module Picky

  class Categories

    each_delegate :load,
                  :analyze,
                  :to => :categories

    # Return all possible combinations for the given token.
    #
    # This checks if it needs to also search through similar
    # tokens, if for example, the token is one with ~.
    # If yes, it puts together all solutions.
    #
    def possible_combinations token
      token.similar? ? similar_possible_for(token) : possible_for(token)
    end

    # Gets all similar tokens and puts together the possible combinations
    # for each found similar token.
    #
    def similar_possible_for token
      tokens = similar_tokens_for token
      inject_possible_for tokens
    end

    # Returns all possible similar tokens for the given token.
    #
    def similar_tokens_for token
      text = token.text
      categories.inject([]) do |result, category|
        next_token = token
        # Note: We could also break off here if not all the available
        #       similars are needed.
        #       Wait for a concrete case that needs this before taking
        #       action.
        #
        while next_token = next_token.next_similar_token(category)
          result << next_token if next_token && next_token.text != text
        end
        result
      end
    end

    #
    #
    def inject_possible_for tokens
      tokens.inject([]) do |result, token|
        possible = possible_categories token
        result + possible_for(token, possible)
      end
    end

    # Returns possible Combinations for the token.
    #
    # Note: The preselected_categories param is an optimization.
    # Note: Returns [] if no categories matched (will produce no result).
    #
    def possible_for token, preselected_categories = nil
      possible = (preselected_categories || possible_categories(token)).inject([]) do |combinations, category|
        combination = category.combination_for token
        combination ? combinations << combination : combinations
      end
      possible
    end

    # This returns the possible categories for this token.
    # If the user has already preselected a category for this token,
    # like "artist:moby", if not just return all for the given token,
    # since all are possible.
    #
    # Note: Once I thought this was called too often. But it is not (18.01.2011).
    #
    def possible_categories token
      token.user_defined_categories || categories
    end

  end

end