feat: add minus operator for money_with_currency

Author: zcesur

priv/repo/migrations/20250511145733_define_minus_operator.exs

@@ -0,0 +1,48 @@
+defmodule Algora.Repo.Migrations.DefineMinusOperator do
+  use Ecto.Migration
+
+  def up do
+    execute("""
+    CREATE OR REPLACE FUNCTION money_sub(money_1 money_with_currency, money_2 money_with_currency)
+    RETURNS money_with_currency
+    IMMUTABLE
+    STRICT
+    LANGUAGE plpgsql
+    SET search_path = ''
+    AS $$
+      DECLARE
+      currency varchar;
+      subtraction numeric;
+      BEGIN
+        IF currency_code(money_1) = currency_code(money_2) THEN
+          currency := currency_code(money_1);
+          subtraction := amount(money_1) - amount(money_2);
+          return row(currency, subtraction);
+        ELSE
+          RAISE EXCEPTION
+            'Incompatible currency codes for - operator. Expected both currency codes to be %', currency_code(money_1)
+            USING HINT = 'Please ensure both columns have the same currency code',
+            ERRCODE = '22033';
+        END IF;
+      END;
+    $$;
+    """)
+    |> Money.Migration.adjust_for_type(repo())
+
+    execute("""
+    CREATE OPERATOR - (
+      leftarg = money_with_currency,
+      rightarg = money_with_currency,
+      procedure = money_sub,
+      commutator = -
+    );
+    """)
+    |> Money.Migration.adjust_for_type(repo())
+  end
+
+  def down do
+    execute("DROP OPERATOR IF EXISTS - (none, money_with_currency);")
+
+    execute("DROP FUNCTION IF EXISTS money_sub(money_with_currency, money_with_currency);")
+  end
+end