rewrite urls , not all urls works - .htaccess

Question

I have blog and I want to rewrite the link
site.com/blog -> for the blog index blog_posts.php
site.com/blog/{post-slug} -> for the single_post.php?post-slug={post-slug}
site.com/blog/topic/{topic} -> for the filtered_posts.php?topic={topic}
my problem is when I access to a post or a topic its access to site.com/blog blog_posts.php
I think because when access to blog_posts.php and write after it any think like kbjsflgjdouihaiufhslkdf access to blog_posts.php
my try
RewriteRule ^blog/([0-9a-zA-Zأ-ي-]+)/ single_post.php?post-slug=$1 [NC,L]
RewriteRule ^blog/ blog_posts.php [NC,L]
RewriteRule ^blog/topic/([0-9a-zA-Zأ-ي-]+)/ filtered_posts.php?topic=$1 [NC,L]
and if there are any thing that tech all about the .htaccess please gimme a link

Answer 1

RewriteRule ^blog/([0-9a-zA-Zأ-ي-]+)/ single_post.php?post-slug=$1 [NC,L]
RewriteRule ^blog/ blog_posts.php [NC,L]
RewriteRule ^blog/topic/([0-9a-zA-Zأ-ي-]+)/ filtered_posts.php?topic=$1 [NC,L]
You need to change the order of the directives and/or make the regex more specific. Order is important - the most specific regex need to be first.
For instance, your first rule ^blog/([0-9a-zA-Zأ-ي-]+)/ will naturally match any URL of the form /blog/topic/<something>, so the request is rewritten to single_post.php and the 3rd rule is never processed.
And your 2nd rule (^blog/), matches anything else that simply starts /blog, so again, the 3rd rule would never be processed.
Your example URLs, eg /blog/{post-slug} do not include a slash suffix, however, the directives you have written look as if you are trying to match one? Although you are not using any end-of-string anchor on the regex, so you are probably matching too much. For instance, the regex ^blog/([0-9a-zA-Zأ-ي-]+)/ will match a URL of the form /blog/{post-slug}/1234/something/etc which is probably not the intention (if it is the intention then it's still a fault as you potentially have a duplicate content issue).
I'm assuming your URLs are as per your example - no trailing slash.
I also queried (in comments) whether /blog a physical directory on the filesystem? If it is then your first example URL, ie. /blog is not canonical since mod_dir will implicitly trigger a 301 redirect to append the trailing slash. I'm assuming this is a physical directory and the canonical URL is actually /blog/, not /blog.
Try the following instead:
RewriteRule ^blog/topic/([0-9a-zA-Zأ-ي-]+)$ filtered_posts.php?topic=$1 [L]
RewriteRule ^blog/([0-9a-zA-Zأ-ي-]+)$ single_post.php?post-slug=$1 [L]
RewriteRule ^blog/$ blog_posts.php [L]
I also remove the NC (nocase) flag. You are already checking for both lowercase and uppercase letters in the regex, but if you are also allowing uppercase letters in other parts of the URL then you potentially have a duplicate content (non-canonical) URL issue that would need to be resolved.
Reference:
https://httpd.apache.org/docs/current/rewrite/intro.html
https://httpd.apache.org/docs/current/mod/mod_rewrite.html