rows_of_ten++;
}
just one increment cuz it wont be more than 9 when divided by 10