A Simple Calendar generator. Very specific for my case - Probably going to make it more configurable one day.

Gemfile

source "https://rubygems.org"

gem "prawn"

gen_cal.rb

require 'rubygems'
require 'bundler/setup'
require 'prawn'

require 'yaml'

MONTHS = %w(Januar Februar März April Mai Juni Juli August September Oktober November Dezember)
DAYS = %w(Mo Di Mi Do Fr Sa So)

YEAR = 2015

EXTRA_MARGIN_VERTICAL = 100
EXTRA_MARGIN_HORIZONTAL = 50

COLOR_NORMAL = "000000"
COLOR_HOLIDAY = "AA0000"

POS_CAL_VERTICAL = 2.5
HEADLINE_SPACE = 50

holidays = YAML.load_file('free_days.yml')

pdf = Prawn::Document.new(page_size: 'A4', bottom_margin: EXTRA_MARGIN_VERTICAL)
pdf.font("fonts/DejaVuSerif.ttf")
pdf.stroke_color = "000000"

def color(condition)
  if condition
    COLOR_HOLIDAY
  else
    COLOR_NORMAL
  end
end

12.times do |month|
  
  pdf.bounding_box([EXTRA_MARGIN_HORIZONTAL,pdf.bounds.height / POS_CAL_VERTICAL], width: pdf.bounds.width - (EXTRA_MARGIN_HORIZONTAL * 2), height: pdf.bounds.height / POS_CAL_VERTICAL) do
    pdf.fill_color = "000000"
    pdf.text(MONTHS[month], align: :center, size: 24)
    
    col_width = pdf.bounds.width / 7
    row_height = (pdf.bounds.height - HEADLINE_SPACE) / 7
    
    
    pdf.bounding_box([0,pdf.bounds.height - HEADLINE_SPACE], :width => pdf.bounds.width) do
      
      DAYS.each_with_index do |day, i|
        pdf.bounding_box([i * col_width, pdf.bounds.height], :width => col_width, height: row_height) do
          pdf.fill_color = color(i > 4)
          pdf.text(day, align: :center, valign: :center)
        end
      end
      row = 0
      day = Date.new(YEAR, month + 1, 1)
      while (day.month == month+1) do
        weekday = day.wday - 1
        weekday = 6 if weekday < 0
        if weekday == 0 && day.day > 1
          row += 1
        end
        pdf.bounding_box([weekday * col_width, pdf.bounds.height - (row + 1) * row_height], :width => col_width, height: row_height) do
          pdf.fill_color = color(weekday > 4 || holidays.include?(day))
          pdf.text(day.day.to_s, align: :center, valign: :center)
        end
        day += 1
      end
    end
  end
  pdf.start_new_page if month < 11 
end
pdf.render_file('calendar.pdf')