Handle installing Pandoc

lib/mix/tasks/pandoc.ex

@@ -1,13 +1,44 @@
 defmodule Mix.Tasks.Pandoc do
-  use Mix.Task
+  @moduledoc """
+  Invokes pandoc with the given args.
 
-  @ext ".md"
+  Usage:
+
+      $ mix pandoc TASK_OPTIONS PROFILE PANDOC_ARGS
+
+  Example:
+
+      $ mix pandoc default documents/hello.md -o priv/static/posts/hello.html
+
+  If pandoc is not installed, it is automatically downloaded. Note the
+  arguments given to this task will be appended to any configured arguments.
+
+  ## Options
+
+    * `--runtime-config` - load the runtime configuration
+      before executing command
+
+  Note flags to control this Mix task must be given before the profile:
+
+      $ mix pandoc --runtime-config default documents/hello.md
+
+  """
+
+  @shortdoc "Invokes pandoc with the profile and args"
+  @compile {:no_warn_undefined, Mix}
+
+  use Mix.Task
 
   @impl true
   def run(args) do
     switches = [runtime_config: :boolean]
     {opts, remaining_args} = OptionParser.parse_head!(args, switches: switches)
 
+    if function_exported?(Mix, :ensure_application!, 1) do
+      Mix.ensure_application!(:inets)
+      Mix.ensure_application!(:ssl)
+    end
+
     if opts[:runtime_config] do
       Mix.Task.run("app.config")
     else
@@ -19,28 +50,11 @@ defmodule Mix.Tasks.Pandoc do
     install_and_run(remaining_args)
   end
 
-  defp install_and_run([profile | _args] = all) do
-    IO.puts("Converting markdown...")
-
-    profile = String.to_atom(profile)
-    config = Application.get_env(:pandoc, profile)
-    args = config[:args] || []
-    opts = [cd: config[:cd] || File.cwd!()]
-
-    out_path = List.last(args)
-    full_out_path = [opts[:cd], out_path] |> Path.join() |> Path.expand()
-    File.rm_rf!(full_out_path)
-    File.mkdir_p!(full_out_path)
-
-    opts[:cd]
-    |> Path.join("*#{@ext}")
-    |> Path.wildcard()
-    |> Enum.each(fn path ->
-      case Pandoc.run(profile, path) do
-        0 -> :ok
-        status -> Mix.raise("`mix pandoc #{Enum.join(all, " ")}` exited with #{status}")
-      end
-    end)
+  defp install_and_run([profile | args] = all) do
+    case Pandoc.install_and_run(String.to_atom(profile), args) do
+      0 -> :ok
+      status -> Mix.raise("`mix pandoc #{Enum.join(all, " ")}` exited with #{status}")
+    end
   end
 
   defp install_and_run([]) do

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