.htaccess redirect based on conditions and parameters - regex

Question

I have tried many answers but none of them seems to work.
WHAT I WANT?
1). I want to redirect this(if it contains the parameters from & to and both of them are not empty):
https://arc.abc.com/mconvertar.php?from=gbp&to=jpy
to
https://arc.abc.com/gbpjpy/
As you can see, we combined the values of from & to
2). And this(if it contains the parameter x along with from & to):
https://arc.abc.com/mconvertar.php?from=gbp&to=jpy&x=13
to
https://arc.abc.com/gbpjpy/x=13
As you can see the 13 is the same as the above url.
3). And if x is empty then:
https://arc.abc.com/mconvertar.php?from=gbp&to=jpy&x=
to
https://arc.abc.com/gbpjpy/x=1
As you can see we set the x value default to 1
WHAT I HAVE TRIED?
RewriteCond %{QUERY_STRING} (^|&)from=[^&\s]&to=[^&\s]&x=[0-9]
RewriteRule ^(.*)$ https://arc.abc.com/gbpjpy/x=%3 [R=301,L]
RewriteCond %{QUERY_STRING} !(^|&)x=($|&)
RewriteRule ^(.*)$ https://arc.abc.com/gbpjpy/x=1 [R=301,L]
RewriteRule ^([^/]*)([^/]*)/([^/]*)\.html$ /mconvertar.php?from=$1&to=$2 [L]
I really appreciate your help, Spent a lot of time

Answer 1

Assuming from parameter is always 3 characters long. You may try these rules in site root .htaccess:
RewriteEngine On
# external redirect from actual URL to pretty one with x=<digit>
RewriteCond %{THE_REQUEST} /mconvertar\.php?from=(\w+)&to=([^\s&]+)&(x=\d+)\s [NC]
RewriteRule ^ /%1%2/%3? [R=302,L]
# external redirect from actual URL to pretty one with x=<empty>
RewriteCond %{THE_REQUEST} /mconvertar\.php?from=(\w+)&to=([^\s&]+)&(x)=\s [NC]
RewriteRule ^ /%1%2/%3=1? [R=302,L]
# internal forward from pretty URL to actual one
RewriteRule ^(\w{3})([^/]+)/(x=\d+)/?$ mconvertar.php?from=$1&to=$2&$3 [L,QSA,NC]