markov chain of varying depth (character level)

Nonsense.rb

# nonsense.rb
# a markov chain of varying depth
# USAGE: make a new nonsense tree, add lines, then chain!
# > non = Nonsense.new 2
# > non.add_line "What is happening"
# > non.add_line "The world is on fire"
# > non.chain
# => "What won hat woren ire worenis hape"

class Nonsense
  def initialize( depth = 8 )
    @tree = {}
    @depth = depth
    @loaded = []
  end

  def add_line( line )
    line = line.split("") + [nil]
    history = []
    line.each do |char|
      key = history.join # "", then "W", then "Wh", etc.
      ensure_tree key
      @tree[key][:freq] += 1
      @tree[key][:next][char] ||= 0
      @tree[key][:next][char] += 1
      history.push char
      # history.push char.downcase
      history.shift if history.length > @depth
    end
    true
  end

  def next( token = "" )
    # token = token.downcase
    return nil unless @tree[token]
    freq = @tree[token][:freq]
    freq = 1 if freq == 0
    check = rand * freq
    pool = 0
    @tree[token][:next].each do |char,occ|
      pool += occ
      return char if check < pool
    end
    # check > freq = this token terminates the line.
    nil
  end

  def chain( seed = "" )
    seed = seed[0...@depth]
    char = self.next seed
    output = [seed]
    history = seed.split("")
    while char
      output.push char
      history.push char
      history.shift if history.length > @depth
      char = self.next history.join
    end
    output.join
  end

  def inspect
    "Nonsense chain of depth #{@depth}"
  end

  private

  def ensure_tree( key )
    @tree[key] ||= {
      freq: 0,
      next: {}
    }
  end
end