"""Environment-sourced configuration classes (12-factor factor 3).

Every value comes from os.environ. No secret, DB URL, or filesystem path
is ever hardcoded; .env.example documents every variable a deployment
must set.
"""
from __future__ import annotations

import os
from datetime import timedelta


def _bool_env(name: str, default: bool = False) -> bool:
    """Parse a boolean-ish environment variable."""
    val = os.environ.get(name)
    return default if val is None else val.strip().lower() in {"1", "true", "yes", "on"}


def _engine_options_for(database_url: str) -> dict:
    """pool_size/pool_recycle are QueuePool-only kwargs.

    BUG FIX (caught by actually booting the app): SQLite's default pool
    classes (NullPool for file DBs, StaticPool for :memory:) raise
    TypeError if handed pool_size/pool_recycle at all — they're not
    silently ignored. Chapter 06 makes SQLite the default engine and
    MySQL the opt-in fallback, so these kwargs are only meaningful (and
    only passed) when DATABASE_URL actually points at a non-SQLite engine.
    """
    if database_url.startswith("sqlite"):
        return {}
    return {
        "pool_size": int(os.environ.get("DB_POOL_SIZE", "3")),
        "pool_recycle": int(os.environ.get("DB_POOL_RECYCLE_SECONDS", "280")),
        "pool_pre_ping": True,
    }


class BaseConfig:
    """Shared config. Subclasses override only what differs per environment."""

    SECRET_KEY: str | None = os.environ.get("SECRET_KEY")

    # Chapter 06: SQLite/WAL default; swappable via DATABASE_URL without code changes.
    SQLALCHEMY_DATABASE_URI: str = os.environ.get("DATABASE_URL", "sqlite:///kavosh.db")
    SQLALCHEMY_ENGINE_OPTIONS: dict = _engine_options_for(SQLALCHEMY_DATABASE_URI)
    SQLALCHEMY_TRACK_MODIFICATIONS = False

    # Chapter 03: 150 max DB connections shared across up to 60 entry
    # processes -> keep each process's pool small. Exposed as its own
    # config key (not just buried inside SQLALCHEMY_ENGINE_OPTIONS) so
    # budget.py can validate the *intended* setting regardless of whether
    # the active engine (SQLite) actually consumes it.
    DB_POOL_SIZE: int = int(os.environ.get("DB_POOL_SIZE", "3"))

    # Chapter 03: filesystem cache, not Redis.
    CACHE_TYPE = os.environ.get("CACHE_TYPE", "FileSystemCache")
    CACHE_DIR = os.environ.get("CACHE_DIR", "/tmp/kavosh-cache")
    CACHE_DEFAULT_TIMEOUT = int(os.environ.get("CACHE_DEFAULT_TIMEOUT", "60"))

    # Chapter 12: secure session cookie flags.
    SESSION_COOKIE_SECURE = _bool_env("SESSION_COOKIE_SECURE", True)
    SESSION_COOKIE_HTTPONLY = True
    SESSION_COOKIE_SAMESITE = "Lax"
    PERMANENT_SESSION_LIFETIME = timedelta(
        hours=int(os.environ.get("SESSION_LIFETIME_HOURS", "12"))
    )

    WTF_CSRF_ENABLED = True

    # Chapter 04/12: upload constraints.
    UPLOAD_MAX_SIZE_MB = int(os.environ.get("UPLOAD_MAX_SIZE_MB", "500"))
    MAX_CONTENT_LENGTH = UPLOAD_MAX_SIZE_MB * 1024 * 1024
    UPLOAD_DIR = os.environ.get("UPLOAD_DIR", "/home/kavosh/uploads")

    PARSE_BATCH_SIZE = int(os.environ.get("PARSE_BATCH_SIZE", "5000"))
    ADMIN_EMAIL = os.environ.get("ADMIN_EMAIL")


class DevConfig(BaseConfig):
    DEBUG = True
    SESSION_COOKIE_SECURE = False  # allow plain-http local dev


class ProdConfig(BaseConfig):
    DEBUG = False


class TestConfig(BaseConfig):
    TESTING = True
    DEBUG = True  # lets asset() tolerate a missing Vite manifest during tests
    SQLALCHEMY_DATABASE_URI = "sqlite:///:memory:"
    SQLALCHEMY_ENGINE_OPTIONS = {}  # always in-memory SQLite regardless of DATABASE_URL
    WTF_CSRF_ENABLED = False


_CONFIGS = {"development": DevConfig, "production": ProdConfig, "testing": TestConfig}


def get_config(config_name: str | None = None):
    """Resolve a config class from FLASK_ENV or an explicit name.

    Defaults to `production` if unset, so an unconfigured deployment never
    silently runs with DEBUG on.
    """
    name = config_name or os.environ.get("FLASK_ENV", "production")
    try:
        return _CONFIGS[name]
    except KeyError as exc:
        raise ValueError(f"Unknown config_name {name!r}; expected one of {list(_CONFIGS)}") from exc