Add selective field printing

Rakefile

@@ -9,11 +9,11 @@ begin
 
   namespace :cucumber do
     Cucumber::Rake::Task.new(:ok) do |t|
-      t.cucumber_opts = "--format progress -t ~@wip -b"
+      t.cucumber_opts = "--format progress -t ~@wip -P"
     end
 
     Cucumber::Rake::Task.new(:wip) do |t|
-      t.cucumber_opts = "--format pretty -t @wip"
+      t.cucumber_opts = "--format pretty -t @wip -P"
     end
   end
 

cucumber.yml

@@ -0,0 +1 @@
+default: --format progress -t ~@wip

features/print_fields.feature

@@ -0,0 +1,44 @@
+Feature: jse prints specific fields from the json
+
+  In order to only show relevant information
+  As a jse user
+  I want to only output specific json fields
+
+  Background:
+  Given I have a log file containing:
+    """
+    {"id":1,"level":"INFO","message":"line one"}
+    {"id":2,"level":"DEBUG","message":"line two"}
+    {"id":3,"level":"ERROR","message":"number three"}
+    {"id":4,"level":"INFO","message":"line four"}
+    """
+
+  Scenario: Printing one field returns just the value
+    When I run "jse --fields=message" on my log file
+    Then I should see:
+    """
+    line one
+    line two
+    number three
+    line four
+    """
+
+  Scenario: Printing multiple fields returns JSON
+    When I run "jse --fields=message,level" on my log file
+    Then I should see:
+    """
+    {"level":"INFO","message":"line one"}
+    {"level":"DEBUG","message":"line two"}
+    {"level":"ERROR","message":"number three"}
+    {"level":"INFO","message":"line four"}
+    """
+
+  Scenario: Fields can be specified with a shorter '-f' flag
+    When I run "jse -f message,level" on my log file
+    Then I should see:
+    """
+    {"level":"INFO","message":"line one"}
+    {"level":"DEBUG","message":"line two"}
+    {"level":"ERROR","message":"number three"}
+    {"level":"INFO","message":"line four"}
+    """

lib/jse.rb

@@ -4,6 +4,9 @@
 require 'jse/stream'
 require 'jse/filter'
 require 'jse/regexp_filter'
+require 'jse/subset_transform'
+require 'jse/to_json_transform'
+require 'jse/field_value_transform'
 
 module JSE
 end

lib/jse/cli.rb

@@ -3,6 +3,7 @@
 module JSE
   module CLI
     def self.execute(stdout, arguments = [])
+      print = []
       parser = OptionParser.new do |opts|
         opts.banner = <<-BANNER.gsub(/^[ \t]*/, '')
         Json Stream Editor.
@@ -12,9 +13,10 @@ def self.execute(stdout, arguments = [])
         Options are:
       BANNER
         opts.separator ""
-        # opts.on("-f", "--fields a,b,c", Array,
-        #         "List of fields to return") do |fields|
-        # end
+        opts.on("-f", "--fields a,b,c", Array,
+                "List of fields to return") do |fields|
+          print = fields
+        end
         opts.on("-h", "--help",
                 "Show this help message.") { stdout.puts opts; exit }
         opts.parse!(arguments)
@@ -31,6 +33,10 @@ def self.execute(stdout, arguments = [])
         stream.filter!(field, text)
       end
 
+      unless print.empty?
+        stream.print!(*print)
+      end
+
       stream.each_line do |line|
         stdout.puts line
       end

lib/jse/field_value_transform.rb

@@ -0,0 +1,11 @@
+module JSE
+  class FieldValueTransform
+    def initialize(field)
+      @field = field
+    end
+
+    def apply(hash)
+      hash[@field]
+    end
+  end
+end

lib/jse/stream.rb

@@ -2,18 +2,19 @@
 
 module JSE
   class Stream
-    attr_accessor :filters
+    attr_accessor :filters, :transforms
     attr_reader :inner
 
     def initialize(inner)
       @inner = inner
+      @transforms = []
       @filters = []
     end
 
     def each_line
       inner.each_line do |line|
         unless filter_chain.eliminates?(line)
-          yield line
+          yield transform_chain.apply(line)
         end
       end
     end
@@ -26,12 +27,46 @@ def filter!(field, text)
       end
     end
 
+    def print!(*field_list)
+      if field_list.size == 1
+        transforms << FieldValueTransform.new(field_list[0])
+      else
+        transforms << SubsetTransform.new(*field_list)
+        transforms << ToJsonTransform.new
+      end
+    end
+
     private
 
     def looks_like_regexp?(string)
       string[0,1] == '/' && string[string.size-1,1] == '/'
     end
 
+    def transform_chain
+      TransformChain.new(transforms)
+    end
+
+    class TransformChain
+      def initialize(transforms)
+        @transforms = transforms
+      end
+
+      def apply(line)
+        begin
+          if @transforms.empty?
+            line
+          else
+            json = JSON.parse(line)
+            @transforms.inject(json){ |j, transform| transform.apply(j) }
+          end
+        rescue JSON::ParserError
+          $stderr.puts "Error parsing line:"
+          $stderr.puts line
+          true
+        end
+      end
+    end
+
     def filter_chain
       FilterChain.new(filters)
     end

lib/jse/subset_transform.rb

@@ -0,0 +1,14 @@
+module JSE
+  class SubsetTransform
+    def initialize(*fields)
+      @fields = fields
+    end
+
+    def apply(json)
+      @fields.inject({}) do |result, field|
+        result[field] = json[field]
+        result
+      end
+    end
+  end
+end

lib/jse/to_json_transform.rb

@@ -0,0 +1,7 @@
+module JSE
+  class ToJsonTransform
+    def apply(obj)
+      obj.to_json
+    end
+  end
+end

spec/jse/stream_spec.rb

@@ -29,6 +29,22 @@ def match?(n)
       end
     end
 
+    class ValueUpcaseTransform
+      def apply(json)
+        updated = json.dup
+        updated['value'] = json['value'].upcase
+        updated
+      end
+    end
+
+    class ValueDoubleTransform
+      def apply(json)
+        updated = json.dup
+        updated['value'] = json['value'] + json['value']
+        updated
+      end
+    end
+
     let(:inner){ mock("Inner Stream") }
     let(:stream){ Stream.new(inner) }
 
@@ -66,26 +82,79 @@ def match?(n)
         end
         results.should == ["{\"value\":4}"]
       end
+
+      it "yeilds every line if there are no filters" do
+        inner.stub(:each_line).and_yield("{\"value\":1}").
+          and_yield("{\"value\":2}")
+        stream.filters = []
+        results = []
+        stream.each_line do |l|
+          results << l
+        end
+        results.should == ["{\"value\":1}", "{\"value\":2}"]
+      end
+
+      it "runs all transforms on the lines" do
+        inner.stub(:each_line).and_yield("{\"value\":\"a\"}").
+          and_yield("{\"value\":\"b\"}").
+          and_yield("{\"value\":\"c\"}")
+        stream.transforms = [ValueUpcaseTransform.new,
+                             ValueDoubleTransform.new,
+                             ToJsonTransform.new]
+        results = []
+        stream.each_line do |l|
+          results << l
+        end
+        results.should == ["{\"value\":\"AA\"}",
+                           "{\"value\":\"BB\"}",
+                           "{\"value\":\"CC\"}"]
+      end
     end
 
     describe "#filter!" do
-      it "adds a new filter to the list" do
+      before do
         stream.filters = []
+      end
+
+      it "adds a new filter to the list" do
         stream.filter!('field', 'text')
         stream.filters.size.should == 1
       end
 
       it "adds a normal filter if it looks like a string" do
-        stream.filters = []
         stream.filter!('field', 'text')
         stream.filters.first.class.should == JSE::Filter
       end
 
       it "adds a regexp filter if it looks like a regexp" do
-        stream.filters = []
         stream.filter!('field', '/^regexp$/')
         stream.filters.first.class.should == JSE::RegexpFilter
       end
     end
+
+    describe "#print!" do
+      before do
+        stream.transforms = []
+      end
+
+      context "only on field is specified" do
+        it "adds on transform" do
+          stream.print!('field')
+          stream.transforms.size.should == 1
+        end
+      end
+
+      context "multiple fields are specified" do
+        it "adds two transforms" do
+          stream.print!('field', 'other')
+          stream.transforms.size.should == 2
+        end
+
+        it "adds a to_json_transform on the end" do
+          stream.print!('field', 'other')
+          stream.transforms.last.class.should == ToJsonTransform
+        end
+      end
+    end
   end
 end

spec/jse/subset_transform_spec.rb

@@ -0,0 +1,14 @@
+require 'spec_helper'
+
+module JSE
+  describe SubsetTransform do
+    describe "#apply" do
+      it "returns the set of fields as a json object" do
+        transform = SubsetTransform.new('name', 'value')
+        json = JSON.parse("{\"name\":\"n\", \"value\":\"v\", \"id\":1}")
+        transform.apply(json).to_json.should ==
+          "{\"name\":\"n\",\"value\":\"v\"}"
+      end
+    end
+  end
+end