# excel_export.py
import csv
from io import StringIO, BytesIO


def _to_csv(headers, rows):
    """生成 UTF-8 BOM 编码的 CSV，兼容 VSCode 和 Excel"""
    buf = StringIO()
    writer = csv.writer(buf)
    writer.writerow(headers)
    writer.writerows(rows)

    output = BytesIO()
    output.write(b'\xef\xbb\xbf')  # UTF-8 BOM
    output.write(buf.getvalue().encode('utf-8'))
    output.seek(0)
    return output


def export_users_to_excel(users):
    headers = ["ID", "用户名", "邮箱", "手机号", "角色", "状态", "完成考试数", "注册时间"]
    rows = []
    for u in users:
        rows.append([
            u.id, u.name, u.email or "", u.phone or "", u.role,
            "已封禁" if u.is_banned else "正常", u.completed_exams,
            u.created_at.strftime("%Y-%m-%d %H:%M:%S") if u.created_at else ""
        ])
    return _to_csv(headers, rows)


def export_exams_to_excel(exams):
    headers = ["ID", "考试名称", "创建者ID", "总分", "时长(分钟)", "状态", "提交数", "创建时间"]
    rows = []
    for e in exams:
        rows.append([
            e.id, e.title, e.creator_id, e.total_score, e.duration, e.status,
            len(e.submissions) if e.submissions else 0,
            e.created_at.strftime("%Y-%m-%d %H:%M:%S") if e.created_at else ""
        ])
    return _to_csv(headers, rows)


def export_submissions_to_excel(submissions):
    headers = ["ID", "考试ID", "考试名称", "用户ID", "用户名", "得分", "总分", "状态", "提交时间"]
    rows = []
    for s in submissions:
        rows.append([
            s.id, s.exam_id, s.exam.title if s.exam else "", s.user_id,
            s.user.name if s.user else "", s.score if s.score is not None else "",
            s.total_score, s.status,
            s.submitted_at.strftime("%Y-%m-%d %H:%M:%S") if s.submitted_at else ""
        ])
    return _to_csv(headers, rows)


def export_contests_to_excel(contests):
    headers = ["ID", "杯赛名称", "主办方", "开始日期", "结束日期", "状态", "参与人数", "创建时间"]
    rows = []
    for c in contests:
        rows.append([
            c.id, c.name, c.organizer or "", c.start_date or "", c.end_date or "",
            c.status, c.participants,
            c.created_at.strftime("%Y-%m-%d %H:%M:%S") if c.created_at else ""
        ])
    return _to_csv(headers, rows)


def export_posts_to_excel(posts):
    headers = ["ID", "标题", "作者", "分类", "浏览数", "回复数", "点赞数", "创建时间"]
    rows = []
    for p in posts:
        rows.append([
            p.id, p.title, p.author.name if p.author else "", p.category or "",
            p.views, p.reply_count, p.like_count,
            p.created_at.strftime("%Y-%m-%d %H:%M:%S") if p.created_at else ""
        ])
    return _to_csv(headers, rows)