thekeele's solution to Markdown on the Elixir track

Instructions

Test suite

Solution

Note:

This exercise has changed since this solution was written.

Refactor a Markdown parser.

The markdown exercise is a refactoring exercise. There is code that parses a given string with Markdown syntax and returns the associated HTML for that string. Even though this code is confusingly written and hard to follow, somehow it works and all the tests are passing! Your challenge is to re-write this code to make it easier to read and maintain while still making sure that all the tests keep passing.

It would be helpful if you made notes of what you did in your refactoring in comments so reviewers can see that, but it isn't strictly necessary. The most important thing is to make the code better!

Running tests

Execute the tests with:

$ elixir markdown_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

markdown_test.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("markdown.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule MarkdownTest do
  use ExUnit.Case

  # @tag :pending
  test "parses normal text as a paragraph" do
    input = "This will be a paragraph"
    expected = "<p>This will be a paragraph</p>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "parsing italics" do
    input = "_This will be italic_"
    expected = "<p><em>This will be italic</em></p>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "parsing bold text" do
    input = "__This will be bold__"
    expected = "<p><strong>This will be bold</strong></p>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "mixed normal, italics and bold text" do
    input = "This will _be_ __mixed__"
    expected = "<p>This will <em>be</em> <strong>mixed</strong></p>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "with h1 header level" do
    input = "# This will be an h1"
    expected = "<h1>This will be an h1</h1>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "with h2 header level" do
    input = "## This will be an h2"
    expected = "<h2>This will be an h2</h2>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "with h6 header level" do
    input = "###### This will be an h6"
    expected = "<h6>This will be an h6</h6>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "unordered lists" do
    input = "* Item 1\n* Item 2"
    expected = "<ul><li>Item 1</li><li>Item 2</li></ul>"
    assert Markdown.parse(input) == expected
  end

  @tag :pending
  test "with a little bit of everything" do
    input = "# Header!\n* __Bold Item__\n* _Italic Item_"

    expected =
      "<h1>Header!</h1><ul><li><strong>Bold Item</strong></li><li><em>Italic Item</em></li></ul>"

    assert Markdown.parse(input) == expected
  end
end

defmodule Markdown do

  @spec parse(String.t()) :: String.t()
  def parse(text) do
    if String.contains?(text, "\n") do
      text
      |> String.split("\n")
      |> process()
    else
      process(text)
    end
  end

  defp process(text) when is_list(text) do
    text
    |> Enum.map_join(&process/1)
    |> String.replace("<li>", "<ul><li>", global: false)
    |> String.replace_trailing("</li>", "</li></ul>")
  end

  defp process(<<"# ", text::binary>>) do
    "<h1>#{text}</h1>"
  end
  defp process(<<"## ", text::binary>>) do
    "<h2>#{text}</h2>"
  end
  defp process(<<"###### ", text::binary>>) do
    "<h6>#{text}</h6>"
  end

  defp process(<<"* ", text::binary>>) do
    "<li>#{replace_with_tags(text)}</li>"
  end

  defp process(text) do
    "<p>#{replace_with_tags(text)}</p>"
  end

  defp replace_with_tags(text) do
    text
    |> String.split(" ")
    |> Enum.map_join(" ", &replace_markdown/1)
  end

  defp replace_markdown(word) do
    cond do
      String.contains?(word, "__") ->
        word |> String.replace_leading("__", "<strong>") |> String.replace_trailing("__", "</strong>")
      String.contains?(word, "_") ->
        word |> String.replace_leading("_", "<em>") |> String.replace_trailing("_", "</em>")
      true ->
        word
    end
  end
end

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thekeele's solution

to Markdown in the Elixir Track