import logging
import os
import sys
from logging.config import fileConfig

from alembic import context
from flask import current_app

USE_TWOPHASE = False

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)
logger = logging.getLogger('alembic.env')

# add your model's MetaData object here
# for 'autogenerate' support
# 将当前目录的父目录(api目录)添加到Python路径中，以便能够导入models模块
sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))


# 获取当前运行的应用数据库引擎和URL
def get_engine():
    try:
        return current_app.extensions['sqlalchemy'].db.engine
    except (KeyError, AttributeError):
        return current_app.extensions['migrate'].db.engine


def get_engine_url():
    try:
        return get_engine().url.render_as_string(hide_password=False).replace(
            '%', '%%')
    except AttributeError:
        return str(get_engine().url).replace('%', '%%')


# 使用当前应用的数据库URL替换配置文件中的URL
config.set_main_option('sqlalchemy.url', get_engine_url())

from models import db

target_metadata = db.Model.metadata

# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
        version_table="alembic_version_extend",
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    # 使用应用的数据库引擎，而不是从配置文件创建
    connectable = get_engine()

    with connectable.connect() as connection:
        context.configure(
            connection=connection, 
            target_metadata=target_metadata,
            version_table="alembic_version_extend",
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()