import sqlite3
from typing import Sequence


class MigrationError(Exception):
    pass


def split_statements(script: str) -> list[str]:
    statements: list[str] = []
    buffer = ""
    for line in script.splitlines(keepends=True):
        buffer += line
        if sqlite3.complete_statement(buffer):
            statements.append(buffer.strip())
            buffer = ""
    if buffer.strip():
        statements.append(buffer.strip())
    return statements


def apply_migration(conn: sqlite3.Connection, index: int, script: str) -> None:
    try:
        conn.execute("BEGIN IMMEDIATE")
        for statement in split_statements(script):
            conn.execute(statement)
        conn.execute(f"PRAGMA user_version={index + 1}")
        conn.execute("COMMIT")
    except Exception as exc:
        try:
            conn.execute("ROLLBACK")
        except sqlite3.Error:
            pass
        raise MigrationError(f"Migration {index} fehlgeschlagen und zurückgerollt: {exc}") from exc


def run_migrations(conn: sqlite3.Connection, migrations: Sequence[str]) -> None:
    version = conn.execute("PRAGMA user_version").fetchone()[0]
    # Im Autocommit-Modus, damit BEGIN/COMMIT ausschließlich hier gesetzt werden (executescript würde implizit committen).
    previous = conn.isolation_level
    conn.isolation_level = None
    try:
        for index in range(version, len(migrations)):
            apply_migration(conn, index, migrations[index])
    finally:
        conn.isolation_level = previous