require 'erb'
require 'ostruct'

module QME
  module MapReduce
  
    # Builds Map and Reduce functions for a particular measure
    class Builder
      attr_reader :id, :params

      # Utility class used to supply a binding to Erb
      class Context < OpenStruct
        # Create a new context
        # @param [Hash] vars a hash of parameter names (String) and values (Object). Each 
        # entry is added as an accessor of the new Context
        def initialize(db, vars)
          super(Context.add_defaults(vars))
          @db = db
        end
      
        # Get a binding that contains all the instance variables
        # @return [Binding]
        def get_binding
          binding
        end
        
        # Add default parameter values if not specified
        def self.add_defaults(vars)
          if !vars.has_key?('enable_logging')
            vars['enable_logging'] = false
          end
          if !vars.has_key?('enable_rationale')
            vars['enable_rationale'] = false
          end
          vars
        end
        
        # Inserts any library code into the measure JS. JS library code is loaded from
        # three locations: the js directory of the quality-measure-engine project, the
        # js sub-directory of the current directory (e.g. measures/js), and the bundles
        # collection of the current database (used by the Rails Web application).
        def init_js_frameworks
          result = ''
          result << 'if (typeof(map)=="undefined") {'
          result << "\n"
          @db['bundles'].find.each do |bundle|
            (bundle['extensions'] || []).each do |ext|
              result << "#{ext}();\n"
            end
          end
          result << "}\n"
          result
        end
      end

      # Create a new Builder
      # @param [Hash] measure_def a JSON hash of the measure, field values may contain Erb directives to inject the values of supplied parameters into the map function
      # @param [Hash] params a hash of parameter names (String or Symbol) and their values
      def initialize(db, measure_def, params)
        @id = measure_def['id']
        @params = {}
        @db = db
        
        # normalize parameters hash to accept either symbol or string keys
        params.each do |name, value|
          @params[name.to_s] = value
        end
        @measure_def = measure_def
        @measure_def.parameters ||= {}
        @measure_def.parameters.each do |parameter, value|
          if !@params.has_key?(parameter)
            raise "No value supplied for measure parameter: #{parameter}"
          end
        end
        # if the map function is specified then replace any erb templates with their values
        # taken from the supplied params
        # always true for actual measures, not always true for unit tests
        if (@measure_def.map_fn)
          template = ERB.new(@measure_def.map_fn)
          context = Context.new(@db, @params)
          @measure_def.map_fn = template.result(context.get_binding)
        end
      end

      # Get the map function for the measure
      # @return [String] the map function
      def map_function
        @measure_def.map_fn
      end

      # Get the reduce function for the measure, this is a simple
      # wrapper for the reduce utility function specified in
      # map-reduce-utils.js
      # @return [String] the reduce function
      def finalize_function
        reduce = 
        "function (key, value) { 
          var patient = value;
          patient.measure_id = \"#{@measure_def['id']}\";\n"
        if @params['test_id'] && @params['test_id'].class==Moped::BSON::ObjectId
          reduce += "  patient.test_id = new ObjectId(\"#{@params['test_id']}\");\n"
        end
        if @measure_def.sub_id
          reduce += "  patient.sub_id = \"#{@measure_def.sub_id}\";\n"
        end
        if @measure_def.nqf_id
          reduce += "  patient.nqf_id = \"#{@measure_def.nqf_id}\";\n"
        end
          
        reduce += "patient.effective_date = #{@params['effective_date']};
                   if (patient.provider_performances) {
                     var tmp = [];
                     for(var i=0; i<patient.provider_performances.length; i++) {
                       var value = patient.provider_performances[i];
                       if ((value['start_date'] <= #{@params['effective_date']} || value['start_date'] == null) && (value['end_date'] >= #{@params['effective_date']} || value['end_date'] == null))
                       tmp.push(value);
                     }
                     if (tmp.length == 0) tmp = null;
                     patient.provider_performances = tmp;
                   }
                   return patient;}"
        
        reduce
      end


    end
  end
end