Introduce from_json as the inverse of to_json

lib/money/money.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 require 'forwardable'
+require 'json'
 
 class Money
  include Comparable
@@ -74,6 +75,16 @@ def from_subunits(subunits, currency_iso, format: :iso4217)
  new(value, currency)
  end
 
+ def from_json(hash_or_string)
+ hash = if hash_or_string.is_a?(Hash)
+ hash_or_string.transform_keys(&:to_sym)
+ else
+ JSON.parse(hash_or_string, symbolize_names: true)
+ end
+
+ Money.new(hash.fetch(:value), hash.fetch(:currency))
+ end
+
  def rational(money1, money2)
  money1.send(:arithmetic, money2) do
  factor = money1.currency.subunit_to_unit * money2.currency.subunit_to_unit

spec/money_spec.rb

@@ -388,6 +388,28 @@
  expect(JSON.dump(Money.new(1.00, "CAD"))).to eq('{"value":"1.00","currency":"CAD"}')
  end
 
+ it "creates Money object from #as_json output" do
+ one_cad = Money.new(1, "CAD")
+ expect(Money.from_json(one_cad.as_json)).to eq(one_cad)
+ end
+
+ it "creates Money object from #to_json output" do
+ one_cad = Money.new(1, "CAD")
+ expect(Money.from_json(one_cad.to_json)).to eq(one_cad)
+ end
+
+ it "creates Money object from JSON-encoded string" do
+ expect(Money.from_json('{ "value": 1.01, "currency": "CAD" }')).to eq(Money.new(1.01, "CAD"))
+ end
+
+ it "creates Money object from JSON-encoded hash" do
+ expect(Money.from_json({value: 1.01, currency: "CAD" })).to eq(Money.new(1.01, "CAD"))
+ end
+
+ it "raises if JSON Hash is malformed in from_json" do
+ expect { Money.from_json({ "val": 1.0 }) }.to raise_error(KeyError)
+ end
+
  it "supports absolute value" do
  expect(Money.new(-1.00).abs).to eq(Money.new(1.00))
  end