Added "do-exercise" command

Runs a single exercise.  Reads the model name out of the header and looks for a
class with that name.

lib/srs/cli.rb

@@ -2,6 +2,7 @@
 require 'srs/cli/help'
 require 'srs/cli/insert-into'
 require 'srs/cli/schedule'
+require 'srs/cli/do-exercise'
 require 'srs/cli/cat'
 
 module SRS
@@ -10,6 +11,7 @@ class << self
 			COMMANDS = { "init"            => :Init,
 			             "insert-into"     => :InsertInto,
 			             "schedule"        => :Schedule,
+			             "do-exercise"     => :DoExercise,
 			             "cat"             => :Cat,
 			             "help"            => :Help }.freeze
 

lib/srs/cli/do-exercise.rb

@@ -0,0 +1,76 @@
+module SRS
+	class CLI
+		class DoExercise
+			def run!(arguments)
+				if not SRS::Workspace.initialised? then
+					puts "Current directory is not an SRS Workspace"
+					return 3
+				end
+
+				sha1 = arguments.shift
+				sha1_start = sha1[0..1]
+				sha1_rest = sha1[2..-1]
+
+				datafile = "exercises/#{sha1_start}/#{sha1_rest}"
+
+				if not File.exists?(datafile) then
+					puts "No content with that ID exists"
+					return 4
+				end
+
+				headers = {}
+				metadata = ""
+				File.open(datafile, "r") do |file|
+					while( line = file.gets() ) do
+						if line.strip.empty? then
+							break
+						end
+
+						keyval = line.split(':').map{|e| e.strip}
+						key = keyval[0]
+						val = keyval[1]
+
+						headers[key] = val
+					end
+					metadata = file.read
+				end
+
+				runModel(sha1, headers, metadata)
+			end
+
+			def runModel(sha1, headers, metadata)
+				if not headers.has_key?("Model") then
+					puts "Exercise #{sha1} has no model!\n"
+					return 6
+				end
+
+				modelclass = headers.delete("Model")
+
+				begin
+					require "./models/#{modelclass}"
+				rescue LoadError
+					begin
+						require "srs/models/#{modelclass}"
+					rescue LoadError
+						puts "Couldn't find model #{modelclass}."
+						return 7
+					end
+				end
+
+				model = SRS::Models.const_get(modelclass.to_sym).new
+				score = model.run(headers, metadata)
+
+				return score == nil ? 0 : score
+			end
+
+			def help()
+				puts <<-EOF
+srs do-exercise <id>
+
+Runs the exercise defined in <id>
+					EOF
+			end
+		end
+	end
+end
+

lib/srs/cli/help.rb

@@ -24,6 +24,7 @@ def summary()
 				puts "    init"
 				puts "    insert-into"
 				puts "    schedule"
+				puts "    do-exercise"
 				puts "    cat"
 				puts "    help"
 			end