Wraps call to api endpoint for returning objects for a map based on some parameters.

circles_controller.rb

class Api::CirclesController < ApplicationController
  def index
    circles_presenter = API::CirclesPresenter.new(params)
    render :json => circles_presenter.to_json,
           :callback => params[:callback]
  end
end

circles_presenter.rb

class API::CirclesPresenter
  extend ActiveSupport::Memoizable

  def initialize(params={})
    @ne   = params[:ne]
    @sw   = params[:sw]
    @pt   = params[:pt]
    @rad  = params[:rad]
  end
  attr_accessor :ne, :sw, :pt, :rad

  def as_json
    { :circles => circles, :count => count }
  end

  def to_json
    Rails.cache.fetch(cache_key, :expires_in => expires_in) do
      as_json.to_json
    end
  end

  def circles
    circles = if bounding_box?
      Circle.all_in_bounding_box(sw, ne)
    elsif point_and_radius?
      Circle.all_in_radius(pt, rad)
    else
      Circle.all
    end
    circles.map{|c| API::CirclePresenter.new(c).as_json}
  end
  memoize :circles

  def count
    if bounding_box?
      Circle.count_in_bounding_box(sw, ne)
    elsif point_and_radius?
      Circle.count_in_radius(pt, rad)
    else
      Circle.count
    end
  end
  memoize :count

  def cache_key
    pieces = ['circles']
    if bounding_box?
      pieces << 'ne' << ne
      pieces << 'sw' << sw
    elsif point_and_radius?
      pieces << 'pt' << pt
      pieces << 'rad' << rad
    else
      pieces << 'all'
    end
    pieces.join('/')
  end

  def bounding_box?
    ne && sw
  end

  def point_and_radius?
    pt && rad
  end

  def expires_in
    if bounding_box? || point_and_radius?
      1.hour
    else
      nil
    end
  end
end