Add support for specifying the output length

lib/scatter_swap.rb

@@ -2,11 +2,11 @@
 require "scatter_swap/hasher"
 
 module ScatterSwap
-  def self.hash(plain_integer, spin = 0)
-    Hasher.new(plain_integer, spin).hash
+  def self.hash(plain_integer, spin = 0, length = 10)
+    Hasher.new(plain_integer, spin, length).hash
   end
 
-  def self.reverse_hash(hashed_integer, spin = 0)
-    Hasher.new(hashed_integer, spin).reverse_hash
+  def self.reverse_hash(hashed_integer, spin = 0, length = 10)
+    Hasher.new(hashed_integer, spin, length).reverse_hash
   end
 end

lib/scatter_swap/hasher.rb

@@ -2,14 +2,15 @@ module ScatterSwap
   class Hasher
     attr_accessor :working_array
 
-    def initialize(original_integer, spin = 0)
+    def initialize(original_integer, spin = 0, length = 10)
       @original_integer = original_integer
       @spin = spin
-      zero_pad = original_integer.to_s.rjust(10, '0')
+      @length = length
+      zero_pad = original_integer.to_s.rjust(length, '0')
       @working_array = zero_pad.split("").collect {|d| d.to_i}
     end
 
-    # obfuscates an integer up to 10 digits in length
+    # obfuscates an integer up to @length digits in length
     def hash
       swap
       scatter
@@ -50,12 +51,12 @@ def unswap
       end
     end
 
-    # Rearrange the order of each digit in a reversable way by using the 
+    # Rearrange the order of each digit in a reversable way by using the
     # sum of the digits (which doesn't change regardless of order)
     # as a key to record how they were scattered
     def scatter
       sum_of_digits = @working_array.inject(:+).to_i
-      @working_array = 10.times.collect do 
+      @working_array = @length.times.collect do
         @working_array.rotate!(spin ^ sum_of_digits).pop
       end
     end
@@ -65,8 +66,8 @@ def unscatter
       scattered_array = @working_array
       sum_of_digits = scattered_array.inject(:+).to_i
       @working_array = []
-      @working_array.tap do |unscatter| 
-        10.times do
+      @working_array.tap do |unscatter|
+        @length.times do
           unscatter.push scattered_array.pop
           unscatter.rotate! (sum_of_digits ^ spin) * -1
         end

spec/scatter_swap_spec.rb

@@ -2,12 +2,19 @@
 require 'scatter_swap'
 
 describe "#hash" do
-  it "should be 10 digits" do
+  it "should be 10 digits by default" do
     100.times do |integer|
       ScatterSwap.hash(integer).to_s.length.should == 10
     end
   end
 
+  it "should accept a length" do
+    100.times do |integer|
+      length = 1 + (integer / 10)
+      ScatterSwap.hash(integer, 0, length).to_s.length.should == length
+    end
+  end
+
   it "should not be sequential" do
     first = ScatterSwap.hash(1)
     second = ScatterSwap.hash(2)
@@ -16,8 +23,22 @@
 
   it "should be reversable" do
     100.times do |integer|
-      hashed = ScatterSwap.hash(integer)
-      ScatterSwap.reverse_hash(hashed).to_i.should == integer
+      length = 1 + (integer / 10)
+      hashed = ScatterSwap.hash(integer, 0, length)
+      ScatterSwap.reverse_hash(hashed, 0, length).to_i.should == integer
+    end
+  end
+
+  context "When hashed_integer length is less than length used in ScatterSwap.hash" do
+    it "should be reversable" do
+      length = 20
+      integer = 2970439418180909067
+
+      hashed = ScatterSwap.hash(integer, 0, length)
+      # => "02792428384994356370"
+
+      ScatterSwap.reverse_hash(hashed, 0, length).to_i.should == integer
+      ScatterSwap.reverse_hash(hashed.to_i, 0, length).to_i.should == integer
     end
   end
 end
@@ -84,4 +105,4 @@
       s.working_array.should == original_array
     end
   end
-end  
+end