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=head1 METHODS

=head2 new

Constructor to set internal variables.

Arguments:
  $offset       - offset of the first item in this set ( 0 indexed )
  $page_size    - number of items per page
  $set_size     - actual number of items in this set
  $total        - total items available

Returns:
 $self

Sample:

  n == highest possible offset
  p == highest possbile page

  $self = bless( {
    next_offset => 5,  -- offset of next page ( 0..n ) or undef if you are 
                          on last page
    set_size => 5,     -- constructor argument
    prev_offset => 0,  -- offset of previous page ( 0..n ) or undef if you 
                          are on first page
    cur_page => 1,     -- the current page number of $offset
    last_page => 21,   -- the last page page for the total passed in ( 1..p )
    last_offset => 100,-- the last possible offset based on number pages ( 0..n )
    total => 103,      -- constructor argument
    next_page => 2,    -- the next possible page ( 1..p ) or undef if on 
                          last page ( offset == last_offset )
    page_size => 5     -- constructor argument
    to => 5,           -- the last member number of current page ( 1..n+1 )
    from => 1,         -- the first member number of current page ( offset+1 )
    prev_page => 1,    -- the previous page ( 1..p ) or undef if on first 
                          page ( offset == 0 )
    offset => 0        -- constructor argument
  }, Activator::Pager );


NOTE: we need to document the assuption of offset not being $to

=cut

sub new {
    my ($pkg, $offset, $page_size, $set_size, $total) = @_;

    my $self = bless {}, $pkg;

    $offset ||= 0;

    if( $page_size < 0 ) { $page_size = $set_size }

    $self->{offset} = $offset;
    $self->{page_size} = $page_size;
    $self->{set_size}  = $set_size;
    $self->{total}  = $total;

    ## error, offset is greater than results?
    if( ( $offset >= $total ) || ( $page_size == 0 ) ) {
        $self->{from} = 0;
        $self->{to}   = 0;
        $self->{total} = 0;
        return $self;
    }

    ## from and to
    $self->{from} = $total > 0 ? $offset+1 : 0;
    $self->{to}   = $offset+$set_size < $total ? $offset+$set_size : $total;

    ## last page number
    #
    # Last page is total/length when evenly divisible. We mod them, if
    # there is remainder, add 1 for the last page. EG: 101/10 == 10
    # pages + 1 on the last page
    #
    # this new hotness courtesy Frank Wallingford
    # TODO: write pager tests, use this formula
    #$self->{last_page} = int(($total + ( $page_size - 1 ) ) / $page_size );

    # old and crufty
    $self->{last_page} = int($total/$page_size) + ( ($total % $page_size > 0) ? 1 : 0 );

    ## last offset
    #
    # Similar to above, we need to subtract 1 length when evenly
    # divisible so that we don't offset off the end of the available
    # results. If there is a remainder, subtract nothing.
    #WARN( qq{  ($self->{last_page} * $page_size) - ( ($total % $page_size > 0) ? 0 : $page_size)  });

    # this new hotness courtesy Frank Wallingford
    # TODO: write pager tests, use this formula
    #$self->{last_offset} = int( ( $total - 1 ) / $page_size ) + 1;

    # old and crufty
    $self->{last_offset} = int($total/$page_size) * $page_size - ( ($total % $page_size > 0) ? 0 : $page_size ); ;


    ## cur page offset
    $self->{cur_page} = int( $offset / $page_size ) + 1;

    ## prev
    if( $offset - $page_size >= 0 ) {
      $self->{prev_offset} = $offset - $page_size;
      $self->{prev_page} = ( $self->{cur_page} - 1 <= 0 ) ? undef : $self->{cur_page} - 1;
    }
    else {
      $self->{prev_offset} = undef;
      $self->{prev_page} = undef;
    }

    ## next
    if( $offset + $page_size < $total ) {
      $self->{next_offset} = $offset + $page_size;
      $self->{next_page} = int( $self->{next_offset}/$page_size ) + 1;
    }
    else {
      $self->{next_offset} = undef;
      $self->{next_page} = undef;