1 files changed, 70 insertions, 0 deletions
diff --git a/lib/mix/tasks/pandoc.install.ex b/lib/mix/tasks/pandoc.install.ex
new file mode 100644
index 0000000..1e36696
--- /dev/null
+++ b/lib/mix/tasks/pandoc.install.ex
@@ -0,0 +1,70 @@
+defmodule Mix.Tasks.Pandoc.Install do
+  @moduledoc """
+  Installs pandoc under `_build`.
+
+  ```bash
+  $ mix pandoc.install
+  $ mix pandoc.install --if-missing
+  ```
+
+  By default, it installs #{Pandoc.latest_version()} but you can configure it
+  in your config files, such as:
+
+      config :pandoc, :version, "#{Pandoc.latest_version()}"
+
+  ## Options
+
+    * `--runtime-config` - load the runtime configuration before executing
+      command
+
+    * `--if-missing` - install only if the given version does not exist
+  """
+
+  @shortdoc "Installs pandoc under _build"
+  @compile {:no_warn_undefined, Mix}
+
+  use Mix.Task
+
+  @impl true
+  def run(args) do
+    valid_options = [runtime_config: :boolean, if_missing: :boolean]
+
+    {opts, base_url} =
+      case OptionParser.parse_head!(args, strict: valid_options) do
+        {opts, []} ->
+          {opts, Pandoc.default_base_url()}
+
+        {opts, [base_url]} ->
+          {opts, base_url}
+
+        {_, _} ->
+          Mix.raise("""
+          Invalid arguments to pandoc.install, expected one of:
+
+              mix pandoc.install
+              mix pandoc.install 'https://github.com/jgm/pandoc/releases/download/$version/pandoc-$version-$target.tar.gz'
+              mix pandoc.install --runtime-config
+              mix pandoc.install --if-missing
+          """)
+      end
+
+    if opts[:runtime_config], do: Mix.Task.run("app.config")
+
+    if opts[:if_missing] && latest_version?() do
+      :ok
+    else
+      if function_exported?(Mix, :ensure_application!, 1) do
+        Mix.ensure_application!(:inets)
+        Mix.ensure_application!(:ssl)
+      end
+
+      Mix.Task.run("loadpaths")
+      Pandoc.install(base_url)
+    end
+  end
+
+  defp latest_version?() do
+    version = Pandoc.configured_version()
+    match?({:ok, ^version}, Pandoc.bin_version())
+  end
+end