# frozen_string_literal: true

module OpenFdaApi
  # A helper to build queries against the openFDA API
  #
  # The API supports five query parameters. The basic building block of queries is the search parameter.
  # Use it to "filter" requests to the API by looking in specific fields for matches.
  # Each endpoint has its own unique fields that can be searched.
  #
  # search:
  #   What to search for, in which fields. If you don't specify a field to search, the API will search in every field.
  # sort:
  #   Sort the results of the search by the specified field in ascending or descending order by using the
  #   :asc or :desc modifier.
  # count:
  #   Count the number of unique values of a certain field, for all the records that matched the search parameter.
  #   By default, the API returns the 1000 most frequent values.
  # limit:
  #   Return up to this number of records that match the search parameter. Currently, the largest allowed value for the
  #   limit parameter is 1000.
  # skip:
  #   Skip this number of records that match the search parameter, then return the matching records that follow.
  #   Use in combination with limit to paginate results. Currently, the largest allowed value for the skip parameter
  #   is 25000. See Paging if you require paging through larger result sets.
  class QueryBuilder
    # @param [Array<Hash>] search
    def initialize(search: [])
      @search = build_search_string(search)
    end

    # @return [String] the query string portion of a request
    def build_query
      # TODO: We currently just build a very basic search string for simple examples like "search=a:b+AND+c:d",
      # but it is possible to construct more complex queries and we will need to support that. Sorting, counting,
      # setting limits, skipping records, pagination, converting spaces, phrase matching, grouping, and using dates and
      # ranges are examples of more complex queries that can be built.
      @search
    end

    private

    def build_search_string(search)
      return "" if search.empty?

      value = if search.count == 1 # AND case
                # Turns [{a: b, c: d}] into "a:b+AND+c:d"
                search.first.map { |k, v| "#{k}:#{v}" }.join("+AND+")
              else # OR case
                # Turns [{a: b}, {c: d}] into "a:b+c:d"
                search.map { |h| "#{h.keys.first}:#{h.values.first}" }.join("+")
              end

      "search=#{value}"
    end
  end
end