Nginx rewrite non-existent files under sub directory with rewrite rules - .htaccess

Question

Nginx rewrite from .php to .php under same location
I am trying to move a site with a large number (93) of .htaccess files from Apache to Nginx.
There are over 800 rewrite rules to convert. To optimize performance, I have decided to
place the rules under separate nested location blocks (61 blocks in total).
But I am having problem with rewriting some of the rules.
Requirements:
/test/abc/pics/ should redirect to /test/abc/wallpapers/
/test/abc/pics/800/a.jpg should be served directly, if the file is present. If it does not exist,
then the request should be rewritten to /test/abc/pics/pic.php, which will
create the file on first request. Subsequent requests will be served directly.
/test/abc should redirect to /test/abc.html
/test/abc.html should be rewritten to /test/index.php
/test/abc/def/year-2014.php should be rewritten to /test/abc/def/index.php
All static files (.gif, .jpg, .png, .mpg....) should be served directly with a very long expiry time.
All files ending in .html should be served directly. If the file does not exist the request should be rewritten to /fallback.php
All files ending in .php or / should be executed by PHP-FPM. If the file does not exist it should be rewritten to /fallback.php
Config:
index index.php;
#
# Location Specific Rules
#
location /test/abc/ {
location /test/abc/pics/ {
# For ensuring 'serve directly, if file exists' condition of Rule 2
try_files $uri #rewrite_pics;
}
location /test/abc/def/ {
try_files $uri $uri/index.php #rewrite_def;
}
}
location /test/ {
rewrite "^/test/([a-z-]+)$" /test/$1.html permanent; # Rule 3
rewrite "^/test/([a-z-]+).html$" /test/index.php?symbol=$1 last; # Rule 4
}
location #rewrite_pics {
rewrite "^/test/abc/pics/$" /test/abc/wallpapers/ permanent; # Rule 1
rewrite "^/test/abc/pics/([0-9]+)/(.*)$" /test/abc/pics/pic.php?width=$1&height=$1&pic=$2 last; # Rule 2
}
location #rewrite_def {
rewrite "(?i)^/test/abc/def/year-([a-z]+).php$" /test/abc/def/index.php?year=$1 last;
}
#
# Fallback Rules
#
location ~* \.(gif|jpg|jpeg|png|ico|3gp|flv|mpg|mpeg|mp4|mp3|swf|txt|xml|pdf|zip)$ {
expires 1M; # Rule 5
try_files $uri /404.php;
}
location ~ (\.php|\.html|/)$ {
try_files $uri "${uri}index.php" /fallback.php =404;
include php-fpm.conf;
}
php-fpm.conf
include fastcgi.conf;
fastcgi_index index.php;
fastcgi_pass 127.0.0.1:9000;
Problem:
Since the fallback rules are regular expressions, they are selected instead of the location specific rules
If I use ~ prefix for all location specific rules, then the fallback rules are never executed.
Request for /test/abc/pics/800/a.jpg will be rewritten to /test/abc/pics/pic.php which will again match the
same location config. So the file is not executed and is downloaded as is.
So, I added 'include php-fpm.conf;' to all location blocks (except named locations). But this causes all
requests under /test/abc/pics/ (including existing .jpg files) to pass to the PHP-FPM. Which leads to an access denied error,
since only .php extension is allowed by security.limit_extensions.
What am I doing wrong here? Is there a simple way to have all existing files served based on their extension
and only non existent files match the location blocks / rewrite rules?