basic transpile

lib/elixir_stan.ex

@@ -1,18 +1,91 @@
+require Logger
+
 defmodule ElixirStan do
   @moduledoc """
   Documentation for `ElixirStan`.
   """
 
   @doc """
-  Hello world.
+  Get the version of the stanc3 executable bundled with the library.
+  """
+  @spec stanc_version :: String.t() | {:error, String.t()}
+  def stanc_version() do
+    case System.cmd(Application.app_dir(:elixir_stan, "/priv/bin/stanc"), ["--version"]) do
+      {version_string, 0} -> String.trim(version_string)
+      {error, _} -> {:error, error}
+    end
+  end
+
+  @doc """
+  Computes the hash of a file used for caching.
+
+  Computes SHA256 of the file and truncates it to 8 bytes, then encodes it in a hex string.
+  """
+  @spec hash_file(binary()) :: String.t()
+  def hash_file(file) when is_binary(file) do
+    <<hash::bitstring-size(64), _::binary>> = :crypto.hash(:sha256, file)
+
+    Base.encode16 hash
+  end
 
-  ## Examples
+  @spec model_tmp_dir(Path.t()) :: binary | {:error, atom}
+  def model_tmp_dir(path) do
+    with {:ok, model_code} <- File.read(path) do
+      model_name = Path.basename(path, ".stan")
+      model_hash = hash_file(model_code)
 
-      iex> ElixirStan.hello()
-      :world
+      Path.join([
+        System.tmp_dir(),
+        "elixir_stan",
+        model_name <> model_hash <> String.replace(stanc_version(), " ", "_")
+      ])
+    end
+  end
+
+  @doc """
+  Transpiles the model into C++ and stores it in a temporary directory.
 
+  Temporary directory is based on `System.tmp_dir()`. An `elixir_stan` directory is created in the system temporary
+  directory and the model is stored in a subdirectory of that. The model directory is based on the model name, the hash
+  of the model code and the version of stanc used to compile it.
   """
-  def hello do
-    :world
+  @spec transpile_model(Path.t()) :: :ok | {:error, any()}
+  def transpile_model(path) do
+    with {:ok, model_code} <- File.read(path) do
+      model_tmp_path = model_tmp_dir(path)
+
+      # Create model dir
+      :ok = File.mkdir_p(model_tmp_path)
+
+      model_tmp_file = Path.join(model_tmp_path, Path.basename(path))
+
+      # Write model code
+      :ok = File.write(model_tmp_file, model_code)
+
+      case System.cmd(Application.app_dir(:elixir_stan, "/priv/bin/stanc"), [model_tmp_file]) do
+        {_, 0} -> :ok
+      end
+    end
+  end
+
+  @doc """
+  Cleans the model tmp directory.
+  """
+  @spec clean_model(Path.t()) :: :ok | {:error, String.t()}
+  def clean_model(path) do
+    model_tmp_path = model_tmp_dir(path)
+
+    # Remove model dir
+    case File.rm_rf(model_tmp_path) do
+      {:ok, _} ->
+        :ok
+
+      {:error, error, file} ->
+        Logger.error(
+          "Could not clean model: #{path}\n\t Error: #{:file.format_error(error)}\n\t File: #{file}"
+        )
+
+        {:error, :file.format_error(error)}
+    end
   end
 end

mix.exs

@@ -14,7 +14,7 @@ defmodule ElixirStan.MixProject do
   # Run "mix help compile.app" to learn about applications.
   def application do
     [
-      extra_applications: [:logger]
+      extra_applications: [:logger, :crypto]
     ]
   end
 

test/data/normal.stan

@@ -0,0 +1,13 @@
+data {
+  int<lower=0> N;
+  vector[N] y;
+}
+
+parameters {
+  real mu;
+  real<lower=0> sigma;
+}
+
+model {
+  y ~ normal(mu, sigma);
+}

test/elixir_stan_test.exs

@@ -2,7 +2,33 @@ defmodule ElixirStanTest do
   use ExUnit.Case
   doctest ElixirStan
 
-  test "greets the world" do
-    assert ElixirStan.hello() == :world
+  test "check stanc version" do
+    assert ElixirStan.stanc_version() == "stanc3 v2.31.0 (Unix)"
+  end
+
+  test "hash test" do
+    assert ElixirStan.hash_file("a") == "CA978112CA1BBDCA"
+  end
+
+  test "check basic temp path" do
+    # assert Application.app_dir(:elixir_stan, "test/data/normal.stan") == "a"
+    assert ElixirStan.model_tmp_dir("test/data/normal.stan") ==
+             "/tmp/elixir_stan/normalA32F3F2E4143ABA4stanc3_v2.31.0_(Unix)"
+  end
+
+  test "check basic transpile and clean" do
+    assert ElixirStan.transpile_model("test/data/normal.stan") == :ok
+
+    assert File.exists?(
+             Path.join(ElixirStan.model_tmp_dir("test/data/normal.stan"), "normal.stan")
+           )
+
+    assert File.exists?(
+             Path.join(ElixirStan.model_tmp_dir("test/data/normal.stan"), "normal.hpp")
+           )
+
+    assert ElixirStan.clean_model("test/data/normal.stan") == :ok
+
+    assert !File.exists?(ElixirStan.model_tmp_dir("test/data/normal.stan"))
   end
 end