Initial certificate system

backend/app/services/certificate_number.py

@@ -0,0 +1,30 @@
+import hashlib
+from datetime import date
+
+from app.core.config import settings
+
+ALPHABET = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"
+
+
+def _to_base32ish(value: int, length: int) -> str:
+    chars: list[str] = []
+    base = len(ALPHABET)
+    while value:
+        value, remainder = divmod(value, base)
+        chars.append(ALPHABET[remainder])
+    encoded = "".join(reversed(chars)) or ALPHABET[0]
+    return encoded[-length:].rjust(length, ALPHABET[0])
+
+
+def _digest_int(payload: str) -> int:
+    digest = hashlib.sha256(payload.encode("utf-8")).digest()
+    return int.from_bytes(digest[:8], "big")
+
+
+def build_certificate_no(sequence_id: int, project_code: str, issue_date: date | None = None) -> str:
+    year = (issue_date or date.today()).year
+    normalized_project = project_code.strip().upper()
+    seed = f"{settings.certificate_no_secret}:{year}:{normalized_project}:{sequence_id}"
+    short_code = _to_base32ish(_digest_int(seed), 7)
+    check_code = _to_base32ish(_digest_int(f"check:{seed}:{short_code}"), 2)
+    return f"PX{year}-{normalized_project}-{short_code}-{check_code}"