Create core/config/settings.py

core/config/settings.py

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+from __future__ import annotations
+
+import functools
+from typing import Literal
+
+from pydantic import Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    """Application settings loaded from environment variables.
+
+    Required variables must be present at startup.
+    Optional variables have sensible defaults.
+    No .env files are used — all values come from os.environ.
+    """
+
+    model_config = SettingsConfigDict(
+        env_file="",
+        env_file_encoding="utf-8",
+        case_sensitive=True,
+        extra="ignore",
+    )
+
+    BOT_TOKEN: str | None = None
+    OPENAI_API_KEY: str | None = None
+    ADMIN_ID: str | None = None
+
+    ADMIN_USERNAME: str = ""
+    PORT: int = Field(default=7860, ge=1, le=65535)
+    SUPPORT_API_KEY: str = ""
+    YOOKASSA_SECRET_KEY: str = ""
+    YOOKASSA_SHOP_ID: str = ""
+    DATABASE_URL: str = ""
+    TELEGRAM_API_SERVER: str = "https://api.telegram.org"
+    WEBHOOK_URL: str = ""
+    DEFAULT_PROVIDER: Literal["openai", "claude", "gemini", "glm", "qwen"] = "openai"
+    LOG_LEVEL: Literal["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"] = "INFO"
+    LOG_FORMAT: Literal["json", "console"] = "json"
+
+    @property
+    def required_fields(self) -> dict[str, str | None]:
+        """Return mapping of required field names to their current values."""
+        return {
+            "BOT_TOKEN": self.BOT_TOKEN,
+            "OPENAI_API_KEY": self.OPENAI_API_KEY,
+            "ADMIN_ID": self.ADMIN_ID,
+        }
+
+
+@functools.lru_cache(maxsize=1)
+def get_settings() -> Settings:
+    """Return the cached Settings singleton.
+
+    Lazy initialization — Settings() is created only on the first call,
+    not at import time. This avoids import-time side effects and allows
+    test fixtures to override environment variables before the first call.
+
+    To reset the cache in tests, call:
+        get_settings.cache_clear()
+    """
+    return Settings()
+