First step rendering a page

The API responds with a bunch of paragraphs which the client converts
into Paragraph objects.

This turns the paragraphs in a PostResponse's Paragraph objects into the
form needed to render them on a page. This includes converting flat list
elements into list elements nested by a UL. And adding a limited markups
along the way.

The array of paragraphs is passed to a recursive function. The function
takes the first paragraph and either wraps the (marked up) contents in a
container tag (like Paragraph or Heading3), and then moves onto the next
tag. If it finds a list, it starts parsing the next paragraphs as a list
instead.

Originally, this was implemented like so:

```crystal
paragraph = paragraphs.shift
if list?
  convert_list([paragraph] + paragraphs)
end
```

However, passing the `paragraphs` after adding it to the already shifted
`paragraph` creates a new object. This means `paragraphs` won't be
mutated and once the list is parsed, it starts with the next element of
the list. Instead, the element is `shift`ed inside each converter.

```crystal
if paragraphs.first == list?
  convert_list(paragraphs)
end

def convert_list(paragraphs)
  paragraph = paragraphs.shift
  # ...
end
```

When rendering, there is an Empty and Container object. These represent
a kind of "null object" for both leafs and parent objects respectively.
They should never actually render. Emptys are filtered out, and
Containers are never created explicitly but this will make the types
pass.

IFrames are a bit of a special case. Each IFrame has custom data on it
that this system would need to be aware of. For now, instead of trying
to parse the seemingly large number of iframe variations and dealing
with embedded iframe problems, this will just keep track of the source
page URL and send the user there with a link.

spec/classes/iframe_media_resolver_spec.cr

@@ -0,0 +1,27 @@
+require "../spec_helper"
+
+include Nodes
+
+describe IFrameMediaResolver do
+  around_each do |example|
+    original_client = IFrameMediaResolver.http_client
+    IFrameMediaResolver.http_client = FakeMediumClient
+    example.run
+    IFrameMediaResolver.http_client = original_client
+  end
+
+  it "returns a url of the embedded page" do
+    iframe = PostResponse::IFrame.from_json <<-JSON
+      {
+        "mediaResource": {
+          "id": "d4515fff7ecd02786e75fc8997c94bbf"
+        }
+      }
+    JSON
+    resolver = IFrameMediaResolver.new(iframe: iframe)
+
+    result = resolver.fetch_href
+
+    result.should eq("https://example.com")
+  end
+end

spec/classes/markup_converter_spec.cr

@@ -0,0 +1,99 @@
+require "../spec_helper"
+
+include Nodes
+
+describe MarkupConverter do
+  it "returns just text with no markups" do
+    json = <<-JSON
+      {
+        "text": "Hello, world",
+        "type": "P",
+        "markups": [],
+        "href": null,
+        "iframe": null,
+        "layout": null,
+        "metadata": null
+      }
+    JSON
+    paragraph = PostResponse::Paragraph.from_json(json)
+
+    result = MarkupConverter.convert(text: paragraph.text, markups: paragraph.markups)
+
+    result.should eq([Text.new(content: "Hello, world")])
+  end
+
+  it "returns just text with multiple markups" do
+    json = <<-JSON
+      {
+        "text": "strong and emphasized only",
+        "type": "P",
+        "markups": [
+          {
+            "title": null,
+            "type": "STRONG",
+            "href": null,
+            "start": 0,
+            "end": 6,
+            "rel": null,
+            "anchorType": null
+          },
+          {
+            "title": null,
+            "type": "EM",
+            "href": null,
+            "start": 11,
+            "end": 21,
+            "rel": null,
+            "anchorType": null
+          }
+        ],
+        "href": null,
+        "iframe": null,
+        "layout": null,
+        "metadata": null
+      }
+    JSON
+    paragraph = PostResponse::Paragraph.from_json(json)
+
+    result = MarkupConverter.convert(text: paragraph.text, markups: paragraph.markups)
+
+    result.should eq([
+      Strong.new(children: [Text.new(content: "strong")] of Child),
+      Text.new(content: " and "),
+      Emphasis.new(children: [Text.new(content: "emphasized")] of Child),
+      Text.new(content: " only"),
+    ])
+  end
+
+  it "returns just text with a code markup" do
+    json = <<-JSON
+      {
+        "text": "inline code",
+        "type": "P",
+        "markups": [
+          {
+            "title": null,
+            "type": "CODE",
+            "href": null,
+            "start": 7,
+            "end": 11,
+            "rel": null,
+            "anchorType": null
+          }
+        ],
+        "href": null,
+        "iframe": null,
+        "layout": null,
+        "metadata": null
+      }
+    JSON
+    paragraph = PostResponse::Paragraph.from_json(json)
+
+    result = MarkupConverter.convert(text: paragraph.text, markups: paragraph.markups)
+
+    result.should eq([
+      Text.new(content: "inline "),
+      Code.new(children: [Text.new(content: "code")] of Child),
+    ])
+  end
+end

spec/classes/paragraph_converter_spec.cr

@@ -0,0 +1,271 @@
+require "../spec_helper"
+
+include Nodes
+
+describe ParagraphConverter do
+  around_each do |example|
+    original_client = IFrameMediaResolver.http_client
+    IFrameMediaResolver.http_client = FakeMediumClient
+    example.run
+    IFrameMediaResolver.http_client = original_client
+  end
+
+  it "converts a simple structure with no markups" do
+    paragraphs = Array(PostResponse::Paragraph).from_json <<-JSON
+      [
+        {
+          "text": "Title",
+          "type": "H3",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        }
+      ]
+    JSON
+    expected = [Heading3.new(children: [Text.new(content: "Title")] of Child)]
+
+    result = ParagraphConverter.new.convert(paragraphs)
+
+    result.should eq expected
+  end
+
+  it "converts a simple structure with a markup" do
+    paragraphs = Array(PostResponse::Paragraph).from_json <<-JSON
+      [
+        {
+          "text": "inline code",
+          "type": "P",
+          "markups": [
+            {
+              "name": null,
+              "title": null,
+              "type": "CODE",
+              "href": null,
+              "start": 7,
+              "end": 11,
+              "rel": null,
+              "anchorType": null
+            }
+          ],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        }
+      ]
+    JSON
+    expected = [
+      Paragraph.new(children: [
+        Text.new(content: "inline "),
+        Code.new(children: [Text.new(content: "code")] of Child),
+      ] of Child)
+    ]
+
+    result = ParagraphConverter.new.convert(paragraphs)
+
+    result.should eq expected
+  end
+
+  it "groups <ul> list items into one list" do
+    paragraphs = Array(PostResponse::Paragraph).from_json <<-JSON
+      [
+        {
+          "text": "One",
+          "type": "ULI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "Two",
+          "type": "ULI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "Not a list item",
+          "type": "P",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        }
+      ]
+    JSON
+    expected = [
+      UnorderedList.new(children: [
+        ListItem.new(children: [Text.new(content: "One")] of Child),
+        ListItem.new(children: [Text.new(content: "Two")] of Child),
+      ] of Child),
+      Paragraph.new(children: [Text.new(content: "Not a list item")] of Child),
+    ]
+
+    result = ParagraphConverter.new.convert(paragraphs)
+
+    result.should eq expected
+  end
+
+  it "groups <ol> list items into one list" do
+    paragraphs = Array(PostResponse::Paragraph).from_json <<-JSON
+      [
+        {
+          "text": "One",
+          "type": "OLI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "Two",
+          "type": "OLI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "Not a list item",
+          "type": "P",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        }
+      ]
+    JSON
+    expected = [
+      OrderedList.new(children: [
+        ListItem.new(children: [Text.new(content: "One")] of Child),
+        ListItem.new(children: [Text.new(content: "Two")] of Child),
+      ] of Child),
+      Paragraph.new(children: [Text.new(content: "Not a list item")] of Child),
+    ]
+
+    result = ParagraphConverter.new.convert(paragraphs)
+
+    result.should eq expected
+  end
+
+  it "converts all the tags" do
+    paragraphs = Array(PostResponse::Paragraph).from_json <<-JSON
+      [
+        {
+          "text": "text",
+          "type": "H3",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "H4",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "P",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "PRE",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "BQ",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "ULI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "OLI",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": null
+        },
+        {
+          "text": "text",
+          "type": "IMG",
+          "markups": [],
+          "href": null,
+          "iframe": null,
+          "layout": null,
+          "metadata": {
+            "id": "1*miroimage.png",
+            "originalWidth": 618,
+            "originalHeight": 682
+          }
+        },
+        {
+          "text": "",
+          "type": "IFRAME",
+          "markups": [],
+          "href": null,
+          "iframe": {
+            "mediaResource": {
+              "id": "7c6231d165bf9fc1853f259a7b55bd14"
+            }
+          },
+          "layout": null,
+          "metadata": null
+        }
+      ]
+    JSON
+    expected = [
+      Heading3.new([Text.new("text")] of Child),
+      Heading4.new([Text.new("text")] of Child),
+      Paragraph.new([Text.new("text")] of Child),
+      Preformatted.new([Text.new("text")] of Child),
+      BlockQuote.new([Text.new("text")] of Child),
+      UnorderedList.new([ListItem.new([Text.new("text")] of Child)] of Child),
+      OrderedList.new([ListItem.new([Text.new("text")] of Child)] of Child),
+      Image.new(src: "1*miroimage.png"),
+      IFrame.new(href: "https://example.com"),
+    ]
+
+    result = ParagraphConverter.new.convert(paragraphs)
+
+    result.should eq expected
+  end
+end

spec/components/page_content_spec.cr

@@ -0,0 +1,189 @@
+require "../spec_helper"
+
+include Nodes
+
+describe PageContent do
+  it "renders a single parent/child node structure" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        Text.new(content: "hi"),
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p>hi</p>)
+  end
+
+  it "renders multiple childrens" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        Text.new(content: "Hello, "),
+        Emphasis.new(children: [
+          Text.new(content: "World!")
+        ] of Child)
+      ] of Child),
+      UnorderedList.new(children: [
+        ListItem.new(children: [
+          Text.new(content: "List!")
+        ] of Child),
+        ListItem.new(children: [
+          Text.new(content: "Again!"),
+        ] of Child)
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p>Hello, <em>World!</em></p><ul><li>List!</li><li>Again!</li></ul>)
+  end
+
+  it "renders a blockquote" do
+    page = Page.new(nodes: [
+      BlockQuote.new(children: [
+        Text.new("Wayne Gretzky. Michael Scott.")
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<blockquote>Wayne Gretzky. Michael Scott.</blockquote>)
+  end
+
+  it "renders code" do
+    page = Page.new(nodes: [
+      Code.new(children: [
+        Text.new("foo = bar")
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<code>foo = bar</code>)
+  end
+
+  it "renders empasis" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        Text.new(content: "This is "),
+        Emphasis.new(children: [
+          Text.new(content: "neat!")
+        ] of Child),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p>This is <em>neat!</em></p>)
+  end
+
+  it "renders an H3" do
+    page = Page.new(nodes: [
+      Heading3.new(children: [
+        Text.new(content: "Title!"),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<h3>Title!</h3>)
+  end
+
+  it "renders an H4" do
+    page = Page.new(nodes: [
+      Heading4.new(children: [
+        Text.new(content: "In Conclusion..."),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<h4>In Conclusion...</h4>)
+  end
+
+  it "renders an image" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        Image.new(src: "image.png"),
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p><img src="https://cdn-images-1.medium.com/image.png"></p>)
+  end
+
+  it "renders an iframe container" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        IFrame.new(href: "https://example.com"),
+      ] of Child)
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p><div class="embedded"><a href="https://example.com">Click to visit embedded content</a></div></p>)
+  end
+
+  it "renders an ordered list" do
+    page = Page.new(nodes: [
+      OrderedList.new(children: [
+        ListItem.new(children: [Text.new("One")] of Child),
+        ListItem.new(children: [Text.new("Two")] of Child),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<ol><li>One</li><li>Two</li></ol>)
+  end
+
+  it "renders an preformatted text" do
+    page = Page.new(nodes: [
+      Paragraph.new(children: [
+        Text.new("Hello, world!"),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<p>Hello, world!</p>)
+  end
+
+  it "renders an preformatted text" do
+    page = Page.new(nodes: [
+      Preformatted.new(children: [
+        Text.new("New\nline"),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<pre>New\nline</pre>)
+  end
+
+  it "renders strong text" do
+    page = Page.new(nodes: [
+      Strong.new(children: [
+        Text.new("Oh yeah!"),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<strong>Oh yeah!</strong>)
+  end
+
+  it "renders an unordered list" do
+    page = Page.new(nodes: [
+      UnorderedList.new(children: [
+        ListItem.new(children: [Text.new("Apple")] of Child),
+        ListItem.new(children: [Text.new("Banana")] of Child),
+      ] of Child),
+    ] of Child)
+
+    html = PageContent.new(page: page).render_to_string
+
+    html.should eq %(<ul><li>Apple</li><li>Banana</li></ul>)
+  end
+end

spec/support/fake_medium_client.cr

@@ -0,0 +1,9 @@
+class FakeMediumClient < MediumClient
+  def self.media_data(media_id : String) : MediaResponse::Root
+    MediaResponse::Root.from_json(
+      <<-JSON
+        {"payload": {"value": {"href": "https://example.com"}}}
+      JSON
+    )
+  end
+end