Unexpected behavior with custom .htaccess rewrite rules - regex

Question

So I have been working on some rewrite rules which aren't working as expected. These are some sample requests I am trying to rewrite:
/ -> /index.php?page=Home
/Home -> /index.php?page=Home
/Teaching/Foo -> /index.php?page=Teaching&id=Foo
/Teaching/Bar -> /index.php?page=Teaching&id=Bar
/Download/ue8 -> /index.php?action=Download&id=ue8
/Download/24a -> /index.php?action=Download&id=24a
(default) -> /index.php?page=Home
** OR ALTERNATIVELY **
(default) -> /index.php?page=FileNotFound
(and maybe rewrite the visible URL to /FileNotFound)
I mainly want to hide as much of the urls as possible and prevent both directory listing and direct access to my files located in specific folders and only allow access to downloadable files via /Download/FileId while having my usual pages for different lectures accesible via /Teaching/SomeLecture.
So far I have been using this snippet for the /Home and /Teaching stuff:
RewriteEngine On
RewriteBase /
# Redirect Trailing Slashes
RewriteRule ^(.*)/$ /$1 [L,R=301]
# Handle Front Controller
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^Teaching/([A-Za-z0-9]*)$ index.php?page=Teaching&id=$1 [L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^Home$ index.php?page=Home [L]
RewriteCond %{THE_REQUEST} ^[A-Z]{3,}\s(.*)/index\.php [NC]
RewriteRule ^ %1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php [L,R=301]
I am not completely sure about all of these directives and I noticed, that there are currently some flaws to it.
Trying to access a non-existant file, e.g. /Files/Bad/Path.pdf, forwards the user to /?page=Home which should be redirected either to /, /Home or display the contents of /index.php?page=FileNotFound without changing the URL at all or redirecting to /FileNotFound depending on the rule of (default). I am not really sure which solution might be the most suitable in this scenario.
Trying to access some folders which do exist results in an infinite redirection loop while folders which do not exist apparently redirect to /. In both cases it feels right to redirect to /FileNotFound I suppose?
Could you please work out a set of rules that might suit my needs in this case?

Answer 1

You have many redundant directives in your .htaccess. Replace all of your .htaccess with this:
# Turn off mod_spelling
<IfModule mod_speling.c>
CheckSpelling off
CheckCaseOnly off
</IfModule>
Options -MultiViews
RewriteEngine On
RewriteBase /
# block direct access to file and directories in these directories
RewriteCond %{REQUEST_URI} !\.(?:jpe?g|gif|bmp|png|tiff|css|js)$ [NC]
RewriteCond %{REQUEST_FILENAME} -d [OR]
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^(Templates|Files) - [NC,F]
# remove index.php
RewriteCond %{THE_REQUEST} /index\.php [NC]
RewriteRule ^(.*?)index\.php$ /$1 [L,R=301,NC,NE]
# Redirect Trailing Slashes
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)/$ /$1 [L,R=301]
# Handle Front Controller
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(Download|Teaching)/([\w-]+)/?$ index.php?page=$1&id=$2 [L,QSA,NC]
RewriteRule ^(Home)?/?$ index.php?page=Home [L,NC,QSA]
Make sure to clear your browser cache before testing this.