#! @perl@ -w -I@libexecdir@/nix

use strict;
use readmanifest;

my $manifestDir = "@localstatedir@/nix/manifests";
my $logFile = "@localstatedir@/log/nix/downloads";

open LOGFILE, ">>$logFile" or die "cannot open log file $logFile";


# Check the arguments.
die unless scalar @ARGV == 1;
my $targetPath = $ARGV[0];

my $date = `date` or die;
chomp $date;
print LOGFILE "$$ get $targetPath $date\n";

print "\n*** Trying to download/patch `$targetPath'\n";


# Load all manifests.
my %narFiles;
my %patches;
my %successors;

for my $manifest (glob "$manifestDir/*.nixmanifest") {
#    print STDERR "reading $manifest\n";
    if (readManifest($manifest, \%narFiles, \%patches, \%successors) < 3) {
        print STDERR "you have an old-style manifest `$manifest'; please delete it\n";
        exit 1;
    }
}


# Build a graph of all store paths that might contribute to the
# construction of $targetPath, and the special node "start".  The
# edges are either patch operations, or downloads of full NAR files.
# The latter edges only occur between "start" and a store path.

my %graph;

$graph{"start"} = {d => 0, pred => undef, edges => []};

my @queue = ();
my $queueFront = 0;
my %done;

sub addToQueue {
    my $v = shift;
    return if defined $done{$v};
    $done{$v} = 1;
    push @queue, $v;
}

sub addNode {
    my $u = shift;
    $graph{$u} = {d => 999999999999, pred => undef, edges => []}
        unless defined $graph{$u};
}

sub addEdge {
    my $u = shift;
    my $v = shift;
    my $w = shift;
    my $type = shift;
    my $info = shift;
    addNode $u;
    push @{$graph{$u}->{edges}},
        {weight => $w, start => $u, end => $v, type => $type, info => $info};
    my $n = scalar @{$graph{$u}->{edges}};
}

addToQueue $targetPath;

sub isValidPath {
    my $p = shift;
    system "@bindir@/nix-store --isvalid '$p' 2> /dev/null";
    return $? == 0;
}

sub parseHash {
    my $hash = shift;
    if ($hash =~ /^(.+):(.+)$/) {
        return ($1, $2);
    } else {
        return ("md5", $hash);
    }
}

while ($queueFront < scalar @queue) {
    my $u = $queue[$queueFront++];
#    print "$u\n";

    addNode $u;

    # If the path already exists, it has distance 0 from the "start"
    # node.
    if (isValidPath($u)) {
        addEdge "start", $u, 0, "present", undef;
    }

    else {

        # Add patch edges.
        my $patchList = $patches{$u};
        foreach my $patch (@{$patchList}) {
            if (isValidPath($patch->{basePath})) {
                # !!! this should be cached
                my ($baseHashAlgo, $baseHash) = parseHash $patch->{baseHash};
                my $format = "--base32";
                $format = "" if $baseHashAlgo eq "md5";
                my $hash = `@bindir@/nix-hash --type '$baseHashAlgo' $format "$patch->{basePath}"`;
                chomp $hash;
#                print "  MY HASH is $hash\n";
                if ($hash ne $baseHash) {
                    print LOGFILE "$$ rejecting $patch->{basePath}\n";
                    next;
                }
            }
#            print "  PATCH from $patch->{basePath}\n";
            addToQueue $patch->{basePath};
            addEdge $patch->{basePath}, $u, $patch->{size}, "patch", $patch;
        }

        # Add NAR file edges to the start node.
        my $narFileList = $narFiles{$u};
        foreach my $narFile (@{$narFileList}) {
#            print "  NAR from $narFile->{url}\n";
            addEdge "start", $u, $narFile->{size}, "narfile", $narFile;
            if ($u eq $targetPath) {
                print LOGFILE "$$ full-download-would-be $narFile->{size}\n";
            }
        }

    }
}


# Run Dijkstra's shortest path algorithm to determine the shortest
# sequence of download and/or patch actions that will produce
# $targetPath.

sub byDistance { # sort by distance, reversed
    return -($graph{$a}->{d} <=> $graph{$b}->{d});
}

my @todo = keys %graph;

while (scalar @todo > 0) {

    # Remove the closest element from the todo list.
    @todo = sort byDistance @todo;
    my $u = pop @todo;

    my $u_ = $graph{$u};

#    print "IN $u $u_->{d}\n";

    foreach my $edge (@{$u_->{edges}}) {
        my $v_ = $graph{$edge->{end}};
        if ($v_->{d} > $u_->{d} + $edge->{weight}) {
            $v_->{d} = $u_->{d} + $edge->{weight};
            # Store the edge; to edge->start is actually the
            # predecessor.
            $v_->{pred} = $edge; 
#            print "  RELAX $edge->{end} $v_->{d}\n";
        }
    }
}


# Retrieve the shortest path from "start" to $targetPath.
my @path = ();
my $cur = $targetPath;
die "don't know how to produce $targetPath\n"
    unless defined $graph{$targetPath}->{pred};
while ($cur ne "start") {
    push @path, $graph{$cur}->{pred};
    $cur = $graph{$cur}->{pred}->{start};
}


# Traverse the shortest path, perform the actions described by the
# edges.
my $curStep = 1;
my $maxStep = scalar @path;

sub downloadFile {
    my $url = shift;
    my ($hashAlgo, $hash) = parseHash(shift);
    $ENV{"PRINT_PATH"} = 1;
    $ENV{"QUIET"} = 1;
    $ENV{"NIX_HASH_ALGO"} = $hashAlgo;
    my ($hash2, $path) = `@bindir@/nix-prefetch-url '$url' '$hash'`;
    chomp $hash2;
    chomp $path;
    die "hash mismatch, expected $hash, got $hash2" if $hash ne $hash2;
    return $path;
}

while (scalar @path > 0) {
    my $edge = pop @path;
    my $u = $edge->{start};
    my $v = $edge->{end};

    print "\n*** Step $curStep/$maxStep: ";
    $curStep++;

    if ($edge->{type} eq "present") {
        print "using already present path `$v'\n";
        print LOGFILE "$$ present $v\n";
    }

    elsif ($edge->{type} eq "patch") {
        my $patch = $edge->{info};
        print "applying patch `$patch->{url}' to `$u' to create `$v'\n";

        print LOGFILE "$$ patch $patch->{url} $patch->{size} $patch->{baseHash} $u $v\n";

        # Download the patch.
        print "  downloading patch...\n";
        my $patchPath = downloadFile "$patch->{url}", "$patch->{hash}";

        # Turn the base path into a NAR archive, to which we can
        # actually apply the patch.
        print "  packing base path...\n";
        system "@bindir@/nix-store --dump $patch->{basePath} > /tmp/nar";
        die "cannot dump `$patch->{basePath}'" if ($? != 0);

        # Apply the patch.
        print "  applying patch...\n";
        system "@libexecdir@/bspatch /tmp/nar /tmp/nar2 $patchPath";
        die "cannot apply patch `$patchPath' to /tmp/nar" if ($? != 0);

        # Unpack the resulting NAR archive into the target path.
        print "  unpacking patched archive...\n";
        system "@bindir@/nix-store --restore $v < /tmp/nar2";
        die "cannot unpack /tmp/nar2 into `$v'" if ($? != 0);
    }

    elsif ($edge->{type} eq "narfile") {
        my $narFile = $edge->{info};
        print "downloading `$narFile->{url}' into `$v'\n";

        print LOGFILE "$$ narfile $narFile->{url} $narFile->{size} $v\n";
        
        # Download the archive.
        print "  downloading archive...\n";
        my $narFilePath = downloadFile "$narFile->{url}", "$narFile->{hash}";

        # Unpack the archive into the target path.
        print "  unpacking archive...\n";
        system "@bunzip2@ < '$narFilePath' | @bindir@/nix-store --restore '$v'";
        die "cannot unpack `$narFilePath' into `$v'" if ($? != 0);
    }
}


print LOGFILE "$$ success\n";
close LOGFILE;