#! /usr/bin/perl -w

my $prefix = $ENV{"NIX"} || "/tmp/nix"; # !!! use prefix
my $etcdir = "$prefix/etc/nix";
my $tmpfile = "$prefix/var/nix/pull.tmp";

my $conffile = "$etcdir/prebuilts.conf";

my @subs;

open CONFFILE, "<$conffile";

while (<CONFFILE>) {

    chomp;
    if (/^\s*(\S+)\s*(\#.*)?$/) {
        my $url = $1;

        print "obtaining list of Nix archives at $url...\n";

	system "wget '$url' -O '$tmpfile' 2> /dev/null"; # !!! escape
	if ($?) { die "`wget' failed"; }
	
	open INDEX, "<$tmpfile";

	while (<INDEX>) {
	    # Get all links to prebuilts, that is, file names of the
	    # form foo-HASH-HASH.tar.bz2.
	    next unless (/HREF=\"([^\"]*)\"/);
	    my $fn = $1;
	    next if $fn =~ /\.\./;
	    next if $fn =~ /\//;
	    next unless $fn =~ /([0-9a-z]{32})-([0-9a-z]{32})\.nar/;
	    my $hash = $2;

	    print "registering $hash -> $url/$fn\n";

	    # Construct a Fix expression that fetches and unpacks a
	    # Nix archive from the network.
	    my $fetch =
              "App(IncludeFix(\"fetchurl/fetchurl.fix\"), " .
              "[(\"url\", \"$url/$fn\"), (\"hash\", \"\")])";
	    my $fixexpr = 
		"App(IncludeFix(\"nar/unnar.fix\"), " .
		"[ (\"nar\", $fetch)" .
		", (\"name\", \"fetched-$hash\")" .
		"])";
	    
	    my $fixfile = "/tmp/nix-pull-tmp.fix";
	    open FIX, ">$fixfile";
	    print FIX $fixexpr;
	    close FIX;

	    # Instantiate a Nix expression from the Fix expression.
	    my $nhash = `fix $fixfile`;
	    $? and die "instantiating Nix archive expression";
	    chomp $nhash;
	    die unless $nhash =~ /^([0-9a-z]{32})$/;

	    push @subs, $hash;
	    push @subs, $nhash;

	}

	close INDEX;

	unlink $tmpfile;
    }

}

system "nix --substitute @subs";
if ($?) { die "`nix --substitute' failed"; }