RewriteRule RegEx - Add another variation of subdirectory level mapping to URL

I am passing one of the following URLs to a site an want it to split into the proper parameters.

http://example.com/storevar?search_term    
http://example.com/storevar/?search_term    
http://example.com/storevar    
http://example.com/storevar/    
http://example.com/storevar/search_term    
http://example.com/storevar/search_term/    
http://example.com/storevar/search_term/mode    
http://example.com/storevar/search_term/mode/

Then they should pass the info to

http://example.com/process.php?store=$1&search=$2&mode=$3

Cuurently the following .HTACCESS file info handles the first 6 items, but not the "mode" info.

Options +FollowSymLinks

RewriteEngine On

# For /storevar?search_term and /storevar/?search_term
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^([^/]+)/?$ /process.php?store=$1&search=%{QUERY_STRING} [L]

# For /storevar/search_term, /storevar/search_term/ and /st开发者_运维问答orevar/
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^([^/]+)(?:/([^/]+))?/?$ /process.php?store=$1&search=$2 [QSA,L]

My RewriteRule RegEx skills are poor, so I am not sure how to deal with all of the possible variations.

How would I add the "mode" variations?

For these:

http://example.com/storevar/search_term/mode    
http://example.com/storevar/search_term/mode/

Use this one:

RewriteRule ^(?!process\.php)([^/]+)(?:/([^/]+)(?:/([^/]+))?)?/?$ /process.php?store=$1&search=$2&mode=$3 [L]