feat(vereinfacht): add client, sync flash and SyncContact change

- Application: create SyncFlash ETS table on start
- Vereinfacht: Client, SyncFlash, sync_member, format_error, sync_members_without_contact
- SyncContact change on Member create_member and update_member
- Member: attribute vereinfacht_contact_id, internal action set_vereinfacht_contact_id

lib/mv/vereinfacht/vereinfacht.ex

@@ -0,0 +1,134 @@
+defmodule Mv.Vereinfacht do
+  @moduledoc """
+  Business logic for Vereinfacht accounting software integration.
+
+  - `sync_member/1` – Sync a single member to the API (create or update contact).
+    Used by Member create/update (SyncContact) and by User actions that update
+    the linked member's email via Ecto (e.g. user email change).
+  - `sync_members_without_contact/0` – Bulk sync of members without a contact ID.
+  """
+  require Ash.Query
+  alias Mv.Vereinfacht.Client
+  alias Mv.Membership.Member
+  alias Mv.Helpers.SystemActor
+  alias Mv.Helpers
+
+  @doc """
+  Syncs a single member to Vereinfacht (create or update finance contact).
+
+  If the member has no `vereinfacht_contact_id`, creates a contact and updates
+  the member with the new ID. If they already have an ID, updates the contact.
+  Uses system actor for any Ash update. Does nothing if Vereinfacht is not configured.
+
+  Returns:
+  - `:ok` – Contact was updated.
+  - `{:ok, member}` – Contact was created and member was updated with the new ID.
+  - `{:error, reason}` – API or update failed.
+  """
+  @spec sync_member(struct()) :: :ok | {:ok, struct()} | {:error, term()}
+  def sync_member(member) do
+    if Mv.Config.vereinfacht_configured?() do
+      do_sync_member(member)
+    else
+      :ok
+    end
+  end
+
+  defp do_sync_member(member) do
+    if present_contact_id?(member.vereinfacht_contact_id) do
+      case Client.update_contact(member.vereinfacht_contact_id, member) do
+        {:ok, _} -> :ok
+        {:error, reason} -> {:error, reason}
+      end
+    else
+      case Client.create_contact(member) do
+        {:ok, contact_id} ->
+          save_contact_id(member, contact_id)
+
+        {:error, reason} ->
+          {:error, reason}
+      end
+    end
+  end
+
+  defp save_contact_id(member, contact_id) do
+    system_actor = SystemActor.get_system_actor()
+    opts = Helpers.ash_actor_opts(system_actor)
+
+    case Ash.update(member, %{vereinfacht_contact_id: contact_id}, [
+           {:action, :set_vereinfacht_contact_id} | opts
+         ]) do
+      {:ok, updated} -> {:ok, updated}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp present_contact_id?(nil), do: false
+  defp present_contact_id?(""), do: false
+  defp present_contact_id?(s) when is_binary(s), do: String.trim(s) != ""
+  defp present_contact_id?(_), do: false
+
+  @doc """
+  Formats an API/request error reason into a short user-facing message.
+
+  Used by SyncContact (flash) and GlobalSettingsLive (sync result list).
+  """
+  @spec format_error(term()) :: String.t()
+  def format_error({:http, _status, detail}) when is_binary(detail), do: "Vereinfacht: " <> detail
+  def format_error({:http, status, _}), do: "Vereinfacht: API error (HTTP #{status})."
+
+  def format_error({:request_failed, _}),
+    do: "Vereinfacht: Request failed (e.g. connection error)."
+
+  def format_error({:invalid_response, _}), do: "Vereinfacht: Invalid API response."
+  def format_error(other), do: "Vereinfacht: " <> inspect(other)
+
+  @doc """
+  Creates Vereinfacht contacts for all members that do not yet have a
+  `vereinfacht_contact_id`. Uses system actor for reads and updates.
+
+  Returns `{:ok, %{synced: count, errors: list}}` where errors is a list of
+  `{member_id, reason}`. Does nothing if Vereinfacht is not configured.
+  """
+  @spec sync_members_without_contact() ::
+          {:ok, %{synced: non_neg_integer(), errors: [{String.t(), term()}]}}
+          | {:error, :not_configured}
+  def sync_members_without_contact do
+    if Mv.Config.vereinfacht_configured?() do
+      system_actor = SystemActor.get_system_actor()
+      opts = Helpers.ash_actor_opts(system_actor)
+
+      query =
+        Member
+        |> Ash.Query.filter(is_nil(vereinfacht_contact_id))
+
+      case Ash.read(query, opts) do
+        {:ok, members} ->
+          do_sync_members(members, opts)
+
+        {:error, _} = err ->
+          err
+      end
+    else
+      {:error, :not_configured}
+    end
+  end
+
+  defp do_sync_members(members, opts) do
+    {synced, errors} =
+      Enum.reduce(members, {0, []}, fn member, {acc_synced, acc_errors} ->
+        {inc, new_errors} = sync_one_member(member, opts)
+        {acc_synced + inc, acc_errors ++ new_errors}
+      end)
+
+    {:ok, %{synced: synced, errors: errors}}
+  end
+
+  defp sync_one_member(member, _opts) do
+    case sync_member(member) do
+      :ok -> {1, []}
+      {:ok, _} -> {1, []}
+      {:error, reason} -> {0, [{member.id, reason}]}
+    end
+  end
+end