"""集中读取和校验项目配置。

配置优先从后端目录的 ``.env`` 读取；若某项未配置，则使用字段右侧的默认值。
Pydantic 会自动把环境变量中的字符串转换成声明的 Python 类型。
"""

from functools import lru_cache
from pathlib import Path
from typing import Literal

from pydantic import Field, field_validator
from pydantic_settings import BaseSettings, SettingsConfigDict

# 当前文件位于 backend/app/core，向上两级就是后端项目根目录。
BACKEND_ROOT = Path(__file__).resolve().parents[2]


class Settings(BaseSettings):
    """应用运行时需要的全部配置及其默认值。"""

    model_config = SettingsConfigDict(
        env_file=BACKEND_ROOT / ".env",
        env_file_encoding="utf-8",
        case_sensitive=False,
        extra="ignore",
    )

    # Literal 限制只能使用列出的三种环境名称，拼写错误会在启动时直接报错。
    app_env: Literal["development", "test", "production"] = "development"
    app_host: str = "127.0.0.1"
    app_port: int = 8000
    app_timezone: str = "Asia/Shanghai"
    app_cors_origins: list[str] = [
        "http://127.0.0.1:5173",
        "http://127.0.0.1:5174",
    ]

    mysql_host: str = "127.0.0.1"
    mysql_port: int = 3306
    mysql_user: str = "zbt_s1"
    mysql_password: str = ""
    mysql_core_database: str = "insurance_s1_core"
    mysql_agent_database: str = "insurance_s1_agent"
    mysql_analytics_database: str = "insurance_s1_analytics"

    redis_url: str = "redis://127.0.0.1:6379/0"
    redis_prefix: str = "ins:s1:"
    agent_rate_limit: int = Field(default=20, ge=1, le=1000)
    agent_rate_window_seconds: int = Field(default=60, ge=1, le=3600)
    agent_hot_state_ttl_seconds: int = Field(default=3600, ge=60, le=86400)
    agent_event_ttl_seconds: int = Field(default=1800, ge=60, le=86400)

    deepseek_api_key: str = ""
    deepseek_base_url: str = "https://api.deepseek.com"
    deepseek_model: str = "deepseek-chat"
    langsmith_api_key: str = ""
    langsmith_endpoint: str = "https://api.smith.langchain.com"
    langsmith_project: str = "智保通-第一阶段-智能投保"
    langsmith_tracing: bool = True

    jwt_access_secret: str = Field(default="development-access-secret-change-me", min_length=32)
    jwt_refresh_secret: str = Field(default="development-refresh-secret-change-me", min_length=32)
    field_encryption_key: str = Field(default="development-field-key-change-me-now", min_length=32)
    dev_fixed_otp: str = Field(default="147258", pattern=r"^\d{6}$")
    dev_tools_enabled: bool = True
    mock_payment_callback_secret: str = Field(
        default="development-mock-payment-secret-change-me",
        min_length=32,
    )

    access_token_minutes: int = 15
    refresh_token_days: int = 7

    # 以下验证器限制程序只能访问本项目约定的数据库，避免误连或误操作其他库。
    @field_validator("mysql_core_database")
    @classmethod
    def validate_core_database(cls, value: str) -> str:
        if value not in {"insurance_s1_core", "insurance_s1_test_core"}:
            raise ValueError("第一阶段Core数据库名称不在白名单")
        return value

    @field_validator("mysql_agent_database")
    @classmethod
    def validate_agent_database(cls, value: str) -> str:
        if value not in {"insurance_s1_agent", "insurance_s1_test_agent"}:
            raise ValueError("第一阶段Agent数据库名称不在白名单")
        return value

    @field_validator("mysql_analytics_database")
    @classmethod
    def validate_analytics_database(cls, value: str) -> str:
        if value not in {"insurance_s1_analytics", "insurance_s1_test_analytics"}:
            raise ValueError("第一阶段Analytics数据库名称不在白名单")
        return value

    @field_validator("redis_prefix")
    @classmethod
    def validate_redis_prefix(cls, value: str) -> str:
        if value != "ins:s1:" and not value.startswith("ins:s1:test:"):
            raise ValueError("第一阶段Redis前缀不在白名单")
        return value


@lru_cache
def get_settings() -> Settings:
    """创建并缓存配置对象，后续调用复用同一个实例。"""
    return Settings()