frc-frecon/frecon

# lib/frecon/mongoid/criteria.rb
#
# Copyright (C) 2015 Christopher Cooper, Sam Craig, Tiger Huang, Vincent Mai, Sam Mercier, and Kristofer Rye
#
# This file is part of FReCon, an API for scouting at FRC Competitions, which is
# licensed under the MIT license.  You should have received a copy of the MIT
# license with this program.  If not, please see
# <http://opensource.org/licenses/MIT>.

require 'mongoid'

# Public: An extension for the Mongoid module.
module Mongoid
    # Public: A monkey-patch for the Mongoid::Criteria class which introduces
    # a #psv_filter method.
    class Criteria

        # Public: Filter by given PSV parameters.
        #
        # PSV is an introduced system that can be used within query strings to
        # narrow a query.  Since HTTP query strings can use '+' to act as spaces
        # within a key-value pair, one can use these pluses to define nested
        # query parameters when querying the database as in an indexing or
        # showing request.
        #
        # psv_parameters - A Hash of PSV strings to comparison values.
        #
        # Examples
        #
        #   Record.all.psv_filter({'participation robot team number' => '2503'})
        #   => #<Mongoid::Criteria ...>
        #
        #   # Since each instance of Record has a :team shortcut method,
        #   # we can just filter it like so.
        #   Record.all.psv_filter({'team number' => '2503'})
        #   => #<Mongoid::Criteria ...>
        #
        # Returns a filtered version of self.
        def psv_filter(psv_parameters = {})
            collection = self

            # Iterate through the Hash of query Strings to values, filtering using
            # each pairing where the key is the query specifier and the value is the
            # value that the last word in the query specifier is equal to.  For
            # multiple key-value pairs, just keep adding specifiers to the chain.
            psv_parameters.each do |psv_string, comparison_value|
                # Split the query String, and convert each subsequent String
                # to a symbol.  Then, reverse the array to make it easy to perform
                # an inside-out operation.
                psv_keys = psv_string.split(/\W/).map do |psv_key|
                    psv_key.to_sym
                end.reverse

                # Get the final key in the query string.
                comparison_key = psv_keys.shift

                # Create a comparison hash to be used to compare <attribute> to
                # <expected value>.
                if comparison_value.length == 0 || comparison_value == '__nil__'
                    comparison_hash = {comparison_key => nil}
                else
                    comparison_hash = {comparison_key => comparison_value}
                end

                # Each of the subsequent keys should be a model name.  Generate a string
                # corresponding to the '<model>' + '_id' for use as the comparison key,
                # and find the model class by generating a constant.
                #
                # Then, nest a comparison around the current comparison hash.
                psv_keys.each do |model|
                    model_id = (model.to_s + '_id').to_sym
                    model_class = ('FReCon::' + model.to_s.capitalize).constantize

                    comparison_hash = {model_id => model_class.in(comparison_hash).map(&:id)}
                end

                # Finally, complete this nested comparison.
                collection = collection.in(comparison_hash)
            end

            # Return the fully-filtered collection.
            collection
        end

    end
end