import hashlib
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import string
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from sqlalchemy import select
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from sqlalchemy.orm import Session
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from app.models import ExaminationExamExaminee
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_ALPHABET = string.digits + string.ascii_uppercase # 0-9A-Z, 36 chars
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def _to_base36(num: int, length: int) -> str:
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"""将非负整数编码为定长 base36 字符串。"""
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chars: list[str] = []
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for _ in range(length):
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num, rem = divmod(num, 36)
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chars.append(_ALPHABET[rem])
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return "".join(reversed(chars))
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def generate_student_no(examinee_id: int, exam_id: int) -> str:
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"""根据考生ID + 考试ID 生成 10 位字母数字编码。"""
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raw = f"{examinee_id}:{exam_id}".encode()
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digest = hashlib.sha256(raw).digest()
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num = int.from_bytes(digest[:8], "big")
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return _to_base36(num, 10)
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def ensure_student_no(db: Session, attempt: ExaminationExamExaminee) -> str:
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"""获取或生成 attempt 的 student_no（幂等，已有则直接返回）。"""
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if attempt.student_no:
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return attempt.student_no
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code = generate_student_no(attempt.examinee_id, attempt.exam_id)
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# 极小概率碰撞时追加区分
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existing = db.scalar(
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select(ExaminationExamExaminee.id).where(
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ExaminationExamExaminee.student_no == code,
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ExaminationExamExaminee.id != attempt.id,
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)
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)
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if existing is not None:
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digest = hashlib.sha256(
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f"{attempt.examinee_id}:{attempt.exam_id}:{attempt.id}".encode()
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).digest()
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code = _to_base36(int.from_bytes(digest[:8], "big"), 10)
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attempt.student_no = code
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db.flush()
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return code
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def find_attempt_by_student_no(
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db: Session, student_no: str
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) -> ExaminationExamExaminee | None:
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"""通过编码反查答卷记录。"""
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return db.scalar(
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select(ExaminationExamExaminee).where(
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ExaminationExamExaminee.student_no == student_no.strip().upper()
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)
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)
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