# db_utils.py
import pyodbc
import datetime
import decimal
from config import SQL_SERVER_CONN, ACCESS_DRIVER


# ================= 表存在性检查 & 自动建表 =================

def table_exists(cursor, schema, table):
    """检查 SQL Server 表是否存在"""
    query = """
        SELECT COUNT(*)
        FROM sys.tables t
        JOIN sys.schemas s ON t.schema_id = s.schema_id
        WHERE s.name = ? AND t.name = ?
    """
    cursor.execute(query, (schema, table))
    return cursor.fetchone()[0] > 0


def ensure_schema(cursor, schema):
    """确保 schema 存在，不存在则创建"""
    cursor.execute("SELECT SCHEMA_ID(?)", (schema,))
    if cursor.fetchone()[0] is None:
        cursor.execute(f"CREATE SCHEMA [{schema}]")


def _access_col_to_sql(col_info, pk_col):
    """将 Access 列描述 (cursor.description 元组) 转为 SQL Server 列定义

    Access ODBC 驱动的 type_code 是 Python 类型对象:
      int              → INT
      str              → NVARCHAR(size)  (size > 4000 时为 Memo 字段 → NVARCHAR(MAX))
      datetime.datetime → DATETIME
      float            → FLOAT
      decimal.Decimal  → DECIMAL(p,s)
      bool             → BIT
    """
    col_name, type_code, _, size, precision, scale, nullable = col_info
    is_pk = (col_name == pk_col)

    if type_code is int:
        sql_type = "INT"
        if is_pk:
            sql_type += " IDENTITY(1,1) PRIMARY KEY"
    elif type_code is float:
        sql_type = "FLOAT"
    elif type_code is bool:
        sql_type = "BIT"
    elif type_code is datetime.datetime:
        sql_type = "DATETIME"
    elif type_code is decimal.Decimal:
        sql_type = f"DECIMAL({precision or 18}, {scale or 0})"
    elif type_code is str:
        # size > 4000 → Access Memo 字段，用 NVARCHAR(MAX)
        if not size or size <= 0 or size > 4000:
            sql_type = "NVARCHAR(MAX)"
        else:
            sql_type = f"NVARCHAR({size})"
        if is_pk:
            sql_type += " PRIMARY KEY"
    else:
        sql_type = "NVARCHAR(255)"
        if is_pk:
            sql_type += " PRIMARY KEY"

    return f"[{col_name}] {sql_type}"


def create_table_from_access(sql_cursor, target_schema, target_table,
                             acc_description, pk_col):
    """根据 Access cursor.description 在 SQL Server 自动建表"""
    col_defs = [_access_col_to_sql(col, pk_col) for col in acc_description]
    full_name = fmt_table(target_schema, target_table)
    col_str = ",\n    ".join(col_defs)
    create_sql = f"CREATE TABLE {full_name} (\n    {col_str}\n)"
    sql_cursor.execute(create_sql)

def get_sql_conn():
    """获取 SQL Server 连接"""
    # 显式添加 TrustServerCertificate=yes 以兼容 ODBC Driver 18+
    conn_str = (
        f"DRIVER={SQL_SERVER_CONN['driver']};SERVER={SQL_SERVER_CONN['server']};"
        f"DATABASE={SQL_SERVER_CONN['database']};UID={SQL_SERVER_CONN['uid']};PWD={SQL_SERVER_CONN['pwd']};"
        "Encrypt=yes;TrustServerCertificate=yes;"
    )
    return pyodbc.connect(conn_str)

def get_access_conn(file_path):
    """获取 Access 连接"""
    conn_str = f"DRIVER={ACCESS_DRIVER};DBQ={file_path};"
    return pyodbc.connect(conn_str)

def fmt_table(schema, table):
    """格式化 SQL Server 表名 [schema].[table]"""
    return f"[{schema}].[{table}]"

def get_columns(cursor, table_name):
    """获取 Access 表的列名"""
    # Access 查询表名加 []
    cursor.execute(f"SELECT TOP 1 * FROM [{table_name}]")
    return [column[0] for column in cursor.description]

def generate_insert_sql(target_schema, target_table, columns):
    """生成带架构的 INSERT 语句"""
    full_table_name = fmt_table(target_schema, target_table)
    col_str = ",".join([f"[{col}]" for col in columns])
    placeholders = ",".join(["?"] * len(columns))
    return f"INSERT INTO {full_table_name} ({col_str}) VALUES ({placeholders})"