unit module System::Query;

sub follower(@path, $idx, $PTR) {
  die "Attempting to find \$*{@path[0].uc}.{@path[1..*].join('.')}"
    if !$PTR.^can("{@path[$idx]}") && $idx < @path.elems;
  return $PTR."{@path[$idx]}"()
    if $idx+1 == @path.elems;
  return follower(@path, $idx+1, $PTR."{@path[$idx]}"());   
}

sub system-collapse($data) is export {
  return $data 
    if $data !~~ Hash && $data !~~ Array;
  my $return = $data.WHAT.new;
  for $data.keys -> $idx {
    given $idx {
      when /^'by-env-exists'/ {
        my $key = $idx.split('.')[1];
        my $value = %*ENV{$key}:exists ?? 'yes' !! 'no';
        return system-collapse($data{$idx}{$value}) if $data{$idx}{$value}:exists;
        die "Unable to resolve path: {$idx} in \%*ENV\nhad: {$value}";
      }
      when /^'by-env'/ {
        my $key = $idx.split('.')[1];
        my $value = %*ENV{$key};
        return system-collapse($data{$idx}{$value}) if defined $value and $data{$idx}{$value}:exists;
        die "Unable to resolve path: {$idx} in \%*ENV\nhad: {$value // ''}";
      }
      when /^'by-' (['distro'|'kernel'|'backend'])/ {
        my $PTR   = $/[0] eq 'distro' ?? 
                      $*DISTRO !! $/[0] eq 'kernel' ??
                      $*KERNEL !! 
                      $*BACKEND;
        my $path  = $idx.split('.');
        my $value = follower($path, 1, $*DISTRO);
        my $fkey;

        if $value ~~ Version {
          my @checks = $data{$idx}.keys.map({ 
            my $suff = $_.substr(*-1);
            %(
              version  => Version.new($suff eq qw<+ ->.any ?? $_.substr(0, *-1) !! $_),
              orig-key => $_,
              ($suff eq qw<+ ->.any ?? suffix  => $suff !! ()),
            )
          }).sort({ $^b<version> cmp $^a<version> });
          for @checks -> $version {
            next unless
              $version<version> cmp $value ~~ Same ||
              ($version<version> cmp $value ~~ Less && $version<suffix> eq '+') ||
              ($version<version> cmp $value ~~ More && $version<suffix> eq '-');
            $fkey = $version<orig-key>;
            last;
          }
        } else { 
          $fkey  = ($data{$idx}{$value}:exists) ?? 
                     $value !!
                     ($data{$idx}{''}:exists) ??
                       '' !!
                       Any;
        }
        
        die "Unable to resolve path: {$path.cache[*-1].join('.')} in \$*DISTRO\nhad: {$value} ~~ {$value.WHAT.^name}"
          if Any ~~ $fkey;
        return system-collapse($data{$idx}{$fkey});
      }
      default {
        my $val = system-collapse($data ~~ Array ?? $data[$idx] !! $data{$idx});
        $return{$idx} = $val
          if $return ~~ Hash;
        $return.push($val)
          if $return ~~ Array;

      }
    };
  }
  return $return;
}