#!/usr/bin/env python3
"""Snapshot a readable SQLite table to JSONL without modifying its source."""
import argparse
import json
import sqlite3
from pathlib import Path


def export(source, table, output):
    source, output = Path(source).resolve(), Path(output).resolve()
    if source == output or output.exists():
        raise ValueError('输出文件已存在或与源文件相同，请使用新的输出路径')
    with source.open('rb') as file:
        if file.read(16) != b'SQLite format 3\x00':
            raise ValueError('源文件不是明文 SQLite；此脚本不解密数据库')
    db = sqlite3.connect(source.as_uri() + '?mode=ro', uri=True, timeout=15)
    snapshot = sqlite3.connect(':memory:')
    created = False
    try:
        # Backup API includes committed WAL contents; never copy only a live .db.
        db.backup(snapshot)
        snapshot.row_factory = sqlite3.Row
        names = [r[0] for r in snapshot.execute("SELECT name FROM sqlite_master WHERE type='table'")]
        if table not in names:
            raise ValueError('消息表不存在，可用表：' + ', '.join(names))
        quoted = '"' + table.replace('"', '""') + '"'
        with output.open('x', encoding='utf-8') as file:
            created = True
            try:
                output.chmod(0o600)
            except OSError:
                pass
            for row in snapshot.execute('SELECT * FROM ' + quoted):
                record = dict(row)
                if any(isinstance(v, bytes) for v in record.values()):
                    raise ValueError('表中含二进制字段，需先解码/转换；不会把 BLOB 假装成消息正文')
                file.write(json.dumps(record, ensure_ascii=False) + '\n')
    except Exception:
        if created and output.exists():
            output.unlink()  # Only the output file exclusively created by this invocation.
        raise
    finally:
        db.close()
        snapshot.close()


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('source', type=Path)
    parser.add_argument('table')
    parser.add_argument('output', type=Path)
    args = parser.parse_args()
    export(args.source, args.table, args.output)
    print('Readable JSONL written to:', args.output.resolve())