remove premailer

lib/html_to_plain_text_interceptor.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+module HtmlToPlainTextInterceptor
+  module_function
+
+  def delivering_email(message)
+    process(message)
+  end
+
+  def previewing_email(message)
+    process(message)
+  end
+
+  def process(message)
+    return message unless html_part(message)
+    return message if message.text_part
+
+    add_text_part(message)
+
+    message
+  end
+
+  def add_text_part(message)
+    html = html_part(message).decoded
+    text = HtmlToPlainText.call(html)
+
+    text_part = Mail::Part.new do
+      content_type 'text/plain; charset=UTF-8'
+      body text
+    end
+
+    if pure_html_message?(message)
+      message.body = nil
+      message.content_type = 'multipart/alternative'
+      message.add_part(text_part)
+      message.add_part(Mail::Part.new do
+        content_type 'text/html; charset=UTF-8'
+        body html
+      end)
+    else
+      alternative = Mail::Part.new(content_type: 'multipart/alternative')
+      alternative.add_part(text_part)
+      alternative.add_part(message.html_part)
+      replace_part(message.parts, message.html_part, alternative)
+    end
+  end
+
+  def pure_html_message?(message)
+    message.content_type.to_s.include?('text/html')
+  end
+
+  def html_part(message)
+    pure_html_message?(message) ? message : message.html_part
+  end
+
+  def replace_part(parts, old_part, new_part)
+    if (index = parts.index(old_part))
+      parts[index] = new_part
+    else
+      parts.each do |part|
+        replace_part(part.parts, old_part, new_part) if part.respond_to?(:parts)
+      end
+    end
+  end
+end