#!/usr/bin/perl
 
 # This script translates a simple definition-based grammar
 # to either C, sh, Javascript, or in (in = identity grammar, i.e.
 # same grammar as input).
 #
 # Input grammar:
 #   (1) comments having ';' or '#' as the first char in the line
 #   (2) a blank line

 #   (3) !include "file"
 #   (4) !define foo bar
 #   (5) !define foo "bar"

 #
 # Environmental variables can be used to override a setting.
 # The special value "null" causes the variable to be undefined.
 # If an environmental value is bracketed, i.e [abc], the brackets
 # will be converted to double quotes prior to output.
 
 sub comment {
   my ($cmt) = @_;
   print "//$cmt\n" if ($mode =~ /^(c|js|h)$/);
   print "#$cmt\n" if ($mode =~ /^(sh|nsi|in)$/);
 }
 
 sub define {
   my ($name, $value) = @_;
   if ($mode eq "sh") {

     $value="true" if !$value;

     print "[ -z \"\$$name\" ] && export $name=$value\n";
     print "[ \"\$$name\" = \"$nulltag\" ] && unset $name\n";
   } else {
     if ($ENV{$name}) {
       $value = $ENV{$name};
       $value = "\"$1\"" if ($value =~ /\[(.*)\]$/);
     }
     if ($value ne $nulltag) {
       print "#define $name $value\n" if ($mode =~ /^(c|h)$/);

       print "!define $name $value\n" if ($mode =~ /^(nsi|in)$/);

       print "var $name=$value;\n" if ($mode eq "js");
     } else {
       print "//#undef $name\n" if ($mode =~ /^(c|h)$/);
       print "#!undef $name\n" if ($mode eq "nsi");

       print ";!undef $name\n" if ($mode eq "in");

       print "//undef $name\n" if ($mode eq "js");
     }
   }
 }
 
 sub include_file {
   local $_;
   $include_file_level++;
   die "!include file nesting too deep" if ($include_file_level > $max_inc_depth);
   my ($parm) = @_;
   my $fn = "$incdir/$parm";
   local *IN;
   open(IN, "< $fn") or die "cannot open $fn";
     while (<IN>) {
       chomp;
       if (/^\s*$/) {
 	print "\n";
       } elsif (/^[#;](.*)$/) {
 	comment ($1);

       } elsif (/^!define\s+(\w+)(?:\s+(.*?))?\s*$/) {

 	define ($1, $2);

       } elsif (/^!include\s+"(.+)"$/) {

 	include_file ($1);
       } else {
 	die "can't parse this line: $_\n";
       }
     }
   $include_file_level--;
 }
 
 die "usage: trans <c|h|sh|js|nsi|in> [-I<dir>] [files ...]" if (@ARGV < 1);
 
 ($mode) = shift(@ARGV);
 die "mode must be one of c, h, sh, js, nsi, or in" if !($mode =~ /^(c|h|sh|js|nsi|in)$/);
 
 $nulltag = "null";
 $max_inc_depth = 10;
 $include_file_level = 0;
 $incdir = ".";
 
 comment(" This file was automatically generated by trans.pl");
 
 while ($arg=shift(@ARGV)) {
   if ($arg =~ /^-/) {
     if ($arg =~ /^-I(.*)$/) {
       $incdir = $1;
     } else {
       die "unrecognized option: $arg";
     }
   } else {
     print "\n";
     include_file ($arg);
   }
 }