class MarkovModel
    def create_model(file, order, unit)
    #unit = "word" or "character"
        @unit = unit
        entire_file = ""
        @order = order
        #read the entire file in
        File.open(file, "r") do |infile|
                cnt=0
                while (line = infile.gets)
                        entire_file += line
                        cnt+=1
                end
        end

        #split the file according to characters or words
        if unit == "word"
                split_on = /\s/
        else
                split_on = ""
        end
        @entire_file_split = entire_file.split(split_on)

        #construct a hash like:
        #first 'order' letters, letter following, increment count
        @model = Hash.new
        i = 0
        @entire_file_split.each do |c|
            this_group = @entire_file_split[i,order]
            next_letter = @entire_file_split[i+order,1]

            #if group doesn't exist, create it
		   if @model[this_group] == nil
		       @model[this_group] = { next_letter => 1 }
            #if group exists, but this "next_letter" hasn't been seen, insert it
            elsif @model[this_group][next_letter] == nil
                @model[this_group][next_letter] = 1
            #if group and next letter exist in model, increment the count
            else
                cur_count_of_next_letter = @model[this_group][next_letter] + 1
                @model[this_group][next_letter] = cur_count_of_next_letter
            end
            i+=1
        end
    end

    def generate_and_print_text(amount)
        start_group = @entire_file_split[0,@order]
        print start_group

        this_group = start_group
        (0..(amount-@order)).each do |i|
            next_letters_to_choose_from = @model[this_group]

            #construct probability hash
            num = 0
            probabilities = {}
            next_letters_to_choose_from.each do |key, value|
                    num += value
                    probabilities[key] = num
            end

            #select next letter
            index = rand(num)
            matches = probabilities.select {|key, value| index <= value }
            sorted_by_value = matches.sort{|a,b| a[1]<=>b[1]}
            next_letter = sorted_by_value[0][0]
            print " " if @unit == "word" #if we're splitting on words
            print next_letter

            #shift the group
            this_group = this_group[1,@order-1] + next_letter.to_ary
        end
    end

    def print_model
        require 'pp'
        PP.pp(@model)
    end
end

file = File.expand_path "source_text.txt"
mm = MarkovModel.new
mm.create_model(file, 7, "character")
mm.generate_and_print_text(2000)
mm.create_model(file, 1, "word")
mm.generate_and_print_text(250)
#mm.print_model