Implement Miscast

Fixes #57

lib/magic/cards/miscast.rb

@@ -0,0 +1,50 @@
+module Magic
+  module Cards
+    Miscast = Instant("Miscast") do
+      cost blue: 1, generic: 1
+    end
+
+    class Miscast < Instant
+      class Choice < Magic::Choice::Effect
+        attr_reader :source, :target
+        def initialize(source:, target:)
+          super(target.player)
+          @source = source
+          @target = target
+        end
+
+        def inspect
+          "#<Miscast::Counter target spell source:#{source}, target:#{target}>"
+        end
+
+        def costs
+          @costs ||= [Costs::Mana.new(generic: 3)]
+        end
+
+        def pay(player, payment)
+          cost = costs.first
+          cost.pay!(player, payment)
+        end
+
+        def resolve!
+          if costs.none?(&:paid?)
+            effect = Effects::CounterSpell.new(source: source, targets: [target], choices: [target])
+            game.add_effect(effect)
+          end
+        end
+      end
+
+      def single_target?
+        true
+      end
+
+      def target_choices
+        game.stack
+      end
+
+      def resolve!(target:)
+        game.choices.add(Choice.new(source: self, target:))
+      end
+    end
+  end
+end

spec/cards/miscast_spec.rb

@@ -0,0 +1,47 @@
+require 'spec_helper'
+
+RSpec.describe Magic::Cards::Miscast do
+  include_context "two player game"
+
+  subject(:miscast) { Card("Miscast") }
+
+  context "with miscast on the stack" do
+    let(:sol_ring) { Card("Sol Ring", owner: p2) }
+
+    before do
+      p2.add_mana(blue: 1)
+      sol_ring_cast = p2.cast(card: sol_ring) do
+        _1.pay_mana(generic: { blue: 1 })
+      end
+
+      p1.add_mana(blue: 2)
+      p1.cast(card: miscast) do
+        _1.pay_mana(generic: { blue: 1}, blue: 1)
+        _1.targeting(sol_ring_cast)
+      end
+      game.tick!
+    end
+
+    it "has a 3 cost choice" do
+      choice = game.choices.first
+      expect(choice.costs.first.generic).to eq(3)
+    end
+
+    it "counters target spell if cost is unpaid" do
+      game.resolve_choice!
+      game.tick!
+
+      expect(sol_ring.zone).to be_graveyard
+    end
+
+    it "does not counter spell if cost is paid" do
+      choice = game.choices.first
+      p2.add_mana(white: 3)
+      choice.pay(p2, generic: { white: 3 })
+
+      game.resolve_choice!
+      game.tick!
+      expect(sol_ring.zone).to be_battlefield
+    end
+  end
+end