#!/usr/bin/env python3
"""Add stable user identity to subscription bindings and access records.

The default invocation only reports schema changes. --apply creates a consistent
SQLite backup before the transaction. Run against an isolated database first.
"""
import argparse
import datetime
import json
from pathlib import Path
import sqlite3


def migrate(db_path: Path, apply: bool = False) -> dict:
    if not db_path.is_file():
        raise ValueError("database must already exist")
    uri = db_path.resolve().as_uri() + ("?mode=rw" if apply else "?mode=ro")
    with sqlite3.connect(uri, uri=True) as db:
        changes = []
        for table in ("sub_bind", "sub_update_record"):
            columns = {row[1] for row in db.execute(f'PRAGMA table_info("{table}")')}
            if not columns:
                raise ValueError(f"required table missing: {table}")
            if "user_id" not in columns:
                changes.append(f"add {table}.user_id")
        duplicates = db.execute(
            "select count(*) from (select username from User group by username having count(*) > 1)"
        ).fetchone()[0]
        if duplicates:
            raise ValueError("ambiguous duplicate usernames; resolve identities before migration")
        result = {"apply": apply, "schema_changes": changes}
        if not apply:
            return result
        stamp = datetime.datetime.now(datetime.timezone.utc).strftime("%Y%m%dT%H%M%S%fZ")
        backup = db_path.with_name(db_path.name + ".before-user-links." + stamp)
        with sqlite3.connect(backup) as snapshot:
            db.backup(snapshot)
        backup.chmod(0o600)
        db.execute("BEGIN IMMEDIATE")
        try:
            for change in changes:
                table = change.split()[1].split(".")[0]
                db.execute(f'ALTER TABLE "{table}" ADD COLUMN user_id INTEGER REFERENCES User(id)')
            for table in ("sub_bind", "sub_update_record"):
                db.execute(f'UPDATE "{table}" SET user_id=(SELECT id FROM User WHERE username="{table}".user) WHERE user_id IS NULL')
            db.execute("CREATE UNIQUE INDEX IF NOT EXISTS User_username_uindex ON User(username)")
            db.execute("CREATE UNIQUE INDEX IF NOT EXISTS idx_sub_bind_user_id ON sub_bind(user_id) WHERE user_id IS NOT NULL")
            db.execute("CREATE INDEX IF NOT EXISTS idx_sub_record_user_id ON sub_update_record(user_id, id)")
            db.commit()
        except BaseException:
            db.rollback()
            raise
        result["backup"] = str(backup)
        result["unresolved_bindings"] = db.execute("select count(*) from sub_bind where user_id is null").fetchone()[0]
        result["unresolved_records"] = db.execute("select count(*) from sub_update_record where user_id is null").fetchone()[0]
        return result


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("database", type=Path)
    parser.add_argument("--apply", action="store_true")
    args = parser.parse_args()
    print(json.dumps(migrate(args.database, args.apply), ensure_ascii=False))