geocoder.rb

require "geocoder/calculations"
require "geocoder/lookup"

##
# Add geocoding functionality to any object.
#
module Geocoder

  ##
  # Implementation of 'included' hook method.
  #
  def self.included(base)
    base.extend ClassMethods
    base.class_eval do

      # scope: geocoded objects
      scope :geocoded,
        :conditions => "#{geocoder_options[:latitude]} IS NOT NULL " +
          "AND #{geocoder_options[:longitude]} IS NOT NULL"

      # scope: not-geocoded objects
      scope :not_geocoded,
        :conditions => "#{geocoder_options[:latitude]} IS NULL " +
          "OR #{geocoder_options[:longitude]} IS NULL"

      ##
      # Find all objects within a radius (in miles) of the given location
      # (address string). Location (the first argument) may be either a string
      # to geocode or an array of coordinates (<tt>[lat,long]</tt>).
      #
      scope :near, lambda{ |location, *args|
        latitude, longitude = location.is_a?(Array) ?
          location : Geocoder::Lookup.coordinates(location)
        if latitude and longitude
          near_scope_options(latitude, longitude, *args)
        else
          {}
        end
      }
    end
  end

  ##
  # Methods which will be class methods of the including class.
  #
  module ClassMethods

    ##
    # Get options hash suitable for passing to ActiveRecord.find to get
    # records within a radius (in miles) of the given point.
    # Options hash may include:
    #
    # +units+   :: <tt>:mi</tt> (default) or <tt>:km</tt>
    # +exclude+ :: an object to exclude (used by the #nearbys method)
    # +order+   :: column(s) for ORDER BY SQL clause
    # +limit+   :: number of records to return (for LIMIT SQL clause)
    # +offset+  :: number of records to skip (for OFFSET SQL clause)
    # +select+  :: string with the SELECT SQL fragment (e.g. “id, name”)
    #
    def near_scope_options(latitude, longitude, radius = 20, options = {})
      radius *= Geocoder::Calculations.km_in_mi if options[:units] == :km
      if ActiveRecord::Base.connection.adapter_name == "SQLite"
        approx_near_scope_options(latitude, longitude, radius, options)
      else
        full_near_scope_options(latitude, longitude, radius, options)
      end
    end


    private # ----------------------------------------------------------------

    ##
    # Scope options hash for use with a database that supports POWER(),
    # SQRT(), PI(), and trigonometric functions (SIN(), COS(), and ASIN()).
    #
    # Taken from the excellent tutorial at:
    # http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL
    #
    def full_near_scope_options(latitude, longitude, radius, options)
      lat_attr = geocoder_options[:latitude]
      lon_attr = geocoder_options[:longitude]
      distance = "3956 * 2 * ASIN(SQRT(" +
        "POWER(SIN((#{latitude} - #{lat_attr}) * " +
        "PI() / 180 / 2), 2) + COS(#{latitude} * PI()/180) * " +
        "COS(#{lat_attr} * PI() / 180) * " +
        "POWER(SIN((#{longitude} - #{lon_attr}) * " +
        "PI() / 180 / 2), 2) ))"
      options[:order] ||= "#{distance} ASC"
      default_near_scope_options(latitude, longitude, radius, options).merge(
        :select => "#{options[:select] || '*'}, #{distance} AS distance",
        :having => "#{distance} <= #{radius}"
      )
    end

    ##
    # Scope options hash for use with a database without trigonometric
    # functions, like SQLite. Approach is to find objects within a square
    # rather than a circle, so results are very approximate (will include
    # objects outside the given radius).
    #
    def approx_near_scope_options(latitude, longitude, radius, options)
      default_near_scope_options(latitude, longitude, radius, options).merge(
        :select => options[:select] || nil
      )
    end

    ##
    # Options used for any near-like scope.
    #
    def default_near_scope_options(latitude, longitude, radius, options)
      lat_attr = geocoder_options[:latitude]
      lon_attr = geocoder_options[:longitude]
      conditions = \
        ["#{lat_attr} BETWEEN ? AND ? AND #{lon_attr} BETWEEN ? AND ?"] +
        coordinate_bounds(latitude, longitude, radius)
      if obj = options[:exclude]
        conditions[0] << " AND id != ?"
        conditions << obj.id
      end
      {
        :group  => columns.map{ |c| "#{table_name}.#{c.name}" }.join(','),
        :order  => options[:order],
        :limit  => options[:limit],
        :offset => options[:offset],
        :conditions => conditions
      }
    end

    ##
    # Get the rough high/low lat/long bounds for a geographic point and
    # radius. Returns an array: <tt>[lat_lo, lat_hi, lon_lo, lon_hi]</tt>.
    # Used to constrain search to a (radius x radius) square.
    #
    def coordinate_bounds(latitude, longitude, radius)
      radius = radius.to_f
      factor = (Math::cos(latitude * Math::PI / 180.0) * 69.0).abs
      [
        latitude  - (radius / 69.0),
        latitude  + (radius / 69.0),
        longitude - (radius / factor),
        longitude + (radius / factor)
      ]
    end
  end

  ##
  # Read the coordinates [lat,lon] of an object. This is not great but it
  # seems cleaner than polluting the instance method namespace.
  #
  def read_coordinates
    [:latitude, :longitude].map{ |i| send self.class.geocoder_options[i] }
  end

  ##
  # Is this object geocoded? (Does it have latitude and longitude?)
  #
  def geocoded?
    read_coordinates.compact.size > 0
  end

  ##
  # Calculate the distance from the object to a point (lat,lon).
  #
  # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
  #
  def distance_to(lat, lon, units = :mi)
    return nil unless geocoded?
    mylat,mylon = read_coordinates
    Geocoder::Calculations.distance_between(mylat, mylon, lat, lon, :units => units)
  end

  ##
  # Get other geocoded objects within a given radius.
  #
  # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
  #
  def nearbys(radius = 20, units = :mi)
    return [] unless geocoded?
    options = {:exclude => self, :units => units}
    self.class.near(read_coordinates, radius, options)
  end

  ##
  # Fetch coordinates and assign +latitude+ and +longitude+. Also returns
  # coordinates as an array: <tt>[lat, lon]</tt>.
  #
  def fetch_coordinates(save = false)
    coords = Geocoder::Lookup.coordinates(
      send(self.class.geocoder_options[:method_name])
    )
    unless coords.blank?
      method = (save ? "update" : "write") + "_attribute"
      send method, self.class.geocoder_options[:latitude],  coords[0]
      send method, self.class.geocoder_options[:longitude], coords[1]
    end
    coords
  end

  ##
  # Fetch coordinates and update (save) +latitude+ and +longitude+ data.
  #
  def fetch_coordinates!
    fetch_coordinates(true)
  end
end

##
# Add geocoded_by method to ActiveRecord::Base so Geocoder is accessible.
#
ActiveRecord::Base.class_eval do

  ##
  # Set attribute names and include the Geocoder module.
  #
  def self.geocoded_by(method_name = :location, options = {})
    class_inheritable_reader :geocoder_options
    write_inheritable_attribute :geocoder_options, {
      :method_name => method_name,
      :latitude    => options[:latitude]  || :latitude,
      :longitude   => options[:longitude] || :longitude
    }
    include Geocoder
  end
end