Add parallel export with configurable concurrency (default: 8)

Use Task.async_stream for parallel org->md export.
Configurable via EXPORT_CONCURRENCY env var or :export_concurrency config.

config/config.exs

@@ -8,7 +8,8 @@ config :org_garden,
   citation_mode: :warn,
   http_port: 8080,
   ws_port: 3001,
-  health_port: 9090
+  health_port: 9090,
+  export_concurrency: 8
 
 config :logger, :console,
   format: "$time $metadata[$level] $message\n",

config/runtime.exs

@@ -40,3 +40,7 @@ config :org_garden,
   http_port: RuntimeConfig.parse_int(System.get_env("PORT"), 8080),
   ws_port: RuntimeConfig.parse_int(System.get_env("WS_PORT"), 3001),
   health_port: RuntimeConfig.parse_int(System.get_env("HEALTH_PORT"), 9090)
+
+# Export parallelism
+config :org_garden,
+  export_concurrency: RuntimeConfig.parse_int(System.get_env("EXPORT_CONCURRENCY"), 8)

lib/org_garden/export.ex

@@ -71,9 +71,15 @@ defmodule OrgGarden.Export do
     e -> {:error, e}
   end
 
+  @default_max_concurrency 8
+
   @doc """
   Export all `.org` files found under `notes_dir`.
 
+  Exports files in parallel for improved performance. The concurrency level
+  can be configured via the `:export_concurrency` application config or
+  the `EXPORT_CONCURRENCY` environment variable. Defaults to #{@default_max_concurrency}.
+
   Returns `{:ok, count}` where `count` is the number of successfully
   exported files, or `{:error, failures}` if any files failed.
   """
@@ -87,13 +93,21 @@ defmodule OrgGarden.Export do
       Logger.warning("No .org files found in #{notes_dir}")
       {:ok, 0}
     else
-      Logger.info("Exporting #{length(org_files)} org file(s) from #{notes_dir}")
+      max_concurrency = get_concurrency()
+      Logger.info("Exporting #{length(org_files)} org file(s) from #{notes_dir} (concurrency: #{max_concurrency})")
 
       results =
-        Enum.map(org_files, fn orgfile ->
-          IO.puts("  exporting: #{orgfile}")
+        org_files
+        |> Task.async_stream(
+          fn orgfile ->
+            Logger.info("  exporting: #{orgfile}")
             {orgfile, export_file(orgfile, notes_dir, output_dir)}
-        end)
+          end,
+          max_concurrency: max_concurrency,
+          timeout: :infinity,
+          ordered: false
+        )
+        |> Enum.map(fn {:ok, result} -> result end)
 
       failures =
         Enum.filter(results, fn
@@ -109,6 +123,10 @@ defmodule OrgGarden.Export do
     end
   end
 
+  defp get_concurrency do
+    Application.get_env(:org_garden, :export_concurrency, @default_max_concurrency)
+  end
+
   @doc """
   Compute the expected `.md` path for a given `.org` file.