class PaperAuth

# File lib/paper-auth.rb, line 7
def initialize ()
end

# File lib/paper-auth.rb, line 10
def create(id, key)
      # Create two hashes, and remove 3 characters from the end
      hash1 = Digest::SHA2.new(512).hexdigest("#{id}#{key}")[0..-4].upcase
      hash2 = Digest::SHA2.new(512).hexdigest("#{key}#{id}")[0..-4].upcase
      # Combine the two hashes to have 250 random characters
      hash = "#{hash1}#{hash2}"
  # Divide the 250 characters into a 10x5 array with 5 characters in each
      table = hash.scan(/#{"(.{5})"*5}/)
  # Initialize the two parts (top and bottom half)
  pair1 = Array.new
  pair2 = Array.new
  # For each array grid...
  for i in 0...10 do
    for j in 0...5 do
      # Strip generates either 0 or 1. If it is 0, 2 characters will be removed from the text. If it is 1, 3 characters will be removed from the text.
      strip = rand(0..1)
      # Generate two random numbers which will be the positition of the number that will be moved.
      remove1 = rand(0..4)
      remove2 = rand(0..4)
      # Make sure that the numbers are not equal.
      while remove1 == remove2
        remove2 = rand(0..4)
      end
      # If strip is 0, remove 2 characters.
      if strip == 0
        # Find the current box we are edititing and split it into characters.
        text = table[i][j].split(//)
        # Replace two of the numbers with a blank.
        text[remove1] = "_"
        text[remove2] = "_"
        # Initialize and update the value.
        pair1[i] ||= []
        pair1[i][j] = text.join
        # Find the current box we are edititing and split it into characters.
        text = table[i][j].split(//)
        # Save the value of the characters we will be removing.
        char1 = text[remove1]
        char2 = text[remove2]
        # Create a new temporary array which default contains "_".
        text = Array.new(5, "_")
        # Update the Array to only hold the two numbers.
        text[remove1] = char1
        text[remove2] = char2
        # Initialize and update the value.
        pair2[i] ||= []
        pair2[i][j] = text.join
      else
        # Find the current box we are edititing and split it into characters.
        text = table[i][j].split(//)
        # Save the value of the characters we will be removing.
        char1 = text[remove1]
        char2 = text[remove2]
        # Create a new temporary array which default contains "_".
        text = Array.new(5, "_")
        # Update the Array to only hold the two numbers.
        text[remove1] = char1
        text[remove2] = char2
        # Initialize and update the value.
        pair1[i] ||= []
        pair1[i][j] = text.join
        # Find the current box we are edititing and split it into characters.
        text = table[i][j].split(//)
        # Replace two of the numbers with a blank.
        text[remove1] = "_"
        text[remove2] = "_"
        # Initialize and update the value.
        pair2[i] ||= []
        pair2[i][j] = text.join
      end 
    end
  end
  # Load the template.
  templates = File.expand_path('../templates', File.dirname(__FILE__))
  content = File.read(templates + '/paper.html.erb')
  template = ERB.new(content)
  # Generate PDF from the template.
  kit = PDFKit.new(template.result(binding))
  kit.stylesheets << templates + '/paper.css'
  return file = kit.to_file('result.pdf')
end

# File lib/paper-auth.rb, line 91
def get
  # Generate random number and letter.
  number = rand(1..10)
  letter = rand(65..69)
  letter = letter.chr
  # Return random coordinate.
  return "#{number}#{letter}"
end

# File lib/paper-auth.rb, line 100
def verify(id, key, grid, value)
  # Create two hashes, and remove 3 characters from the end
  hash1   = Digest::SHA2.new(512).hexdigest("#{id}#{key}")[0..-4].upcase
  hash2 = Digest::SHA2.new(512).hexdigest("#{key}#{id}")[0..-4].upcase
  # Combine the two hashes to have 250 random characters
  hash = "#{hash1}#{hash2}"
  # Divide the 250 characters into a 10x5 array with 5 characters in each
  table = hash.scan(/#{"(.{5})"*5}/)
  # Split the coordinate of the grid point.
  grid = grid.split(//)
  number = grid[0].to_i - 1
  letter = grid[1].upcase.ord - 65
  # Search the table for the correct answer.
  answer = table[number][letter].downcase
  # If the answer equals to the value, then it returns true, otherwise it returns false.
  if answer == value.downcase
    return true
  else
    return false
  end
end