Rewrite link rule, conflicting files and folders - mod-rewrite

Question

Been trying to resolve this problem with a rewrite rule that assigns a subdomain to a root directory of the same name, for example.
ddd.example.com will link to "/_projects/ddd" directory, that works fine and I have no trouble with it, the issue is that any files or directories I have in the root directory "/" can be accessed from the subdomain ddd.example.com.
Here is an example directory structure
example.com = "/"
"index.php"
ddd.example.com = "/_projects/ddd"
no files
So if for instance I access ddd.example.com/index.php, it will resolve to using the file located example.com/index.php which is located a directory below.
Here is the rewrite rule for .htaccess
# Skip rewrite if subdomain is www
RewriteCond %{HTTP_HOST} !^www\. [NC]
# Extract (required) subdomain to %1
RewriteCond %{HTTP_HOST} ^([^.]+)\.example\.com(:80)?$
# Redirect to domain if requested URL does not resolve to existing subdirectory path
RewriteCond %{DOCUMENT_ROOT}/_projects/%1 !-d
RewriteRule (.*) http://example.com/ [NC,R=301]
# Skip rewrite if subdomain is www
RewriteCond %{HTTP_HOST} !^www\. [NC]
# Extract (required) subdomain to %1
RewriteCond %{HTTP_HOST} ^([^.]+)\.example\.com(:80)?$
# Skip rewrite if requested URL does not resolve to existing subdirectory path or file
RewriteCond %{DOCUMENT_ROOT}/_projects/%1/$1 -f [OR]
RewriteCond %{DOCUMENT_ROOT}/_projects/%1/$1 -d
RewriteRule (.*) /_projects/%1/$1 [NC,L]

Answer 1

What if your RewriteConds fail? Then the URL falls through and is not rewritten. And so it accesses the document root. I would just create separate VirtualHost entries for every single supported subdomain. (How many are there?)
Suppose the client asks for http://sub.example.com/index.php.
Suppose that there exists an /_projects/sub/index.php.
Your RewriteCond-s will see that /_projects/sub/index.php exists as a file, and then skip the rewrite. But if the rewrite is skipped, then there is no redirect to /_projects/sub/. So what document is fetched in that case? You guessed it, /index.php.
You should unconditionally redirect these subdomains to their proper places (subject only to checks against looping).
Why did you split the rewrite into two, one doing an internal redirect? The internal redirect isn't rewriting the whole URL to example.com, and so it stays in the subdomain. It looks like you can get into a loop there.

Answer 2

My attempt at rewriting was to do this essentially.
Pseudo Code:
if (subdomain-directory != exists)
redirect them to the home page
else
rewrite the request for the subdomain
I could only accomplish that using two rules, I haven't found any other way to accomplish this, so this was my attempt.
The condition in question actually works fine, if I have an index.php in the /_projects/sub directory then it will use that file and the same for any other file I put in there.
I have absolutely no idea how I can accomplish this with mod_rewrite, I have played around with it for the best part of a few weeks to no avail, searched endlessly for possible solutions and have not made any progress.

Answer 3

Resolved the problem, seems that there was a looping problem that was breaking the rewrite.
##### Subdomain to subfolder
# Fix missing trailing slashes.
#RewriteCond %{HTTP_HOST} !^(www\.)?example\.com$ [NC]
#RewriteCond %{HTTP_HOST} ^(www\.)?([^\.]+)\.example\.com$ [NC]
#RewriteCond %{DOCUMENT_ROOT}/%2%{REQUEST_URI}/ -d
#RewriteRule [^/]$ %{REQUEST_URI}/ [R=301,L]
# Rewrite sub domains.
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteCond %{HTTP_HOST} !^(www\.)?example\.com$ [NC]
RewriteCond %{HTTP_HOST} ^(www\.)?([^\.]+)\.example\.com$ [NC]
RewriteRule ^(.*)$ /projects/%2/$1 [QSA,L]