Add markdown problem

Author: Yeong Sheng, Tan

config.json

@@ -38,6 +38,7 @@
     "parallel-letter-frequency",
     "binary",
     "luhn",
+    "markdown",
     "gigasecond",
     "queen-attack",
     "pascals-triangle",
@@ -272,6 +273,12 @@
       "topics": [
       ]
     },
+    {
+      "slug": "markdown",
+      "difficulty": 1,
+      "topics": [
+      ]
+    },
     {
       "slug": "gigasecond",
       "difficulty": 1,

exercises/markdown/example.exs

@@ -0,0 +1,81 @@
+defmodule Markdown do
+  @bold_md "__"
+  @header_md "#"
+  @italic_md "_"
+  @list_md "*"
+
+  @bold_open_tag "<em>"
+  @bold_close_tag "</em>"
+  @italic_open_tag "<i>"
+  @italic_close_tag "</i>"
+  @unordered_list_open_tag "<ul>"
+  @unordered_list_close_tag "</ul>"
+  @list_item_open_tag "<li>"
+  @list_item_close_tag "</li>"
+  @paragraph_open_tag "<p>"
+  @paragraph_close_tag "</p>"
+  @header_partial_open_tag "<h"
+  @header_partial_close_tag "</h"
+
+  def parse(markdown) do
+    String.split(markdown, "\n") |> parse_line
+  end
+
+  defp parse_line(markdown_split_by_newline) do
+    Enum.map_join(markdown_split_by_newline, fn(text_with_md) -> process_md(text_with_md) end) |> patch_line_with_unordered_list_tag
+  end
+
+  defp process_md(text_with_md) do
+    cond do
+      String.starts_with?(text_with_md, "#") -> parse_header_md_level(text_with_md) |> enclose_with_header_tag
+      String.starts_with?(text_with_md, "*") -> parse_list_md_level(text_with_md)
+      true                                   -> String.split(text_with_md) |> enclose_with_paragraph_tag
+    end
+  end
+
+  defp parse_header_md_level(header_md_with_text) do
+    [header_md | header_text] = String.split(header_md_with_text)
+    {to_string(String.length(header_md)), Enum.join(header_text, " ")}
+  end
+
+  defp parse_list_md_level(list_md_with_text) do
+    list_text = String.trim_leading(list_md_with_text, "* ") |> String.split
+    @list_item_open_tag <> join_words_with_tags(list_text) <> @list_item_close_tag
+  end
+
+  defp enclose_with_header_tag({header_level, header_text_line}) do
+    @header_partial_open_tag <> header_level <> ">" <> header_text_line <> @header_partial_close_tag <> header_level <> ">"
+  end
+
+  defp enclose_with_paragraph_tag(text_with_md) do
+    @paragraph_open_tag <> join_words_with_tags(text_with_md) <> @paragraph_close_tag
+  end
+
+  defp join_words_with_tags(text_with_md) do
+    Enum.map_join(text_with_md, " ", fn(word_with_md) -> replace_md_with_tag(word_with_md) end)
+  end
+
+  defp replace_md_with_tag(word_with_md) do
+    replace_prefix_md(word_with_md) |> replace_suffix_md
+  end
+
+  defp replace_prefix_md(word_with_md) do
+    cond do
+      word_with_md =~ ~r/^[#{@italic_md}{1}][^#{@italic_md}+]/ -> String.replace_prefix(word_with_md, @italic_md, @italic_open_tag)
+      word_with_md =~ ~r/^#{@bold_md}{1}/ -> String.replace_prefix(word_with_md, @bold_md, @bold_open_tag)
+      true -> word_with_md
+    end
+  end
+
+  defp replace_suffix_md(word_with_md) do
+    cond do
+      word_with_md =~ ~r/[^#{@italic_md}{1}][#{@italic_md}{1}]$/ -> String.replace_suffix(word_with_md, @italic_md, @italic_close_tag)
+      word_with_md =~ ~r/#{@bold_md}{1}$/ -> String.replace_suffix(word_with_md, @bold_md, @bold_close_tag)
+      true -> word_with_md
+    end
+  end
+
+  defp patch_line_with_unordered_list_tag(html_line) do
+    String.replace(html_line, @list_item_open_tag, @unordered_list_open_tag <> @list_item_open_tag, global: false) |> String.replace_suffix(@list_item_close_tag, @list_item_close_tag <> @unordered_list_close_tag)
+  end
+end

exercises/markdown/markdown.exs

@@ -0,0 +1,18 @@
+defmodule Markdown do
+  @doc """
+    Parses a given string with Markdown syntax and returns the associated HTML for that string.
+
+    ## Examples
+
+    iex> Markdown.parse("This is a paragraph")
+    "<p>This is a paragraph</p>"
+
+    iex> Markdown.parse("#Header!\n* __Bold Item__\n* _Italic Item_")
+    "<h1>Header!</h1><ul><li><em>Bold Item</em></li><li><i>Italic Item</i></li></ul>"
+  """
+
+  @spec parse(String.t) :: String.t
+  def parse(markdown) do
+
+  end
+end

exercises/markdown/markdown_test.exs

@@ -0,0 +1,73 @@
+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><i>This will be italic</i></p>"
+    assert Markdown.parse(input) == expected
+  end
+
+  @tag :pending
+  test "parsing bold text" do
+    input = "__This will be bold__"
+    expected = "<p><em>This will be bold</em></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 <i>be</i> <em>mixed</em></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><em>Bold Item</em></li><li><i>Italic Item</i></li></ul>"
+    assert Markdown.parse(input) == expected
+  end
+end