articles_helper.rb

module ArticlesHelper
  def tag_popularity_as_hex(tag_count)
    # must use floats
    # most saturated colour possible, used for a highly used tag
    max_r = 255.0
    max_g = 0.0
    max_b = 0.0

    # least saturated colour possible, used for tags that are rarely used
    min_r = 255.0
    min_g = 255.0
    min_b = 255.0

    # percentage of times this tag has been used
    total_tag_count = 0.0
    Article.all_tag_counts.each do |tag|
      total_tag_count += tag.count
    end
    tag_dominance = (tag_count / total_tag_count * 100)

    # we find the distance between each value, i.e. between 100% and 1%
    range_r = min_r - max_r
    range_g = min_g - max_g
    range_b = min_b - max_b

    # then find 1% of each range
    one_r = range_r / 100
    one_g = range_g / 100
    one_b = range_b / 100

    # now we can calculate the rgb values
    red   = (one_r * tag_dominance) + max_r
    green = (one_g * tag_dominance) + max_g
    blue  = (one_b * tag_dominance) + max_b

    # we then multiply the one percent of the range by the tag percentage and add the original value back in
    hex = "#%02x%02x%02x" % [red, green, blue]
  end
end