Rewrite urls depending on the host - nginx

Question

I have a Nginx server which serves a Symfony app.
But this app may receive requests from different hosts (which are for now simulated in /etc/hosts), and for each host, there is a kind of cache directory located in the public directory, having their own name:
|-src
|-var
|-...
|-public
| |-host1.com
| | |-file1
| | |-file2
| |-host2.com
| | |-file1
| | |-...
URIs can be of the following form (please note the absence of the subdirectory name):
https://host1.com/file1
In this case, I want Nginx to check if the public/host1.com/file1 exists. So I need to setup a kind of rewrite rule from /file1 to /host1.com/file1.
If the file exists, Nginx has to serve it. But if not (i.e. https://host1.com/file53), I want Nginx to redirect to the Symfony app, so that this one can generate the missing file, and serve it.
How can I do this with Nginx?
Here is my try. Without the 3 lines below the comment, it is working as a classic server.
server {
listen 80;
root /var/www/project/public;
location / {
##############################################
# Here is my try, but Nginx crashes with this:
##############################################
if ($host = "host1.com") {
try_files /host1.com$uri /index.php$is_args$args;
}
try_files $uri /index.php$is_args$args;
}
location ~ ^/index\.php(/|$) {
fastcgi_pass myapp:9000;
fastcgi_split_path_info ^(.+\.php)(/.*)$;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param DOCUMENT_ROOT $realpath_root;
}
location ~* \.(jpg|jpeg|gif|css|png|js|ico|html|eof|woff|ttf)$ {
if (-f $request_filename) {
expires 30d;
access_log off;
}
}
location ~ \.php$ {
return 404;
}
rewrite_log on;
error_log /var/log/nginx/project_error.log notice;
access_log /var/log/nginx/project_access.log;
}

Answer 1

As suggested in the comments, using different server blocks was the solution.
I also had problems with the following part, which was blocking all the image requests without logging it, which had caused misunderstandings in my debugging process:
location ~* \.(jpg|jpeg|gif|css|png|js|ico|html|eof|woff|ttf)$ {
if (-f $request_filename) {
expires 30d;
access_log off;
}
}