blocks_for helper

gistfile1.rb

# Iterates over an array and creates a bunch of "blocks" containing the
# yielded content. Example:
#
#   <% urls = [
#     "http://inventivelabs.com.au",
#     "http://booki.sh",
#     "http://nomify.com",
#     "http://rungs.com.au",
#     "http://getslipcase.com"
#   ] %>
#   <% blocks_for(urls, 2) do |url, pos| %>
#     <%= link_to(url, url) %>
#   <% end %>
#
#   ... produces ...
#
#   <div class="block_first">
#     <a href="http://inventivelabs.com.au">http://inventivelabs.com.au</a>
#     <a href="http://booki.sh">http://booki.sh</a>
#   </div>
#   <div>
#     <a href="http://nomify.com">http://nomify.com</a>
#     <a href="http://rungs.com.au">http://rungs.com.au</a>
#   </div>
#   <div class="block_last">
#     <a href="http://getslipcase.com">http://getslipcase.com</a>
#   </div>
#
#
# Options:
#
#    - :block_tag (defaults to "div")
#    - :first_block_class (defaults to "block_first")
#    - :last_block_class (defaults to "block_last")
#
# All other options are passed directly to block tag.
#
# Yielded to block:
#
#   |obj, pos, index|
#
# ... where 'pos' is an object you can interrogate like this:
#
#   pos.first? -> true if first object in the block
#   pos.last? -> true if the per-block-th object in the block
#   pos.middle? -> true if not first or last object in the block
#
# Not that if per-block is say, 6, and the array is 20 items long, the
# last block will contain 2 objects -- no object will have pos.last? in
# this block.
#
def blocks_for(array, per_block, options = {}, &blk)
  options = options.with_indifferent_access

  block_tag = options.delete(:block_tag) || "div"
  first_class = options.delete(:first_block_class) || "block_first"
  first_class += " #{options[:class]}"
  last_class = options.delete(:last_block_class) || "block_last"
  last_class += " #{options[:class]}"

  blocks = []
  bits = []

  new_block = lambda { |cursor|
    opts = options
    if cursor < per_block
      opts = opts.merge(:class => first_class.strip)
    elsif cursor > (array.size - per_block)
      opts = opts.merge(:class => last_class.strip)
    end
    blocks << content_tag(block_tag, bits.join("\n"), opts)
    bits = []
  }

  array.each_with_index { |obj, i|
    mod_i = i % per_block
    pos = ActiveSupport::StringInquirer.new(
      mod_i == 0 ? "first" : mod_i == per_block - 1 ? "last" : "middle"
    )
    bits << capture(obj, pos, mod_i, &blk)
    new_block.call(i)  if pos.last?
  }
  new_block.call(array.size - 1)  if bits.any?

  concat(blocks.join("\n"))
end