# frozen_string_literal: true

require 'rumale/base/estimator'
require 'rumale/base/transformer'
require 'rumale/validation'

module Rumale
  # This module consists of the classes that perform preprocessings.
  module Preprocessing
    # Normalize samples by scaling each feature to a given range.
    #
    # @example
    #   require 'rumale/preprocessing/min_max_scaler'
    #
    #   normalizer = Rumale::Preprocessing::MinMaxScaler.new(feature_range: [0.0, 1.0])
    #   new_training_samples = normalizer.fit_transform(training_samples)
    #   new_testing_samples = normalizer.transform(testing_samples)
    class MinMaxScaler < ::Rumale::Base::Estimator
      include ::Rumale::Base::Transformer

      # Return the vector consists of the minimum value for each feature.
      # @return [Numo::DFloat] (shape: [n_features])
      attr_reader :min_vec

      # Return the vector consists of the maximum value for each feature.
      # @return [Numo::DFloat] (shape: [n_features])
      attr_reader :max_vec

      # Creates a new normalizer for scaling each feature to a given range.
      #
      # @param feature_range [Array<Float>] The desired range of samples.
      def initialize(feature_range: [0.0, 1.0])
        super()
        @params = { feature_range: feature_range }
      end

      # Calculate the minimum and maximum value of each feature for scaling.
      #
      # @overload fit(x) -> MinMaxScaler
      #
      # @param x [Numo::DFloat] (shape: [n_samples, n_features]) The samples to calculate the minimum and maximum values.
      # @return [MinMaxScaler]
      def fit(x, _y = nil)
        x = ::Rumale::Validation.check_convert_sample_array(x)

        @min_vec = x.min(0)
        @max_vec = x.max(0)
        self
      end

      # Calculate the minimum and maximum values, and then normalize samples to feature_range.
      #
      # @overload fit_transform(x) -> Numo::DFloat
      #
      # @param x [Numo::DFloat] (shape: [n_samples, n_features]) The samples to calculate the minimum and maximum values.
      # @return [Numo::DFloat] The scaled samples.
      def fit_transform(x, _y = nil)
        x = ::Rumale::Validation.check_convert_sample_array(x)

        fit(x).transform(x)
      end

      # Perform scaling the given samples according to feature_range.
      #
      # @param x [Numo::DFloat] (shape: [n_samples, n_features]) The samples to be scaled.
      # @return [Numo::DFloat] The scaled samples.
      def transform(x)
        x = ::Rumale::Validation.check_convert_sample_array(x)

        n_samples, = x.shape
        dif_vec = @max_vec - @min_vec
        dif_vec[dif_vec.eq(0)] = 1.0
        nx = (x - @min_vec.tile(n_samples, 1)) / dif_vec.tile(n_samples, 1)
        nx * (@params[:feature_range][1] - @params[:feature_range][0]) + @params[:feature_range][0]
      end
    end
  end
end