Logic to generate pdf from archived invoices stored in s3

generate_pdf_archived_invoice.php

// CONSTANTS defined in whiteboard_migration.module.
// Will be accessible when this module is installed on whiteboard.
define('WHITEBOARD_INVOICE_HEADER_START_COMMENT', 'Header begins here for invoice #');
define('WHITEBOARD_INVOICE_HEADER_END_COMMENT', 'Header ends here for invoice #');
define('WHITEBOARD_INVOICE_BODY_START_COMMENT', 'Body begins here for invoice #');
define('WHITEBOARD_INVOICE_BODY_END_COMMENT', 'Body ends here for invoice #');
define('WHITEBOARD_INVOICE_FOOTER_START_COMMENT', 'Footer begins here for invoice #');
define('WHITEBOARD_INVOICE_FOOTER_END_COMMENT', 'Footer ends here for invoice #');

$header_start_comment = '<!--' . WHITEBOARD_INVOICE_HEADER_START_COMMENT . $invoice_vid . '-->';
$header_end_comment = '<!--' . WHITEBOARD_INVOICE_HEADER_END_COMMENT . $invoice_vid . '-->';
$body_start_comment = '<!--' . WHITEBOARD_INVOICE_BODY_START_COMMENT . $invoice_vid . '-->';
$body_end_comment = '<!--' . WHITEBOARD_INVOICE_BODY_END_COMMENT_COMMENT . $invoice_vid . '-->';
$footer_start_comment = '<!--' . WHITEBOARD_INVOICE_FOOTER_START_COMMENT . $invoice_vid . '-->';
$footer_end_comment = '<!--' . WHITEBOARD_INVOICE_FOOTER_END_COMMENT . $invoice_vid . '-->';

$invoice_node = node_load($nid, $vid);
$invoice_markup = file_get_contents($invoice_node->field_invoice_content_online[0]['value']);

preg_match('/' . $header_start_comment . '[a-z|A-Z|\s|\S|\d|\D]*' . $header_end_comment . '/', $invoice_markup, $header_matches);
preg_match('/' . $body_start_comment . '[a-z|A-Z|\s|\S|\d|\D]*' . $body_end_comment . '/', $invoice_markup, $body_matches);
preg_match('/' . $footer_start_comment . '[a-z|A-Z|\s|\S|\d|\D]*' . $footer_end_comment . '/', $invoice_markup, $footer_matches);

/**
 * $header_matches[0]: will have the same content that should be in $headerHTML @L#2069 global.inc
 * $body_matches[0]: will have the same content that should be in $htmlData @L#2068 global.inc
 * $footer_matches[0]: will have the same content that should be in $footerHTML @L#2070 global.inc
 */