permalink_fu.rb

begin
  require "active_support"
rescue LoadError
  require "rubygems"
  require "active_support"
end

module PermalinkFu

  def self.escape(str)
    if defined?(ActiveSupport::Multibyte::Chars)
      s = str.mb_chars.normalize(:kd)
    else
      begin
        s = ActiveSupport::Multibyte::Handlers::UTF8Handler.normalize(str.to_s, :kd)
      rescue ActiveSupport::Multibyte::Handlers::EncodingError
        require 'iconv'
        s = Iconv.iconv('ascii//translit//IGNORE', 'utf-8', str).first.to_s
      end
    end

    s.gsub!(/[^\w -]+/n, '')  # strip unwanted characters
    s.strip! # ohh la la
    s.downcase!
    s.gsub!(/[ -]+/, '-')  # separate by single dashes
    s
  end
  
  def self.included(base)
    base.extend ClassMethods
  end
  
  module ClassMethods
    # Specifies the given field(s) as a permalink, meaning it is passed through PermalinkFu.escape and set to the permalink_field.  This
    # is done
    #
    #   class Foo < ActiveRecord::Base
    #     # stores permalink form of #title to the #permalink attribute
    #     has_permalink :title
    #   
    #     # stores a permalink form of "#{category}-#{title}" to the #permalink attribute
    #   
    #     has_permalink [:category, :title]
    #   
    #     # stores permalink form of #title to the #category_permalink attribute
    #     has_permalink [:category, :title], :as => :category_permalink
    #
    #     # add a scope
    #     has_permalink :title, :scope => :blog_id
    #
    #     # add a scope and specify the permalink field name
    #     has_permalink :title, :as => :slug, :scope => :blog_id
    #   end
    #
    def has_permalink(*args)
      options = args.extract_options!
      attr_names = args.first || :to_s
      write_inheritable_attribute(:permalink_attributes,  Array(attr_names))
      write_inheritable_attribute(:permalink_field,       (options.delete(:as) || 'permalink').to_s)
      write_inheritable_attribute(:permalink_options,     options)

      %w{permalink_attributes permalink_field permalink_options}.each do |v|
        class_inheritable_reader(v.to_sym)
      end

      before_validation :create_unique_permalink
      evaluate_attribute_method permalink_field, "def #{self.permalink_field}=(new_value);write_attribute(:#{self.permalink_field}, PermalinkFu.escape(new_value));end", "#{self.permalink_field}="
      extend  PermalinkFinders

      case options[:param]
      when false
        # nothing
      when :permalink
        include ToParam
      else
        include ToParamWithID
      end
    end
  end
  
  module ToParam
    def to_param
      send(self.class.read_inheritable_attribute(:permalink_field))
    end
  end
  
  module ToParamWithID
    def to_param
      permalink = send(self.class.read_inheritable_attribute(:permalink_field))
      return super if new_record? || permalink.blank?
      "#{id}-#{permalink}"
    end
  end
  
  module PermalinkFinders
    def find_by_permalink(value)
      find(:first, :conditions => { permalink_field => value  })
    end
    
    def find_by_permalink!(value)
      find_by_permalink(value) ||
      raise(ActiveRecord::RecordNotFound, "Couldn't find #{name} with permalink #{value.inspect}")
    end
  end
  
protected
  def create_unique_permalink
    return unless should_create_permalink?
    if send(self.class.read_inheritable_attribute(:permalink_field)).to_s.empty?
      send("#{self.class.read_inheritable_attribute(:permalink_field)}=", create_permalink_for(self.class.read_inheritable_attribute(:permalink_attributes)))
    end
    
    limit   = self.class.columns_hash[self.class.read_inheritable_attribute(:permalink_field)].limit
    base    = send("#{self.class.read_inheritable_attribute(:permalink_field)}=", 
                   send(self.class.read_inheritable_attribute(:permalink_field))[0..limit - 1])
    
    return unless self.class.read_inheritable_attribute(:permalink_options)[:param]

    counter = 1
    # oh how i wish i could use a hash for conditions
    conditions = ["#{self.class.read_inheritable_attribute(:permalink_field)} = ?", base]
    unless new_record?
      conditions.first << " and id != ?"
      conditions       << id
    end
    if self.class.read_inheritable_attribute(:permalink_options)[:scope]
      conditions.first << " and #{self.class.read_inheritable_attribute(:permalink_options)[:scope]} = ?"
      conditions       << send(self.class.read_inheritable_attribute(:permalink_options)[:scope])
    end
    while self.class.exists?(conditions)
      suffix = "-#{counter += 1}"
      conditions[1] = "#{base[0..limit-suffix.size-1]}#{suffix}"
      send("#{self.class.read_inheritable_attribute(:permalink_field)}=", conditions[1])
    end
    send("#{self.class.read_inheritable_attribute(:permalink_field)}")
  end

  def create_permalink_for(attr_names)
    attr_names.collect { |attr_name| send(attr_name).to_s } * " "
  end

private
  def should_create_permalink?
    if self.class.read_inheritable_attribute(:permalink_options)[:if]
      evaluate_method(self.class.read_inheritable_attribute(:permalink_options)[:if])
    elsif self.class.read_inheritable_attribute(:permalink_options)[:unless]
      !evaluate_method(self.class.read_inheritable_attribute(:permalink_options)[:unless])
    else
      true
    end
  end

  def evaluate_method(method)
    case method
    when Symbol
      send(method)
    when String
      eval(method, instance_eval { binding })
    when Proc, Method
      method.call(self)
    end
  end
end