Use Yaml to generate markdown header

spec/medium/post_spec.cr

@@ -37,7 +37,7 @@ describe Medium::Post do
     it "render full page" do
       subject = Medium::Post.from_json(post_fixture)
       content, assets = subject.to_md
-      content.size.should eq(3322)
+      content.size.should eq(3324)
       assets.size.should eq(1)
       assets.keys.should eq([
         "ab24f0b378f797307fddc32f10a99685.html",
@@ -51,7 +51,7 @@ describe Medium::Post do
       subject.ctx = ::Medup::Context.new(settings)
 
       content, assets = subject.to_md
-      content.size.should eq(3048)
+      content.size.should eq(3050)
       assets.keys.should eq([
         "0*FbFs8aNmqNLKw4BM.png",
         "ab24f0b378f797307fddc32f10a99685.html",

src/medium/post.cr

@@ -1,4 +1,5 @@
 require "json_mapping"
+require "yaml"
 
 require "./post/*"
 
@@ -30,23 +31,24 @@ module Medium
     end
 
     def to_md
-      result = "---\n\
-        url: #{mediumUrl}\n\
-        canonical_url: #{canonicalUrl}\n\
-        title: #{@title}\n\
-        subtitle: #{subtitle}\n\
-        slug: #{@slug}\n\
-        description: #{seo_description}\n\
-        tags: #{tags}\n"
-      assets = Hash(String, String).new
-
-      unless @user.nil?
-        user = @user.not_nil!
-        result += "author: #{user.name}\n\
-          username: #{user.username}\n"
+      header = {
+        "url"           => mediumUrl,
+        "canonical_url" => canonicalUrl,
+        "title"         => @title,
+        "subtitle"      => subtitle,
+        "slug"          => @slug,
+        "description"   => seo_description,
+        "tags"          => tags,
+      }
+      user = @user
+      if !user.nil?
+        header["author"] = user.name
+        header["username"] = user.username
       end
 
-      result += "---\n\n"
+      result = header.to_yaml + "---\n\n"
+
+      assets = Hash(String, String).new
       footer = "\n"
 
       @content.bodyModel.paragraphs.map do |paragraph|