"""Tiny migration runner for the numbered SQL files in ./migrations.

Each file runs once, in its own transaction, and is recorded in
elec.schema_migrations with a checksum. Editing an applied file is refused
rather than silently ignored - add a new numbered file instead.
"""
from __future__ import annotations

import hashlib
import logging
from pathlib import Path
from typing import List

from app.electronics.db.connection import connect

logger = logging.getLogger(__name__)

MIGRATIONS_DIR = Path(__file__).resolve().parent / "migrations"

_BOOTSTRAP = """
CREATE SCHEMA IF NOT EXISTS elec;
CREATE TABLE IF NOT EXISTS elec.schema_migrations (
    version    TEXT PRIMARY KEY,
    checksum   TEXT NOT NULL,
    applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
"""


def _files() -> List[Path]:
    return sorted(MIGRATIONS_DIR.glob("[0-9][0-9][0-9][0-9]_*.sql"))


def run_migrations() -> List[str]:
    """Apply pending migrations. Returns the versions applied by this call."""
    applied_now: List[str] = []
    with connect() as conn:
        conn.execute(_BOOTSTRAP)
        conn.commit()
        done = {
            r["version"]: r["checksum"]
            for r in conn.execute("SELECT version, checksum FROM elec.schema_migrations")
        }
        for path in _files():
            sql = path.read_text(encoding="utf-8")
            checksum = hashlib.sha256(sql.encode("utf-8")).hexdigest()
            version = path.stem
            if version in done:
                if done[version] != checksum:
                    raise RuntimeError(
                        f"Migration {version} was edited after it was applied. "
                        f"Revert the edit and add a new numbered migration instead."
                    )
                continue
            logger.info("Applying migration %s", version)
            with conn.transaction():
                conn.execute(sql)
                conn.execute(
                    "INSERT INTO elec.schema_migrations (version, checksum) VALUES (%s, %s)",
                    (version, checksum),
                )
            applied_now.append(version)
    return applied_now