roqua/quby_engine

# frozen_string_literal: true

# A lookup tree to find values by multiple arguments.
#
# Example tree:
# Inhibitie:
#   male:
#     10...11:
#       -Infinity...10: 39
#       10...20: 42
#     11...12:
#       -Infinity...10: 40
#       10...20: : 43
#   female:
#     10...11: 38
#     ...
#
# with levels:
# ['scale', 'gender', 'age', 'raw', 'norm']
#
# will allow a lookup like:
# lookup({age: 10, raw: 5, scale: 'Inhibitie', gender: 'male'})` => 39
#
# Keys in the tree will be matched by hash lookup of the parameter value with the following exeptions:
# floats: can be found by integer as well
# strings: can be found by symbol as well.
# enumerables: will find the first key for which `include?(param)` returns true.
module Quby::TableBackend
  class RangeTree
    # @param tree [Hash<>] hash of hashes leading from parameter values/ranges to a result.
    # @params levels [Array<String>] the argument name for each level of the tree.
    def initialize(levels:, tree:)
      @levels = levels
      @tree = tree
    end

    # Given a parameters hash that contains a value or range for every
    # level in the tree, find and return the normscore.
    # ie. `lookup({age: 10, raw: 5, scale: 'Inhibitie', gender: 'male'})` => 39
    def lookup(parameters)
      validate_parameters(parameters)
      lookup_score(parameters)
    end

    private

    # All parameters must be present to do a lookup but the order does not matter.
    def validate_parameters(parameters)
      if @levels[0...-1].sort != parameters.keys.map(&:to_s).sort
        fail 'Incompatible score parameters found'
      end
    end

    # Reduce the tree (a hash) to a normscore by looking up the correct values/ranges
    # for each column in @levels.
    # Returns a single normscore when found.
    # Returns nil and reports to AppSignal when normscore could not be found.
    def lookup_score(parameters)
      @levels[0...-1].reduce(@tree) do |node, level|
        value = parameters[level.to_sym]
        # binding.pry
        case node.first.first # all keys for one level are the same type.
        when String
          node[value.to_s] # from csv it's always a string, but should also allow symbol param.
        when Float
          node[value.to_f] # from csv it's always a float, but should also allow int param.
        when Enumerable
          node.find { |k, _v| k.include? value }.last
        else
          node[value]
        end
      end
    rescue StandardError => exception
      # Normscore could not be found for the given parameters.
      if defined? Roqua::Support::Errors
        Roqua::Support::Errors.report(exception, parameters: parameters)
      end
      nil
    end
  end
end