Class: Barcode1DTools::Plessey

Inherits:
Barcode1D show all
Defined in:
lib/barcode1dtools/plessey.rb

Overview

Barcode1DTools::Plessey - Create and decode bar patterns for Plessey. The value encoded is a string which may contain the digits 0-9 and the letters A-F (0-15 hexadecimal).

According to Wikipedia, a Plessey code should contain a two digit CRC8 checksum. This code does not provide checksum generation or validation.

Plessey is a terrible symbology in modern terms and should not be used in any new applications.

Example

val = "2898289238AF"
bc = Barcode1DTools::Plessey.new(val)
pattern = bc.bars
rle_pattern = bc.rle
width = bc.width

The object created is immutable.

Barcode1DTools::Plessey creates the patterns that you need to display Plessey barcodes. It can also decode a simple w/n string.

Plessey characters consist of 4 bars and 4 spaces. The representation is simply binary where a binary “0” is represented as a narrow bar followed by a wide space and a binary “1” is a wide bar followed by a narrow space. The bits are ordered ascending, so 9 is 1001 binary, “wn nw nw wn” in w/n format.

Formats

There are three formats for the returned pattern:

bars - 1s and 0s specifying black lines and white spaces. Actual characters can be changed from “1” and 0“ with options :line_character and :space_character.

rle - Run-length-encoded version of the pattern. The first number is always a black line, with subsequent digits alternating between spaces and lines. The digits specify the width of each line or space.

wn - The native format for this barcode type. The string consists of a series of “w” and “n” characters. The first item is always a black line, with subsequent characters alternating between spaces and lines. A “wide” item is twice the width of a “narrow” item.

The “width” method will tell you the total end-to-end width, in units, of the entire barcode.

Rendering

The author is aware of no standards for display.

Constant Summary collapse

CHAR_SEQUENCE =

Character sequence - 0-based offset in this string is character number

"0123456789ABCDEF"
PATTERNS =

Patterns for making bar codes

{
  '0'=> {'val'=>0 ,'wn'=>'nwnwnwnw'},
  '1'=> {'val'=>1 ,'wn'=>'wnnwnwnw'},
  '2'=> {'val'=>2 ,'wn'=>'nwwnnwnw'},
  '3'=> {'val'=>3 ,'wn'=>'wnwnnwnw'},
  '4'=> {'val'=>4 ,'wn'=>'nwnwwnnw'},
  '5'=> {'val'=>5 ,'wn'=>'wnnwwnnw'},
  '6'=> {'val'=>6 ,'wn'=>'nwwnwnnw'},
  '7'=> {'val'=>7 ,'wn'=>'wnwnwnnw'},
  '8'=> {'val'=>8 ,'wn'=>'nwnwnwwn'},
  '9'=> {'val'=>9 ,'wn'=>'wnnwnwwn'},
  'A'=> {'val'=>10 ,'wn'=>'nwwnnwwn'},
  'B'=> {'val'=>11 ,'wn'=>'wnwnnwwn'},
  'C'=> {'val'=>12 ,'wn'=>'nwnwwnwn'},
  'D'=> {'val'=>13 ,'wn'=>'wnnwwnwn'},
  'E'=> {'val'=>14 ,'wn'=>'nwwnwnwn'},
  'F'=> {'val'=>15 ,'wn'=>'wnwnwnwn'}
}
GUARD_PATTERN_LEFT_WN =

Left guard pattern

'wnwnnwwn'
GUARD_PATTERN_RIGHT_WN =

Right guard pattern

'wnwnnwnw'
DEFAULT_OPTIONS = 
{
  :line_character => '1',
  :space_character => '0',
  :w_character => 'w',
  :n_character => 'n',
  :wn_ratio => '2'
}

Instance Attribute Summary

Attributes inherited from Barcode1D

#check_digit, #encoded_string, #options, #value

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Barcode1D

bar_pair, bars_to_rle, rle_to_bars, rle_to_wn, wn_pair, wn_to_rle

Constructor Details

#initialize(value, options = {}) ⇒ Plessey

Create a new Plessey barcode object with the given value. Options are :line_character, :space_character, :w_character, and :n_character.

Raises:



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# File 'lib/barcode1dtools/plessey.rb', line 177

def initialize(value, options = {})

  @options = DEFAULT_OPTIONS.merge(options)

  # Can we encode this value?
  raise UnencodableCharactersError unless self.class.can_encode?(value)

  @value = value.to_s
  @encoded_string = value.to_s
  @check_digit = nil
end

Class Method Details

.can_encode?(value) ⇒ Boolean

Plessey can encode digits and A-F. Returns “true” if the given value is encodable.

Returns:

  • (Boolean) 


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# File 'lib/barcode1dtools/plessey.rb', line 108

def can_encode?(value)
  value.to_s =~ /\A[0-9A-F]+\z/
end

.decode(str, options = {}) ⇒ Object

Decode a string in rle format. This will return a Plessey object.



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# File 'lib/barcode1dtools/plessey.rb', line 126

def decode(str, options = {})
  if str =~ /[^1-3]/ && str =~ /[^wn]/
    raise UnencodableCharactersError, "Pattern must be rle or wn"
  end

  # ensure a wn string
  if str =~ /[1-3]/
    str = str.tr('123','nww')
  end

  if str.reverse =~ /\A#{GUARD_PATTERN_LEFT_WN}.*?#{GUARD_PATTERN_RIGHT_WN}\z/
    str.reverse!
  end

  unless str =~ /\A#{GUARD_PATTERN_LEFT_WN}(.*?)#{GUARD_PATTERN_RIGHT_WN}\z/
    raise UnencodableCharactersError, "Start/stop pattern is not detected."
  end

  wn_pattern = $1

  # Each pattern is 4 bars and 4 spaces, with a space between.
  unless wn_pattern.size % 8 == 0
    raise UnencodableCharactersError, "Wrong number of bars."
  end

  decoded_string = ''

  wn_pattern.scan(/.{8}/).each do |chunk|

    found = false

    PATTERNS.each do |char,hsh|
      if chunk == hsh['wn']
        decoded_string += char
        found = true
        break;
      end
    end

    raise UndecodableCharactersError, "Invalid sequence: #{chunk}" unless found

  end

  Plessey.new(decoded_string, options)
end

.generate_check_digit_for(value) ⇒ Object

We don’t generate check digits for Plessey, so this will raise an error.

Raises:



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# File 'lib/barcode1dtools/plessey.rb', line 114

def generate_check_digit_for(value)
  raise NotImplementedError
end

.validate_check_digit_for(value) ⇒ Object

We don’t generate check digits for Plessey, so this will raise an error.

Raises:



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# File 'lib/barcode1dtools/plessey.rb', line 120

def validate_check_digit_for(value)
  raise NotImplementedError
end

Instance Method Details

#bars ⇒ Object

Returns 1s and 0s (for “black” and “white”)



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# File 'lib/barcode1dtools/plessey.rb', line 200

def bars
  @bars ||= self.class.rle_to_bars(self.rle, @options)
end

#rle ⇒ Object

Returns a run-length-encoded string representation



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# File 'lib/barcode1dtools/plessey.rb', line 195

def rle
  @rle ||= self.class.wn_to_rle(self.wn, @options)
end

#width ⇒ Object

Returns the total unit width of the bar code



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# File 'lib/barcode1dtools/plessey.rb', line 205

def width
  @width ||= rle.split('').inject(0) { |a,c| a + c.to_i }
end

#wn ⇒ Object

Returns a string of “w” or “n” (“wide” and “narrow”)



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# File 'lib/barcode1dtools/plessey.rb', line 190

def wn
  @wn ||= wn_str.tr('wn', @options[:w_character].to_s + @options[:n_character].to_s)
end