#!/usr/bin/env python3
"""Copy assistant data from SQLite to PostgreSQL."""

from __future__ import annotations

import argparse
import os
import sys
from pathlib import Path

from sqlalchemy import create_engine, inspect, text

BACKEND_ROOT = Path(__file__).resolve().parents[1]
if str(BACKEND_ROOT) not in sys.path:
    sys.path.insert(0, str(BACKEND_ROOT))

from app.db import models  # noqa: F401
from app.db.base import Base


def _row_count(engine, table: str) -> int:
    inspector = inspect(engine)
    if not inspector.has_table(table):
        return 0
    with engine.connect() as conn:
        return int(conn.execute(text(f'SELECT COUNT(*) FROM "{table}"')).scalar() or 0)


def _copy_table(src_engine, dst_engine, table_name: str, columns: list[str]) -> int:
    col_sql = ", ".join(f'"{c}"' for c in columns)
    select_sql = f'SELECT {col_sql} FROM "{table_name}"'
    insert_sql = f'INSERT INTO "{table_name}" ({col_sql}) VALUES ({", ".join(f":{c}" for c in columns)})'

    with src_engine.connect() as src_conn:
        rows = src_conn.execute(text(select_sql)).mappings().all()
    if not rows:
        return 0

    with dst_engine.begin() as dst_conn:
        for row in rows:
            dst_conn.execute(text(insert_sql), dict(row))
    return len(rows)


def _reset_serial(dst_engine, table_name: str) -> None:
    with dst_engine.begin() as conn:
        conn.execute(
            text(
                f"SELECT setval(pg_get_serial_sequence('{table_name}', 'id'), "
                f"COALESCE((SELECT MAX(id) FROM \"{table_name}\"), 1), true)"
            )
        )


def _truncate_all(dst_engine) -> None:
    table_names = [t.name for t in Base.metadata.sorted_tables]
    if not table_names:
        return
    joined = ", ".join(f'"{name}"' for name in table_names)
    with dst_engine.begin() as conn:
        conn.execute(text(f"TRUNCATE TABLE {joined} RESTART IDENTITY CASCADE"))


def main() -> int:
    parser = argparse.ArgumentParser(description="Migrate SQLite assistant.db to PostgreSQL")
    parser.add_argument(
        "--sqlite-path",
        default=os.environ.get("SQLITE_PATH", "./data/assistant.db"),
        help="Path to SQLite database file",
    )
    parser.add_argument(
        "--database-url",
        default=os.environ.get("DATABASE_URL", ""),
        help="PostgreSQL DATABASE_URL (postgresql+psycopg2://...)",
    )
    parser.add_argument("--dry-run", action="store_true", help="Print row counts only")
    parser.add_argument("--force", action="store_true", help="Truncate PostgreSQL tables before import")
    args = parser.parse_args()

    if not args.database_url.startswith("postgresql"):
        print("ERROR: DATABASE_URL must be a PostgreSQL URL (postgresql+psycopg2://...)")
        return 1

    sqlite_path = Path(args.sqlite_path)
    if not sqlite_path.is_file():
        print(f"ERROR: SQLite file not found: {sqlite_path}")
        return 1

    src_engine = create_engine(f"sqlite:///{sqlite_path.as_posix()}")
    dst_engine = create_engine(args.database_url)

    src_tables = set(inspect(src_engine).get_table_names())
    extra_tables = [t for t in ("_schema_migrations",) if t in src_tables]

    if args.dry_run:
        print(f"Dry run: {sqlite_path} -> PostgreSQL")
        total = 0
        for table in Base.metadata.sorted_tables:
            count = _row_count(src_engine, table.name) if table.name in src_tables else 0
            if count:
                print(f"  {table.name}: {count}")
                total += count
        for name in extra_tables:
            count = _row_count(src_engine, name)
            if count:
                print(f"  {name}: {count}")
                total += count
        print(f"Total rows: {total}")
        return 0

    existing_users = _row_count(dst_engine, "users")
    if existing_users > 0 and not args.force:
        print(
            f"ERROR: PostgreSQL already has {existing_users} user(s). "
            "Use --force to truncate and re-import, or migrate to an empty database."
        )
        return 1

    Base.metadata.create_all(bind=dst_engine)

    if args.force and existing_users > 0:
        print("Truncating PostgreSQL tables...")
        _truncate_all(dst_engine)

    copied = 0
    for table in Base.metadata.sorted_tables:
        if table.name not in src_tables:
            continue
        columns = [col.name for col in table.columns]
        count = _copy_table(src_engine, dst_engine, table.name, columns)
        if count:
            print(f"  {table.name}: {count} rows")
            copied += count
        if "id" in columns and count > 0:
            _reset_serial(dst_engine, table.name)

    for name in extra_tables:
        inspector = inspect(src_engine)
        cols = [col["name"] for col in inspector.get_columns(name)]
        count = _copy_table(src_engine, dst_engine, name, cols)
        if count:
            print(f"  {name}: {count} rows")
            copied += count

    print(f"Migration complete: {copied} rows copied from {sqlite_path}")
    print("SQLite file kept as backup. Update .env DATABASE_URL if not already pointing to PostgreSQL.")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())