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 under the
   8 # terms of the GNU General Public License as published by the Free Software
   9 # Foundation; either version 2 of the License, or (at your option) any later
  10 # version.
  11 #
  12 # Koha is distributed in the hope that it will be useful, but WITHOUT ANY
  13 # WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  14 # A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License along
  17 # with Koha; if not, write to the Free Software Foundation, Inc.,
  18 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  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 Data::Dumper;
  36
  37 use vars qw($VERSION @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS);
  38 BEGIN {
  39     $VERSION = 3.03;
  40     require Exporter;
  41     @ISA = qw(Exporter);
  42     @EXPORT_OK = qw(
  43         &CreateQueue
  44         &GetHoldsQueueItems
  45
  46         &TransportCostMatrix
  47         &UpdateTransportCostMatrix
  48      );
  49 }
  50
  51
  52 =head1 FUNCTIONS
  53
  54 =head2 TransportCostMatrix
  55
  56   TransportCostMatrix();
  57
  58 Returns Transport Cost Matrix as a hashref <to branch code> => <from branch code> => cost
  59
  60 =cut
  61
  62 sub TransportCostMatrix {
  63     my $dbh   = C4::Context->dbh;
  64     my $transport_costs = $dbh->selectall_arrayref("SELECT * FROM transport_cost",{ Slice => {} });
  65
  66     my %transport_cost_matrix;
  67     foreach (@$transport_costs) {
  68         my $from = $_->{frombranch};
  69         my $to = $_->{tobranch};
  70         my $cost = $_->{cost};
  71         my $disabled = $_->{disable_transfer};
  72         $transport_cost_matrix{$to}{$from} = { cost => $cost, disable_transfer => $disabled };
  73     }
  74     return \%transport_cost_matrix;
  75 }
  76
  77 =head2 UpdateTransportCostMatrix
  78
  79   UpdateTransportCostMatrix($records);
  80
  81 Updates full Transport Cost Matrix table. $records is an arrayref of records.
  82 Records: { frombranch => <code>, tobranch => <code>, cost => <figure>, disable_transfer => <0,1> }
  83
  84 =cut
  85
  86 sub UpdateTransportCostMatrix {
  87     my ($records) = @_;
  88     my $dbh   = C4::Context->dbh;
  89
  90     my $sth = $dbh->prepare("INSERT INTO transport_cost (frombranch, tobranch, cost, disable_transfer) VALUES (?, ?, ?, ?)");
  91
  92     $dbh->do("TRUNCATE TABLE transport_cost");
  93     foreach (@$records) {
  94         my $cost = $_->{cost};
  95         my $from = $_->{frombranch};
  96         my $to = $_->{tobranch};
  97         if ($_->{disable_transfer}) {
  98             $cost ||= 0;
  99         }
 100         elsif ( !defined ($cost) || ($cost !~ m/(0|[1-9][0-9]*)(\.[0-9]*)?/o) ) {
 101             warn  "Invalid $from -> $to cost $cost - must be a number >= 0, disablig";
 102             $cost = 0;
 103             $_->{disable_transfer} = 1;
 104         }
 105         $sth->execute( $from, $to, $cost, $_->{disable_transfer} ? 1 : 0 );
 106     }
 107 }
 108
 109 =head2 GetHoldsQueueItems
 110
 111   GetHoldsQueueItems($branch);
 112
 113 Returns hold queue for a holding branch. If branch is omitted, then whole queue is returned
 114
 115 =cut
 116
 117 sub GetHoldsQueueItems {
 118     my ($branchlimit) = @_;
 119     my $dbh   = C4::Context->dbh;
 120
 121     my @bind_params = ();
 122     my $query = q/SELECT tmp_holdsqueue.*, biblio.author, items.ccode, items.itype, biblioitems.itemtype, items.location, items.enumchron, items.cn_sort, biblioitems.publishercode,biblio.copyrightdate,biblioitems.publicationyear,biblioitems.pages,biblioitems.size,biblioitems.publicationyear,biblioitems.isbn,items.copynumber
 123                   FROM tmp_holdsqueue
 124                        JOIN biblio      USING (biblionumber)
 125                   LEFT JOIN biblioitems USING (biblionumber)
 126                   LEFT JOIN items       USING (  itemnumber)
 127                 /;
 128     if ($branchlimit) {
 129         $query .=" WHERE tmp_holdsqueue.holdingbranch = ?";
 130         push @bind_params, $branchlimit;
 131     }
 132     $query .= " ORDER BY ccode, location, cn_sort, author, title, pickbranch, reservedate";
 133     my $sth = $dbh->prepare($query);
 134     $sth->execute(@bind_params);
 135     my $items = [];
 136     while ( my $row = $sth->fetchrow_hashref ){
 137         $row->{reservedate} = format_date($row->{reservedate});
 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
 302 =cut
 303
 304 sub GetItemsAvailableToFillHoldRequestsForBib {
 305     my ($biblionumber, $branches_to_use) = @_;
 306
 307     my $dbh = C4::Context->dbh;
 308     my $items_query = "SELECT itemnumber, homebranch, holdingbranch, itemtypes.itemtype AS itype
 309                        FROM items ";
 310
 311     if (C4::Context->preference('item-level_itypes')) {
 312         $items_query .=   "LEFT JOIN itemtypes ON (itemtypes.itemtype = items.itype) ";
 313     } else {
 314         $items_query .=   "JOIN biblioitems USING (biblioitemnumber)
 315                            LEFT JOIN itemtypes USING (itemtype) ";
 316     }
 317     $items_query .=   "WHERE items.notforloan = 0
 318                        AND holdingbranch IS NOT NULL
 319                        AND itemlost = 0
 320                        AND wthdrawn = 0";
 321     $items_query .= "  AND damaged = 0" unless C4::Context->preference('AllowHoldsOnDamagedItems');
 322     $items_query .= "  AND items.onloan IS NULL
 323                        AND (itemtypes.notforloan IS NULL OR itemtypes.notforloan = 0)
 324                        AND itemnumber NOT IN (
 325                            SELECT itemnumber
 326                            FROM reserves
 327                            WHERE biblionumber = ?
 328                            AND itemnumber IS NOT NULL
 329                            AND (found IS NOT NULL OR priority = 0)
 330                         )
 331                        AND items.biblionumber = ?";
 332     $items_query .=  " AND damaged = 0 "
 333       unless C4::Context->preference('AllowHoldsOnDamagedItems');
 334
 335     my @params = ($biblionumber, $biblionumber);
 336     if ($branches_to_use && @$branches_to_use) {
 337         $items_query .= " AND holdingbranch IN (" . join (",", map { "?" } @$branches_to_use) . ")";
 338         push @params, @$branches_to_use;
 339     }
 340     my $sth = $dbh->prepare($items_query);
 341     $sth->execute(@params);
 342
 343     my $itm = $sth->fetchall_arrayref({});
 344     my @items = grep { ! scalar GetTransfers($_->{itemnumber}) } @$itm;
 345     return [ grep {
 346         my $rule = GetBranchItemRule($_->{homebranch}, $_->{itype});
 347         $_->{holdallowed} = $rule->{holdallowed} != 0
 348     } @items ];
 349 }
 350
 351 =head2 MapItemsToHoldRequests
 352
 353   MapItemsToHoldRequests($hold_requests, $available_items, $branches, $transport_cost_matrix)
 354
 355 =cut
 356
 357 sub MapItemsToHoldRequests {
 358     my ($hold_requests, $available_items, $branches_to_use, $transport_cost_matrix) = @_;
 359
 360     # handle trival cases
 361     return unless scalar(@$hold_requests) > 0;
 362     return unless scalar(@$available_items) > 0;
 363
 364     my $automatic_return = C4::Context->preference("AutomaticItemReturn");
 365
 366     # identify item-level requests
 367     my %specific_items_requested = map { $_->{itemnumber} => 1 }
 368                                    grep { defined($_->{itemnumber}) }
 369                                    @$hold_requests;
 370
 371     # group available items by itemnumber
 372     my %items_by_itemnumber = map { $_->{itemnumber} => $_ } @$available_items;
 373
 374     # items already allocated
 375     my %allocated_items = ();
 376
 377     # map of items to hold requests
 378     my %item_map = ();
 379
 380     # figure out which item-level requests can be filled
 381     my $num_items_remaining = scalar(@$available_items);
 382     foreach my $request (@$hold_requests) {
 383         last if $num_items_remaining == 0;
 384
 385         # is this an item-level request?
 386         if (defined($request->{itemnumber})) {
 387             # fill it if possible; if not skip it
 388             if (exists $items_by_itemnumber{$request->{itemnumber}} and
 389                 not exists $allocated_items{$request->{itemnumber}}) {
 390                 $item_map{$request->{itemnumber}} = {
 391                     borrowernumber => $request->{borrowernumber},
 392                     biblionumber => $request->{biblionumber},
 393                     holdingbranch =>  $items_by_itemnumber{$request->{itemnumber}}->{holdingbranch},
 394                     pickup_branch => $request->{branchcode} || $request->{borrowerbranch},
 395                     item_level => 1,
 396                     reservedate => $request->{reservedate},
 397                     reservenotes => $request->{reservenotes},
 398                 };
 399                 $allocated_items{$request->{itemnumber}}++;
 400                 $num_items_remaining--;
 401             }
 402         } else {
 403             # it's title-level request that will take up one item
 404             $num_items_remaining--;
 405         }
 406     }
 407
 408     # group available items by branch
 409     my %items_by_branch = ();
 410     foreach my $item (@$available_items) {
 411         next unless $item->{holdallowed};
 412
 413         push @{ $items_by_branch{ $item->{holdingbranch} } }, $item
 414           unless exists $allocated_items{ $item->{itemnumber} };
 415     }
 416     return \%item_map unless keys %items_by_branch;
 417
 418     # now handle the title-level requests
 419     $num_items_remaining = scalar(@$available_items) - scalar(keys %allocated_items);
 420     my $pull_branches;
 421     foreach my $request (@$hold_requests) {
 422         last if $num_items_remaining == 0;
 423         next if defined($request->{itemnumber}); # already handled these
 424
 425         # look for local match first
 426         my $pickup_branch = $request->{branchcode} || $request->{borrowerbranch};
 427         my ($itemnumber, $holdingbranch);
 428
 429         my $holding_branch_items = $automatic_return ? undef : $items_by_branch{$pickup_branch};
 430         if ( $holding_branch_items ) {
 431             foreach my $item (@$holding_branch_items) {
 432                 if ( $request->{borrowerbranch} eq $item->{homebranch} ) {
 433                     $itemnumber = $item->{itemnumber};
 434                     last;
 435                 }
 436             }
 437             $holdingbranch = $pickup_branch;
 438             $itemnumber ||= $holding_branch_items->[0]->{itemnumber};
 439         }
 440         elsif ($transport_cost_matrix) {
 441             $pull_branches = [keys %items_by_branch];
 442             $holdingbranch = least_cost_branch( $pickup_branch, $pull_branches, $transport_cost_matrix );
 443             if ( $holdingbranch ) {
 444
 445                 my $holding_branch_items = $items_by_branch{$holdingbranch};
 446                 foreach my $item (@$holding_branch_items) {
 447                     next if $request->{borrowerbranch} ne $item->{homebranch};
 448
 449                     $itemnumber = $item->{itemnumber};
 450                     last;
 451                 }
 452                 $itemnumber ||= $holding_branch_items->[0]->{itemnumber};
 453             }
 454             else {
 455                 warn "No transport costs for $pickup_branch";
 456             }
 457         }
 458
 459         unless ($itemnumber) {
 460             # not found yet, fall back to basics
 461             if ($branches_to_use) {
 462                 $pull_branches = $branches_to_use;
 463             } else {
 464                 $pull_branches = [keys %items_by_branch];
 465             }
 466             PULL_BRANCHES:
 467             foreach my $branch (@$pull_branches) {
 468                 my $holding_branch_items = $items_by_branch{$branch}
 469                   or next;
 470
 471                 $holdingbranch ||= $branch;
 472                 foreach my $item (@$holding_branch_items) {
 473                     next if $pickup_branch ne $item->{homebranch};
 474
 475                     $itemnumber = $item->{itemnumber};
 476                     $holdingbranch = $branch;
 477                     last PULL_BRANCHES;
 478                 }
 479             }
 480             $itemnumber ||= $items_by_branch{$holdingbranch}->[0]->{itemnumber}
 481               if $holdingbranch;
 482         }
 483
 484         if ($itemnumber) {
 485             my $holding_branch_items = $items_by_branch{$holdingbranch}
 486               or die "Have $itemnumber, $holdingbranch, but no items!";
 487             @$holding_branch_items = grep { $_->{itemnumber} != $itemnumber } @$holding_branch_items;
 488             delete $items_by_branch{$holdingbranch} unless @$holding_branch_items;
 489
 490             $item_map{$itemnumber} = {
 491                 borrowernumber => $request->{borrowernumber},
 492                 biblionumber => $request->{biblionumber},
 493                 holdingbranch => $holdingbranch,
 494                 pickup_branch => $pickup_branch,
 495                 item_level => 0,
 496                 reservedate => $request->{reservedate},
 497                 reservenotes => $request->{reservenotes},
 498             };
 499             $num_items_remaining--;
 500         }
 501     }
 502     return \%item_map;
 503 }
 504
 505 =head2 CreatePickListFromItemMap
 506
 507 =cut
 508
 509 sub CreatePicklistFromItemMap {
 510     my $item_map = shift;
 511
 512     my $dbh = C4::Context->dbh;
 513
 514     my $sth_load=$dbh->prepare("
 515         INSERT INTO tmp_holdsqueue (biblionumber,itemnumber,barcode,surname,firstname,phone,borrowernumber,
 516                                     cardnumber,reservedate,title, itemcallnumber,
 517                                     holdingbranch,pickbranch,notes, item_level_request)
 518         VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)
 519     ");
 520
 521     foreach my $itemnumber  (sort keys %$item_map) {
 522         my $mapped_item = $item_map->{$itemnumber};
 523         my $biblionumber = $mapped_item->{biblionumber};
 524         my $borrowernumber = $mapped_item->{borrowernumber};
 525         my $pickbranch = $mapped_item->{pickup_branch};
 526         my $holdingbranch = $mapped_item->{holdingbranch};
 527         my $reservedate = $mapped_item->{reservedate};
 528         my $reservenotes = $mapped_item->{reservenotes};
 529         my $item_level = $mapped_item->{item_level};
 530
 531         my $item = GetItem($itemnumber);
 532         my $barcode = $item->{barcode};
 533         my $itemcallnumber = $item->{itemcallnumber};
 534
 535         my $borrower = GetMember('borrowernumber'=>$borrowernumber);
 536         my $cardnumber = $borrower->{'cardnumber'};
 537         my $surname = $borrower->{'surname'};
 538         my $firstname = $borrower->{'firstname'};
 539         my $phone = $borrower->{'phone'};
 540
 541         my $bib = GetBiblioData($biblionumber);
 542         my $title = $bib->{title};
 543
 544         $sth_load->execute($biblionumber, $itemnumber, $barcode, $surname, $firstname, $phone, $borrowernumber,
 545                            $cardnumber, $reservedate, $title, $itemcallnumber,
 546                            $holdingbranch, $pickbranch, $reservenotes, $item_level);
 547     }
 548 }
 549
 550 =head2 AddToHoldTargetMap
 551
 552 =cut
 553
 554 sub AddToHoldTargetMap {
 555     my $item_map = shift;
 556
 557     my $dbh = C4::Context->dbh;
 558
 559     my $insert_sql = q(
 560         INSERT INTO hold_fill_targets (borrowernumber, biblionumber, itemnumber, source_branchcode, item_level_request)
 561                                VALUES (?, ?, ?, ?, ?)
 562     );
 563     my $sth_insert = $dbh->prepare($insert_sql);
 564
 565     foreach my $itemnumber (keys %$item_map) {
 566         my $mapped_item = $item_map->{$itemnumber};
 567         $sth_insert->execute($mapped_item->{borrowernumber}, $mapped_item->{biblionumber}, $itemnumber,
 568                              $mapped_item->{holdingbranch}, $mapped_item->{item_level});
 569     }
 570 }
 571
 572 # Helper functions, not part of any interface
 573
 574 sub _trim {
 575     return $_[0] unless $_[0];
 576     $_[0] =~ s/^\s+//;
 577     $_[0] =~ s/\s+$//;
 578     $_[0];
 579 }
 580
 581 sub load_branches_to_pull_from {
 582     my $static_branch_list = C4::Context->preference("StaticHoldsQueueWeight")
 583       or return;
 584
 585     my @branches_to_use = map _trim($_), split /,/, $static_branch_list;
 586
 587     @branches_to_use = shuffle(@branches_to_use) if  C4::Context->preference("RandomizeHoldsQueueWeight");
 588
 589     return \@branches_to_use;
 590 }
 591
 592 sub least_cost_branch {
 593
 594     #$from - arrayref
 595     my ($to, $from, $transport_cost_matrix) = @_;
 596
 597 # Nothing really spectacular: supply to branch, a list of potential from branches
 598 # and find the minimum from - to value from the transport_cost_matrix
 599     return $from->[0] if @$from == 1;
 600
 601     my ($least_cost, @branch);
 602     foreach (@$from) {
 603         my $cell = $transport_cost_matrix->{$to}{$_};
 604         next if $cell->{disable_transfer};
 605
 606         my $cost = $cell->{cost};
 607         next unless defined $cost; # XXX should this be reported?
 608
 609         unless (defined $least_cost) {
 610             $least_cost = $cost;
 611             push @branch, $_;
 612             next;
 613         }
 614
 615         next if $cost > $least_cost;
 616
 617         if ($cost == $least_cost) {
 618             push @branch, $_;
 619             next;
 620         }
 621
 622         @branch = ($_);
 623         $least_cost = $cost;
 624     }
 625
 626     return $branch[0];
 627
 628     # XXX return a random @branch with minimum cost instead of the first one;
 629     # return $branch[0] if @branch == 1;
 630 }
 631
 632
 633 1;