Encoding and decoding

Gemfile.lock

@@ -0,0 +1,24 @@
+PATH
+  remote: .
+  specs:
+    polylines (0.0.1)
+
+GEM
+  remote: http://rubygems.org/
+  specs:
+    diff-lcs (1.1.2)
+    rspec (2.4.0)
+      rspec-core (~> 2.4.0)
+      rspec-expectations (~> 2.4.0)
+      rspec-mocks (~> 2.4.0)
+    rspec-core (2.4.0)
+    rspec-expectations (2.4.0)
+      diff-lcs (~> 1.1.2)
+    rspec-mocks (2.4.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  polylines!
+  rspec (= 2.4.0)

Rakefile

@@ -1,2 +1,12 @@
+require "rake"
+require "rake/tasklib"
 require 'bundler'
 Bundler::GemHelper.install_tasks
+
+Bundler.require
+
+require "rspec/core/rake_task"
+
+RSpec::Core::RakeTask.new(:rspec)
+
+task :default => [:rspec]

lib/polylines.rb

@@ -1,3 +1,4 @@
 module Polylines
-  # Your code goes here...
+  autoload :Encoder, "polylines/encoder"
+  autoload :Decoder, "polylines/decoder"
 end

lib/polylines/decoder.rb

@@ -0,0 +1,84 @@
+module Polylines
+  class Decoder
+    def self.decode_polyline(polyline)
+      set = []
+
+      points_with_deltas = polyline.split(//).inject([]) do |charset, char|
+        set << char
+
+        if ((char[0] - 63) & 0x20) == 0
+          charset << set.join
+          set = []
+        end
+
+        charset
+      end.map {|set| decode(set) }
+
+      points = [[points_with_deltas.shift, points_with_deltas.shift]]
+
+      while points_with_deltas.any?
+        new_latitude  = points.last[0] + points_with_deltas.shift
+        new_longitude = points.last[1] + points_with_deltas.shift
+        points << [new_latitude, new_longitude]
+      end
+
+      points
+    end
+
+    def self.decode(string)
+      decimal_values  = step_11(string)
+      decimal_values  = step_10(decimal_values)
+      xord_values     = step_8(decimal_values)
+      five_bit_chunks = step_7(xord_values)
+      binary_string   = step_6(five_bit_chunks)
+
+      negative = binary_string[-1, 1] == "1"
+
+      number = binary_string.to_i(2)
+      number = step_5(number) if negative
+      number = step_4(number)
+      number = step_3(number) if negative
+      step_2(number)
+    end
+
+    def self.step_2(number)
+      number.to_f/1e5
+    end
+
+    def self.step_3(number)
+      number -= 1
+      number = ~number
+      number *= -1
+    end
+
+    def self.step_4(number)
+      number >> 1
+    end
+
+    def self.step_5(number)
+      ~number
+    end
+
+    def self.step_6(five_bit_chunks)
+      five_bit_chunks.map do |chunk|
+        "%05b" % chunk
+      end.join
+    end
+
+    def self.step_7(five_bit_chunks)
+      five_bit_chunks.reverse
+    end
+
+    def self.step_8(decimal_values)
+      decimal_values[0..-2].map {|value| 0x20 ^ value } << decimal_values.last
+    end
+
+    def self.step_10(values)
+      values.map {|value| value - 63 }
+    end
+
+    def self.step_11(string)
+      string.split(//).map {|char| char[0] }
+    end
+  end
+end

lib/polylines/encoder.rb

@@ -0,0 +1,72 @@
+module Polylines
+  class Encoder
+    def self.encode_points(points)
+      delta_latitude, delta_longitude = 0, 0
+
+      points.inject([]) do |polyline, (latitude, longitude)|
+        polyline << encode(latitude - delta_latitude)
+        polyline << encode(longitude - delta_longitude)
+        delta_latitude, delta_longitude = latitude, longitude
+        polyline
+      end.join
+    end
+
+    def self.encode(number)
+      negative = number < 0
+      number = step_2(number)
+      number = step_3(number) if negative
+      number = step_4(number)
+      number = step_5(number) if negative
+
+      five_bit_chunks = step_6(number)
+      five_bit_chunks = step_7(five_bit_chunks)
+      ord_values      = step_8(five_bit_chunks)
+      decimal_values  = step_10(ord_values)
+
+      step_11(decimal_values)
+    end
+
+    def self.step_2(number)
+      (number * 1e5).round
+    end
+
+    def self.step_3(number)
+      number *= -1
+      number = ~number
+      number += 1
+    end
+
+    def self.step_4(number)
+      number << 1
+    end
+
+    def self.step_5(number)
+      ~number
+    end
+
+    def self.step_6(number)
+      [].tap do |numbers|
+        while number > 0 do
+          numbers.unshift(number & 0x1f)
+          number = number >> 5
+        end
+      end
+    end
+
+    def self.step_7(five_bit_chunks)
+      five_bit_chunks.reverse
+    end
+
+    def self.step_8(five_bit_chunks)
+      five_bit_chunks[0..-2].map {|chunk| 0x20 | chunk } << five_bit_chunks.last
+    end
+
+    def self.step_10(values)
+      values.map {|value| value + 63 }
+    end
+
+    def self.step_11(values)
+      values.map(&:chr).join
+    end
+  end
+end

polylines.gemspec

@@ -15,4 +15,6 @@ Gem::Specification.new do |s|
   s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
   s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
   s.require_paths = ["lib"]
+
+  s.add_development_dependency("rspec", "2.4.0")
 end

spec/polylines/decoder_spec.rb

@@ -0,0 +1,16 @@
+require "spec_helper"
+
+describe Polylines::Decoder, ".decode" do
+  it "decodes a single point" do
+    Polylines::Decoder.decode("`~oia@").should be_within(0.00001).of(-179.9832104)
+  end
+end
+
+describe Polylines::Decoder, ".decode_polyline" do
+  let(:polyline) { "_p~iF~ps|U_ulLnnqC_mqNvxq`@" }
+  let(:points)   { [[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]] }
+
+  it "decodes a polyline correctly" do
+    Polylines::Decoder.decode_polyline(polyline).should == points
+  end
+end

spec/polylines/encoder_spec.rb

@@ -0,0 +1,16 @@
+require "spec_helper"
+
+describe Polylines::Encoder, ".encode" do
+  it "encodes a single point" do
+    Polylines::Encoder.encode(-179.9832104).should == "`~oia@"
+  end
+end
+
+describe Polylines::Encoder, ".encode_points" do
+  let(:polyline) { "_p~iF~ps|U_ulLnnqC_mqNvxq`@" }
+  let(:points)   { [[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]] }
+
+  it "encodes points correctly" do
+    Polylines::Encoder.encode_points(points).should == polyline
+  end
+end

spec/spec_helper.rb

@@ -0,0 +1,7 @@
+require "rubygems"
+require "bundler/setup"
+
+require "polylines"
+# 
+# RSpec.configure do |config|
+# end