"""Author RAG Chatbot SaaS — Application Configuration.

All environment variables are defined here via pydantic BaseSettings.
NEVER hardcode any value anywhere else in the codebase.
Import `get_settings()` wherever configuration is needed.
"""

from functools import lru_cache
from typing import Literal

from pydantic import AliasChoices, EmailStr, Field, field_validator, model_validator
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    """Central configuration loaded from environment variables."""

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

    # ─── App ──────────────────────────────────────────────
    APP_NAME: str = "AuthorBot"
    APP_ENV: Literal["development", "staging", "production"] = "development"
    DEBUG: bool = False
    SECRET_KEY: str = Field(
        default="change-me-set-a-real-secret-key-in-hf-secrets-32chars",
        min_length=32,
    )
    JWT_PRIVATE_KEY: str | None = None                     # RS256 private key (PEM)
    JWT_PUBLIC_KEY: str | None = None                      # RS256 public key (PEM)
    JWT_ALGORITHM: str = "HS256"
    ACCESS_TOKEN_EXPIRE_MINUTES: int = 480   # 8 hours — short-lived, auto-refreshed
    REFRESH_TOKEN_EXPIRE_DAYS: int = 30      # 30 days — stay logged in until explicit logout
    MAX_CONCURRENT_SESSIONS: int = 3

    # ─── Database ─────────────────────────────────────────
    # HF Spaces persistent bucket: sqlite+aiosqlite:////data/db.sqlite
    DATABASE_URL: str = Field(default="sqlite+aiosqlite:////data/db.sqlite")
    DB_POOL_SIZE: int = 10
    DB_MAX_OVERFLOW: int = 20

    # ─── Redis ────────────────────────────────────────────
    REDIS_URL: str = Field(default="redis://localhost:6379/0")
    REDIS_PASSWORD: str = Field(default="", exclude=True, description="Redis AUTH (required in production)")
    REDIS_DECODE_RESPONSES: bool = True

    # ─── ChromaDB ─────────────────────────────────────────
    CHROMA_CLIENT_MODE: Literal["http", "persistent"] = "persistent"
    CHROMA_HOST: str = "localhost"
    CHROMA_PORT: int = 8000
    CHROMA_PERSIST_DIR: str = "/data/chroma"

    # ─── OpenAI ───────────────────────────────────────────
    OPENAI_API_KEY: str = Field(default="")
    OPENAI_CHAT_MODEL: str = "gpt-4o"                   # Never change without approval
    OPENAI_EMBEDDING_MODEL: str = "text-embedding-3-small"
    OPENAI_MAX_RETRIES: int = 3
    OPENAI_RETRY_DELAY_BASE_SECONDS: float = 1.0        # Exponential backoff base

    # ─── Google Books (catalog / platform presence) ───────
    GOOGLE_BOOKS_API_KEY: str = Field(default="")

    # ─── Retailer APIs (optional env fallback — SuperAdmin DB overrides) ──
    RAINFOREST_API_KEY: str = Field(default="", description="Amazon product API (Rainforest)")

    # ─── RAG Pipeline ─────────────────────────────────────
    RAG_MAX_CONTEXT_TOKENS: int = 4096                  # Hard limit, never exceed
    RAG_MAX_RESPONSE_TOKENS: int = 200
    RAG_RETRIEVAL_TOP_K: int = 10
    RAG_RERANK_TOP_N: int = 5
    RAG_RERANK_MIN_SCORE: float = 0.3
    RAG_FAITHFULNESS_THRESHOLD: float = 0.55
    RAG_BOOK_CONFIDENCE_THRESHOLD: float = 0.75         # Below → show book selector
    RAG_SESSION_HISTORY_TURNS: int = 10
    RAG_SESSION_TTL_MINUTES: int = 30
    RAG_TEMPERATURE: float = 0.7
    RAG_REWRITER_MAX_TOKENS: int = 300
    RAG_MAX_INPUT_CHARS: int = 800              # Hard input cap (B2 fix — was 2000 silent truncation)

    # ─── Chunking ─────────────────────────────────────────
    CHUNK_SIZE: int = 512
    CHUNK_OVERLAP: int = 64
    EMBEDDING_BATCH_SIZE: int = 100

    # ─── File Upload ──────────────────────────────────────
    UPLOAD_MAX_FILE_SIZE_MB: int = 50
    UPLOAD_CHUNK_SIZE_MB: int = 5
    UPLOAD_STORAGE_PATH: str = "/data/uploads"
    SUPPORTED_FILE_EXTENSIONS: list[str] = ["pdf", "epub", "docx", "txt"]

    # ─── Email (Gmail SMTP) ───────────────────────────────
    SMTP_HOST: str = "smtp.gmail.com"
    SMTP_PORT: int = 465
    SMTP_USE_SSL: bool = True
    SMTP_USERNAME: EmailStr | None = Field(
        default=None,
        validation_alias=AliasChoices("SMTP_USERNAME", "GMAIL_USER"),
    )
    SMTP_PASSWORD: str | None = Field(
        default=None,
        validation_alias=AliasChoices("SMTP_PASSWORD", "GMAIL_APP_PASSWORD"),
    )
    EMAIL_FROM_NAME: str = "AuthorBot"
    EMAIL_FROM_ADDRESS: EmailStr | None = Field(
        default=None,
        validation_alias=AliasChoices("EMAIL_FROM_ADDRESS", "GMAIL_USER"),
    )
    SUPPORT_EMAIL: EmailStr | None = Field(
        default=None,
        description="Destination for publish-help requests; falls back to SMTP_USERNAME",
    )

    # ─── Rate Limiting ────────────────────────────────────
    RATE_LIMIT_CHAT_PER_MINUTE: int = 60
    RATE_LIMIT_AUTH_PER_MINUTE: int = 10
    RATE_LIMIT_VISITOR_PER_HOUR: int = 60       # Per visitor fingerprint (engaged sales chats)
    MAX_LOGIN_ATTEMPTS: int = 5
    LOCKOUT_DURATION_MINUTES: int = 15

    # ─── Analytics ────────────────────────────────────────
    GEO_DB_PATH: str = "./geoip/GeoLite2-City.mmdb"
    ANALYTICS_RETENTION_DAYS: int = 365
    BOT_USER_AGENTS_BLOCKLIST: list[str] = [
        "Googlebot", "bingbot", "Slurp", "DuckDuckBot",
        "Baiduspider", "YandexBot", "facebookexternalhit",
    ]

    # ─── SuperAdmin ───────────────────────────────────────
    SUPERADMIN_2FA_ISSUER: str = "AuthorBot SuperAdmin"
    SUBSCRIPTION_TOKEN_ALGORITHM: str = "HS256"
    SUBSCRIPTION_SECRET: str | None = Field(
        default=None,
        validation_alias=AliasChoices("SUBSCRIPTION_SECRET", "SUBSCRIPTION_TOKEN_SECRET"),
    )
    DEMO_SUBSCRIPTION_TOKEN: str | None = Field(
        default=None,
        validation_alias=AliasChoices("DEMO_SUBSCRIPTION_TOKEN", "SUBSCRIPTION_TOKEN"),
    )
    SUPERADMIN_TOTP_SECRET: str | None = Field(default=None, exclude=True)

    # Seed superadmin account on first startup (set via HF Secrets)
    SUPERADMIN_EMAIL: str | None = Field(
        default=None,
        validation_alias=AliasChoices("SUPERADMIN_EMAIL", "SUPER_ADMIN_USER"),
    )
    SUPERADMIN_PASSWORD: str | None = Field(
        default=None,
        validation_alias=AliasChoices("SUPERADMIN_PASSWORD", "SUPER_ADMIN_PASS"),
        exclude=True,
    )

    # ─── Token Budgets (defaults, overridden per plan) ────
    PLAN_MONTHLY_TOKENS: int = 500_000
    PLAN_QUARTERLY_TOKENS: int = 1_500_000
    PLAN_SEMI_ANNUAL_TOKENS: int = 3_000_000
    PLAN_ANNUAL_TOKENS: int = 7_000_000
    TOKEN_WARNING_THRESHOLD_PCT: float = 0.80
    TOKEN_ALERT_THRESHOLD_PCT: float = 0.95

    # ─── Stripe Billing ───────────────────────────────────
    # Test mode: sk_test_...  (default — safe to commit .env.example with placeholder)
    # Live mode: sk_live_...  (set in production .env — zero code changes needed)
    STRIPE_SECRET_KEY: str = Field(default="", description="Stripe secret key (sk_test_... or sk_live_...)")
    STRIPE_PUBLISHABLE_KEY: str = Field(default="", description="Stripe publishable key (pk_test_... or pk_live_...)")
    STRIPE_WEBHOOK_SECRET: str = Field(default="", description="Stripe webhook signing secret (whsec_...)")

    # ─── Frontend / Widget ────────────────────────────────
    SAAS_CDN_URL: str = "http://localhost:3000"         # Widget script served from here
    ALLOWED_ORIGINS: list[str] = ["http://localhost:3000"]
    FRONTEND_URL: str = Field(
        default="http://localhost:3000",
        description="Base URL of the Next.js marketing website (for Stripe redirect URLs)",
    )

    # ─── Auth / Password Reset ────────────────────────────
    PASSWORD_RESET_EXPIRE_MINUTES: int = 60   # Reset tokens expire after 1 hour

    # ─── Celery ───────────────────────────────────────────
    CELERY_BROKER_URL: str = Field(default="redis://localhost:6379/1")
    CELERY_RESULT_BACKEND: str = Field(default="redis://localhost:6379/2")

    # ─── Observability ────────────────────────────────────
    SENTRY_DSN: str | None = None  # R-100: Set via env to enable error tracking

    @field_validator("SECRET_KEY")
    @classmethod
    def secret_key_must_be_strong(cls, v: str) -> str:
        """Enforce minimum secret key entropy."""
        if len(v) < 32:
            raise ValueError("SECRET_KEY must be at least 32 characters long")
        return v

    @model_validator(mode="after")
    def apply_hf_secret_defaults(self) -> "Settings":
        """Fill derived settings from legacy Hugging Face secret names."""
        from app.core.redis_url import redis_url_has_auth, redis_url_with_auth

        if self.EMAIL_FROM_ADDRESS is None and self.SMTP_USERNAME is not None:
            self.EMAIL_FROM_ADDRESS = self.SMTP_USERNAME
        if self.SUPPORT_EMAIL is None and self.SMTP_USERNAME is not None:
            self.SUPPORT_EMAIL = self.SMTP_USERNAME

        if self.REDIS_PASSWORD:
            self.REDIS_URL = redis_url_with_auth(self.REDIS_URL, self.REDIS_PASSWORD)
            self.CELERY_BROKER_URL = redis_url_with_auth(self.CELERY_BROKER_URL, self.REDIS_PASSWORD)
            self.CELERY_RESULT_BACKEND = redis_url_with_auth(
                self.CELERY_RESULT_BACKEND, self.REDIS_PASSWORD,
            )

        if self.APP_ENV == "production" and not redis_url_has_auth(self.REDIS_URL):
            raise ValueError(
                "REDIS_PASSWORD or password in REDIS_URL is required when APP_ENV=production",
            )
        return self


@lru_cache
def get_settings() -> Settings:
    """Return cached settings instance. Use this everywhere."""
    return Settings()