# require 'forwardable'

module Geokit
  # Contains class and instance methods providing distance calcuation services.
  # This module is meant to be mixed into classes containing lat and lng
  # attributes where distance calculation is desired.
  #
  # At present, two forms of distance calculations are provided:
  #
  # * Pythagorean Theory (flat Earth) - which assumes the world is flat and
  #   loses accuracy over long distances.
  # * Haversine (sphere) - which is fairly accurate, but at a performance cost.
  #
  # Distance units supported are :miles, :kms, and :nms.
  module Mappable
    # Mix below class methods into the includer.
    def self.included(receiver) # :nodoc:
      receiver.extend ClassMethods
    end

    module ClassMethods #:nodoc:
      PI_DIV_RAD = Math::PI / 180
      EARTH_RADIUS_IN_METERS = 6_376_772.71
      METERS_PER_LATITUDE_DEGREE = 111_181.9

      EARTH_RADIUS = {}
      PER_LATITUDE_DEGREE = {}

      # Returns the distance between two points.  The from and to parameters are
      # required to have lat and lng attributes.  Valid options are:
      # :units - valid values are :miles, :kms, :nms
      # (Geokit::default_units is the default)
      # :formula - valid values are :flat or :sphere
      # (Geokit::default_formula is the default)
      def distance_between(from, to, options = {})
        units = get_units!(options)
        from  = Geokit::LatLng.normalize(from)
        to    = Geokit::LatLng.normalize(to)
        return 0.0 if from == to # fixes a "zero-distance" bug

        formula = options[:formula] || Geokit.default_formula
        case formula
        when :sphere then distance_between_sphere(from, to, units)
        when :flat   then distance_between_flat(from, to, units)
        end
      end

      def distance_between_sphere(from, to, units)
        lat_sin = Math.sin(deg2rad(from.lat)) * Math.sin(deg2rad(to.lat))
        lat_cos = Math.cos(deg2rad(from.lat)) * Math.cos(deg2rad(to.lat))
        lng_cos = Math.cos(deg2rad(to.lng) - deg2rad(from.lng))
        units_sphere_multiplier(units) * Math.acos(lat_sin + lat_cos * lng_cos)
      rescue *math_error_classes
        0.0
      end

      def distance_between_flat(from, to, units)
        lat_length = units_per_latitude_degree(units) * (from.lat - to.lat)
        lng_length = units_per_longitude_degree(from.lat, units) *
                     (from.lng - to.lng)
        Math.sqrt(lat_length**2 + lng_length**2)
      end

      # Ruby 1.9 raises {Math::DomainError}, but it is not defined in Ruby 1.8
      def math_error_classes
        return [Errno::EDOM, Math::DomainError] if defined?(Math::DomainError)
        [Errno::EDOM]
      end

      # Returns heading in degrees (0 is north, 90 is east, 180 is south, etc)
      # from the first point to the second point. Typicaly, the instance methods
      # will be used instead of this method.
      def heading_between(from, to)
        from = Geokit::LatLng.normalize(from)
        to = Geokit::LatLng.normalize(to)

        d_lng = deg2rad(to.lng - from.lng)
        from_lat = deg2rad(from.lat)
        to_lat = deg2rad(to.lat)
        y = Math.sin(d_lng) * Math.cos(to_lat)
        x = Math.cos(from_lat) * Math.sin(to_lat) -
            Math.sin(from_lat) * Math.cos(to_lat) * Math.cos(d_lng)
        to_heading(Math.atan2(y, x))
      end

      # Given a start point, distance, and heading (in degrees), provides
      # an endpoint. Returns a LatLng instance. Typically, the instance method
      # will be used instead of this method.
      def endpoint(start, heading, distance, options = {})
        units   = get_units!(options)
        ratio   = distance.to_f / units_sphere_multiplier(units)
        start   = Geokit::LatLng.normalize(start)
        lat     = deg2rad(start.lat)
        lng     = deg2rad(start.lng)
        heading = deg2rad(heading)

        sin_ratio = Math.sin(ratio)
        cos_ratio = Math.cos(ratio)
        sin_lat = Math.sin(lat)
        cos_lat = Math.cos(lat)

        end_lat = Math.asin(sin_lat * cos_ratio +
                            cos_lat * sin_ratio * Math.cos(heading))

        end_lng = lng + Math.atan2(Math.sin(heading) * sin_ratio * cos_lat,
                                   cos_ratio - sin_lat * Math.sin(end_lat))

        LatLng.new(rad2deg(end_lat), rad2deg(end_lng))
      end

      # Returns the midpoint, given two points. Returns a LatLng.
      # Typically, the instance method will be used instead of this method.
      # Valid option:
      #   :units - valid values are :miles, :kms, or :nms
      #   (:miles is the default)
      def midpoint_between(from, to, options = {})
        from = Geokit::LatLng.normalize(from)

        heading = from.heading_to(to)
        distance = from.distance_to(to, options)
        from.endpoint(heading, distance / 2, options)
      end

      # Geocodes a location using the multi geocoder.
      def geocode(location, options = {})
        res = Geocoders::MultiGeocoder.geocode(location, options)
        return res if res.success?
        raise Geokit::Geocoders::GeocodeError
      end

      # Given a decimal degree like -87.660333
      # return a 3-element array like [ -87, 39, 37.198... ]
      def decimal_to_dms(deg)
        return false unless deg.is_a?(Numeric)
        # seconds is 0...3599.999, representing the entire fractional part.
        seconds = (deg.abs % 1.0) * 3600.0
        [
          deg.to_i,               # degrees as positive or negative integer
          (seconds / 60).to_i,    # minutes as positive integer
          (seconds % 60)          # seconds as positive float
        ]
      end

      def deg2rad(degrees)
        degrees.to_f / 180.0 * Math::PI
      end

      def rad2deg(rad)
        rad.to_f * 180.0 / Math::PI
      end

      def to_heading(rad)
        (rad2deg(rad) + 360) % 360
      end

      def self.register_unit(key, in_meters)
        EARTH_RADIUS[key] = EARTH_RADIUS_IN_METERS * in_meters
        PER_LATITUDE_DEGREE[key] = METERS_PER_LATITUDE_DEGREE * in_meters
      end

      register_unit :meters, 1
      register_unit :kms,   1 / 1000.0
      register_unit :miles, 1 / 1609.0
      register_unit :nms,   0.0005400722448725917

      # Returns the multiplier used to obtain the correct distance units.
      # TODO: make more accurate by coping
      # http://msi.nga.mil/MSISiteContent/StaticFiles/Calculators/degree.html
      def units_sphere_multiplier(units)
        EARTH_RADIUS[units]
      end

      # Returns the number of units per latitude degree.
      def units_per_latitude_degree(units)
        PER_LATITUDE_DEGREE[units]
      end

      # Returns the number units per longitude degree.
      def units_per_longitude_degree(lat, units)
        units_sphere_multiplier(units) * Math.cos(lat * PI_DIV_RAD) * PI_DIV_RAD
      end

      # Extracts units from options. Returns Geokit::default_units when not present.
      # Raise an exception when given unsupported unit of length
      def get_units!(options = {})
        units = options[:units]
        units = Geokit.default_units if units.nil?
        [:miles, :kms, :meters, :nms].include?(units) or
          raise ArgumentError, "#{units} is an unsupported unit of length."
        units
      end
    end

    # -----------------------------------------------------------------------------------------------
    # Instance methods below here
    # -----------------------------------------------------------------------------------------------

    # Extracts a LatLng instance. Use with models that are acts_as_mappable
    def to_lat_lng
      if instance_of?(Geokit::LatLng) || instance_of?(Geokit::GeoLoc)
        return self
      end
      lat = send(self.class.lat_column_name)
      lng = send(self.class.lng_column_name)
      LatLng.new(lat, lng)
    end

    # Returns the distance from another point.  The other point parameter is
    # required to have lat and lng attributes.  Valid options are:
    # :units - valid values are :miles, :kms, :or :nms (:miles is the default)
    # :formula - valid values are :flat or :sphere (:sphere is the default)
    def distance_to(other, options = {})
      self.class.distance_between(self, other, options)
    end
    alias_method :distance_from, :distance_to

    # Returns heading in degrees (0 is north, 90 is east, 180 is south, etc) to
    # the given point. The given point can be a LatLng or a string to be
    # Geocoded
    def heading_to(other)
      self.class.heading_between(self, other)
    end

    # Returns heading in degrees (0 is north, 90 is east, 180 is south, etc)
    # FROM the given point. The given point can be a LatLng or a string to be
    # Geocoded
    def heading_from(other)
      self.class.heading_between(other, self)
    end

    # Returns the endpoint, given a heading (in degrees) and distance.
    # Valid option:
    # :units - valid values are :miles, :kms, or :nms (:miles is the default)
    def endpoint(heading, distance, options = {})
      self.class.endpoint(self, heading, distance, options)
    end

    # Returns the midpoint, given another point on the map.
    # Valid option:
    # :units - valid values are :miles, :kms, or :nms (:miles is the default)
    def midpoint_to(other, options = {})
      self.class.midpoint_between(self, other, options)
    end
  end
end