From 92325c05b1c3fff6f2fae3357886c26c1d804ecb Mon Sep 17 00:00:00 2001
From: Kodi Craft <kodi@kdcf.me>
Date: Sun, 7 Jul 2024 18:23:14 +0200
Subject: [PATCH] Implement deserialization for varints and varlongs

---
 lib/data.ex        | 40 +++++++++++++++++++++++++++++++++++++++-
 test/data_test.exs | 41 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/lib/data.ex b/lib/data.ex
index ac87ee1..a084805 100644
--- a/lib/data.ex
+++ b/lib/data.ex
@@ -77,7 +77,7 @@ defmodule Amethyst.Minecraft.Read do
     {[], binary}
   end
 
-  def bool({acc, <<value, rest::bitstring>>}) do
+  def bool({acc, <<value, rest::binary>>}) do
     {[value != 0 | acc], rest}
   end
 
@@ -112,4 +112,42 @@ defmodule Amethyst.Minecraft.Read do
   def double({acc, <<value::64-float-big, rest::binary>>}) do
     {[value | acc], rest}
   end
+
+  def varint(tuple, read \\ 0, nacc \\ 0)
+  def varint({acc, <<1::1, value::7, rest::binary>>}, read, nacc) when read < 5 do
+    varint({acc, rest}, read + 1, nacc + (value <<< (7 * read)))
+  end
+  def varint({acc, <<0::1, value::7, rest::binary>>}, read, nacc) do
+    total = nacc + (value <<< (7 * read))
+    <<value::32-signed>> = <<total::32-unsigned>>
+    {[value | acc], rest}
+  end
+  def varint(_, read, _) when read >= 5 do
+    raise RuntimeError, "Got a varint which is too big!"
+  end
+  def varint({_, ""}, _, _) do
+    raise RuntimeError, "Got an incomplete varint!"
+  end
+
+  def varlong(tuple, read \\ 0, nacc \\ 0)
+  def varlong({acc, <<1::1, value::7, rest::binary>>}, read, nacc) when read < 10 do
+    varlong({acc, rest}, read + 1, nacc + (value <<< (7 * read)))
+  end
+  def varlong({acc, <<0::1, value::7, rest::binary>>}, read, nacc) do
+    total = nacc + (value <<< (7 * read))
+    <<value::64-signed>> = <<total::64-unsigned>>
+    {[value | acc], rest}
+  end
+  def varlong(_, read, _) when read >= 10 do
+    raise RuntimeError, "Got a varint which is too big!"
+  end
+  def varlong({_, ""}, _, _) do
+    raise RuntimeError, "Got an incomplete varint!"
+  end
+
+  def string({acc, data}) do
+    {[length], rest} = start(data) |> varint()
+    <<value::binary-size(length), rest::binary>> = rest
+    {[value | acc], rest}
+  end
 end
diff --git a/test/data_test.exs b/test/data_test.exs
index b3fd4c7..51a19b9 100644
--- a/test/data_test.exs
+++ b/test/data_test.exs
@@ -1,7 +1,11 @@
 defmodule WriteTest do
   use ExUnit.Case
+
+  @moduledoc """
+  This module contains tests for the Amethyst.Minecraft.Write module.
+  """
+
   doctest Amethyst.Minecraft.Write
-  doctest Amethyst.Minecraft.Read
 
   test "writing a varint" do
     assert Amethyst.Minecraft.Write.varint(0) == <<0x00>>
@@ -28,3 +32,38 @@ defmodule WriteTest do
     assert Amethyst.Minecraft.Write.string("") == <<0x00>>
   end
 end
+
+defmodule ReadTest do
+  use ExUnit.Case
+
+  @moduledoc """
+  This module contains tests for the Amethyst.Minecraft.Read module.
+  """
+
+  doctest Amethyst.Minecraft.Read
+
+  test "reading a varint" do
+    assert Amethyst.Minecraft.Read.start(<<0x00>>) |> Amethyst.Minecraft.Read.varint() == {[0], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x7F>>) |> Amethyst.Minecraft.Read.varint() == {[127], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x80, 0x01>>) |> Amethyst.Minecraft.Read.varint() == {[128], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0x01>>) |> Amethyst.Minecraft.Read.varint() == {[255], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0xFF, 0xFF, 0xFF, 0x07>>) |> Amethyst.Minecraft.Read.varint() == {[2_147_483_647], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0xFF, 0xFF, 0xFF, 0x0F>>) |> Amethyst.Minecraft.Read.varint() == {[-1], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x80, 0x80, 0x80, 0x80, 0x08>>) |> Amethyst.Minecraft.Read.varint() == {[-2_147_483_648], ""}
+  end
+
+  test "reading a varlong" do
+    assert Amethyst.Minecraft.Read.start(<<0x00>>) |> Amethyst.Minecraft.Read.varlong() == {[0], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x7F>>) |> Amethyst.Minecraft.Read.varlong() == {[127], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x80, 0x01>>) |> Amethyst.Minecraft.Read.varlong() == {[128], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0x01>>) |> Amethyst.Minecraft.Read.varlong() == {[255], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0xFF, 0xFF, 0xFF, 0x07>>) |> Amethyst.Minecraft.Read.varlong() == {[2_147_483_647], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x7F>>) |> Amethyst.Minecraft.Read.varlong() == {[9_223_372_036_854_775_807], ""}
+    assert Amethyst.Minecraft.Read.start(<<0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01>>) |> Amethyst.Minecraft.Read.varlong() == {[-1], ""}
+  end
+
+  test "reading a string" do
+    assert Amethyst.Minecraft.Read.start(<<0x0D, "Hello, world!">>) |> Amethyst.Minecraft.Read.string() == {["Hello, world!"], ""}
+    assert Amethyst.Minecraft.Read.start(<<0x00>>) |> Amethyst.Minecraft.Read.string() == {[""], ""}
+  end
+end