module Geocluster

# File lib/geocluster.rb, line 14
def cluster_coordinates(coordinates, options = {})
  # Set default options
  options = {
    :precision => 3, # the higher, the finer the clusters will be
    :limit => nil,   # max number of returned clusters; set to nil to get all
    :nucleus => true # if true, centers clusters over where most of its coordinates are; if false, centers clusters geographically among all coordinates it absorbs
  }.merge!(options)

  # Convert coordinates into geohashes to easily find neighboring coordinates
  geohashes = coordinates.map{ |c| GeoHash.encode(c.first, c.last, 24) }
  # ["u33dc0cpnnf4", "u281zd9xrtww", "u1hcy2ukdhpb", "u1hg6jsr0znd", "u33616p4rb8v", "u0vug9dwefde", "u0yjjd6jk0yv"]

  # Get stripped to first {precision} chars and unique
  # coordinates; these are the keys for a temporary hash
  cut_hashes = geohashes.map{ |h| h[0..options[:precision] - 1]}
  keys = cut_hashes.uniq
  # ["u33", "u28", "u1h", "u0v", "u0y"]

  # Get occurences count for keys
  values = keys.map{ |h| cut_hashes.count(h)}
  # [2, 1, 2, 1, 1]

  # Convert keys and values to hash which
  # associates geo-clusters with coodinates count
  clusters_hash = Hash[keys.zip(values)]
  # {"u33"=>2, "u28"=>1, "u1h"=>2, "u0v"=>1, "u0y"=>1}

  # Sort by count desc (turns clusters into an
  # array); at this point, we have all clusters and
  # the number of coodinates per cluster
  clusters = clusters_hash.sort_by{ |key, value| value }.reverse
  # [["u33", 2], ["u1h", 2], ["u0v", 1], ["u28", 1], ["u0y", 1]]

  # Only take into account up until limit
  unless options[:limit].nil?
    clusters = clusters[0..options[:limit] - 1]
  end

  # Iterate over clusters and find center
  # (either geographical or nucleus)
  coordinates_with_counts = []
  if options[:nucleus] == true
    clusters.each do |cluster|
      # Select geohashes from cluster matching the first {precision} chars
      select_hashes = geohashes.select{ |g| g[0..options[:precision] - 1] == cluster.first }
      
      # Get array of associations between select hash and no. of occurences of that select hash in cluster
      select_hashes_with_counts = select_hashes.map{ |s| { "#{s}" => select_hashes.count(s) } }

      # Get select hash with the most occurences in cluster and add to all top coordinates in clusters
      # Calculating the geographic center is needed because Geohash.decode returns a geo-square
      top_hash = select_hashes_with_counts.sort_by{ |hash| hash.values.first }.reverse.first.keys.first
      coordinates_with_counts << { :coordinates => Geocoder::Calculations.geographic_center(GeoHash.decode(top_hash)), :count => cluster.last }
    end
  else
    clusters.each do |cluster|
      # Select geohashes from cluster matching the first {precision} chars
      select_hashes = geohashes.select{ |g| g[0..options[:precision] - 1] == cluster.first }

      # Transform geohashes into coordinates
      select_coordinates = select_hashes.map{ |s| Geocoder::Calculations.geographic_center(GeoHash.decode(s)) }

      # Calculate geographical center of all coordinates in this cluster and assign to array of all centers
      # Calculating the geographic center is needed because Geohash.decode returns a geo-square
      centered_coordinates_pair = Geocoder::Calculations.geographic_center(select_coordinates)
      coordinates_with_counts << { :coordinates => centered_coordinates_pair, :count => cluster.last }
    end
  end

  # At this point, coordinates_with_counts looks like
  # [{:coordinates => [33.83140579999999, -118.2820165], :count => 7}, { :coordinates => [52.52000659999998, 13.404954000000002], :count => 2}]
  # In this example, seven coordinates in cluster one, two coordinates in cluster two
  coordinates_with_counts
end