First try

.gitignore

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+/tmp

.rspec

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+--color

Gemfile

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+
+gem 'rspec'
+gem 'guard-rspec'

Gemfile.lock

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+GEM
+  specs:
+    celluloid (0.15.2)
+      timers (~> 1.1.0)
+    coderay (1.0.9)
+    diff-lcs (1.2.4)
+    ffi (1.9.0)
+    formatador (0.2.4)
+    guard (2.0.3)
+      formatador (>= 0.2.4)
+      listen (~> 2.0)
+      lumberjack (~> 1.0)
+      pry (>= 0.9.12)
+      thor (>= 0.18.1)
+    guard-rspec (3.1.0)
+      guard (>= 1.8)
+      rspec (~> 2.13)
+    listen (2.0.1)
+      celluloid (>= 0.15.2)
+      rb-fsevent (>= 0.9.3)
+      rb-inotify (>= 0.9)
+    lumberjack (1.0.4)
+    method_source (0.8.2)
+    pry (0.9.12.2)
+      coderay (~> 1.0.5)
+      method_source (~> 0.8)
+      slop (~> 3.4)
+    rb-fsevent (0.9.3)
+    rb-inotify (0.9.2)
+      ffi (>= 0.5.0)
+    rspec (2.14.1)
+      rspec-core (~> 2.14.0)
+      rspec-expectations (~> 2.14.0)
+      rspec-mocks (~> 2.14.0)
+    rspec-core (2.14.5)
+    rspec-expectations (2.14.3)
+      diff-lcs (>= 1.1.3, < 2.0)
+    rspec-mocks (2.14.3)
+    slop (3.4.6)
+    thor (0.18.1)
+    timers (1.1.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  guard-rspec
+  rspec

Guardfile

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+
+guard :rspec, cli: "--tag ~@external" do
+  watch(%r{^spec/.+_spec\.rb$})
+  watch(%r{^lib/(.+)\.rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
+  watch('spec/spec_helper.rb')  { "spec" }
+  watch(%r{^spec/support/.+\.rb$}) { "spec" }
+end

lib/sudoku_reader.rb

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+
+class SudokuReader
+
+  def self.reader_from_file(file_path)
+    reader = SudokuReader.new
+    reader.read(file_path)
+    reader
+  end
+
+  attr_reader :grid
+
+  def initialize
+    @grid = []
+  end
+
+  def read(file_path)
+    open(file_path).each do |line|
+      parsed_line = parse_line line
+      @grid << parsed_line if parsed_line
+    end
+  end
+
+  def parse_line(line)
+    line.split(/[^\d\.]+/) unless separator_line? line
+  end
+
+  def separator_line?(line)
+    line =~/^-+/
+  end
+end

lib/sudoku_validator.rb

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+class SudokuValidator
+
+  attr_reader :grid
+  attr_reader :errors
+
+  def initialize(file_path)
+    @grid = SudokuReader.reader_from_file(file_path).grid
+    @errors = {
+      invalid: {
+        column: [],
+        row: [],
+        subgrid: []
+      },
+      incomplete: {
+        column: [],
+        row: [],
+        subgrid: []
+      }
+    }
+  end
+
+  def valid_array?(array)
+    numbers_only(array).uniq.length == numbers_only(array).length
+  end
+
+  def complete_array?(array)
+    numbers_only(array).length == 9
+  end
+
+  def numbers_only(array)
+    array.reject { |el| el == "." }
+  end
+
+  def array_is?(validation_type, array)
+    if validation_type == :invalid
+      not valid_array? array
+    else
+      not complete_array? array
+    end
+  end
+
+  def row(i)
+    grid[i-1]
+  end
+
+  def column(i)
+    grid.map { |row| row[i-1] }
+  end
+
+  # subgrid is laid out as below
+  #           1-based                        0-based
+  #       1       2       3              0       1       2     <- grid_index for column
+  #     1 - 3   4 - 6   7 - 9          0 - 2   3 - 5   6 - 8
+  #   1 . . . | . . . | . . .        0 . . . | . . . | . . .
+  # 1 | . 1 . | . 2 . | . 3 .      0 | . 0 . | . 1 . | . 2 .
+  #   3 . . . | . . . | . . .        2 . . . | . . . | . . .
+  #     +-----+-------+-----+          +-----+-------+-----+
+  #   4 . . . | . . . | . . .        3 . . . | . . . | . . .
+  # 2 | . 4 . | . 5 . | . 6 .      1 | . 3 . | . 4 . | . 5 .
+  #   6 . . . | . . . | . . .        5 . . . | . . . | . . .
+  #     +-----+-------+-----+          +-----+-------+-----+
+  #   7 . . . | . . . | . . .        6 . . . | . . . | . . .
+  # 3 | . 7 . | . 8 . | . 9 .      2 | . 6 . | . 7 . | . 8 .
+  #   9 . . . | . . . | . . .        8 . . . | . . . | . . .
+  #
+  #                                ^
+  #                                grid_index for row
+  #
+  def subgrid(i)
+    grid[row_starts_for_grid(i), 3].map do |row| 
+      row[column_starts_for_grid(i), 3]
+    end.flatten
+  end
+
+  def row_starts_for_grid(i)
+    zero_based(i) / 3 * 3
+  end
+
+  def column_starts_for_grid(i)
+    zero_based(i) % 3 * 3
+  end
+
+  def zero_based(i)
+    i - 1
+  end
+
+  def validate!
+    reset_errors!
+    [:invalid, :incomplete].each do |error_type|
+      [:row, :column, :subgrid].each do |array_type|
+        (1..9).each do |i|          
+          errors[error_type][array_type] << i if array_is? error_type, send(array_type, i)
+        end
+      end
+    end
+  end
+
+  def valid?
+    [:row, :column, :subgrid].all? { |array_type| errors[:invalid][array_type].none? }
+  end
+
+  def complete?
+    [:row, :column, :subgrid].all? { |array_type| errors[:incomplete][array_type].none? }
+  end
+
+  def reset_errors!
+    [:invalid, :incomplete].each do |error_type|
+      [:row, :column, :subgrid].each do |array_type| 
+        errors[error_type][array_type].clear
+      end
+    end
+  end
+
+  def error_messages(type)
+    errors[type].map do |key, vals| 
+      "#{type} #{key}s: #{vals.join(", ")}" if vals.any? 
+    end.compact.sort
+  end
+end

spec/fixtures/invalid_complete.sudoku

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+8 5 9 |6 1 2 |4 3 7 
+7 2 3 |8 5 4 |1 6 9 
+1 6 4 |3 7 9 |5 2 8 
+------+------+------
+9 8 6 |1 4 7 |3 5 2 
+3 7 5 |8 6 2 |9 1 4 
+2 4 1 |5 9 3 |7 8 6 
+------+------+------
+4 3 2 |9 8 1 |6 7 5 
+6 1 7 |4 2 5 |8 9 3 
+5 9 8 |7 3 6 |2 4 1 

spec/fixtures/invalid_incomplete.sudoku

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+8 5 . |. . 2 |4 . . 
+7 2 . |. 8 . |. . 9 
+. . 4 |. . . |. . . 
+------+------+------
+. . . |1 . 7 |. . 2 
+3 . 5 |. . . |9 . . 
+. 4 . |. . . |. . . 
+------+------+------
+. 5 . |. 8 . |. 7 . 
+. 1 7 |. . . |. . . 
+. . . |. 3 6 |. 4 . 

spec/fixtures/valid_complete.sudoku

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+8 5 9 |6 1 2 |4 3 7 
+7 2 3 |8 5 4 |1 6 9 
+1 6 4 |3 7 9 |5 2 8 
+------+------+------
+9 8 6 |1 4 7 |3 5 2 
+3 7 5 |2 6 8 |9 1 4 
+2 4 1 |5 9 3 |7 8 6 
+------+------+------
+4 3 2 |9 8 1 |6 7 5 
+6 1 7 |4 2 5 |8 9 3 
+5 9 8 |7 3 6 |2 4 1 

spec/fixtures/valid_incomplete.sudoku

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+8 5 . |. . 2 |4 . . 
+7 2 . |. . . |. . 9 
+. . 4 |. . . |. . . 
+------+------+------
+. . . |1 . 7 |. . 2 
+3 . 5 |. . . |9 . . 
+. 4 . |. . . |. . . 
+------+------+------
+. . . |. 8 . |. 7 . 
+. 1 7 |. . . |. . . 
+. . . |. 3 6 |. 4 . 

spec/lib/sudoku_reader_spec.rb

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+require 'spec_helper'
+
+describe SudokuReader do
+
+  let(:reader) { SudokuReader.new }
+
+  describe '#parse_line' do
+    it 'returns an array' do
+      parsed_line = reader.parse_line "8 5 9 |6 1 2 |4 3 7 "
+
+      expect(parsed_line).to eq ["8", "5", "9", "6", "1", "2", "4", "3", "7"]
+
+      parsed_line = reader.parse_line ". . . |. 8 . |. 7 . "
+
+      expect(parsed_line).to eq [".", ".", ".", ".", "8", ".", ".", "7", "."]
+
+      parsed_line = reader.parse_line "------+------+------"      
+
+      expect(parsed_line).to be_nil
+    end
+  end
+
+  describe '#separator_line?' do
+    it 'returns true if the line is -----' do
+      line = "------+------+------"
+
+      expect(reader.separator_line?(line)).to be_true
+
+      line = "8 5 9 |6 1 2 |4 3 7 "
+
+      expect(reader.separator_line?(line)).to be_false
+
+      line = ". . . |. 8 . |. 7 . "
+
+      expect(reader.separator_line?(line)).to be_false
+    end
+  end
+
+  describe '#read' do
+    it 'reads and stores the file into an array' do
+      reader.read fixture_path('valid_incomplete.sudoku')
+
+      expect(reader.grid.length).to eq 9 # rows
+      reader.grid.each do |row|
+        expect(row.length).to eq 9 # columns
+      end
+      expect(reader.grid[0][4]).to eq "."
+      expect(reader.grid[2][2]).to eq "4"
+    end
+  end
+
+  describe '#reader_from_file' do
+    it 'creates an instance of reader with a grid generated from file' do
+      reader = SudokuReader.reader_from_file(fixture_path('valid_incomplete.sudoku'))
+
+      expect(reader.grid.length).to eq 9
+      expect(reader.grid[0][4]).to eq "."
+      expect(reader.grid[2][2]).to eq "4"
+    end
+  end
+end