how to access functions within php files using .htacess like codeigniter - php

Question

I have a scenario where I want something similar to Codeigniter.
In Codeigniter my url is like:
http://www.example.com/filename/methodname
Now I want similar thing but using plain core PHP and .htaccess.
How is that possible ?
I want to have a index.php inside my folder and then redirect the http requests accordingly.
Searching the web I found this :
RewriteEngine on
RewriteRule ^([a-z0-9_-]+)\.html$ index.php/page/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond $1 !^(index\.php|asset|robots\.txt)
RewriteRule ^(.*)$ index.php/$1 [L]
But I have little knowledge of .htaccess and don't know how this could help.
So I want an answer with example to understand how this can be achieved using .htaccess.
What would I need to do on my PHP side ?

Answer 1

Routing
Having urls like /filename/methodname is generally called routing. You have half of it done already; what you show in .htaccess is the part that will redirect all traffic towards an index.php file.
# starts rewrite engine
RewriteEngine on
# redirects direct .html page calls to their corresponding pages
RewriteRule ^([a-z0-9_-]+)\.html$ index.php/page/$1 [L]
# for anything that is not a file
RewriteCond %{REQUEST_FILENAME} !-f
# and for anything that is not a directory
RewriteCond %{REQUEST_FILENAME} !-d
# except if it's a robot
RewriteCond $1 !^(index\.php|asset|robots\.txt)
# send all that to index.php
RewriteRule ^(.*)$ index.php/$1 [L]
That index file will then parse the url and call relevant handlers with relevant arguments based on what matched.
How to create one such parser, or router, is beyond the scope of a single answer, but basically depends on the use of $_SERVER['REQUEST_URI'] and an array of urls with their corresponding handlers.
Solution
This is a "solved problem", and while it is interesting to implement such a thing by yourself, I would recommend simply to use a library that does it for you. I personally use Fast-Route, a pretty straightforward library that allows for customization in the way you handle routes, but if you google for "php routers" you will find plenty of them.
Of Filename/Methodname
(opinions follow from here on)
This point should be rethinked. While with psr-4 (and psr-0, and probably psr-whatever) the correspondance between a specific class and its file is that the file is named after the class it contains, I believe it better to not think about this as filename/methodname but rather section/action, or whatever speaks best of what the url actually does.
Moreover, if you start using namespaces (which you should do if your oop code becomes slightly more complicated than a hello world page), you obviously won't pass full namespaces in urls, and they actually are irrelevant to your users.