"""SQLite 数据库连接与会话管理。

配置来源（优先级从高到低）：进程环境变量 → 仓库根 ``.env`` →
``backend/.env`` → 代码里的默认值。``.env`` 在本模块导入时即被读入，
因此 ``DATABASE_URL`` / ``CORS_ORIGINS`` / ``JWT_SECRET`` 等都在此生效。
"""
from __future__ import annotations

import os
import sys
from pathlib import Path

from sqlalchemy import create_engine, event
from sqlalchemy import inspect, text
from sqlalchemy.orm import DeclarativeBase, sessionmaker


REPO_ROOT = Path(__file__).resolve().parent.parent
DEFAULT_DB_PATH = REPO_ROOT / "data" / "math.db"
BACKEND_DIR = Path(__file__).resolve().parent


def _load_env_files() -> None:
    """读取 ``.env``：仓库根优先，``backend/.env`` 只补前者没有的键。

    已经存在的环境变量不会被覆盖，所以容器/脚本用 ``DATABASE_URL=…``
    直接启动时仍然以环境变量为准。
    """
    try:
        from dotenv import load_dotenv
    except ImportError:
        # 不静默：否则 .env 会被“看起来没生效”地忽略掉
        print(
            "[config] 未安装 python-dotenv，.env 不会生效。"
            "请执行：backend/.venv/bin/pip install -r backend/requirements.txt",
            file=sys.stderr,
        )
        return
    for path in (REPO_ROOT / ".env", BACKEND_DIR / ".env"):
        if path.is_file():
            load_dotenv(path, override=False)


_load_env_files()


class Base(DeclarativeBase):
    pass


def _engine_url() -> str:
    url = os.getenv("DATABASE_URL", "").strip()
    if url:
        return url
    DEFAULT_DB_PATH.parent.mkdir(parents=True, exist_ok=True)
    return f"sqlite:///{DEFAULT_DB_PATH}"


DATABASE_URL = _engine_url()
connect_args = {"check_same_thread": False} if DATABASE_URL.startswith("sqlite") else {}

engine = create_engine(DATABASE_URL, connect_args=connect_args)
SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)


if DATABASE_URL.startswith("sqlite"):
    @event.listens_for(engine, "connect")
    def _enable_sqlite_foreign_keys(dbapi_connection, _connection_record):
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA foreign_keys=ON")
        cursor.close()


def ensure_schema() -> None:
    """建表并为旧库补充新增列（SQLite 不会由 create_all 自动加列）。

    只做**表与字段**层面的对齐，不写任何业务数据：后端每次启动都可以安全
    重放。种子数据与历史数据迁移只在初始化时执行 ——
    ``cd backend && .venv/bin/python -m seed``。
    """
    Base.metadata.create_all(bind=engine)
    inspector = inspect(engine)

    additions: dict[str, list[tuple[str, str]]] = {
        "questions": [
            ("chapter_id", "INTEGER"),
            ("difficulty", "INTEGER NOT NULL DEFAULT 1"),
            ("is_generated", "BOOLEAN NOT NULL DEFAULT 0"),
            ("used_count", "INTEGER NOT NULL DEFAULT 0"),
        ],
        "llm_settings": [
            ("name", "VARCHAR(128) NOT NULL DEFAULT ''"),
            ("is_default", "BOOLEAN NOT NULL DEFAULT 0"),
            ("created_at", "DATETIME"),
            ("max_tokens", "INTEGER"),
        ],
        "attempt_items": [
            ("knowledge_names", "TEXT NOT NULL DEFAULT '[]'"),
        ],
        "knowledge": [
            ("domain", "VARCHAR(16) NOT NULL DEFAULT '初等'"),
            ("category", "VARCHAR(64) NOT NULL DEFAULT ''"),
        ],
        "error_entries": [
            ("attempt_id", "INTEGER"),
            ("question_id", "INTEGER"),
            ("stem", "TEXT NOT NULL DEFAULT ''"),
            ("options", "TEXT NOT NULL DEFAULT ''"),
            ("selected", "INTEGER"),
            ("correct_index", "INTEGER"),
            ("explanation", "TEXT NOT NULL DEFAULT ''"),
            ("knowledge_names", "TEXT NOT NULL DEFAULT '[]'"),
        ],
        "attempt_sessions": [
            ("chapter_id", "INTEGER"),
        ],
        "chapters": [
            ("ebook_page", "INTEGER NOT NULL DEFAULT 0"),
        ],
        "textbooks": [
            ("ebook_file", "VARCHAR(256) NOT NULL DEFAULT ''"),
            ("ebook_name", "VARCHAR(256) NOT NULL DEFAULT ''"),
            ("ebook_format", "VARCHAR(8) NOT NULL DEFAULT ''"),
            ("ebook_size", "INTEGER NOT NULL DEFAULT 0"),
            ("ebook_pages", "INTEGER NOT NULL DEFAULT 0"),
            ("ebook_uploaded_at", "DATETIME"),
        ],
        "knowledge_resources": [
            ("course_id", "INTEGER"),
        ],
        "daily_completions": [
            ("chapter_id", "INTEGER"),
            ("rating", "VARCHAR(16) NOT NULL DEFAULT ''"),
        ],
    }
    for table_name, columns in additions.items():
        if table_name not in inspector.get_table_names():
            continue
        existing = {
            column["name"] for column in inspector.get_columns(table_name)
        }
        for name, definition in columns:
            if name in existing:
                continue
            with engine.begin() as connection:
                connection.execute(
                    text(
                        f"ALTER TABLE {table_name} "
                        f"ADD COLUMN {name} {definition}"
                    )
                )


def migrate_legacy_courses() -> None:
    """把旧 textbooks 表里的“在线课程”行搬到 courses 表，并去掉 kind 列。

    教材与课程从此各用一张表：教材带章节目录与电子书，课程只有外链。
    属于数据迁移，只在 ``python -m seed`` 初始化时执行；调用前需先跑
    ``ensure_schema()``（要用到新补的 ``knowledge_resources.course_id``）。
    幂等：kind 列不存在（已迁移过）时直接返回。
    """
    inspector = inspect(engine)
    tables = inspector.get_table_names()
    if "textbooks" not in tables or "courses" not in tables:
        return
    columns = {column["name"] for column in inspector.get_columns("textbooks")}
    if "kind" not in columns:
        return

    with engine.begin() as connection:
        rows = connection.execute(
            text(
                "SELECT id, name, publisher, link, grade, description, position "
                "FROM textbooks WHERE kind = 'course'"
            )
        ).fetchall()
        for row in rows:
            exists = connection.execute(
                text("SELECT id FROM courses WHERE name = :name"),
                {"name": row[1]},
            ).first()
            if exists is None:
                connection.execute(
                    text(
                        "INSERT INTO courses "
                        "(name, provider, url, grade, description, position) "
                        "VALUES (:name, :provider, :url, :grade, :description, :position)"
                    ),
                    {
                        "name": row[1],
                        "provider": row[2] or "",
                        "url": row[3] or "",
                        "grade": row[4] or "",
                        "description": row[5] or "",
                        "position": row[6] or 0,
                    },
                )
                exists = connection.execute(
                    text("SELECT id FROM courses WHERE name = :name"),
                    {"name": row[1]},
                ).first()
            # 知识点上的视频资源改挂课程，删教材行时不会被级联删掉
            connection.execute(
                text(
                    "UPDATE knowledge_resources "
                    "SET course_id = :course_id, textbook_id = NULL "
                    "WHERE textbook_id = :textbook_id"
                ),
                {"course_id": exists[0], "textbook_id": row[0]},
            )
        connection.execute(text("DELETE FROM textbooks WHERE kind = 'course'"))
        connection.execute(text("ALTER TABLE textbooks DROP COLUMN kind"))


def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()