#251, Fix left trimming of 99 when charset C

barcode/codex.py

@@ -191,16 +191,14 @@ def _is_char_fnc1_char(self, char):
 
     def _maybe_switch_charset(self, pos: int) -> list[int]:
         char = self.code[pos]
-        next_ = self.code[pos : pos + 10]
 
         def look_next() -> bool:
-            digits = 0
-            for c in next_:
-                if c.isdigit():
-                    digits += 1
-                else:
-                    break
-            return digits > 3
+            if pos == 0 and self._is_char_fnc1_char(self.code[0]):
+                return True
+
+            minimum_sequential_digits = 4
+            code_slice = self.code[pos : pos + minimum_sequential_digits]
+            return len(code_slice) == minimum_sequential_digits and code_slice.isdigit()
 
         codes: list[int] = []
         if self._charset == "C" and not char.isdigit():
@@ -267,8 +265,12 @@ def _convert_or_buffer(self, char: str) -> int | None:
         raise RuntimeError(f"Character {char} could not be converted in charset C.")
 
     def _try_to_optimize(self, encoded: list[int]) -> list[int]:
-        if encoded[1] in code128.TO:
-            encoded[:2] = [code128.TO[encoded[1]]]
+        if len(encoded) < 2 or encoded[0] not in (code128.START_CODES["A"], code128.START_CODES["B"], code128.START_CODES["C"]):
+            return encoded
+
+        if encoded[1] in code128.TO and not ((encoded[0] == code128.START_CODES["C"]) and (encoded[1] < 100)):
+            return [code128.TO[encoded[1]]] + encoded[2:]
+
         return encoded
 
     def _calculate_checksum(self, encoded: list[int]) -> int:

tests/test_builds.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from barcode import get_barcode
+from barcode.charsets.code128 import START_CODES, CODES
 
 
 def test_ean8_builds() -> None:
@@ -15,3 +16,14 @@ def test_ean8_builds_with_longer_bars() -> None:
     ean = get_barcode("ean8", "40267708", options={"guardbar": True})
     bc = ean.build()
     assert ref == bc[0]
+
+
+def test_code128_builds() -> None:
+    gen_000000 = get_barcode("code128", "000000")
+    code_000000 = gen_000000.build()
+    gen_999999 = get_barcode("code128", "999999")
+    gen_999999._charset = "B" ## this will be swapped to C.
+    code_999999 = gen_999999.build()
+    assert gen_999999._charset == "C"
+    assert len(code_000000[0]) == len(code_999999[0])
+    assert code_000000[0].startswith(CODES[START_CODES["C"]])