#! /usr/bin/perl -w

my $tmpfile = "@localstatedir@/nix/pull.tmp";
my $conffile = "@sysconfdir@/nix/prebuilts.conf";

my @subs;
my @sucs;

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 $fn =~ /-([0-9a-z]{32})(-s-([0-9a-z]{32}))?\.nar.bz2$/;
            my $hash = $1;
            my $fshash = $3;

            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\"), (\"md5\", \"ignore\")])";
            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;

            # Does the name encode a successor relation?
            if (defined $fshash) {
                print "NORMAL $fshash -> $hash\n";
                push @sucs, $fshash;
                push @sucs, $hash;
            }
        }

        close INDEX;

        unlink $tmpfile;
    }

}

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

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