From 90ed8acb0ae41cd5f7ccd798b4264858ae95004f Mon Sep 17 00:00:00 2001
From: "Michael B. Klein" <mbklein@gmail.com>
Date: Mon, 27 Jan 2025 16:17:41 +0000
Subject: [PATCH] Add support for Level 2 Group Qualifiers

---
 lib/edtf/parser.ex         |  9 ++++++---
 lib/edtf/parser/helpers.ex | 27 ++++++++++++++++++++++-----
 test/edtf/date_test.exs    | 10 ++++++++++
 3 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/lib/edtf/parser.ex b/lib/edtf/parser.ex
index 156d3fb..380e15b 100644
--- a/lib/edtf/parser.ex
+++ b/lib/edtf/parser.ex
@@ -18,21 +18,24 @@ defmodule EDTF.Parser do
 
   # Signed year with optional qualifier
   qualified_year =
-    optional(component_qualifier |> tag(:qualifier))
+    optional(component_qualifier |> tag(:pre_qualifier))
     |> concat(optional(sign) |> tag(:sign))
     |> concat(year |> tag(:value))
+    |> concat(optional(component_qualifier |> tag(:post_qualifier)))
     |> post_traverse({Helpers, :bitmask, [0]})
 
   # Month with optional qualifier
   qualified_month =
-    optional(component_qualifier |> tag(:qualifier))
+    optional(component_qualifier |> tag(:pre_qualifier))
     |> concat(month |> tag(:value))
+    |> concat(optional(component_qualifier |> tag(:post_qualifier)))
     |> post_traverse({Helpers, :bitmask, [4]})
 
   # Day with optional qualifier
   qualified_day =
-    optional(component_qualifier |> tag(:qualifier))
+    optional(component_qualifier |> tag(:pre_qualifier))
     |> concat(day |> tag(:value))
+    |> concat(optional(component_qualifier |> tag(:post_qualifier)))
     |> post_traverse({Helpers, :bitmask, [6]})
 
   # Basic [-]YYYY[-MM[-DD]] with optional qualifiers
diff --git a/lib/edtf/parser/helpers.ex b/lib/edtf/parser/helpers.ex
index 80ccf0f..5fcedc8 100644
--- a/lib/edtf/parser/helpers.ex
+++ b/lib/edtf/parser/helpers.ex
@@ -24,28 +24,42 @@ defmodule EDTF.Parser.Helpers do
   being fully masked (15 for year, 48 for month, or 192 for day). Unspecified digits
   (`X`) flip individual bits.
 
+  A pre-component qualifier results in only that component being masked. A post-
+  component qualifier results in that component plus all components to the left
+  being masked.
+
   Example:
     ```elixir
     iex> bitmask("-%02", [value: ~c"200X", sign: ~c"-"], %{}, nil, nil, 0)
     {"-%02", [[value: -2000, attributes: [unspecified: 8]]], %{}}
 
-    iex> bitmask("", [value: ~c"02", qualifier: ~c"%"], %{}, nil, nil, 4)
+    iex> bitmask("", [value: ~c"02", pre_qualifier: ~c"%"], %{}, nil, nil, 4)
     {"", [[value: 2, attributes: [approximate: 48, uncertain: 48]]], %{}}
+
+    iex> bitmask("", [value: ~c"02", post_qualifier: ~c"%"], %{}, nil, nil, 4)
+    {"", [[value: 2, attributes: [approximate: 63, uncertain: 63]]], %{}}
     ```
   """
   def bitmask(rest, value, context, _line, _offset, shift) do
+    qualifier =
+      cond do
+        Keyword.get(value, :pre_qualifier) -> {:pre, Keyword.get(value, :pre_qualifier)}
+        Keyword.get(value, :post_qualifier) -> {:post, Keyword.get(value, :post_qualifier)}
+        true -> nil
+      end
+
     {rest,
      [
        bitmask(
          Keyword.get(value, :value),
          Keyword.get(value, :sign, ~c""),
-         Keyword.get(value, :qualifier, ~c""),
+         qualifier,
          shift
        )
      ], context}
   end
 
-  def bitmask(bitstring, sign, [], shift) do
+  def bitmask(bitstring, sign, nil, shift) do
     {output, mask} =
       bitstring
       |> Enum.with_index()
@@ -71,8 +85,8 @@ defmodule EDTF.Parser.Helpers do
     end
   end
 
-  def bitmask(bitstring, sign, qualifier, shift) do
-    mask = ((1 <<< length(bitstring)) - 1) <<< shift
+  def bitmask(bitstring, sign, {qualifier_position, qualifier}, shift) do
+    mask = calculate_mask(bitstring, shift, qualifier_position)
 
     attributes =
       Map.get(@qualifier_attributes, qualifier)
@@ -84,6 +98,9 @@ defmodule EDTF.Parser.Helpers do
     ]
   end
 
+  defp calculate_mask(bitstring, shift, :pre), do: ((1 <<< length(bitstring)) - 1) <<< shift
+  defp calculate_mask(bitstring, shift, :post), do: (1 <<< (length(bitstring) + shift)) - 1
+
   @doc """
   Apply a parsed sign to a parsed integer value.
 
diff --git a/test/edtf/date_test.exs b/test/edtf/date_test.exs
index 81482f6..933f840 100644
--- a/test/edtf/date_test.exs
+++ b/test/edtf/date_test.exs
@@ -96,6 +96,16 @@ defmodule EDTF.DateTest do
       assert subject.attributes[:uncertain] == 192
       refute subject.attributes[:unspecified]
     end
+
+    @tag edtf: "1978-02?-23"
+    test "approximate month and year", %{subject: subject} do
+      assert subject.type == :date
+      assert subject.values == [1978, 1, 23]
+      assert subject.level == 2
+      refute subject.attributes[:approximate]
+      assert subject.attributes[:uncertain] == 63
+      refute subject.attributes[:unspecified]
+    end
   end
 
   describe "unspecified" do