#! /usr/bin/env perl
##
## Copyright (C) by Argonne National Laboratory
##     See COPYRIGHT in top-level directory
##

# Parse C or header files to search for MPI_T control variable
# and category info, then output the info in source code form.

use strict;
use warnings;
use File::Basename qw(basename);
use Data::Dumper;
use Getopt::Long;

# Help perl find the YAML parsing module
use lib 'maint/local_perl/lib';
use YAML::Tiny qw();

# To format README file
use Text::Wrap;
$Text::Wrap::unexpand = 0; # disable hard tabs in output

##################################################

my @dirs = qw(src/mpi src/mpi_t src/nameserv src/util src/binding src/include src/mpid src/pmi);

# set true to enable debug output
my $debug = 0;
my @cvars = ();
my %cvars; # used for duplication detection
my @categories=();
my $yaml = YAML::Tiny->new();
my @cfiles = ();
my %skipfiles = ();

# namespace prefix for function names
my $fn_ns = "MPIR_T_cvar";
# namespace prefix for variable and type names
my $ns = "MPIR_CVAR";
# an alternative namespace used for environment variables, unused if set to ""
my $alt_ns = "MPIR_PARAM";
# deprecated prefix for backward compatibility
my $dep_ns = "MPICH";

# Default :output source files
# NOTE: it's important to use single quote. abs_srcdir may contain sigils
#   e.g. /var/lib/jenkins/workspace/hzhou-custom@2/config/ch3-sock/label/centos64
my $header_file = 'src/include/mpir_cvars.h';
my $c_file      = 'src/util/mpir_cvars.c';
my $readme_file = 'README.envvar';

sub Usage {
    print <<EOT;

Usage: $0 [OPTIONS]

Supported options:
    --help              - this output (optional)
    --debug             - enable some debugging output (optional)
    --namespace=STR     - use STR as variable/type prefix in generated code (optional, default=$ns)
    --alt-namespace=STR - use STR as alternative variable/type prefix in generated code (optional, default=$alt_ns)
    --header=STR        - specify the header file name (optional, default=$header_file)
    --c-file=STR        - specify the C file name (optional, default=$c_file)
    --readme-file=STR   - specify the readme file name (optional, default=$readme_file)
    --skip=STR          - skip parsing files as specified (optional)

EOT
    exit 1;
}

# Step 1: Process options
my $skipline = "";
GetOptions(
    "help!"           => \&Usage,
    "debug!"          => \$debug,
    "namespace=s"     => \$ns,
    "alt-namespace=s" => \$alt_ns,
    "header=s"        => \$header_file,
    "c-file=s"        => \$c_file,
    "readme-file=s"   => \$readme_file,
    "skips=s"         => \$skipline
) or Usage();

my @skips = split(/[:,;\s]+/, $skipline);
%skipfiles = map {$_ => 1} @skips;

# Step 2: Search all cfiles and put them in @cfiles.
foreach my $dir (@dirs) {
    ExpandDir($dir);
}

# Step 3: Parse each cfile and put results in  @cvars and @categories.
foreach my $cfile (@cfiles) {
    ProcessFile($cfile);
}

# Step 4: Preprocess cvars:
# *) Make sure that all categories referenced by cvars actually exist
# *) Strip out the prefix of their name (normally, MPIR_CVAR)
die "missing 'cvars', stopped" unless (@cvars);
my %cat_hash = map {$_->{name} => 1} @categories;

foreach my $p (@cvars) {
    unless (exists $cat_hash{$p->{category}}) {
        warn "Category '".$p->{category}."' referenced by '".$p->{name}."' was not found";
    }
    $p->{name} =~ s/${ns}_//;
    if (exists $p->{'alt-env'}) {
        my @alts = split(/[:,;\s]+/, $p->{'alt-env'});
        foreach my $elmt (@alts) {
            $elmt =~ s/${ns}_//;
        }
        $p->{'alt-env'} = [@alts];
    }
}

# Step 5: Output cvars and categories
print "Categories include: \n".Dumper(@categories) if $debug;
print "Cvars include :\n".Dumper(@cvars)."\n" if $debug;

my $run_timestamp = gmtime($ENV{SOURCE_DATE_EPOCH} || time)." UTC";
my $uc_ns = uc($ns);

# Setup output files
open(OUTPUT_H,      '>', $header_file);
open(OUTPUT_C,      '>', $c_file);
open(OUTPUT_README, '>', $readme_file);

#===============================================================
# Step 5.1: Dump the header file.
my $hdr_guard = Header2InclGuard($header_file);
print OUTPUT_H <<EOT;
/*
 * Copyright (C) by Argonne National Laboratory
 *     See COPYRIGHT in top-level directory
 */

/* Automatically generated
 *   by:   $0
 *   on:   $run_timestamp
 *
 * DO NOT EDIT!!!
 */

#if !defined($hdr_guard)
#define $hdr_guard

#include "mpitimpl.h" /* for MPIR_T_cvar_range_value_t */

/* Initializes cvar values from the environment */
int ${fn_ns}_init(void);
int ${fn_ns}_finalize(void);

/* Extern declarations for each cvar
 * (definitions in $c_file) */

EOT

our %enum_groups;
foreach my $p (@cvars) {
    printf OUTPUT_H "/* declared in $p->{location} */\n";
    printf OUTPUT_H "extern %s ${uc_ns}_%s;\n", Type2Ctype($p->{type}), $p->{name};
    if($p->{type} eq "enum"){
        my @enum;
        while($p->{description}=~/^\s*(\w+)\s+-\s/mg){
            # i.e. leading word followed with ' - '
            push @enum, $1;
        }
        $p->{enum} = \@enum;
        my @t;
        foreach my $a (@enum){
            push @t, "    MPIR_CVAR_$p->{name}_$a,";
        }
        die "Failed to parse enum lists in $p->{name}\n" if !@t;

        if ($p->{group}) {
            if (!$enum_groups{$p->{group}}) {
                $enum_groups{$p->{group}} = [];
            }
            my $g = $enum_groups{$p->{group}};
            push @$g, @t;
        }
        else {
            $t[-1]=~s/,$//;
            print OUTPUT_H "enum $p->{name}_choice {\n";
            foreach my $l (@t){
                print OUTPUT_H "$l\n";
            }
            print OUTPUT_H "};\n";
        }
    }
}
foreach my $g (sort keys %enum_groups){
    my $t = $enum_groups{$g};
    print OUTPUT_H "int MPIR_$g\_from_str(const char *s);\n";
    $t->[-1]=~s/,$//;
    print OUTPUT_H "enum $g\_group_t {\n";
    foreach my $l (@$t){
        print OUTPUT_H "$l\n";
    }
    print OUTPUT_H "};\n";
}

print OUTPUT_H <<EOT;

/* TODO: this should be defined elsewhere */
#define ${ns}_assert MPIR_Assert

/* Arbitrary, simplifies interaction with external interfaces like MPI_T_ */
#define ${uc_ns}_MAX_STRLEN (384)

/* Shortens enum value comparisons */
#define ${uc_ns}_ENUM_IS(A, a) (${uc_ns}_ ## A == ${uc_ns}_ ## A ## _ ## a)

#endif /* $hdr_guard */
EOT
close(OUTPUT_H);

#===============================================================
# Step 5.2: Dump the C file.
print OUTPUT_C <<EOT;
/*
 * Copyright (C) by Argonne National Laboratory
 *     See COPYRIGHT in top-level directory
 */
/* automatically generated
 *   by:   $0
 *   at:   $run_timestamp
 *
 * DO NOT EDIT!!!
 */

#include "mpiimpl.h"

/* Actual storage for cvars */
EOT
# Output the definitions
foreach my $p (@cvars) {
    my $type = Type2Ctype($p->{type});
    print OUTPUT_C "$type ${uc_ns}_$p->{name};\n";
}

# Generate the init function.
print OUTPUT_C <<EOT;

int ${fn_ns}_init(void)
{
    int mpi_errno = MPI_SUCCESS;
    int rc, got_rc;
    const char *tmp_str;
    MPIR_T_cvar_value_t defaultval;

    int debug = 0;
    rc = MPL_env2bool("MPICH_DEBUG_CVARS", &debug);
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","MPICH_DEBUG_CVARS");
    rc = MPL_env2bool("MPIR_PARAM_DEBUG_CVARS", &debug);
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","MPIR_PARAM_DEBUG_CVARS");
    rc = MPL_env2bool("MPIR_CVAR_DEBUG_CVARS", &debug);
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","MPIR_CVAR_DEBUG_CVARS");

EOT

# Register categories
foreach my $cat (@categories) {
    my $desc = $cat->{description};
    $desc =~ s/"/\\"/g;
    printf OUTPUT_C qq(    /* declared in $cat->{location} */\n);
    printf OUTPUT_C qq(    MPIR_T_cat_add_desc(%s\n%s);\n\n),
        qq("$cat->{name}",),
        qq(        "$desc");
}

# Register and init cvars
foreach my $p (@cvars) {
    my $count = get_cvar_count($p);
    my $mpi_dtype = get_cvar_mpi_dtype($p);
    my ($dftvar, $dftval) = get_cvar_dft_var_val($p);

    if ($p->{class} eq 'device') {
        print OUTPUT_C "#if defined MPID_$p->{name}\n";
        print OUTPUT_C "    $dftvar = MPID_$p->{name};\n";
        print OUTPUT_C "#else\n";
        print OUTPUT_C "    $dftvar = $dftval;\n";
        print OUTPUT_C "#endif /* MPID_$p->{name} */\n\n";
    } else {
        print OUTPUT_C "    $dftvar = $dftval;\n";
    }

    # Register the cvar
    my $desc = $p->{description};
    $desc =~ s/"/\\"/g;
    $desc =~ s/\n/\\n"\n"/g;
    printf OUTPUT_C qq(    MPIR_T_CVAR_REGISTER_STATIC(\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s);\n),
        qq(        $mpi_dtype,),
        qq(        ${uc_ns}_$p->{name}, /* name */),
        qq(        &${uc_ns}_$p->{name}, /* address */),
        qq(        $count, /* count */),
        qq(        $p->{verbosity},),
        qq(        $p->{scope},),
        qq(        defaultval,),
        qq(        "$p->{category}", /* category */),
        qq(        "$desc");

    my $var_name = "${uc_ns}_" . $p->{name};
    if ($p->{type} ne 'string') {
        print OUTPUT_C "    $var_name = $dftvar;\n";
    }

    if ($p->{type} eq 'string') {
        # we will strdup the tmp_str
        print OUTPUT_C "    tmp_str = defaultval.str;\n";
    }
    elsif ($p->{type} eq 'enum') {
        print OUTPUT_C "    tmp_str=NULL;\n";
    }

    # Get the env variable value.
    my $env_fn = Type2EnvFn($p->{type});
    my @env_names = ();

    # Process extra envs first so the primary always wins
    push @env_names, map { "${dep_ns}_$_" } @{$p->{'alt-env'}};
    push @env_names, map { "${alt_ns}_$_" } @{$p->{'alt-env'}};
    push @env_names, map { "${uc_ns}_$_" } @{$p->{'alt-env'}};
    push @env_names, "${dep_ns}_" . $p->{name};
    push @env_names, "${alt_ns}_" . $p->{name};
    push @env_names, "${uc_ns}_" . $p->{name};

    print OUTPUT_C "    got_rc = 0;\n";
    foreach my $env_name (@env_names) {
        # assumes rc is defined
        if ($p->{type} eq 'range') {
print OUTPUT_C <<EOT;
    rc = MPL_env2${env_fn}("$env_name", &($var_name.low), &($var_name.high));
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","$env_name");
    got_rc += rc;
EOT
        }
        elsif ($p->{type} eq 'string' or $p->{type} eq 'enum') {
print OUTPUT_C <<EOT;
    rc = MPL_env2${env_fn}("$env_name", &tmp_str);
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","$env_name");
    got_rc += rc;
EOT
        }
        else {
print OUTPUT_C <<EOT;
    rc = MPL_env2${env_fn}("$env_name", &($var_name));
    MPIR_ERR_CHKANDJUMP1((-1 == rc),mpi_errno,MPI_ERR_OTHER,"**envvarparse","**envvarparse %s","$env_name");
    got_rc += rc;
EOT
        }
    }

    # debugging
    print OUTPUT_C "    if (got_rc && debug) {\n";
    if ($p->{type} eq 'string' or $p->{type} eq 'enum') {
        print OUTPUT_C "        printf(\"CVAR: $var_name = %s\\n\", tmp_str);\n";
    } elsif ($p->{type} eq "range") {
        print OUTPUT_C "        printf(\"CVAR: $var_name = %d-%d\\n\", $var_name.low, $var_name.high);\n";
    } else {
        print OUTPUT_C "        printf(\"CVAR: $var_name = %d\\n\", $var_name);\n";
    }
    print OUTPUT_C "    }\n";

    # post process
    if ($p->{type} eq 'string') {
print OUTPUT_C <<EOT;
    if (tmp_str != NULL) {
        ${var_name} = MPL_strdup(tmp_str);
        ${ns}_assert(${var_name});
        if (${var_name} == NULL) {
            MPIR_CHKMEM_SETERR(mpi_errno, strlen(tmp_str), "dup of string for ${var_name}");
            goto fn_fail;
        }
    }
    else {
        ${var_name} = NULL;
    }
EOT
    }
    elsif ($p->{type} eq 'enum') {
        print OUTPUT_C "    if (tmp_str != NULL) {\n";
        my $c = "if";
        my $sp = ' ' x 8;
        foreach my $a (@{$p->{enum}}){
            print OUTPUT_C $sp, "$c (0 == strcmp(tmp_str, \"$a\"))\n";
            print OUTPUT_C $sp, "    $var_name = $var_name\_$a;\n";
            $c = "else if";
        }
        print OUTPUT_C $sp, "else {\n";
        print OUTPUT_C $sp, "    mpi_errno = MPIR_Err_create_code(MPI_SUCCESS, MPIR_ERR_RECOVERABLE, __func__, __LINE__,MPI_ERR_OTHER, \"**cvar_val\", \"**cvar_val %s %s\", \"$var_name\", tmp_str);\n";
        print OUTPUT_C $sp, "    goto fn_fail;\n";
        print OUTPUT_C $sp, "}\n";
        print OUTPUT_C "    }\n";
    }
    print OUTPUT_C "\n";
}

print OUTPUT_C <<EOT;
fn_exit:
    return mpi_errno;
fn_fail:
    goto fn_exit;
}

EOT

print OUTPUT_C <<EOT;
int ${fn_ns}_finalize(void)
{
    int mpi_errno = MPI_SUCCESS;

EOT

foreach my $p (@cvars) {
    my $var_name = "${uc_ns}_" . $p->{name};

    if ($p->{type} eq 'string') {
        # Need to cleanup after whatever was strduped by the init routine
print OUTPUT_C <<EOT;
    MPL_free((char *)${var_name});
    ${var_name} = NULL;

EOT
    }
}

print OUTPUT_C <<EOT;
    return mpi_errno;
}

EOT

foreach my $g (sort keys %enum_groups){
    my $t = $enum_groups{$g};
    print OUTPUT_C "int MPIR_$g\_from_str(const char *s) {\n";
    my $t_if="if";
    foreach my $l (@$t){
        $l=~s/,$//;
        print OUTPUT_C "    $t_if (strcmp(s, \"$l\")==0) return $l;\n";
        $t_if = "else if";
    }
    print OUTPUT_C "    else return -1;\n";
    print OUTPUT_C "}\n";
}

close(OUTPUT_C);

#===============================================================
#Step 5.3 Dump the readme file
print OUTPUT_README <<EOT;
Copyright (C) by Argonne National Laboratory
    See COPYRIGHT in top-level directory

Automatically generated
  by:   $0
  at:   $run_timestamp
DO NOT EDIT!!!

This file lists the various environment variables available to change the
behavior of the MPICH library.  These are intended to be used by advanced
users.
---------------------------------------------------------------------------

EOT

foreach my $p (@cvars) {
    my @env_names = ();
    my $first;
    my $alt;
    my $default;

    # process extra envs first so the primary always wins
    push @env_names, "${alt_ns}_" . $p->{name};
    push @env_names, "${dep_ns}_" . $p->{name};
    push @env_names, map { "${uc_ns}_$_" } @{$p->{'alt-env'}};
    push @env_names, map { "${alt_ns}_$_" } @{$p->{'alt-env'}};
    push @env_names, map { "${dep_ns}_$_" } @{$p->{'alt-env'}};

    print OUTPUT_README "${uc_ns}_$p->{name}\n";

    $first = 1;
    foreach $alt (@env_names) {
        if ($first) {
            print OUTPUT_README "    Aliases: $alt\n";
        } else {
            print OUTPUT_README "             $alt\n";
        }
        $first = 0;
    }

    print OUTPUT_README wrap("    Description: ", "        ", $p->{description} . "\n");
    $default = FmtDefault($p->{name}, $p->{default}, $p->{type});
    print OUTPUT_README "    Default: $default\n";
    print OUTPUT_README "\n";
}

close(OUTPUT_README);

#===============================================================
# Helper subroutines used in this script

sub get_cvar_count {
    my $p = shift;

    if ($p->{type} eq "string") {
        return "${uc_ns}_MAX_STRLEN";
    }
    elsif ($p->{type} eq 'range') {
        return 2;
    }
    else {
        return 1;
    }
}

sub get_cvar_mpi_dtype {
    my $p = shift;

    if ($p->{type} eq 'string') {
        return "MPI_CHAR";
    }
    elsif ($p->{type} eq 'int' or $p->{type} eq 'boolean') {
        return "MPI_INT";
    }
    elsif ($p->{type} eq 'double') {
        return "MPI_DOUBLE";
    }
    elsif ($p->{type} eq 'range') {
        return "MPI_INT";
    }
    elsif ($p->{type} eq 'enum') {
        return "MPI_INT";
    }
    else {
        die "unknown type $p->{type}, stopped";
    }
}

sub get_cvar_dft_var_val {
    my $p = shift;

    my $dftvar;
    my $dftval = FmtDefault($p->{name}, $p->{default}, $p->{type});
    if ($p->{type} eq 'string') {
        $dftvar = "defaultval.str";
        $dftval = "(const char *) $dftval";
    }
    elsif ($p->{type} eq 'int' or $p->{type} eq 'boolean') {
        $dftvar = "defaultval.d";
    }
    elsif ($p->{type} eq 'double') {
        $dftvar = "defaultval.f";
    }
    elsif ($p->{type} eq 'range') {
        $dftvar = "defaultval.range";
        $dftval = "(MPIR_T_cvar_range_value_t) $dftval";
    }
    elsif ($p->{type} eq 'enum') {
        $dftvar = "defaultval.d";
    }
    else {
        die "unknown type $p->{type}, stopped";
    }
    return ($dftvar, $dftval);
}

#---------------------------------------------------------------
# Transform a cvar type to a C-language type
sub Type2Ctype {
    my $type = shift;
    my %typemap = (
        'int'     => 'int',
        'double'  => 'double',
        'string'  => 'const char *',
        'boolean' => 'int',
        'range'   => "MPIR_T_cvar_range_value_t",
        'enum'    => 'int',
    );
    die "unknown type '$type', stopped" unless exists $typemap{$type};
    return $typemap{$type};
}

# Transform a default value into a C value
sub FmtDefault {
    my $name = shift;
    my $val = shift;
    my $type = shift;

    if ($type eq 'string') {
        $val =~ s/"/\\"/g;
        if ($val eq 'NULL' or $val eq 'null') { return "NULL"; }
        else { return qq("$val"); }
    }
    elsif ($type eq 'boolean') {
        if    ($val =~ m/^(0|f(alse)?|no?)$/i)   { return qq(0); }
        elsif ($val =~ m/^(1|t(rue)?|y(es)?)$/i) { return qq(1); }
        else {
            warn "WARNING: type='$type', bad val='$val', continuing";
            return qq(0); # fail-false
        }
    }
    elsif ($type eq 'range') {
        if ($val !~ "-?[0-9]+:-?[0-9]+") {
            die "Unable to parse range value '$val', stopped";
        }
        $val =~ s/:/,/;
        return qq({$val});
    }
    elsif ($type eq 'enum') {
        return "MPIR_CVAR_$name\_$val";
    }
    else {
        return qq($val);
    }
}

# turns /path/foo_BAR-baz.h into FOO_BAR_BAZ_H_INCLUDED
sub Header2InclGuard {
    my $header_file = shift;
    my $guard = basename($header_file);
    $guard =~ tr/a-z\-./A-Z__/;
    $guard .= "_INCLUDED";
    die "guard contains whitespace, stopped" if ($guard =~ m/\s/);
    return $guard;
}

sub Type2EnvFn {
    my $type = shift;
    my %typemap = (
        'int' =>  'int',
        'string' => 'str',
        'boolean' => 'bool',
        'double' => 'double',
        'range' => 'range',
        'enum' => 'str',
    );

    die "unknown type '$type', stopped" unless exists $typemap{$type};
    return $typemap{$type};
}

# Parse a file, search the MPI_T_CVAR_INFO_BLOCK if any.
# Distill cvars and categories from the block.
# Push the results to back of @cvars and @categories respectively.
sub ProcessFile {
    my $cfile = $_[0];
    my $cvar_info_block = undef;
    my $in_cvar_info_block = 0;

    #print "Processing file $cfile\n" if $debug;
    open my $CFILE_HANDLE, "< $cfile" or die "Error: open file $cfile -- $!\n";
    while (<$CFILE_HANDLE>) {
        if (/END_MPI_T_CVAR_INFO_BLOCK/) {
            last;
        } elsif ($in_cvar_info_block) {
            $cvar_info_block .= $_;
        } elsif (/BEGIN_MPI_T_CVAR_INFO_BLOCK/) {
            $in_cvar_info_block = 1;
            print "Found MPI_T_CVAR_INFO_BLOCK in $cfile\n" if $debug;
        }
    }
    close $CFILE_HANDLE;

    # Do some checking to ensure a correct cvar info block, also
    # add file locations to help users' debugging.
    if ($cvar_info_block) {
        my $info = ($yaml->read_string($cvar_info_block))->[0];
        if (exists $info->{cvars}) {
            # Remember location where the cvar is defined. Put that into
            # comments of the generated *.h file so that users know where
            # to look when meeting compilation errors.
            foreach my $cvar (@{$info->{cvars}}) {
                $cvar->{location} = $cfile;
                die "ERROR: cvar has no name in $cfile\n" unless exists $cvar->{name};
                die "ERROR: cvar $cvar->{name} has no type in $cfile\n" unless exists $cvar->{type};
                die "ERROR: cvar $cvar->{name} has no verbosity in $cfile\n" unless exists $cvar->{verbosity};
                die "ERROR: cvar $cvar->{name} has no scope in $cfile\n" unless exists $cvar->{scope};
                die "ERROR: cvar $cvar->{name} has no class in $cfile\n" unless exists $cvar->{class};
                die "ERROR: cvar $cvar->{name} has no description in $cfile\n" unless exists $cvar->{description};
            }
            foreach my $cvar (@{$info->{cvars}}) {
                if (!$cvars{$cvar->{name}}) {
                    $cvars{$cvar->{name}} = $cvar;
                    push (@cvars, $cvar);
                } else {
                    my $prev = $cvars{$cvar->{name}};
                    if (cvar_cmp($prev, $cvar) != 0) {
                        die "ERROR: duplicate CVAR definition, $cvar->{name}, and they are not the same\n";
                    }
                }
            }
        }

        if (exists $info->{categories}) {
            # Do the same trick to categories
            foreach my $cat (@{$info->{categories}}) {
                $cat->{location} = $cfile;
                die "ERROR: category has no name in $cfile\n" unless exists $cat->{name};
                die "ERROR: category $cat->{name} has no description in $cfile\n"
                    unless exists $cat->{description};
            }
            push (@categories, @{$info->{categories}});
        }
    }
}

# Search cfiles recursively in the directory passed in.
# Push file names along with their paths to back of @cfiles.
sub ExpandDir {
    my $dir = $_[0];
    my @subdirs = ();
    my $DIR_HANDLE;
    opendir $DIR_HANDLE, "$dir" or die "Error: open directory $dir -- $!\n";
    for my $filename (sort readdir $DIR_HANDLE) {
        if ($filename =~ /^\./) {
            next;
        } elsif (-d "$dir/$filename") {
            $subdirs[$#subdirs + 1] = "$dir/$filename";
        } elsif ($filename =~ /^cvars.txt$/) {
            $cfiles[$#cfiles + 1] = "$dir/$filename";
        } elsif ($filename =~ /(.*\.[Cchi])(pp){0,1}$/) {
            if (!defined($skipfiles{"$dir/$filename"}))
            {
                $cfiles[$#cfiles + 1] = "$dir/$filename";
            }
        }
    }
    closedir $DIR_HANDLE;

    # Recursively search subdirs
    foreach $dir (@subdirs) {
        ExpandDir($dir);
    }
}

# Compare two cvar, return 0 if they are duplicate and compatible. Other wise, return non-zero.
# This is useful so we can have duplicated cvar definition is separate modules, e.g. ch3:ofi and ch4:ofi.
sub cvar_cmp {
    my ($a, $b) = @_;
    if ($a->{category} ne $b->{category}) {
        return 1;
    }
    if ($a->{type} ne $b->{type}) {
        return 1;
    }
    if ($a->{default} ne $b->{default}) {
        return 1;
    }
    if ($a->{scope} ne $b->{scope}) {
        return 1;
    }
    if ($a->{class} ne $b->{class}) {
        return 1;
    }
    if ($a->{verbosity} ne $b->{verbosity}) {
        return 1;
    }
    # they are the same
    return 0;
}