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

    ##
    # 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)
      address_method = self.class.geocoder_options[:user_address]
      unless address_method.is_a? Symbol
        raise Geocoder::ConfigurationError,
          "You are attempting to fetch coordinates but have not specified " +
          "a method which provides an address for the object."
      end
      coords = Geocoder::Lookup.coordinates(send(address_method))
      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

    ##
    # Fetch address and assign +address+ attribute. Also returns
    # address as a string.
    #
    def fetch_address(save = false)
      lat_attr = self.class.geocoder_options[:latitude]
      lon_attr = self.class.geocoder_options[:longitude]
      unless lat_attr.is_a?(Symbol) and lon_attr.is_a?(Symbol)
        raise Geocoder::ConfigurationError,
          "You are attempting to fetch an address but have not specified " +
          "attributes which provide coordinates for the object."
      end
      address = Geocoder::Lookup.address(send(lat_attr), send(lon_attr))
      unless address.blank?
        method = (save ? "update" : "write") + "_attribute"
        send method, self.class.geocoder_options[:fetched_address], address
      end
      address
    end

    ##
    # Fetch address and update (save) +address+ data.
    #
    def fetch_address!
      fetch_address(true)
    end
  end
end