X-Git-Url: https://code.th-h.de/?p=usenet%2Fnewsstats.git;a=blobdiff_plain;f=lib%2FNewsStats.pm;fp=lib%2FNewsStats.pm;h=8a62179915a12342f48733006938c08e4f8ce511;hp=0000000000000000000000000000000000000000;hb=1af57a53905788c99a088bb6b17088293c0224d1;hpb=07c0b2589af779c33d5d35b6a7fa0e7883201674

diff --git a/lib/NewsStats.pm b/lib/NewsStats.pm
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--- /dev/null
+++ b/lib/NewsStats.pm
@@ -0,0 +1,780 @@
+# NewsStats.pm
+#
+# Library functions for the NewsStats package.
+#
+# Copyright (c) 2010-2013 Thomas Hochstein <thh@inter.net>
+#
+# This module can be redistributed and/or modified under the same terms under 
+# which Perl itself is published.
+
+package NewsStats;
+
+use strict;
+use warnings;
+our ($VERSION, @ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS);
+
+require Exporter;
+@ISA = qw(Exporter);
+@EXPORT = qw(
+  $MyVersion
+  $PackageVersion
+  $FullPath
+  $HomePath
+  ShowVersion
+  ShowPOD
+  ReadConfig
+  OverrideConfig
+  InitDB
+  Bleat
+);
+@EXPORT_OK = qw(
+  GetTimePeriod
+  LastMonth
+  SplitPeriod
+  ListMonth
+  ListNewsgroups
+  ParseHierarchies
+  ReadGroupList
+  OutputData
+  FormatOutput
+  SQLHierarchies
+  SQLSortOrder
+  SQLGroupList
+  SQLSetBounds
+  SQLBuildClause
+  GetMaxLength
+);
+%EXPORT_TAGS = ( TimePeriods => [qw(GetTimePeriod LastMonth SplitPeriod
+                                 ListMonth)],
+                 Output      => [qw(OutputData FormatOutput)],
+                 SQLHelper   => [qw(SQLHierarchies SQLSortOrder SQLGroupList
+                                 SQLSetBounds SQLBuildClause GetMaxLength)]);
+$VERSION = '0.01';
+our $PackageVersion = '0.01';
+
+use Data::Dumper;
+use File::Basename;
+use Cwd qw(realpath);
+
+use Config::Auto;
+use DBI;
+
+#####-------------------------------- Vars --------------------------------#####
+
+# save $0 in $FullPath
+our $FullPath = $0;
+# strip filename and /bin or /install directory to create the $HomePath
+our $HomePath = dirname(realpath($0));
+$HomePath =~ s/\/(bin|install)//;
+# trim $0
+$0 =~ s%.*/%%;
+# set version string
+our $MyVersion = "$0 $::VERSION (NewsStats.pm $VERSION)";
+
+#####------------------------------- Basics -------------------------------#####
+
+################################################################################
+
+################################################################################
+sub ShowVersion {
+################################################################################
+### display version and exit
+  print "NewsStats v$PackageVersion\n$MyVersion\n";
+  print "Copyright (c) 2010-2012 Thomas Hochstein <thh\@inter.net>\n";
+  print "This program is free software; you may redistribute it ".
+        "and/or modify it under the same terms as Perl itself.\n";
+  exit(100);
+};
+################################################################################
+
+################################################################################
+sub ShowPOD {
+################################################################################
+### feed myself to perldoc and exit
+  exec('perldoc', $FullPath);
+  exit(100);
+};
+################################################################################
+
+################################################################################
+sub ReadConfig {
+################################################################################
+### read config via Config::Auto
+### IN : $ConfFile: config filename
+### OUT: reference to a hash containing the configuration
+  my ($ConfFile) = @_;
+  # set default
+  $ConfFile = $HomePath . '/etc/newsstats.conf' if !$ConfFile;
+  # mandatory configuration options
+  my @Mandatory = ('DBDriver','DBHost','DBUser','DBPw','DBDatabase',
+                   'DBTableRaw','DBTableGrps');
+  # read config via Config::Auto
+  my $ConfR = Config::Auto::parse($ConfFile, format => 'equal');
+  my %Conf  = %{$ConfR};
+  # check for mandatory options
+  foreach (@Mandatory) {
+    &Bleat(2,sprintf("Mandatory configuration option %s is not set!",$_))
+      if (!defined($Conf{$_}));
+  }
+  # $Conf{'TLH'} is checked in gatherstats.pl
+  return $ConfR;
+};
+################################################################################
+
+################################################################################
+sub OverrideConfig {
+################################################################################
+### override configuration values
+### IN : $ConfigR  : reference to configuration hash
+###      $OverrideR: reference to a hash containing overrides
+  my ($ConfigR,$OverrideR) = @_;
+  my %Override = %$OverrideR;
+  # Config hash empty?
+  &Bleat(1,"Empty configuration hash passed to OverrideConfig()")
+    if ( keys %$ConfigR < 1);
+  # return if no overrides
+  return if (keys %Override < 1 or keys %$ConfigR < 1);
+  foreach my $Key (keys %Override) {
+    $$ConfigR{$Key} = $Override{$Key};
+  };
+};
+################################################################################
+
+################################################################################
+sub InitDB {
+################################################################################
+### initialise database connection
+### IN : $ConfigR: reference to configuration hash
+###      $Die    : if TRUE, die if connection fails
+### OUT: DBHandle
+  my ($ConfigR,$Die) = @_;
+  my %Conf = %$ConfigR;
+  my $DBHandle = DBI->connect(sprintf('DBI:%s:database=%s;host=%s',
+                                      $Conf{'DBDriver'},$Conf{'DBDatabase'},
+                                      $Conf{'DBHost'}), $Conf{'DBUser'},
+                                      $Conf{'DBPw'}, { PrintError => 0 });
+  if (!$DBHandle) {
+    &Bleat(2,$DBI::errstr) if (defined($Die) and $Die);
+    &Bleat(1,$DBI::errstr);
+  };
+  return $DBHandle;
+};
+################################################################################
+
+################################################################################
+sub Bleat {
+################################################################################
+### print warning or error messages and terminate in case of error
+### IN : $Level  : 1 = warning, 2 = error
+###      $Message: warning or error message
+  my ($Level,$Message) = @_;
+  if ($Level == 1) {
+    warn "$0 W: $Message\n"
+  } elsif ($Level == 2) {
+    die "$0 E: $Message\n"
+  } else {
+    print "$0: $Message\n"
+  }
+};
+################################################################################
+
+#####------------------------------ GetStats ------------------------------#####
+
+################################################################################
+sub ListNewsgroups {
+################################################################################
+### explode a (scalar) list of newsgroup names to a list of newsgroup and
+### hierarchy names where every newsgroup and hierarchy appears only once:
+### de.alt.test,de.alt.admin -> de.ALL, de.alt.ALL, de.alt.test, de.alt.admin
+### IN : $Newsgroups  : a list of newsgroups (content of Newsgroups: header)
+###      $TLH         : top level hierarchy (all other newsgroups are ignored)
+###      $ValidGroupsR: reference to a hash containing all valid newsgroups
+###                     as keys
+### OUT: %Newsgroups  : hash containing all newsgroup and hierarchy names as keys
+  my ($Newsgroups,$TLH,$ValidGroupsR) = @_;
+  my %ValidGroups = %{$ValidGroupsR} if $ValidGroupsR;
+  my %Newsgroups;
+  chomp($Newsgroups);
+  # remove whitespace from contents of Newsgroups:
+  $Newsgroups =~ s/\s//;
+  # call &HierarchyCount for each newsgroup in $Newsgroups:
+  for (split /,/, $Newsgroups) {
+    # don't count newsgroup/hierarchy in wrong TLH
+    next if($TLH and !/^$TLH/);
+    # don't count invalid newsgroups
+    if(%ValidGroups and !defined($ValidGroups{$_})) {
+      warn (sprintf("DROPPED: %s\n",$_));
+      next;
+    }
+    # add original newsgroup to %Newsgroups
+    $Newsgroups{$_} = 1;
+    # add all hierarchy elements to %Newsgroups, amended by '.ALL',
+    # i.e. de.alt.ALL and de.ALL
+    foreach (ParseHierarchies($_)) {
+      $Newsgroups{$_.'.ALL'} = 1;
+    }
+  };
+  return %Newsgroups;
+};
+
+################################################################################
+sub ParseHierarchies {
+################################################################################
+### return a list of all hierarchy levels a newsgroup belongs to
+### (for de.alt.test.moderated that would be de/de.alt/de.alt.test)
+### IN : $Newsgroup  : a newsgroup name
+### OUT: @Hierarchies: array containing all hierarchies the newsgroup belongs to
+  my ($Newsgroup) = @_;
+  my @Hierarchies;
+  # strip trailing dots
+  $Newsgroup =~ s/(.+)\.+$/$1/;
+  # butcher newsgroup name by "." and add each hierarchy to @Hierarchies
+  # i.e. de.alt.test: "de.alt" and "de"
+  while ($Newsgroup =~ /\./) {
+    $Newsgroup =~ s/^((?:\.?[^.]+)*)\.[^.]+$/$1/;
+    push @Hierarchies, $Newsgroup;
+  };
+  return @Hierarchies;
+};
+
+################################################################################
+sub ReadGroupList {
+################################################################################
+### read a list of valid newsgroups from file (each group on one line,
+### ignoring everything after the first whitespace and so accepting files
+### in checkgroups format as well as (parts of) an INN active file)
+### IN : $Filename    : file to read
+### OUT: \%ValidGroups: hash containing all valid newsgroups
+  my ($Filename) = @_;
+  my %ValidGroups;
+  open (my $LIST,"<$Filename") or &Bleat(2,"Cannot read $Filename: $!");
+  while (<$LIST>) {
+    s/^\s*(\S+).*$/$1/;
+    chomp;
+    next if /^$/;
+    $ValidGroups{$_} = '1';
+  };
+  close $LIST;
+  return \%ValidGroups;
+};
+
+################################################################################
+
+#####----------------------------- TimePeriods ----------------------------#####
+
+################################################################################
+sub GetTimePeriod {
+################################################################################
+### get a time period to act on from --month option;
+### if empty, default to last month
+### IN : $Month: may be empty, 'YYYY-MM', 'YYYY-MM:YYYY-MM' or 'all'
+### OUT: $Verbal,$SQL: verbal description and WHERE-clause
+###                    of the chosen time period
+  my ($Month) = @_;
+  # define result variables
+  my ($Verbal, $SQL);
+  # define a regular expression for a month
+  my $REMonth = '\d{4}-\d{2}';
+  
+  # default to last month if option is not set
+  if(!$Month) {
+    $Month = &LastMonth;
+  }
+  
+  # check for valid input
+  if ($Month =~ /^$REMonth$/) {
+    # single month (YYYY-MM)
+    ($Month) = &CheckMonth($Month);
+    $Verbal  = $Month;
+    $SQL     = sprintf("month = '%s'",$Month);
+  } elsif ($Month =~ /^$REMonth:$REMonth$/) {
+    # time period (YYYY-MM:YYYY-MM)
+    $Verbal = sprintf('%s to %s',&SplitPeriod($Month));
+    $SQL    = sprintf("month BETWEEN '%s' AND '%s'",&SplitPeriod($Month));
+  } elsif ($Month =~ /^all$/i) {
+    # special case: ALL
+    $Verbal = 'all time';
+    $SQL    = '';
+  } else {
+    # invalid input
+    return (undef,undef);
+  }
+  
+  return ($Verbal,$SQL);
+};
+
+################################################################################
+sub LastMonth {
+################################################################################
+### get last month from todays date in YYYY-MM format
+### OUT: last month as YYYY-MM
+  # get today's date
+  my (undef,undef,undef,undef,$Month,$Year,undef,undef,undef) = localtime(time);
+  # $Month is already defined from 0 to 11, so no need to decrease it by 1
+  $Year += 1900;
+  if ($Month < 1) {
+    $Month = 12;
+    $Year--;
+  };
+  # return last month
+  return sprintf('%4d-%02d',$Year,$Month);
+};
+
+################################################################################
+sub CheckMonth {
+################################################################################
+### check if input (in YYYY-MM form) is valid with MM between 01 and 12;
+### otherwise, fix it
+### IN : @Month: array of month
+### OUT: @Month: a valid month
+  my (@Month) = @_;
+  foreach my $Month (@Month) {
+    my ($OldMonth) = $Month;
+    my ($CalMonth) = substr ($Month, -2);
+    if ($CalMonth < 1 or $CalMonth > 12) {
+      $CalMonth = '12' if $CalMonth > 12;
+      $CalMonth = '01' if $CalMonth < 1;
+      substr($Month, -2) = $CalMonth;
+      &Bleat(1,sprintf("'%s' is an invalid date (MM must be between '01' ".
+                       "and '12'), set to '%s'.",$OldMonth,$Month));
+    }
+  }
+  return @Month;
+};
+
+################################################################################
+sub SplitPeriod {
+################################################################################
+### split a time period denoted by YYYY-MM:YYYY-MM into start and end month
+### IN : $Period: time period
+### OUT: $StartMonth, $EndMonth
+  my ($Period) = @_;
+  my ($StartMonth, $EndMonth) = split /:/, $Period;
+  ($StartMonth,$EndMonth) = CheckMonth($StartMonth,$EndMonth);
+  # switch parameters as necessary
+  if ($EndMonth gt $StartMonth) {
+    return ($StartMonth, $EndMonth);
+  } else {
+    return ($EndMonth, $StartMonth);
+  };
+};
+
+################################################################################
+sub ListMonth {
+################################################################################
+### return a list of months (YYYY-MM) between start and end month
+### IN : $MonthExpression ('YYYY-MM' or 'YYYY-MM to YYYY-MM')
+### OUT: @Months: array containing all months from $MonthExpression enumerated
+  my ($MonthExpression )= @_;
+  # return if single month
+  return ($MonthExpression) if ($MonthExpression =~ /^\d{4}-\d{2}$/);
+  # parse $MonthExpression
+  my ($StartMonth, $EndMonth) = split(' to ',$MonthExpression);
+  # set $Year, $Month from $StartMonth
+  my ($Year, $Month) = split /-/, $StartMonth;
+  # define @Months
+  my (@Months);
+  until ("$Year-$Month" gt $EndMonth) {
+    push @Months, "$Year-$Month";
+    $Month = "$Month"; # force string context
+    $Month++;
+    if ($Month > 12) {
+      $Month = '01';
+      $Year++;
+    };
+  };
+  return @Months;
+};
+
+#####---------------------------- OutputFormats ---------------------------#####
+
+################################################################################
+sub OutputData {
+################################################################################
+### read database query results from DBHandle and print results with formatting
+### IN : $Format   : format specifier
+###      $Comments : print or suppress all comments for machine-readable output
+###      $GroupBy  : primary sorting order (month or key)
+###      $Precision: number of digits right of decimal point (0 or 2)
+###      $ValidKeys: reference to a hash containing all valid keys
+###      $FileTempl: file name template (--filetemplate): filetempl-YYYY-MM
+###      $DBQuery  : database query handle with executed query,
+###                 containing $Month, $Key, $Value
+###      $PadField : padding length for key field (optional) for 'pretty'
+###      $PadValue : padding length for value field (optional) for 'pretty'
+  my ($Format, $Comments, $GroupBy, $Precision, $ValidKeys, $FileTempl,
+      $DBQuery, $PadField, $PadValue) = @_;
+  my %ValidKeys = %{$ValidKeys} if $ValidKeys;
+  my ($FileName, $Handle, $OUT);
+  our $LastIteration;
+  
+  # define output types
+  my %LegalOutput;
+  @LegalOutput{('dump','list','pretty')} = ();
+  # bail out if format is unknown
+  &Bleat(2,"Unknown output type '$Format'!") if !exists($LegalOutput{$Format});
+
+  while (my ($Month, $Key, $Value) = $DBQuery->fetchrow_array) {
+    # don't display invalid keys
+    if(%ValidKeys and !defined($ValidKeys{$Key})) {
+      # FIXME
+      # &Bleat(1,sprintf("DROPPED: %s",$Key));
+      next;
+    };
+    # care for correct sorting order and abstract from month and keys:
+    # $Caption will be $Month or $Key, according to sorting order,
+    # and $Key will be $Key or $Month, respectively
+    my $Caption;
+    if ($GroupBy eq 'key') {
+      $Caption = $Key;
+      $Key     = $Month;
+    } else {
+      $Caption = $Month;
+    }
+    # set output file handle
+    if (!$FileTempl) {
+      $Handle = *STDOUT{IO}; # set $Handle to a reference to STDOUT
+    } elsif (!defined($LastIteration) or $LastIteration ne $Caption) {
+      close $OUT if ($LastIteration);
+      # safeguards for filename creation:
+      # replace potential problem characters with '_'
+      $FileName = sprintf('%s-%s',$FileTempl,$Caption);
+      $FileName =~ s/[^a-zA-Z0-9_-]+/_/g; 
+      open ($OUT,">$FileName")
+        or &Bleat(2,sprintf("Cannot open output file '%s': $!",
+                            $FileName));
+      $Handle = $OUT;
+    };
+    print $Handle &FormatOutput($Format, $Comments, $Caption, $Key, $Value,
+                                $Precision, $PadField, $PadValue);
+    $LastIteration = $Caption;
+  };
+  close $OUT if ($FileTempl);
+};
+
+################################################################################
+sub FormatOutput {
+################################################################################
+### format information for output according to format specifier
+### IN : $Format   : format specifier
+###      $Comments : print or suppress all comments for machine-readable output
+###      $Caption  : month (as YYYY-MM) or $Key, according to sorting order
+###      $Key      : newsgroup, client, ... or $Month, as above
+###      $Value    : number of postings with that attribute
+###      $Precision: number of digits right of decimal point (0 or 2)
+###      $PadField : padding length for key field (optional) for 'pretty'
+###      $PadValue : padding length for value field (optional) for 'pretty'
+### OUT: $Output: formatted output
+  my ($Format, $Comments, $Caption, $Key, $Value, $Precision, $PadField,
+      $PadValue) = @_;
+  my ($Output);
+  # keep last caption in mind
+  our ($LastIteration);
+  # create one line of output
+  if ($Format eq 'dump') {
+    # output as dump (key value)
+    $Output = sprintf ("# %s:\n",$Caption)
+      if ($Comments and (!defined($LastIteration) or $Caption ne $LastIteration));
+    $Output .= sprintf ("%s %u\n",$Key,$Value);
+  } elsif ($Format eq 'list') {
+    # output as list (caption key value)
+    $Output = sprintf ("%s %s %u\n",$Caption,$Key,$Value);
+  } elsif ($Format eq 'pretty') {
+    # output as a table
+    $Output = sprintf ("# ----- %s:\n",$Caption)
+      if ($Comments and (!defined($LastIteration) or $Caption ne $LastIteration));
+    # increase $PadValue for numbers with decimal point
+    $PadValue += $Precision+1 if $Precision;
+    # add padding if $PadField is set; $PadValue HAS to be set then
+    $Output .= sprintf ($PadField ?
+                        sprintf("%%-%us%%s %%%u.*f\n",$PadField,$PadValue) :
+                        "%s%s %.*f\n",$Key,$Comments ? ':' : '',
+                        $Precision,$Value);
+  };
+  return $Output;
+};
+
+#####------------------------- QueryModifications -------------------------#####
+
+################################################################################
+sub SQLHierarchies {
+################################################################################
+### add exclusion of hierarchy levels (de.alt.ALL) from SQL query by
+### amending the WHERE clause if $ShowHierarchies is false (or don't, if it is
+### true, accordingly)
+### IN : $ShowHierarchies: boolean value
+### OUT: SQL code
+  my ($ShowHierarchies) = @_;
+  return $ShowHierarchies ? '' : "newsgroup NOT LIKE '%.ALL'";
+};
+
+################################################################################
+sub GetMaxLength {
+################################################################################
+### get length of longest fields in future query result
+### IN : $DBHandle    : database handle
+###      $Table       : table to query
+###      $Field       : field (key!, i.e. month, newsgroup, ...) to check
+###      $Value       : field (value!, i.e. postings) to check
+###      $WhereClause : WHERE clause
+###      $HavingClause: HAVING clause
+###      @BindVars    : bind variables for WHERE clause
+### OUT: $FieldLength : length of longest instance of $Field
+###      $ValueLength : length of longest instance of $Value
+  my ($DBHandle,$Table,$Field,$Value,$WhereClause,$HavingClause,@BindVars) = @_;
+  my $DBQuery = $DBHandle->prepare(sprintf("SELECT MAX(LENGTH(%s)),".
+                                           "MAX(%s) ".
+                                           "FROM %s %s %s",$Field,,$Value,
+                                           $Table,$WhereClause,$HavingClause ?
+                                           'GROUP BY newsgroup' . $HavingClause .
+                                           ' ORDER BY LENGTH(newsgroup) '.
+                                           'DESC LIMIT 1': ''));
+  $DBQuery->execute(@BindVars) or &Bleat(1,sprintf("Can't get field length ".
+                                                   "for '%s' from table '%s': ".
+                                                   "$DBI::errstr",$Field,$Table));
+  my ($FieldLength,$ValueMax) = $DBQuery->fetchrow_array;
+  my $ValueLength = length($ValueMax) if ($ValueMax);
+  return ($FieldLength,$ValueLength);
+};
+
+################################################################################
+sub SQLSortOrder {
+################################################################################
+### build a SQL 'ORDER BY' clause from $OptGroupBy (primary sorting) and
+### $OptOrderBy (secondary sorting), both ascending or descending;
+### descending sorting order is done by adding '-desc'
+### IN : $GroupBy: primary sort by 'month' (default) or 'newsgroups'
+###      $OrderBy: secondary sort by month/newsgroups (default)
+###                or number of 'postings'
+### OUT: a SQL ORDER BY clause
+  my ($GroupBy,$OrderBy) = @_;
+  my ($GroupSort,$OrderSort) = ('','');
+  # $GroupBy (primary sorting)
+  if (!$GroupBy) {
+    $GroupBy   = 'month';
+  } else {
+    ($GroupBy, $GroupSort) = SQLParseOrder($GroupBy);
+    if ($GroupBy =~ /group/i) {
+      $GroupBy   = 'newsgroup';
+    } else {
+      $GroupBy   = 'month';
+    }
+  }
+  my $Secondary = ($GroupBy eq 'month') ? 'newsgroup' : 'month';
+  # $OrderBy (secondary sorting)
+  if (!$OrderBy) {
+    $OrderBy = $Secondary;
+  } else {
+    ($OrderBy, $OrderSort) = SQLParseOrder($OrderBy);
+    if ($OrderBy =~ /posting/i) {
+      $OrderBy = "postings $OrderSort, $Secondary";
+    } else {
+      $OrderBy = "$Secondary $OrderSort";
+    }
+  }
+  return ($GroupBy,&SQLBuildClause('order',"$GroupBy $GroupSort",$OrderBy));
+};
+
+################################################################################
+sub SQLParseOrder {
+################################################################################
+### parse $OptGroupBy or $OptOrderBy option of the form param[-desc], e.g.
+### 'month', 'month-desc', 'newsgroups-desc', but also just 'desc'
+### IN : $OrderOption: order option (see above)
+### OUT: parameter to sort by,
+###      sort order ('DESC' or nothing, meaning 'ASC')
+  my ($OrderOption) = @_;
+  my $SortOrder = '';
+  if ($OrderOption =~ s/-?desc$//i) {
+    $SortOrder = 'DESC';
+  } else {
+    $OrderOption =~ s/-?asc$//i
+  }
+  return ($OrderOption,$SortOrder);
+};
+
+################################################################################
+sub SQLGroupList {
+################################################################################
+### explode list of newsgroups separated by : (with wildcards)
+### to a SQL 'WHERE' expression
+### IN : $Newsgroups: list of newsgroups (group.one.*:group.two:group.three.*)
+### OUT: SQL code to become part of a 'WHERE' clause,
+###      list of newsgroups for SQL bindings
+  my ($Newsgroups) = @_;
+  # substitute '*' wildcard with SQL wildcard character '%'
+  $Newsgroups =~ s/\*/%/g;
+  return (undef,undef) if !CheckValidNewsgroups($Newsgroups);
+  # just one newsgroup?
+  return (SQLGroupWildcard($Newsgroups),$Newsgroups) if $Newsgroups !~ /:/;
+  my ($SQL,@WildcardGroups,@NoWildcardGroups);
+  # list of newsgroups separated by ':'
+  my @GroupList = split /:/, $Newsgroups;
+  foreach (@GroupList) {
+    if ($_ !~ /%/) {
+      # add to list of newsgroup names WITHOUT wildcard
+      push (@NoWildcardGroups,$_);
+    } else {
+      # add to list of newsgroup names WITH wildcard
+      push (@WildcardGroups,$_);
+      # add wildcard to SQL clause
+      # 'OR' if SQL clause is not empty
+      $SQL .= ' OR ' if $SQL;
+      $SQL .= 'newsgroup LIKE ?'
+    }
+  };
+  if (scalar(@NoWildcardGroups)) {
+    # add 'OR' if SQL clause is not empty
+    $SQL .= ' OR ' if $SQL;
+    if (scalar(@NoWildcardGroups) < 2) {
+      # special case: just one newsgroup without wildcard
+      $SQL .= 'newsgroup = ?';
+    } else {
+      # create list of newsgroups to include: 'newsgroup IN (...)'
+      $SQL .= 'newsgroup IN (';
+      my $SQLin;
+      foreach (@NoWildcardGroups) {
+        $SQLin .= ',' if $SQLin;
+        $SQLin .= '?';
+      }
+      # add list to SQL clause
+      $SQL .= $SQLin .= ')';
+    }
+  }
+  # add brackets '()' to SQL clause as needed (more than one wildcard group)
+  if (scalar(@WildcardGroups)) {
+    $SQL = '(' . $SQL .')';
+  }
+  # rebuild @GroupList in (now) correct order
+  @GroupList = (@WildcardGroups,@NoWildcardGroups);
+  return ($SQL,@GroupList);
+};
+
+################################################################################
+sub SQLGroupWildcard {
+################################################################################
+### build a valid SQL 'WHERE' expression with or without wildcards
+### IN : $Newsgroup: newsgroup expression, probably with wildcard
+###                  (group.name or group.name.%)
+### OUT: SQL code to become part of a 'WHERE' clause
+  my ($Newsgroup) = @_;
+  if ($Newsgroup !~ /%/) {
+    return 'newsgroup = ?';
+  } else {
+    return 'newsgroup LIKE ?';
+  }
+};
+
+################################################################################
+sub SQLSetBounds {
+################################################################################
+### set upper and/or lower boundary (number of postings)
+### IN : $Type: 'level', 'average', 'sum' or 'default'
+###      $LowBound,$UppBound: lower/upper boundary, respectively
+### OUT: SQL code to become part of a WHERE or HAVING clause
+  my ($Type,$LowBound,$UppBound) = @_;
+  ($LowBound,$UppBound) = SQLCheckNumber($LowBound,$UppBound);
+  if($LowBound and $UppBound and $LowBound > $UppBound) {
+    &Bleat(1,"Lower boundary $LowBound is larger than Upper boundary ".
+             "$UppBound, exchanging boundaries.");
+    ($LowBound,$UppBound) = ($UppBound,$LowBound);
+  }
+  # default to 'default'
+  my $WhereHavingFunction = 'postings';
+  # set $LowBound to SQL statement:
+  # 'WHERE postings >=', 'HAVING MIN(postings) >=' or 'HAVING AVG(postings) >='
+  if ($Type eq 'level') {
+    $WhereHavingFunction = 'MIN(postings)'
+  } elsif ($Type eq 'average') {
+    $WhereHavingFunction = 'AVG(postings)'
+  } elsif ($Type eq 'sum') {
+    $WhereHavingFunction = 'SUM(postings)'
+  }
+  $LowBound = sprintf('%s >= '.$LowBound,$WhereHavingFunction) if ($LowBound);
+  # set $LowBound to SQL statement:
+  # 'WHERE postings <=', 'HAVING MAX(postings) <=' or 'HAVING AVG(postings) <='
+  if ($Type eq 'level') {
+    $WhereHavingFunction = 'MAX(postings)'
+  } elsif ($Type eq 'average') {
+    $WhereHavingFunction = 'AVG(postings)'
+  } elsif ($Type eq 'sum') {
+    $WhereHavingFunction = 'SUM(postings)'
+  }
+  $UppBound = sprintf('%s <= '.$UppBound,$WhereHavingFunction) if ($UppBound);
+  return ($LowBound,$UppBound);
+};
+
+################################################################################
+sub SQLCheckNumber {
+################################################################################
+### check if input is a valid positive integer; otherwise, make it one
+### IN : @Numbers: array of parameters
+### OUT: @Numbers: a valid positive integer
+  my (@Numbers) = @_;
+  foreach my $Number (@Numbers) {
+    if ($Number and $Number < 0) {
+      &Bleat(1,"Boundary $Number is < 0, set to ".-$Number);
+      $Number = -$Number;
+    }
+    $Number = '' if ($Number and $Number !~ /^\d+$/);
+  }
+  return @Numbers;
+};
+
+################################################################################
+sub SQLBuildClause {
+################################################################################
+### build a valid SQL WHERE, GROUP BY, ORDER BY or HAVING clause
+### from multiple expressions which *may* be empty
+### IN : $Type: 'where', 'having', 'group' or 'order'
+###      @Expressions: array of expressions
+### OUT: $SQLClause: a SQL clause
+  my ($Type,@Expressions) = @_;
+  my ($SQLClause,$Separator,$Statement);
+  # set separator ('AND' or ',')
+  if ($Type eq 'where' or $Type eq 'having') {
+    $Separator = 'AND';
+  } else {
+    $Separator = ',';
+  }
+  # set statement
+  if ($Type eq 'where') {
+    $Statement = 'WHERE';
+  } elsif ($Type eq 'order') {
+    $Statement = 'ORDER BY';
+  } elsif ($Type eq 'having') {
+    $Statement = 'HAVING';
+  } else {
+    $Statement = 'GROUP BY';
+  }
+  # build query from expressions with separators
+  foreach my $Expression (@Expressions) {
+    if ($Expression) {
+      $SQLClause .= " $Separator " if ($SQLClause);
+      $SQLClause .= $Expression;
+    }
+  }
+  # add statement in front if not already present
+  $SQLClause = " $Statement " . $SQLClause
+    if ($SQLClause and $SQLClause !~ /$Statement/);
+  return $SQLClause;
+};
+
+#####--------------------------- Verifications ----------------------------#####
+
+################################################################################
+sub CheckValidNewsgroups {
+################################################################################
+### syntax check of newgroup list
+### IN : $Newsgroups: list of newsgroups (group.one.*:group.two:group.three.*)
+### OUT: boolean
+  my ($Newsgroups) = @_;
+  my $InvalidCharRegExp = ',; ';
+  return ($Newsgroups =~ /[$InvalidCharRegExp]/) ? 0 : 1;
+};
+
+
+#####------------------------------- done ---------------------------------#####
+1;
+
+