how_would_i_parse_a_flat_ruby_hash_in_to_a_nested.rb

input = { 
  "builder_rule_0_filter"=>"artist_name", 
  "builder_rule_0_operator"=>"contains", 
  "builder_rule_0_value_0"=>"New Found Glory", 

  "builder_rule_1_filter"=>"bpm", 
  "builder_rule_1_operator"=>"less", 
  "builder_rule_1_value_0"=>"150", 

  "builder_rule_2_filter"=>"days_ago", 
  "builder_rule_2_operator"=>"less", 
  "builder_rule_2_value_0"=>"40", 

  "builder_rule_3_filter"=>"release_date_start", 
  "builder_rule_3_operator"=>"between", 
  "builder_rule_3_value_0"=>"2019-01-01", 
  "builder_rule_3_value_1"=>"2019-12-31", 
}



Key = Struct.new(:id, :attr)

Rule = Struct.new(:filter, :operator, :values) do
  def process_key!(key, value)
    case key.attr
    when "filter" then self.filter = value
    when "operator" then self.operator = value
    when "value"
      self.values ||= []
      values << value
    end
  end

  def to_h
    { "filter" => filter,
      "operator" => operator,
      "values" => values.map.with_index { |v, i| [i, v] }.to_h }
  end
end

rules = {}

input.each do |key, value|
  key = Key.new(*key.split("_")[2..3])
  rule = rules[key.id] ||= Rule.new
  rule.process_key!(key, value)
end

rules.each do |key, value|
  rules[key] = value.to_h
end

puts rules.inspect