require 'candy/crunch'
require 'candy/hash'

module Candy
  
  # Handles Mongo queries for cursors upon a particular Mongo collection.  
  module Collection
    FIND_OPTIONS = [:fields, :skip, :limit, :sort, :hint, :snapshot, :timeout]
    UP_SORTS = [Mongo::ASCENDING, 'ascending', 'asc', :ascending, :asc, 1, :up]
    DOWN_SORTS = [Mongo::DESCENDING, 'descending', 'desc', :descending, :desc, -1, :down]
    
    include Enumerable

    module ClassMethods
      include Crunch::ClassMethods
      
      attr_reader :_candy_piece
      
      # Sets the collection that all queries run against, qualified by
      # the namespace of the current class.  (I.e., if this class is 
      # BigModule::LittleModule::People, `collects :person` will look for
      # a collection named "BigModule::LittleModule::Person".) You can also 
      # specify a class that includes Candy::Piece that will be instantiated
      # for all found records. Otherwise the collection name is used as a 
      # default, and CandyHash is a fallback.
      def collects(collection, piece = nil)
        collectible = namespace + camelcase(collection)
        piecemeal = (piece ? namespace + camelcase(piece) : collectible)
        self.collection = collectible
        @_candy_piece = Kernel.qualified_const_get(piecemeal) || CandyHash
      end
      
      def all(options={})
        self.new(options)
      end
      
      def method_missing(name, *args, &block)
        coll = self.new
        coll.send(name, *args, &block)
      end  
    private
      # Retrieves the 'BlahModule::BleeModule::' part of the class name, so that we
      # can put other things in the same namespace.
      def namespace
        name[/^.*::/] || '' # Hooray for greedy matching
      end

      # Modified from ActiveSupport (http://rubyonrails.org)
      def camelcase(stringy)
        stringy.to_s.gsub(/(?:^|_)(.)/) {$1.upcase}
      end
      
      # Creates a method in the same namespace as the included class that points to
      # 'all', for easier semantics.
      def self.extended(receiver)
        Factory.magic_method(receiver, 'all', 'conditions={}')
      end
      
    end  # Here endeth the ClassMethods module
   
    def initialize(*args, &block)
      conditions = args.pop || {}
      super
      @_candy_query = {}
      if conditions.is_a?(Hash)
        @_candy_options = {:fields => '_id'}.merge(extract_options(conditions))
        @_candy_query.merge!(conditions)
      else
        @_candy_options = {:fields => '_id'}
      end
      refresh_cursor
    end
    
    def method_missing(name, *args, &block)
      if @_candy_cursor.respond_to?(name)
        @_candy_cursor.send(name, *args, &block)
      elsif FIND_OPTIONS.include?(name)
        @_candy_options[name] = args.shift
        refresh_cursor
        self
      else
        @_candy_query[name] = args.shift
        @_candy_query.merge!(args) if args.is_a?(Hash)
        refresh_cursor
        self
      end
    end
      
    
    # Makes our collection enumerable.  This relies heavily on Mongo::Cursor methods --
    # we only reimplement it so that the objects we return can be Candy objects.
    def each
      while this = @_candy_cursor.next_document
        yield self.class._candy_piece.new(this)
      end
    end
    
    # Get our next document as a Candy object, if there is one.
    def next
      if this = @_candy_cursor.next_document
        self.class._candy_piece.new(this)
      end
    end
    
    # Determines the sort order for this collection, with somewhat simpler semantics than
    # the MongoDB options.  Each value is either a field name (which defaults to ascending sort)
    # or a direction (which modifies the field name immediately prior) or a two-element array of
    # same.  Direction can be :up or :down in addition to Mongo's accepted values of :ascending, 
    # 'asc', 1, etc.  
    #
    # As an added bonus, sorts can also be chained.  If you call #sort more than once then all
    # sorts will be applied in the order in which you called them.
    def sort(*fields)
      @_candy_sort ||= []
      temp_sort = []
      until fields.flatten.empty?
        this = fields.pop  # We're going backwards so that we can test for modifiers
        if UP_SORTS.include?(this)
          temp_sort.unshift [fields.pop, Mongo::ASCENDING]
        elsif DOWN_SORTS.include?(this)
          temp_sort.unshift [fields.pop, Mongo::DESCENDING]
        else
          temp_sort.unshift [this, Mongo::ASCENDING]
        end
      end
      @_candy_sort += temp_sort
      @_candy_cursor.sort(@_candy_sort)
      self
    end
          
          
  private
      
    def refresh_cursor
      @_candy_cursor = self.class.collection.find(@_candy_query, @_candy_options)
    end
    
    def extract_options(hash)
      options = {}
      (FIND_OPTIONS & hash.keys).each do |key|
        options[key] = hash.delete(key)
      end
      options
    end
    
    def self.included(receiver)
      receiver.extend         ClassMethods
    end
  end
end