<?php
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

//Check everything exists before using it
if ( ! isset( $_SERVER['HTTP_ACCEPT_ENCODING'] ) ) {
	$_SERVER['HTTP_ACCEPT_ENCODING'] = '';
}
if ( ! isset( $_SERVER['HTTP_USER_AGENT'] ) ) {
	$_SERVER['HTTP_USER_AGENT'] = '';
}

// Determine supported compression method
$gzip    = strstr( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' );
$deflate = strstr( $_SERVER['HTTP_ACCEPT_ENCODING'], 'deflate' );

// Determine used compression method
$encoding = $gzip ? 'gzip' : ( $deflate ? 'deflate' : 'none' );

// Check for buggy versions of Internet Explorer
if ( ! strstr( $_SERVER['HTTP_USER_AGENT'], 'Opera' ) &&
	preg_match( '/^Mozilla\/4\.0 \(compatible; MSIE ([0-9]\.[0-9])/i', $_SERVER['HTTP_USER_AGENT'], $matches ) ) {
	$version = floatval( $matches[1] );

	if ( $version < 6 ) {
		$encoding = 'none';
	}

	if ( $version == 6 && ! strstr( $_SERVER['HTTP_USER_AGENT'], 'EV1' ) ) {
		$encoding = 'none';
	}
}

//Some servers compress the output of PHP - Don't break in those cases
if ( ini_get( 'output_handler' ) == 'ob_gzhandler' || ini_get( 'zlib.output_compression' ) == 1 ) {
	$encoding = 'none';
}

//Get data
$contents = file_get_contents( __FILE__ . '.' . $encoding );

// first check if we have to send 304
$eTag    = md5( $contents );
$modTime = filemtime( __FILE__ . '.none' );

$eTagMatch    = ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && strpos( $_SERVER['HTTP_IF_NONE_MATCH'], $eTag ) );
$modTimeMatch = ( isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) && strtotime( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) === $modTime );

if ( ( $modTimeMatch ) || ( $eTagMatch ) ) {
	header( 'HTTP/1.1 304 Not Modified' );
	header( 'Connection: close' );
} else {
	// send all sorts of headers
	$expireTime = 60 * 60 * 24 * 356; // 1y max according to RFC

	if ( isset( $encoding ) && $encoding != 'none' ) {
		header( 'Content-Encoding: ' . $encoding );
	}
	header( 'Vary: Accept-Encoding' );
	header( 'Content-Length: ' . strlen( $contents ) );
	header( 'Content-type: %%CONTENT%%; charset=utf-8' );
	header( 'Cache-Control: max-age=' . $expireTime . ', public, must-revalidate' );
	header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + $expireTime ) . ' GMT' ); //10 years
	header( 'ETag: ' . $eTag );
	header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s', $modTime ) . ' GMT' );

	// send output
	// phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Cached/compressed file content cannot be escaped
	echo $contents;
}