fixed_row.rb

require "date"
require "time"

class FixedRow
  attr_accessor :formats
  
  def initialize
    @columns = []
    @formats = {
      :datetime => lambda {|x| Date.parse(x) }
    }
    @data = {}
    
    yield(self) if block_given?
  end
  
  # Define a column to parse out
  # <b>Name</b>: name of column. Eg: <tt>:first</tt>
  # <b>Range</b>: Array of starting element and length of substring. <tt>Eg: [0, 5]</tt>
  # <b>parse_block</b>: block takes one param and returns Object to store for column.
  # Eg: <tt>{|col| Date.parse(col) }</tt>
  # 
  def column name, range, type=nil, &parse_block
    rf = {:name => name, :range => range, :type => type}
    rf[:block] = parse_block if block_given?
    @columns << rf
  end
  
  # Parse the actual row into columns
  # Raises RuntimeError if a block raises an error.
  def parse text
    @columns.each do |r|
      # Pull out the sub string
      substr = text[*r[:range]]
      # See if theres a type
      if r.has_key?(:type) && @formats.has_key?(r[:type])
        substr = @formats[r[:type]].call(text)
      # Check if there's a block
      elsif r.has_key?(:block)
        # Make sure we catch any errors in the block
        begin
          substr = r[:block].call(substr)
        rescue Exception => e
          raise "Error parsing col '#{r[:name].inspect}': #{e.message}"
        end
      end
      # 
      @data[r[:name]] = substr
    end
  end
    
  # Return the data for the column name.
  # Returns nil if column unknown.
  def get col_name
    @data[col_name]
  end
  
  # Lets us grab columns as if they were attributes of the object
  def method_missing(name, *args)
    self.get(name) || super
  end
end

# Define the columns when creating the object
a = FixedRow.new do |r|
  r.column :first, [0, 5]
  r.column :last, [6, 7]
end

# Or add them afterwards
a.column(:dob, [14, 10], :datetime)
a.column(:time, [25, 5]) {|x| Time.parse(x) }


a.parse("caius durling 1987-11-09 15:15")

a.get(:first) # => "caius"
a.first       # => "caius"
a.get(:last)  # => "durling"
a.last        # => "durling"
a.get(:dob)   # => #<Date: 4894217/2,0,2299161>
a.dob         # => #<Date: 4894217/2,0,2299161>
a.get(:dob).to_s # => "1987-11-09"
a.time        # => Wed Mar 18 15:15:00 +0000 2009
a.get(:"doesn't exist") # => nil
a.whoop! # => 
# ~> -:60:in `method_missing': undefined method `whoop!' for #<FixedRow:0x7c948> (NoMethodError)
# ~> 	from -:86