feat: add csv export

lib/mv/membership/members_csv.ex

@@ -0,0 +1,91 @@
+defmodule Mv.Membership.MembersCSV do
+  @moduledoc """
+  Exports members to CSV (RFC 4180) as iodata.
+
+  Uses NimbleCSV.RFC4180 for encoding. Member fields are formatted as strings;
+  custom field values use the same formatting logic as the member overview (neutral formatter).
+  Column order for custom fields follows the key order of the `custom_fields_by_id` map.
+  """
+  alias Mv.Membership.CustomFieldValueFormatter
+  alias NimbleCSV.RFC4180
+
+  @doc """
+  Exports a list of members to CSV iodata.
+
+  - `members` - List of member structs (with optional `custom_field_values` loaded)
+  - `member_fields` - List of member field names (strings, e.g. `["first_name", "email"]`)
+  - `custom_fields_by_id` - Map of custom_field_id => %CustomField{}. Key order defines column order.
+
+  Returns iodata suitable for `IO.iodata_to_binary/1` or sending as response body.
+  """
+  @spec export(
+          [struct()],
+          [String.t()],
+          %{optional(String.t() | Ecto.UUID.t()) => struct()}
+        ) :: iodata()
+  def export(members, member_fields, custom_fields_by_id) when is_list(members) do
+    custom_entries = custom_field_entries(custom_fields_by_id)
+    header = build_header(member_fields, custom_entries)
+    rows = Enum.map(members, &build_row(&1, member_fields, custom_entries))
+    RFC4180.dump_to_iodata([header | rows])
+  end
+
+  defp custom_field_entries(by_id) when is_map(by_id) do
+    Enum.map(by_id, fn {id, cf} -> {to_string(id), cf} end)
+  end
+
+  defp build_header(member_fields, custom_entries) do
+    member_headers = member_fields
+    custom_headers = Enum.map(custom_entries, fn {_id, cf} -> cf.name end)
+    member_headers ++ custom_headers
+  end
+
+  defp build_row(member, member_fields, custom_entries) do
+    member_cells = Enum.map(member_fields, &format_member_field(member, &1))
+
+    custom_cells =
+      Enum.map(custom_entries, fn {id, cf} -> format_custom_field(member, id, cf) end)
+
+    member_cells ++ custom_cells
+  end
+
+  defp format_member_field(member, field_name) do
+    key = member_field_key(field_name)
+    value = Map.get(member, key)
+    format_member_value(value)
+  end
+
+  defp member_field_key(field_name) when is_binary(field_name) do
+    try do
+      String.to_existing_atom(field_name)
+    rescue
+      ArgumentError -> field_name
+    end
+  end
+
+  defp format_member_value(nil), do: ""
+  defp format_member_value(true), do: "true"
+  defp format_member_value(false), do: "false"
+  defp format_member_value(%Date{} = d), do: Date.to_iso8601(d)
+  defp format_member_value(%DateTime{} = dt), do: DateTime.to_iso8601(dt)
+  defp format_member_value(%NaiveDateTime{} = dt), do: NaiveDateTime.to_iso8601(dt)
+  defp format_member_value(value), do: to_string(value)
+
+  defp format_custom_field(member, custom_field_id, custom_field) do
+    cfv = find_custom_field_value(member, custom_field_id)
+
+    if cfv,
+      do: CustomFieldValueFormatter.format_custom_field_value(cfv.value, custom_field),
+      else: ""
+  end
+
+  defp find_custom_field_value(member, custom_field_id) do
+    values = Map.get(member, :custom_field_values) || []
+    id_str = to_string(custom_field_id)
+
+    Enum.find(values, fn cfv ->
+      to_string(cfv.custom_field_id) == id_str or
+        (Map.get(cfv, :custom_field) && to_string(cfv.custom_field.id) == id_str)
+    end)
+  end
+end