"""Export a consistent SQLite snapshot without modifying the source database."""
import argparse
import os
from pathlib import Path
import sqlite3
import sys
import tempfile


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("source", type=Path)
    parser.add_argument("output", type=Path)
    args = parser.parse_args()
    source = args.source.resolve(strict=True)
    output = args.output.resolve()
    if output.exists():
        parser.error("Output already exists; choose a new filename.")
    output.parent.mkdir(parents=True, exist_ok=True)
    # Refuse to overwrite either the original database or an earlier export.
    with tempfile.TemporaryDirectory(prefix="csr-sqlite-export-") as temporary:
        snapshot = Path(temporary) / "snapshot.sqlite3"
        origin = sqlite3.connect(source.as_uri() + "?mode=ro", uri=True)
        destination = sqlite3.connect(snapshot)
        try:
            origin.backup(destination)
        finally:
            destination.close()
            origin.close()
        os.environ["SQLITE_MIGRATION_SNAPSHOT"] = str(snapshot)
        os.environ["DJANGO_SETTINGS_MODULE"] = "csr_inventory.sqlite_migration_settings"
        sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
        import django
        django.setup()
        from django.core.management import call_command
        from django.db import connections
        try:
            call_command("migrate", interactive=False, verbosity=0)
            with output.open("x", encoding="utf-8") as stream:
                os.chmod(output, 0o600)
                try:
                    call_command(
                        "dumpdata", natural_foreign=True,
                        exclude=["contenttypes", "auth.permission", "sessions.session"],
                        stdout=stream, verbosity=0,
                    )
                except BaseException:
                    stream.close()
                    output.unlink()
                    raise
        finally:
            connections.close_all()
    print(f"Export created: {output}. Original SQLite database unchanged.")


if __name__ == "__main__":
    main()