"""
Shared helpers for all Phase 1 SQLite → Postgres migration scripts.

Usage in each script:
    from migration.utils import open_sqlite, get_pg, log_run, parse_dt, parse_json
"""

import json
import sys
from datetime import datetime, timezone
from pathlib import Path

import aiosqlite
from sqlalchemy import text
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession

from config import settings


# ── SQLite ────────────────────────────────────────────────────────────────────

async def open_sqlite() -> aiosqlite.Connection:
    """Open the SQLite database (read-only; no writes during migration)."""
    db_path = Path(settings.sqlite_db_path)
    if not db_path.exists():
        print(f"ERROR: SQLite database not found at {db_path.resolve()}", file=sys.stderr)
        sys.exit(1)
    conn = await aiosqlite.connect(str(db_path))
    conn.row_factory = aiosqlite.Row
    return conn


# ── Postgres ──────────────────────────────────────────────────────────────────

def _make_pg_session() -> async_sessionmaker:
    engine = create_async_engine(settings.database_url, pool_size=5, echo=False)
    return async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


AsyncPgSession = _make_pg_session()


# ── Type helpers ──────────────────────────────────────────────────────────────

def parse_dt(value: str | None) -> datetime | None:
    """Parse a SQLite TEXT timestamp → timezone-aware datetime (UTC)."""
    if not value:
        return None
    for fmt in (
        "%Y-%m-%dT%H:%M:%S.%f",
        "%Y-%m-%dT%H:%M:%S",
        "%Y-%m-%d %H:%M:%S.%f",
        "%Y-%m-%d %H:%M:%S",
        "%Y-%m-%d",
    ):
        try:
            dt = datetime.strptime(value, fmt)
            return dt.replace(tzinfo=timezone.utc)
        except ValueError:
            continue
    # ISO format with offset — let fromisoformat handle it
    try:
        dt = datetime.fromisoformat(value)
        if dt.tzinfo is None:
            dt = dt.replace(tzinfo=timezone.utc)
        return dt
    except ValueError:
        pass
    print(f"WARNING: could not parse timestamp {value!r} — using now()", file=sys.stderr)
    return datetime.now(timezone.utc)


def parse_json(value: str | None, default=None):
    """Parse a SQLite TEXT JSON column → Python object."""
    if value is None:
        return default
    try:
        return json.loads(value)
    except (json.JSONDecodeError, TypeError):
        return default


# ── Migration run log ─────────────────────────────────────────────────────────

async def log_run(
    script_name: str,
    source_rows: int,
    dest_rows: int,
    success: bool = True,
    notes: str | None = None,
) -> None:
    """Insert a row into _migration_runs recording this script's execution."""
    async with AsyncPgSession() as session:
        await session.execute(
            text("""
                INSERT INTO _migration_runs
                    (script_name, ran_at, source_rows, dest_rows, success, notes)
                VALUES
                    (:script_name, now(), :source_rows, :dest_rows, :success, :notes)
            """),
            {
                "script_name": script_name,
                "source_rows": source_rows,
                "dest_rows":   dest_rows,
                "success":     "ok" if success else "error",
                "notes":       notes,
            },
        )
        await session.commit()


# ── Count helper ──────────────────────────────────────────────────────────────

async def pg_count(session: AsyncSession, table: str) -> int:
    row = await session.execute(text(f"SELECT COUNT(*) FROM {table}"))
    return row.scalar()