Add Erlang version

erlang/.gitignore

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+/_build
+/*.txt

erlang/README.md

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+# Erlang
+
+## Prerequisites
+
+- Erlang/OTP 20 or later
+
+## Running Tests
+
+```
+./rebar3 eunit
+```

erlang/include/gilded_rose.hrl

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+-record(item, {
+  name :: binary(),
+  sell_in = 0 :: integer(),
+  quality = 0 :: integer()
+}).

erlang/rebar.config

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+{erl_opts, [warnings_as_errors]}.
+{eunit_opts, [verbose]}.

erlang/src/gilded_rose.app.src

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+{application, gilded_rose, [{vsn, "0.1"}]}.

erlang/src/gilded_rose.erl

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+-module(gilded_rose).
+
+-include("gilded_rose.hrl").
+
+-export([
+  update_quality/1
+]).
+
+-spec update_quality([#item{}]) -> [#item{}].
+update_quality(Items) ->
+  lists:map(fun update_item/1, Items).
+
+-spec update_item(#item{}) -> #item{}.
+update_item(Item = #item{name = Name}) ->
+  Item1 = if
+    Name /= "Aged Brie" andalso Name /= "Backstage passes to a TAFKAL80ETC concert" ->
+      if
+        Item#item.quality > 0 ->
+          if
+            Name /= "Sulfuras, Hand of Ragnaros" ->
+              Item#item{quality = Item#item.quality - 1};
+            true ->
+              Item
+          end;
+        true ->
+          Item
+      end;
+    true ->
+      if
+        Item#item.quality < 50 ->
+          Item2 = Item#item{quality = Item#item.quality + 1},
+          if
+            Name == "Backstage passes to a TAFKAL80ETC concert" ->
+              Item3 = if
+                Item2#item.sell_in < 11 ->
+                  if
+                    Item2#item.quality < 50 ->
+                      Item2#item{quality = Item2#item.quality + 1};
+                    true -> Item2
+                  end;
+                true -> Item2
+              end,
+              if
+                Item3#item.sell_in < 6 ->
+                  if
+                    Item3#item.quality < 50 ->
+                      Item3#item{quality = Item3#item.quality + 1};
+                    true -> Item3
+                  end;
+                true -> Item3
+              end;
+            true -> Item2
+          end;
+        true -> Item
+      end
+  end,
+  Item4 = if
+    Name /= "Sulfuras, Hand of Ragnaros" ->
+      Item1#item{sell_in = Item1#item.sell_in - 1};
+    true -> Item1
+  end,
+  if
+    Item4#item.sell_in < 0 ->
+      if
+        Name /= "Aged Brie" ->
+          if
+            Name /= "Backstage passes to a TAFKAL80ETC concert" ->
+              if
+                Item4#item.quality > 0 ->
+                  if
+                    Name /= "Sulfuras, Hand of Ragnaros" ->
+                      Item4#item{quality = Item4#item.quality - 1};
+                    true -> Item4
+                  end;
+                true -> Item4
+              end;
+            true -> Item4#item{quality = Item4#item.quality - Item4#item.quality}
+          end;
+        true ->
+          if
+            Item4#item.quality < 50 ->
+              Item4#item{quality = Item4#item.quality + 1};
+            true -> Item4
+          end
+      end;
+    true -> Item4
+  end.

erlang/test/gilded_rose_tests.erl

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+-module(gilded_rose_tests).
+
+-include("gilded_rose.hrl").
+-include_lib("eunit/include/eunit.hrl").
+
+-define(ITEMS, [
+  #item{name = "+5 Dexterity Vest", sell_in = 10, quality = 20},
+  #item{name = "Aged Brie", sell_in = 2, quality = 0},
+  #item{name = "Elixir of the Mongoose", sell_in = 5, quality = 7},
+  #item{name = "Sulfuras, Hand of Ragnaros", sell_in = 0, quality = 80},
+  #item{name = "Sulfuras, Hand of Ragnaros", sell_in = -1, quality = 80},
+  #item{name = "Backstage passes to a TAFKAL80ETC concert", sell_in = 15, quality = 20},
+  #item{name = "Backstage passes to a TAFKAL80ETC concert", sell_in = 10, quality = 49},
+  #item{name = "Backstage passes to a TAFKAL80ETC concert", sell_in = 5, quality = 49},
+  #item{name = "Conjured Mana Cake", sell_in = 3, quality = 6}
+]).
+
+golden_master_test() ->
+  Days = 30,
+  {ok, IoDevice} = file:open("actual_output.txt", [write]),
+  try
+    lists:foldl(fun(Day, Items) ->
+      io:format(IoDevice, "-------- day ~p --------~n", [Day]),
+      io:format(IoDevice, "name, sellIn, quality~n", []),
+      lists:foreach(fun(#item{name = Name, sell_in = SellIn, quality = Quality}) ->
+        io:format(IoDevice, "~s, ~p, ~p~n", [Name, SellIn, Quality])
+      end, Items),
+      io:nl(IoDevice),
+      gilded_rose:update_quality(Items)
+    end, ?ITEMS, lists:seq(0, Days - 1))
+  after
+    file:close(IoDevice)
+  end,
+  case file:read_file("expected_output.txt") of
+    {ok, ExpectedFile} ->
+      {ok, ActualFile} = file:read_file("actual_output.txt"),
+      ?assertEqual(ExpectedFile, ActualFile);
+    {error, Reason} ->
+      ?debugFmt("Could not read file 'expected_output.txt': ~p", [Reason])
+  end.
+
+update_quality_test_() -> [
+  {"first test", ?_assertMatch([#item{}], gilded_rose:update_quality([#item{}]))}
+].