get_n_cache.php

<?php declare(strict_types=1);

// this may be defined in the enviroment, not in the code.
// or can we find a system path for auto setup persistent cache ?
define('CACHE_FILE_TEMPLATE','/home/seb/.cache/test_php_{file}.txt');

// usage : get some data : get('the key') // return some string content
print 'get("the stuff to fetch") -> "'.get('some stuffx.').'"'.PHP_EOL;

// you can also use the 'tool' functions
//print 'cache file for yep : '.cache_file_path('yep');

// --- the functions ---

// main function
function get(string $key): ?string {
	return cached($key) ?? cache($key, fetch($key) );
}

function cached(string $key): ?string {
	$content = @fread(cache_file_stream($key),filesize(cache_file_path($key)));
	return $content === false ? null : $content;
}

function fetch(string $x): string {
    return "$x content, fetched at ".(new DateTime())->format(DateTime::RFC822);
}

function cache(string $key, string $content): string {
	if(false === fwrite(cache_file_stream($key), $content)) {
		throw new FailToWriteToFile(cache_file_path($key));
	};
	return $content;
}

// --- sub functions ---

/** @return resource */
function cache_file_stream(string $x)/*: resource*/ {
	if(false === ($resource = fopen(cache_file_path($x), 'c+'))) {
		throw new FailToOpenFile(cache_file_path($x));
	}
	return $resource;
}

function cache_file_path(string $x): string {
	return strtr(CACHE_FILE_TEMPLATE,['{file}' => crc32($x)]);
}

class FailToOpenFile extends \RuntimeException {};