From 312285b165b06cd1c09d881c6d8b569fa6aac575 Mon Sep 17 00:00:00 2001
From: Norberto Oliveira Junior <norbejunior@gmail.com>
Date: Sun, 18 Apr 2021 12:26:45 -0300
Subject: [PATCH] Add new way to set from transitions

* Add macro `Machinist.from/2` that expects a state
  and a block of `to` statements
---
 README.md               | 24 +++++++++++++++++++++++-
 lib/machinist.ex        | 40 ++++++++++++++++++++++++++++++++++++++++
 mix.exs                 |  4 ++--
 test/machinist_test.exs | 33 +++++++++++++++++++++++++++++++--
 4 files changed, 96 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index 261fb6b..ec00b6e 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ You can install `machinist` by adding it  to your list of dependencies in `mix.e
 ```elixir
 def deps do
   [
-    {:machinist, "~> 0.3.0"}
+    {:machinist, "~> 0.4.0"}
   ]
 end
 ```
@@ -77,6 +77,28 @@ iex> Door.transit(door_opened, event: "lock")
 {:error, :not_allowed}
 ```
 
+### Group same-state `from` definitions
+
+In the example above we could group the `from :unlocked` definitions like this:
+
+```elixir
+# ...
+transitions do
+  from :locked, to: :unlocked, event: "unlock"
+  from :unlocked do
+    to :locked, event: "lock"
+    to :opened, event: "open"
+  end
+  from :opened, to: :closed,   event: "close"
+  from :closed, to: :opened,   event: "open"
+  from :closed, to: :locked,   event: "lock"
+end
+# ...
+```
+
+This is an option to a better organization and an increase of readability when having
+a large number of `from` definitions with a same state.
+
 ### Setting different attribute name that holds the state
 
 By default `machinist` expects the struct being updated holds a `state` attribute, if you hold state in a different attribute, just pass the name as an atom, as follows:
diff --git a/lib/machinist.ex b/lib/machinist.ex
index e9d89c2..1c14653 100644
--- a/lib/machinist.ex
+++ b/lib/machinist.ex
@@ -51,6 +51,26 @@ defmodule Machinist do
       iex> Door.transit(door_opened, event: "lock")
       iex> {:error, :not_allowed}
 
+  ### Group same-state `from` definitions
+
+  In the example above we also could group the `from :unlocked` definitions like this:
+
+      # ...
+      transitions do
+        from :locked,   to: :unlocked, event: "unlock"
+        from :unlocked do
+          to :locked, event: "lock"
+          to :opened, event: "open"
+        end
+        from :opened,   to: :closed,   event: "close"
+        from :closed,   to: :opened,   event: "open"
+        from :closed,   to: :locked,   event: "lock"
+      end
+      # ...
+
+  This is an option to a better organization and an increase of readability when having
+  a large number of `from` definitions with a same state.
+
   ### Setting different attribute name that holds the state
 
   By default `machinist` expects the struct being updated holds a `state` attribute,
@@ -346,7 +366,27 @@ defmodule Machinist do
 
       from _state, to: :expired, event: "enrollment_expired"
   """
+  defmacro from(state, do: {_, _line, to_statements}) do
+    define_transitions(state, to_statements)
+  end
+
   defmacro from(state, to: new_state, event: event) do
+    define_transition(state, to: new_state, event: event)
+  end
+
+  @doc false
+  defp define_transitions(_state, []), do: []
+
+  @doc false
+  defp define_transitions(state, [{:to, _line, [new_state, [event: event]]} | transitions]) do
+    [
+      define_transition(state, to: new_state, event: event)
+      | define_transitions(state, transitions)
+    ]
+  end
+
+  @doc false
+  defp define_transition(state, to: new_state, event: event) do
     quote do
       @impl true
       def transit(%@__struct__{@__attr__ => unquote(state)} = resource, event: unquote(event)) do
diff --git a/mix.exs b/mix.exs
index 6c69d35..3b4976d 100644
--- a/mix.exs
+++ b/mix.exs
@@ -1,13 +1,13 @@
 defmodule Machinist.MixProject do
   use Mix.Project
 
-  @version "0.3.0"
+  @version "0.4.0"
   @repo_url "https://github.com/norbajunior/machinist"
 
   def project do
     [
       app: :machinist,
-      version: "0.3.0",
+      version: @version,
       elixir: "~> 1.6",
       start_permanent: Mix.env() == :prod,
       deps: deps(),
diff --git a/test/machinist_test.exs b/test/machinist_test.exs
index 787eac6..2541a46 100644
--- a/test/machinist_test.exs
+++ b/test/machinist_test.exs
@@ -131,8 +131,12 @@ defmodule MachinistTest do
       transitions do
         from(:new, to: :registered, event: "register")
         from(:registered, to: :interview_scheduled, event: "schedule_interview")
-        from(:interview_scheduled, to: :approved, event: "approve_interview")
-        from(:interview_scheduled, to: :repproved, event: "reprove_interview")
+
+        from :interview_scheduled do
+          to(:approved, event: "approve_interview")
+          to(:repproved, event: "reprove_interview")
+        end
+
         from(:approved, to: :enrolled, event: "enroll")
         from(_state, to: :application_expired, event: "application_expired")
       end
@@ -152,4 +156,29 @@ defmodule MachinistTest do
         Example5.transit(%Example5{state: :approved}, event: "application_expired")
     end
   end
+
+  describe "a example with passing a block of transitions to from" do
+    defmodule Example6 do
+      defstruct state: :test
+
+      use Machinist
+
+      transitions do
+        from(:test, to: :test1, event: "test1")
+
+        from :test1 do
+          to(:test2, event: "test2")
+          to(:test3, event: "test3")
+          to(:test4, event: "test4")
+        end
+      end
+    end
+
+    test "all transitions" do
+      assert {:ok, example} = Example6.transit(%Example6{}, event: "test1")
+      assert {:ok, %Example6{state: :test2}} = Example6.transit(example, event: "test2")
+      assert {:ok, %Example6{state: :test3}} = Example6.transit(example, event: "test3")
+      assert {:ok, %Example6{state: :test4}} = Example6.transit(example, event: "test4")
+    end
+  end
 end