allows the emails to have before/after callbacks. Fixes #65

spec/callbacks_spec.cr

@@ -0,0 +1,89 @@
+require "./spec_helper"
+
+abstract class BaseTestEmail < Carbon::Email
+end
+
+BaseTestEmail.configure do |setting|
+  setting.adapter = Carbon::DevAdapter.new
+end
+
+private class EmailWithBeforeCallbacks < BaseTestEmail
+  subject "My great subject"
+  from Carbon::Address.new("[email protected]")
+  to Carbon::Address.new("[email protected]")
+
+  property ran_before_callback : Bool = false
+
+  before_send do
+    self.ran_before_callback = true
+  end
+end
+
+private class EmailWithAfterCallbacks < BaseTestEmail
+  subject "My great subject"
+  from Carbon::Address.new("[email protected]")
+  to Carbon::Address.new("[email protected]")
+
+  property ran_after_callback : Bool = false
+
+  after_send do |_response|
+    self.ran_after_callback = true
+  end
+end
+
+private class EmailWithBothBeforeAndAfterCallbacks < BaseTestEmail
+  subject "My great subject"
+  from Carbon::Address.new("[email protected]")
+  to Carbon::Address.new("[email protected]")
+
+  property ran_before_callback : Bool = false
+  property ran_after_callback : Bool = false
+
+  before_send :mark_before_send
+  after_send :mark_after_send
+
+  private def mark_before_send
+    self.ran_before_callback = true
+  end
+
+  private def mark_after_send(_response)
+    self.ran_after_callback = true
+  end
+end
+
+describe "before/after callbacks" do
+  context "before an email is sent" do
+    it "runs the before_send callback" do
+      email = EmailWithBeforeCallbacks.new
+      email.ran_before_callback.should eq(false)
+      email.deliver
+      Carbon.should have_delivered_emails
+
+      email.ran_before_callback.should eq(true)
+    end
+  end
+
+  context "after an email is sent" do
+    it "runs the after_send callback" do
+      email = EmailWithAfterCallbacks.new
+      email.ran_after_callback.should eq(false)
+      email.deliver
+      Carbon.should have_delivered_emails
+
+      email.ran_after_callback.should eq(true)
+    end
+  end
+
+  context "running both callbacks" do
+    it "runs both callbacks" do
+      email = EmailWithBothBeforeAndAfterCallbacks.new
+      email.ran_before_callback.should eq(false)
+      email.ran_after_callback.should eq(false)
+      email.deliver
+      Carbon.should have_delivered_emails
+
+      email.ran_before_callback.should eq(true)
+      email.ran_after_callback.should eq(true)
+    end
+  end
+end

src/carbon/callbacks.cr

@@ -0,0 +1,81 @@
+module Carbon::Callbacks
+  # Runs the given method before the adapter calls `deliver_now`
+  #
+  # ```
+  # before_send :attach_metadata
+  #
+  # private def attach_metadata
+  #   #...
+  # end
+  # ```
+  macro before_send(method_name)
+    before_send do
+      {{ method_name.id }}
+    end
+  end
+
+  # Runs the block before the adapter calls `deliver_now`
+  #
+  # ```
+  # before_send do
+  #   #...
+  # end
+  # ```
+  macro before_send
+    def before_send
+      {% if @type.methods.map(&.name).includes?(:before_send.id) %}
+        previous_def
+      {% else %}
+        super
+      {% end %}
+
+      {{ yield }}
+    end
+  end
+
+  # Runs the given method after the adapter calls `deliver_now`.
+  # Passes in the return value of the adapter's `deliver_now` method.
+  #
+  # ```
+  # after_send :mark_email_as_sent
+  #
+  # private def mark_email_as_sent(response)
+  #   # ...
+  # end
+  # ```
+  macro after_send(method_name)
+    after_send do |object|
+      {{ method_name.id }}(object)
+    end
+  end
+
+  # Runs the block after the adapter calls `deliver_now`, and passes the
+  # return value of the adapter's `deliver_now` method to the block.
+  #
+  # ```
+  # after_send do |response|
+  #   # ...
+  # end
+  # ```
+  macro after_send(&block)
+    {%
+      if block.args.size != 1
+        raise <<-ERR
+        The 'after_send' callback requires exactly 1 block arg to be passed.
+        Example:
+          after_send { |value| some_method(value) }
+        ERR
+      end
+    %}
+    def after_send(%object)
+      {% if @type.methods.map(&.name).includes?(:after_send.id) %}
+        previous_def
+      {% else %}
+        super
+      {% end %}
+
+      {{ block.args.first }} = %object
+      {{ block.body }}
+    end
+  end
+end

src/carbon/email.cr

@@ -1,6 +1,7 @@
 require "ecr"
 
 abstract class Carbon::Email
+  include Carbon::Callbacks
   alias Recipients = Carbon::Emailable | Array(Carbon::Emailable)
 
   abstract def subject : String
@@ -25,6 +26,10 @@ abstract class Carbon::Email
 
   def html_layout(content_io : IO); end
 
+  def before_send; end
+
+  def after_send(result); end
+
   getter headers
 
   macro inherited
@@ -122,7 +127,9 @@ abstract class Carbon::Email
   end
 
   def deliver
-    settings.adapter.deliver_now(self)
+    before_send
+    response = settings.adapter.deliver_now(self)
+    after_send(response)
   end
 
   def deliver_later