Add HTML email support

lib/generators/supermail/email/templates/email.rb.tt

@@ -4,4 +4,8 @@ class <%= class_name %>Email < ApplicationEmail
   def body = <<~PLAIN
 
   PLAIN
+
+  def html_body = <<~HTML
+
+  HTML
 end

lib/generators/supermail/install/templates/application_email.rb.tt

@@ -10,4 +10,12 @@ class ApplicationEmail < Supermail::Rails::Base
      The Example.com Team
      _
   end
+
+  def html_body
+    <<~HTML
+      #{yield if block_given?}
+      <p>Best,</p>
+      <p>The Example.com Team</p>
+    HTML
+  end
 end

lib/supermail.rb

@@ -13,22 +13,57 @@ class Base
           :deliver,
           :deliver_now,
           :deliver_later,
-          :message,
-        to: :action_mailer_base_mail
+        to: :message
+
+      def message
+        @message ||= action_mailer_base_mail
+      end
 
       def to = nil
       def from = nil
       def subject = nil
       def cc = []
       def bcc = []
       def body = ""
+      def html_body = nil
 
       # Generate a mailto: URL with appropriate escaping.
       def mailto = MailTo.href(to:, from:, cc:, bcc:, subject:, body:)
       alias :mail_to :mailto
 
       private def action_mailer_base_mail
-        ActionMailer::Base.mail(to:, from:, cc:, bcc:, subject:, body:)
+        if html_body && !html_body.empty?
+          # Multipart email with both text and HTML
+          # Capture values to avoid context issues in blocks
+          email_to = to
+          email_from = from
+          email_cc = cc
+          email_bcc = bcc
+          email_subject = subject
+          text_body = body
+          html_content = html_body
+
+          Mail.new do
+            to email_to
+            from email_from
+            cc email_cc if email_cc && !email_cc.empty?
+            bcc email_bcc if email_bcc && !email_bcc.empty?
+            subject email_subject
+
+            text_part do
+              body text_body
+            end
+
+            html_part do
+              content_type 'text/html; charset=UTF-8'
+              body html_content
+            end
+          end
+        else
+          # Plain text only
+          # ActionMailer::Base.mail returns a MessageDelivery, extract the message
+          ActionMailer::Base.mail(to:, from:, cc:, bcc:, subject:, body:).message
+        end
       end
     end
   end

spec/supermail_spec.rb

@@ -59,3 +59,178 @@ def initialize(to:, from:, subject:, body:, cc: [], bcc: [])
     end
   end
 end
+
+class HtmlMailer < Supermail::Rails::Base
+  def initialize(to:, from:, subject:, body:, html_body:)
+    @to = to
+    @from = from
+    @subject = subject
+    @body = body
+    @html_body = html_body
+  end
+
+  attr_reader :to, :from, :subject, :body, :html_body
+end
+
+RSpec.describe HtmlMailer do
+  let(:email) { described_class.new(
+    to: "user@example.com",
+    from: "support@example.com",
+    subject: "Hello",
+    body: "Hi there",
+    html_body: "<p>Hi there</p>")
+  }
+  let(:message) { email.message }
+
+  it "creates a multipart email" do
+    expect(message.multipart?).to be true
+  end
+
+  it "includes text part" do
+    text_part = message.text_part
+    expect(text_part).not_to be_nil
+    expect(text_part.body.to_s).to eq("Hi there")
+  end
+
+  it "includes html part" do
+    html_part = message.html_part
+    expect(html_part).not_to be_nil
+    expect(html_part.body.to_s).to eq("<p>Hi there</p>")
+  end
+
+  context "when html_body is nil" do
+    let(:email) { described_class.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "Hi there",
+      html_body: nil)
+    }
+
+    it "creates a plain text email" do
+      expect(message.multipart?).to be false
+      expect(message.body.to_s).to eq("Hi there")
+    end
+  end
+
+  context "when html_body is empty" do
+    let(:email) { described_class.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "Hi there",
+      html_body: "")
+    }
+
+    it "creates a plain text email" do
+      expect(message.multipart?).to be false
+      expect(message.body.to_s).to eq("Hi there")
+    end
+  end
+
+  context "when html_body contains only whitespace" do
+    let(:email) { described_class.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "Hi there",
+      html_body: "   \n\t  ")
+    }
+
+    it "creates a multipart email" do
+      # Mail gem may strip whitespace-only content, which is expected behavior
+      expect(message.multipart?).to be true
+    end
+  end
+
+  context "with cc and bcc" do
+    class HtmlMailerWithCc < Supermail::Rails::Base
+      def initialize(to:, from:, subject:, body:, html_body:, cc:, bcc:)
+        @to = to
+        @from = from
+        @subject = subject
+        @body = body
+        @html_body = html_body
+        @cc = cc
+        @bcc = bcc
+      end
+
+      attr_reader :to, :from, :subject, :body, :html_body, :cc, :bcc
+    end
+
+    let(:email) { HtmlMailerWithCc.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "Hi there",
+      html_body: "<p>Hi there</p>",
+      cc: ["cc@example.com"],
+      bcc: ["bcc@example.com"])
+    }
+    let(:message) { email.message }
+
+    it "includes cc recipients" do
+      expect(message.cc).to eq(["cc@example.com"])
+    end
+
+    it "includes bcc recipients" do
+      expect(message.bcc).to eq(["bcc@example.com"])
+    end
+
+    it "creates a multipart email" do
+      expect(message.multipart?).to be true
+    end
+  end
+
+  context "html part content type" do
+    it "sets correct content type" do
+      html_part = message.html_part
+      expect(html_part.content_type).to include("text/html")
+      expect(html_part.content_type).to include("charset=UTF-8")
+    end
+  end
+
+  context "delivery methods" do
+    let(:email) { described_class.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "Hi there",
+      html_body: "<p>Hi there</p>")
+    }
+
+    it "responds to deliver" do
+      expect(email).to respond_to(:deliver)
+    end
+
+    it "responds to deliver_now" do
+      expect(email).to respond_to(:deliver_now)
+    end
+
+    it "responds to deliver_later" do
+      expect(email).to respond_to(:deliver_later)
+    end
+  end
+
+  context "when body is empty but html_body is present" do
+    let(:email) { described_class.new(
+      to: "user@example.com",
+      from: "support@example.com",
+      subject: "Hello",
+      body: "",
+      html_body: "<p>Hi there</p>")
+    }
+
+    it "creates a multipart email" do
+      expect(message.multipart?).to be true
+    end
+
+    it "includes empty text part" do
+      expect(message.text_part.body.to_s).to eq("")
+    end
+
+    it "includes html part" do
+      expect(message.html_part.body.to_s).to eq("<p>Hi there</p>")
+    end
+  end
+end