Magic encoder: fix codepage usage (#580)

* add unit test for issue pointed out by @scott-r in #570

* swap order of encoder search

As described by @scott-r in
Magic encoder does not use
previously used code pages
when possible #570
Thank you!

CHANGELOG.rst

@@ -12,11 +12,15 @@ changes
 - has
 - changed
 
+- fix the encoding search so that lower encodings are found first
+
 contributors
 ^^^^^^^^^^^^
 - list
 - contributors
 
+-  Scott Rotondo  in `#570 <https://github.com/python-escpos/python-escpos/issues/570>`_
+
 2023-05-11 - Version 3.0a9 - "Pride Comes Before A Fall"
 --------------------------------------------------------
 This release is the 10th alpha release of the new version 3.0.

doc/spelling_wordlist.txt

@@ -67,6 +67,7 @@ Heuel
 Qian
 Lehtonen
 Kanzler
+Rotondo
 
 barcode
 barcodes

src/escpos/magicencode.py

@@ -155,7 +155,8 @@ class Encoder(object):
 
     def __encoding_sort_func(self, item):
         key, index = item
-        return (key in self.used_encodings, index)
+        used = key in self.used_encodings
+        return (not used, index)
 
     def find_suitable_encoding(self, char):
         """Search in a specific order for a suitable encoding.

test/test_magicencode.py

@@ -32,6 +32,13 @@ class TestEncoder:
         assert not Encoder({"CP437": 1}).find_suitable_encoding("€")
         assert Encoder({"CP858": 1}).find_suitable_encoding("€") == "CP858"
 
+    def test_find_suitable_encoding_unnecessary_codepage_swap(self):
+        enc = Encoder({"CP857": 1, "CP437": 2, "CP1252": 3, "CP852": 4, "CP858": 5})
+        # desired behavior would be that the encoder always stays in the lower
+        # available codepages if possible
+        for character in ("Á", "É", "Í", "Ó", "Ú"):
+            assert enc.find_suitable_encoding(character) == "CP857"
+
     def test_get_encoding(self):
         with pytest.raises(ValueError):
             Encoder({}).get_encoding_name("latin1")