C4/HoldsQueue.pm

   1 package C4::HoldsQueue;
   2
   3 # Copyright 2011 Catalyst IT
   4 #
   5 # This file is part of Koha.
   6 #
   7 # Koha is free software; you can redistribute it and/or modify it
   8 # under the terms of the GNU General Public License as published by
   9 # the Free Software Foundation; either version 3 of the License, or
  10 # (at your option) any later version.
  11 #
  12 # Koha is distributed in the hope that it will be useful, but
  13 # WITHOUT ANY WARRANTY; without even the implied warranty of
  14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  15 # GNU General Public License for more details.
  16 #
  17 # You should have received a copy of the GNU General Public License
  18 # along with Koha; if not, see <http://www.gnu.org/licenses>.
  19
  20 # FIXME: expand perldoc, explain intended logic
  21
  22 use strict;
  23 use warnings;
  24
  25 use C4::Context;
  26 use C4::Search;
  27 use C4::Items;
  28 use C4::Branch;
  29 use C4::Circulation;
  30 use C4::Members;
  31 use C4::Biblio;
  32 use C4::Dates qw/format_date/;
  33
  34 use List::Util qw(shuffle);
  35 use List::MoreUtils qw(any);
  36 use Data::Dumper;
  37
  38 use vars qw($VERSION @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS);
  39 BEGIN {
  40     $VERSION = 3.03;
  41     require Exporter;
  42     @ISA = qw(Exporter);
  43     @EXPORT_OK = qw(
  44         &CreateQueue
  45         &GetHoldsQueueItems
  46
  47         &TransportCostMatrix
  48         &UpdateTransportCostMatrix
  49      );
  50 }
  51
  52
  53 =head1 FUNCTIONS
  54
  55 =head2 TransportCostMatrix
  56
  57   TransportCostMatrix();
  58
  59 Returns Transport Cost Matrix as a hashref <to branch code> => <from branch code> => cost
  60
  61 =cut
  62
  63 sub TransportCostMatrix {
  64     my $dbh   = C4::Context->dbh;
  65     my $transport_costs = $dbh->selectall_arrayref("SELECT * FROM transport_cost",{ Slice => {} });
  66
  67     my %transport_cost_matrix;
  68     foreach (@$transport_costs) {
  69         my $from = $_->{frombranch};
  70         my $to = $_->{tobranch};
  71         my $cost = $_->{cost};
  72         my $disabled = $_->{disable_transfer};
  73         $transport_cost_matrix{$to}{$from} = { cost => $cost, disable_transfer => $disabled };
  74     }
  75     return \%transport_cost_matrix;
  76 }
  77
  78 =head2 UpdateTransportCostMatrix
  79
  80   UpdateTransportCostMatrix($records);
  81
  82 Updates full Transport Cost Matrix table. $records is an arrayref of records.
  83 Records: { frombranch => <code>, tobranch => <code>, cost => <figure>, disable_transfer => <0,1> }
  84
  85 =cut
  86
  87 sub UpdateTransportCostMatrix {
  88     my ($records) = @_;
  89     my $dbh   = C4::Context->dbh;
  90
  91     my $sth = $dbh->prepare("INSERT INTO transport_cost (frombranch, tobranch, cost, disable_transfer) VALUES (?, ?, ?, ?)");
  92
  93     $dbh->do("TRUNCATE TABLE transport_cost");
  94     foreach (@$records) {
  95         my $cost = $_->{cost};
  96         my $from = $_->{frombranch};
  97         my $to = $_->{tobranch};
  98         if ($_->{disable_transfer}) {
  99             $cost ||= 0;
 100         }
 101         elsif ( !defined ($cost) || ($cost !~ m/(0|[1-9][0-9]*)(\.[0-9]*)?/o) ) {
 102             warn  "Invalid $from -> $to cost $cost - must be a number >= 0, disablig";
 103             $cost = 0;
 104             $_->{disable_transfer} = 1;
 105         }
 106         $sth->execute( $from, $to, $cost, $_->{disable_transfer} ? 1 : 0 );
 107     }
 108 }
 109
 110 =head2 GetHoldsQueueItems
 111
 112   GetHoldsQueueItems($branch);
 113
 114 Returns hold queue for a holding branch. If branch is omitted, then whole queue is returned
 115
 116 =cut
 117
 118 sub GetHoldsQueueItems {
 119     my ($branchlimit) = @_;
 120     my $dbh   = C4::Context->dbh;
 121
 122     my @bind_params = ();
 123     my $query = q/SELECT tmp_holdsqueue.*, biblio.author, items.ccode, items.itype, biblioitems.itemtype, items.location, items.enumchron, items.cn_sort, biblioitems.publishercode,biblio.copyrightdate,biblioitems.publicationyear,biblioitems.pages,biblioitems.size,biblioitems.publicationyear,biblioitems.isbn,items.copynumber
 124                   FROM tmp_holdsqueue
 125                        JOIN biblio      USING (biblionumber)
 126                   LEFT JOIN biblioitems USING (biblionumber)
 127                   LEFT JOIN items       USING (  itemnumber)
 128                 /;
 129     if ($branchlimit) {
 130         $query .=" WHERE tmp_holdsqueue.holdingbranch = ?";
 131         push @bind_params, $branchlimit;
 132     }
 133     $query .= " ORDER BY ccode, location, cn_sort, author, title, pickbranch, reservedate";
 134     my $sth = $dbh->prepare($query);
 135     $sth->execute(@bind_params);
 136     my $items = [];
 137     while ( my $row = $sth->fetchrow_hashref ){
 138         my $record = GetMarcBiblio($row->{biblionumber});
 139         if ($record){
 140             $row->{subtitle} = GetRecordValue('subtitle',$record,'')->[0]->{subfield};
 141             $row->{parts} = GetRecordValue('parts',$record,'')->[0]->{subfield};
 142             $row->{numbers} = GetRecordValue('numbers',$record,'')->[0]->{subfield};
 143         }
 144
 145         # return the bib-level or item-level itype per syspref
 146         if (!C4::Context->preference('item-level_itypes')) {
 147             $row->{itype} = $row->{itemtype};
 148         }
 149         delete $row->{itemtype};
 150
 151         push @$items, $row;
 152     }
 153     return $items;
 154 }
 155
 156 =head2 CreateQueue
 157
 158   CreateQueue();
 159
 160 Top level function that turns reserves into tmp_holdsqueue and hold_fill_targets.
 161
 162 =cut
 163
 164 sub CreateQueue {
 165     my $dbh   = C4::Context->dbh;
 166
 167     $dbh->do("DELETE FROM tmp_holdsqueue");  # clear the old table for new info
 168     $dbh->do("DELETE FROM hold_fill_targets");
 169
 170     my $total_bibs            = 0;
 171     my $total_requests        = 0;
 172     my $total_available_items = 0;
 173     my $num_items_mapped      = 0;
 174
 175     my $branches_to_use;
 176     my $transport_cost_matrix;
 177     my $use_transport_cost_matrix = C4::Context->preference("UseTransportCostMatrix");
 178     if ($use_transport_cost_matrix) {
 179         $transport_cost_matrix = TransportCostMatrix();
 180         unless (keys %$transport_cost_matrix) {
 181             warn "UseTransportCostMatrix set to yes, but matrix not populated";
 182             undef $transport_cost_matrix;
 183         }
 184     }
 185     unless ($transport_cost_matrix) {
 186         $branches_to_use = load_branches_to_pull_from();
 187     }
 188
 189     my $bibs_with_pending_requests = GetBibsWithPendingHoldRequests();
 190
 191     foreach my $biblionumber (@$bibs_with_pending_requests) {
 192         $total_bibs++;
 193         my $hold_requests   = GetPendingHoldRequestsForBib($biblionumber);
 194         my $available_items = GetItemsAvailableToFillHoldRequestsForBib($biblionumber, $branches_to_use);
 195         $total_requests        += scalar(@$hold_requests);
 196         $total_available_items += scalar(@$available_items);
 197
 198         my $item_map = MapItemsToHoldRequests($hold_requests, $available_items, $branches_to_use, $transport_cost_matrix);
 199         $item_map  or next;
 200         my $item_map_size = scalar(keys %$item_map)
 201           or next;
 202
 203         $num_items_mapped += $item_map_size;
 204         CreatePicklistFromItemMap($item_map);
 205         AddToHoldTargetMap($item_map);
 206         if (($item_map_size < scalar(@$hold_requests  )) and
 207             ($item_map_size < scalar(@$available_items))) {
 208             # DOUBLE CHECK, but this is probably OK - unfilled item-level requests
 209             # FIXME
 210             #warn "unfilled requests for $biblionumber";
 211             #warn Dumper($hold_requests), Dumper($available_items), Dumper($item_map);
 212         }
 213     }
 214 }
 215
 216 =head2 GetBibsWithPendingHoldRequests
 217
 218   my $biblionumber_aref = GetBibsWithPendingHoldRequests();
 219
 220 Return an arrayref of the biblionumbers of all bibs
 221 that have one or more unfilled hold requests.
 222
 223 =cut
 224
 225 sub GetBibsWithPendingHoldRequests {
 226     my $dbh = C4::Context->dbh;
 227
 228     my $bib_query = "SELECT DISTINCT biblionumber
 229                      FROM reserves
 230                      WHERE found IS NULL
 231                      AND priority > 0
 232                      AND reservedate <= CURRENT_DATE()
 233                      AND suspend = 0
 234                      ";
 235     my $sth = $dbh->prepare($bib_query);
 236
 237     $sth->execute();
 238     my $biblionumbers = $sth->fetchall_arrayref();
 239
 240     return [ map { $_->[0] } @$biblionumbers ];
 241 }
 242
 243 =head2 GetPendingHoldRequestsForBib
 244
 245   my $requests = GetPendingHoldRequestsForBib($biblionumber);
 246
 247 Returns an arrayref of hashrefs to pending, unfilled hold requests
 248 on the bib identified by $biblionumber.  The following keys
 249 are present in each hashref:
 250
 251     biblionumber
 252     borrowernumber
 253     itemnumber
 254     priority
 255     branchcode
 256     reservedate
 257     reservenotes
 258     borrowerbranch
 259
 260 The arrayref is sorted in order of increasing priority.
 261
 262 =cut
 263
 264 sub GetPendingHoldRequestsForBib {
 265     my $biblionumber = shift;
 266
 267     my $dbh = C4::Context->dbh;
 268
 269     my $request_query = "SELECT biblionumber, borrowernumber, itemnumber, priority, reserves.branchcode,
 270                                 reservedate, reservenotes, borrowers.branchcode AS borrowerbranch
 271                          FROM reserves
 272                          JOIN borrowers USING (borrowernumber)
 273                          WHERE biblionumber = ?
 274                          AND found IS NULL
 275                          AND priority > 0
 276                          AND reservedate <= CURRENT_DATE()
 277                          AND suspend = 0
 278                          ORDER BY priority";
 279     my $sth = $dbh->prepare($request_query);
 280     $sth->execute($biblionumber);
 281
 282     my $requests = $sth->fetchall_arrayref({});
 283     return $requests;
 284
 285 }
 286
 287 =head2 GetItemsAvailableToFillHoldRequestsForBib
 288
 289   my $available_items = GetItemsAvailableToFillHoldRequestsForBib($biblionumber, $branches_ar);
 290
 291 Returns an arrayref of items available to fill hold requests
 292 for the bib identified by C<$biblionumber>.  An item is available
 293 to fill a hold request if and only if:
 294
 295     * it is not on loan
 296     * it is not withdrawn
 297     * it is not marked notforloan
 298     * it is not currently in transit
 299     * it is not lost
 300     * it is not sitting on the hold shelf
 301     * it is not damaged (unless AllowHoldsOnDamagedItems is on)
 302
 303 =cut
 304
 305 sub GetItemsAvailableToFillHoldRequestsForBib {
 306     my ($biblionumber, $branches_to_use) = @_;
 307
 308     my $dbh = C4::Context->dbh;
 309     my $items_query = "SELECT itemnumber, homebranch, holdingbranch, itemtypes.itemtype AS itype
 310                        FROM items ";
 311
 312     if (C4::Context->preference('item-level_itypes')) {
 313         $items_query .=   "LEFT JOIN itemtypes ON (itemtypes.itemtype = items.itype) ";
 314     } else {
 315         $items_query .=   "JOIN biblioitems USING (biblioitemnumber)
 316                            LEFT JOIN itemtypes USING (itemtype) ";
 317     }
 318     $items_query .=   "WHERE items.notforloan = 0
 319                        AND holdingbranch IS NOT NULL
 320                        AND itemlost = 0
 321                        AND withdrawn = 0";
 322     $items_query .= "  AND damaged = 0" unless C4::Context->preference('AllowHoldsOnDamagedItems');
 323     $items_query .= "  AND items.onloan IS NULL
 324                        AND (itemtypes.notforloan IS NULL OR itemtypes.notforloan = 0)
 325                        AND itemnumber NOT IN (
 326                            SELECT itemnumber
 327                            FROM reserves
 328                            WHERE biblionumber = ?
 329                            AND itemnumber IS NOT NULL
 330                            AND (found IS NOT NULL OR priority = 0)
 331                         )
 332                        AND items.biblionumber = ?";
 333
 334     my @params = ($biblionumber, $biblionumber);
 335     if ($branches_to_use && @$branches_to_use) {
 336         $items_query .= " AND holdingbranch IN (" . join (",", map { "?" } @$branches_to_use) . ")";
 337         push @params, @$branches_to_use;
 338     }
 339     my $sth = $dbh->prepare($items_query);
 340     $sth->execute(@params);
 341
 342     my $itm = $sth->fetchall_arrayref({});
 343     my @items = grep { ! scalar GetTransfers($_->{itemnumber}) } @$itm;
 344     return [ grep {
 345         my $rule = GetBranchItemRule($_->{homebranch}, $_->{itype});
 346         $_->{holdallowed} = $rule->{holdallowed};
 347     } @items ];
 348 }
 349
 350 =head2 MapItemsToHoldRequests
 351
 352   MapItemsToHoldRequests($hold_requests, $available_items, $branches, $transport_cost_matrix)
 353
 354 =cut
 355
 356 sub MapItemsToHoldRequests {
 357     my ($hold_requests, $available_items, $branches_to_use, $transport_cost_matrix) = @_;
 358
 359     # handle trival cases
 360     return unless scalar(@$hold_requests) > 0;
 361     return unless scalar(@$available_items) > 0;
 362
 363     # identify item-level requests
 364     my %specific_items_requested = map { $_->{itemnumber} => 1 }
 365                                    grep { defined($_->{itemnumber}) }
 366                                    @$hold_requests;
 367
 368     # group available items by itemnumber
 369     my %items_by_itemnumber = map { $_->{itemnumber} => $_ } @$available_items;
 370
 371     # items already allocated
 372     my %allocated_items = ();
 373
 374     # map of items to hold requests
 375     my %item_map = ();
 376
 377     # figure out which item-level requests can be filled
 378     my $num_items_remaining = scalar(@$available_items);
 379     foreach my $request (@$hold_requests) {
 380         last if $num_items_remaining == 0;
 381
 382         # is this an item-level request?
 383         if (defined($request->{itemnumber})) {
 384             # fill it if possible; if not skip it
 385             if (exists $items_by_itemnumber{$request->{itemnumber}} and
 386                 not exists $allocated_items{$request->{itemnumber}}) {
 387                 $item_map{$request->{itemnumber}} = {
 388                     borrowernumber => $request->{borrowernumber},
 389                     biblionumber => $request->{biblionumber},
 390                     holdingbranch =>  $items_by_itemnumber{$request->{itemnumber}}->{holdingbranch},
 391                     pickup_branch => $request->{branchcode} || $request->{borrowerbranch},
 392                     item_level => 1,
 393                     reservedate => $request->{reservedate},
 394                     reservenotes => $request->{reservenotes},
 395                 };
 396                 $allocated_items{$request->{itemnumber}}++;
 397                 $num_items_remaining--;
 398             }
 399         } else {
 400             # it's title-level request that will take up one item
 401             $num_items_remaining--;
 402         }
 403     }
 404
 405     # group available items by branch
 406     my %items_by_branch = ();
 407     foreach my $item (@$available_items) {
 408         next unless $item->{holdallowed};
 409
 410         push @{ $items_by_branch{ $item->{holdingbranch} } }, $item
 411           unless exists $allocated_items{ $item->{itemnumber} };
 412     }
 413     return \%item_map unless keys %items_by_branch;
 414
 415     # now handle the title-level requests
 416     $num_items_remaining = scalar(@$available_items) - scalar(keys %allocated_items);
 417     my $pull_branches;
 418     foreach my $request (@$hold_requests) {
 419         last if $num_items_remaining == 0;
 420         next if defined($request->{itemnumber}); # already handled these
 421
 422         # look for local match first
 423         my $pickup_branch = $request->{branchcode} || $request->{borrowerbranch};
 424         my ($itemnumber, $holdingbranch);
 425
 426         my $holding_branch_items = $items_by_branch{$pickup_branch};
 427         if ( $holding_branch_items ) {
 428             foreach my $item (@$holding_branch_items) {
 429                 if ( $request->{borrowerbranch} eq $item->{homebranch} ) {
 430                     $itemnumber = $item->{itemnumber};
 431                     last;
 432                 }
 433             }
 434             $holdingbranch = $pickup_branch;
 435         }
 436         elsif ($transport_cost_matrix) {
 437             $pull_branches = [keys %items_by_branch];
 438             $holdingbranch = least_cost_branch( $pickup_branch, $pull_branches, $transport_cost_matrix );
 439             if ( $holdingbranch ) {
 440
 441                 my $holding_branch_items = $items_by_branch{$holdingbranch};
 442                 foreach my $item (@$holding_branch_items) {
 443                     next if $request->{borrowerbranch} ne $item->{homebranch};
 444
 445                     $itemnumber = $item->{itemnumber};
 446                     last;
 447                 }
 448             }
 449             else {
 450                 warn "No transport costs for $pickup_branch";
 451             }
 452         }
 453
 454         unless ($itemnumber) {
 455             # not found yet, fall back to basics
 456             if ($branches_to_use) {
 457                 $pull_branches = $branches_to_use;
 458             } else {
 459                 $pull_branches = [keys %items_by_branch];
 460             }
 461             PULL_BRANCHES:
 462             foreach my $branch (@$pull_branches) {
 463                 my $holding_branch_items = $items_by_branch{$branch}
 464                   or next;
 465
 466                 $holdingbranch ||= $branch;
 467                 foreach my $item (@$holding_branch_items) {
 468                     next if $pickup_branch ne $item->{homebranch};
 469                     next if ( $item->{holdallowed} == 1 && $item->{homebranch} ne $request->{borrowerbranch} );
 470
 471                     $itemnumber = $item->{itemnumber};
 472                     $holdingbranch = $branch;
 473                     last PULL_BRANCHES;
 474                 }
 475             }
 476
 477             unless ( $itemnumber ) {
 478                 foreach my $current_item ( @{ $items_by_branch{$holdingbranch} } ) {
 479                     if ( $holdingbranch && ( $current_item->{holdallowed} == 2 || $request->{borrowerbranch} eq $current_item->{homebranch} ) ) {
 480                         $itemnumber = $current_item->{itemnumber};
 481                         last; # quit this loop as soon as we have a suitable item
 482                     }
 483                 }
 484             }
 485         }
 486
 487         if ($itemnumber) {
 488             my $holding_branch_items = $items_by_branch{$holdingbranch}
 489               or die "Have $itemnumber, $holdingbranch, but no items!";
 490             @$holding_branch_items = grep { $_->{itemnumber} != $itemnumber } @$holding_branch_items;
 491             delete $items_by_branch{$holdingbranch} unless @$holding_branch_items;
 492
 493             $item_map{$itemnumber} = {
 494                 borrowernumber => $request->{borrowernumber},
 495                 biblionumber => $request->{biblionumber},
 496                 holdingbranch => $holdingbranch,
 497                 pickup_branch => $pickup_branch,
 498                 item_level => 0,
 499                 reservedate => $request->{reservedate},
 500                 reservenotes => $request->{reservenotes},
 501             };
 502             $num_items_remaining--;
 503         }
 504     }
 505     return \%item_map;
 506 }
 507
 508 =head2 CreatePickListFromItemMap
 509
 510 =cut
 511
 512 sub CreatePicklistFromItemMap {
 513     my $item_map = shift;
 514
 515     my $dbh = C4::Context->dbh;
 516
 517     my $sth_load=$dbh->prepare("
 518         INSERT INTO tmp_holdsqueue (biblionumber,itemnumber,barcode,surname,firstname,phone,borrowernumber,
 519                                     cardnumber,reservedate,title, itemcallnumber,
 520                                     holdingbranch,pickbranch,notes, item_level_request)
 521         VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)
 522     ");
 523
 524     foreach my $itemnumber  (sort keys %$item_map) {
 525         my $mapped_item = $item_map->{$itemnumber};
 526         my $biblionumber = $mapped_item->{biblionumber};
 527         my $borrowernumber = $mapped_item->{borrowernumber};
 528         my $pickbranch = $mapped_item->{pickup_branch};
 529         my $holdingbranch = $mapped_item->{holdingbranch};
 530         my $reservedate = $mapped_item->{reservedate};
 531         my $reservenotes = $mapped_item->{reservenotes};
 532         my $item_level = $mapped_item->{item_level};
 533
 534         my $item = GetItem($itemnumber);
 535         my $barcode = $item->{barcode};
 536         my $itemcallnumber = $item->{itemcallnumber};
 537
 538         my $borrower = GetMember('borrowernumber'=>$borrowernumber);
 539         my $cardnumber = $borrower->{'cardnumber'};
 540         my $surname = $borrower->{'surname'};
 541         my $firstname = $borrower->{'firstname'};
 542         my $phone = $borrower->{'phone'};
 543
 544         my $bib = GetBiblioData($biblionumber);
 545         my $title = $bib->{title};
 546
 547         $sth_load->execute($biblionumber, $itemnumber, $barcode, $surname, $firstname, $phone, $borrowernumber,
 548                            $cardnumber, $reservedate, $title, $itemcallnumber,
 549                            $holdingbranch, $pickbranch, $reservenotes, $item_level);
 550     }
 551 }
 552
 553 =head2 AddToHoldTargetMap
 554
 555 =cut
 556
 557 sub AddToHoldTargetMap {
 558     my $item_map = shift;
 559
 560     my $dbh = C4::Context->dbh;
 561
 562     my $insert_sql = q(
 563         INSERT INTO hold_fill_targets (borrowernumber, biblionumber, itemnumber, source_branchcode, item_level_request)
 564                                VALUES (?, ?, ?, ?, ?)
 565     );
 566     my $sth_insert = $dbh->prepare($insert_sql);
 567
 568     foreach my $itemnumber (keys %$item_map) {
 569         my $mapped_item = $item_map->{$itemnumber};
 570         $sth_insert->execute($mapped_item->{borrowernumber}, $mapped_item->{biblionumber}, $itemnumber,
 571                              $mapped_item->{holdingbranch}, $mapped_item->{item_level});
 572     }
 573 }
 574
 575 # Helper functions, not part of any interface
 576
 577 sub _trim {
 578     return $_[0] unless $_[0];
 579     $_[0] =~ s/^\s+//;
 580     $_[0] =~ s/\s+$//;
 581     $_[0];
 582 }
 583
 584 sub load_branches_to_pull_from {
 585     my $static_branch_list = C4::Context->preference("StaticHoldsQueueWeight")
 586       or return;
 587
 588     my @branches_to_use = map _trim($_), split /,/, $static_branch_list;
 589
 590     @branches_to_use = shuffle(@branches_to_use) if  C4::Context->preference("RandomizeHoldsQueueWeight");
 591
 592     return \@branches_to_use;
 593 }
 594
 595 sub least_cost_branch {
 596
 597     #$from - arrayref
 598     my ($to, $from, $transport_cost_matrix) = @_;
 599
 600     # Nothing really spectacular: supply to branch, a list of potential from branches
 601     # and find the minimum from - to value from the transport_cost_matrix
 602     return $from->[0] if @$from == 1;
 603
 604     # If the pickup library is in the list of libraries to pull from,
 605     # return that library right away, it is obviously the least costly
 606     return ($to) if any { $_ eq $to } @$from;
 607
 608     my ($least_cost, @branch);
 609     foreach (@$from) {
 610         my $cell = $transport_cost_matrix->{$to}{$_};
 611         next if $cell->{disable_transfer};
 612
 613         my $cost = $cell->{cost};
 614         next unless defined $cost; # XXX should this be reported?
 615
 616         unless (defined $least_cost) {
 617             $least_cost = $cost;
 618             push @branch, $_;
 619             next;
 620         }
 621
 622         next if $cost > $least_cost;
 623
 624         if ($cost == $least_cost) {
 625             push @branch, $_;
 626             next;
 627         }
 628
 629         @branch = ($_);
 630         $least_cost = $cost;
 631     }
 632
 633     return $branch[0];
 634
 635     # XXX return a random @branch with minimum cost instead of the first one;
 636     # return $branch[0] if @branch == 1;
 637 }
 638
 639
 640 1;