import hashlib
import logging
from dataclasses import dataclass
from datetime import UTC, datetime, timedelta
from pathlib import Path
from typing import Any

import jwt
from jinja2 import Template
from jwt.exceptions import InvalidTokenError

from fluksio.core import security
from fluksio.core.config import settings

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

#: How long to wait on the mail server before giving up on one message.
SMTP_TIMEOUT_S = 10


@dataclass
class EmailData:
    html_content: str
    subject: str


def render_email_template(*, template_name: str, context: dict[str, Any]) -> str:
    template_str = (
        Path(__file__).parent / "email-templates" / "build" / template_name
    ).read_text()
    html_content = Template(template_str).render(context)
    return html_content


def send_email(
    *,
    email_to: str,
    subject: str = "",
    html_content: str = "",
) -> None:
    assert settings.emails_enabled, "no provided configuration for email variables"
    try:
        import emails  # type: ignore
    except ImportError:
        raise RuntimeError(
            "sending mail needs the server extra: pip install 'fluksio[server]'"
        ) from None
    message = emails.Message(
        subject=subject,
        html=html_content,
        mail_from=(settings.EMAILS_FROM_NAME, settings.EMAILS_FROM_EMAIL),
    )
    # With no timeout smtplib inherits the socket default, which is none at
    # all — an unreachable mail host then held a threadpool worker until the
    # kernel gave up, from a route anybody can call.
    smtp_options: dict[str, Any] = {
        "host": settings.SMTP_HOST,
        "port": settings.SMTP_PORT,
        "timeout": SMTP_TIMEOUT_S,
    }
    if settings.SMTP_TLS:
        smtp_options["tls"] = True
    elif settings.SMTP_SSL:
        smtp_options["ssl"] = True
    if settings.SMTP_USER:
        smtp_options["user"] = settings.SMTP_USER
    if settings.SMTP_PASSWORD:
        smtp_options["password"] = settings.SMTP_PASSWORD
    response = message.send(to=email_to, smtp=smtp_options)
    logger.info(f"send email result: {response}")


def generate_test_email(email_to: str) -> EmailData:
    project_name = settings.PROJECT_NAME
    subject = f"{project_name} - Test email"
    html_content = render_email_template(
        template_name="test_email.html",
        context={"project_name": settings.PROJECT_NAME, "email": email_to},
    )
    return EmailData(html_content=html_content, subject=subject)


def generate_reset_password_email(email_to: str, email: str, token: str) -> EmailData:
    project_name = settings.PROJECT_NAME
    subject = f"{project_name} - Password recovery for user {email}"
    link = f"{settings.FRONTEND_HOST}/reset-password?token={token}"
    html_content = render_email_template(
        template_name="reset_password.html",
        context={
            "project_name": settings.PROJECT_NAME,
            "username": email,
            "email": email_to,
            "valid_hours": settings.EMAIL_RESET_TOKEN_EXPIRE_HOURS,
            "link": link,
        },
    )
    return EmailData(html_content=html_content, subject=subject)


def generate_new_account_email(
    email_to: str, username: str, password: str
) -> EmailData:
    project_name = settings.PROJECT_NAME
    subject = f"{project_name} - New account for user {username}"
    html_content = render_email_template(
        template_name="new_account.html",
        context={
            "project_name": settings.PROJECT_NAME,
            "username": username,
            "password": password,
            "email": email_to,
            "link": settings.FRONTEND_HOST,
        },
    )
    return EmailData(html_content=html_content, subject=subject)


def password_fingerprint(hashed_password: str) -> str:
    """A short digest of the stored hash, for binding a reset link to it.

    What makes a reset token single-use without a table of spent ones: the
    hash changes the moment the password does, so the link that set it stops
    verifying. It was replayable for the whole 48 hours otherwise.
    """
    return hashlib.sha256(hashed_password.encode()).hexdigest()[:16]


def generate_password_reset_token(email: str, hashed_password: str = "") -> str:
    delta = timedelta(hours=settings.EMAIL_RESET_TOKEN_EXPIRE_HOURS)
    now = datetime.now(UTC)
    expires = now + delta
    exp = expires.timestamp()
    encoded_jwt = jwt.encode(
        {
            "exp": exp,
            "nbf": now,
            "sub": email,
            "pwd": password_fingerprint(hashed_password),
        },
        settings.SECRET_KEY,
        algorithm=security.ALGORITHM,
    )
    return encoded_jwt


def verify_password_reset_token(token: str) -> tuple[str, str] | None:
    """The email the token names and the password hash it was minted against."""
    try:
        decoded_token = jwt.decode(
            token, settings.SECRET_KEY, algorithms=[security.ALGORITHM]
        )
        return str(decoded_token["sub"]), str(decoded_token.get("pwd", ""))
    except InvalidTokenError:
        return None