from __future__ import annotations

from dataclasses import dataclass, field
from datetime import datetime, timedelta, timezone
from hmac import compare_digest
from typing import Any, Dict, Iterable, Literal, Type

from jose import ExpiredSignatureError, JWTError, jwt
from passlib.context import CryptContext

try:  # pragma: no cover - compatibility shim for passlib/argon2 warning
    import importlib.metadata as importlib_metadata
    import argon2  # type: ignore

    setattr(argon2, "__version__", importlib_metadata.version("argon2-cffi"))
except Exception:  # pragma: no cover - executed only when metadata lookup fails
    pass

from pydantic import BaseModel, Field, ValidationError

password_context = CryptContext(schemes=["argon2"], deprecated="auto")


def hash_password(password: str) -> str:
    """Derive a secure hash for a plain-text password."""

    return password_context.hash(password)


def verify_password(candidate: str, hashed: str) -> bool:
    """Verify that a candidate password matches a stored hash."""

    try:
        return password_context.verify(candidate, hashed)
    except ValueError:
        # Raised when the stored hash is malformed or uses an unknown scheme.
        return False


class TokenError(Exception):
    """Base class for token encoding/decoding issues."""


class TokenDecodeError(TokenError):
    """Raised when a token cannot be decoded or validated."""


class TokenExpiredError(TokenError):
    """Raised when a token has expired."""


class TokenTypeMismatchError(TokenError):
    """Raised when a token type does not match the expected flavour."""


TokenKind = Literal["access", "refresh"]


class TokenPayload(BaseModel):
    """Shared fields for CalMiner JWT payloads."""

    sub: str
    exp: int
    type: TokenKind
    scopes: list[str] = Field(default_factory=list)

    @property
    def expires_at(self) -> datetime:
        return datetime.fromtimestamp(self.exp, tz=timezone.utc)


@dataclass(slots=True)
class JWTSettings:
    """Runtime configuration for JWT encoding and validation."""

    secret_key: str
    algorithm: str = "HS256"
    access_token_ttl: timedelta = field(
        default_factory=lambda: timedelta(minutes=15))
    refresh_token_ttl: timedelta = field(
        default_factory=lambda: timedelta(days=7))


def create_access_token(
    subject: str,
    settings: JWTSettings,
    *,
    scopes: Iterable[str] | None = None,
    expires_delta: timedelta | None = None,
    extra_claims: Dict[str, Any] | None = None,
) -> str:
    """Issue a signed access token for the provided subject."""

    lifetime = expires_delta or settings.access_token_ttl
    return _create_token(
        subject=subject,
        token_type="access",
        settings=settings,
        lifetime=lifetime,
        scopes=scopes,
        extra_claims=extra_claims,
    )


def create_refresh_token(
    subject: str,
    settings: JWTSettings,
    *,
    scopes: Iterable[str] | None = None,
    expires_delta: timedelta | None = None,
    extra_claims: Dict[str, Any] | None = None,
) -> str:
    """Issue a signed refresh token for the provided subject."""

    lifetime = expires_delta or settings.refresh_token_ttl
    return _create_token(
        subject=subject,
        token_type="refresh",
        settings=settings,
        lifetime=lifetime,
        scopes=scopes,
        extra_claims=extra_claims,
    )


def decode_access_token(token: str, settings: JWTSettings) -> TokenPayload:
    """Validate and decode an access token."""

    return _decode_token(token, settings, expected_type="access")


def decode_refresh_token(token: str, settings: JWTSettings) -> TokenPayload:
    """Validate and decode a refresh token."""

    return _decode_token(token, settings, expected_type="refresh")


def _create_token(
    *,
    subject: str,
    token_type: TokenKind,
    settings: JWTSettings,
    lifetime: timedelta,
    scopes: Iterable[str] | None,
    extra_claims: Dict[str, Any] | None,
) -> str:
    now = datetime.now(timezone.utc)
    expire = now + lifetime
    payload: Dict[str, Any] = {
        "sub": subject,
        "type": token_type,
        "iat": int(now.timestamp()),
        "exp": int(expire.timestamp()),
    }
    if scopes:
        payload["scopes"] = list(scopes)
    if extra_claims:
        payload.update(extra_claims)

    return jwt.encode(payload, settings.secret_key, algorithm=settings.algorithm)


def _decode_token(
    token: str,
    settings: JWTSettings,
    expected_type: TokenKind,
) -> TokenPayload:
    try:
        decoded = jwt.decode(
            token,
            settings.secret_key,
            algorithms=[settings.algorithm],
            options={"verify_aud": False},
        )
    except ExpiredSignatureError as exc:  # pragma: no cover - jose marks this path
        raise TokenExpiredError("Token has expired") from exc
    except JWTError as exc:  # pragma: no cover - jose error bubble
        raise TokenDecodeError("Unable to decode token") from exc

    expected_token = jwt.encode(
        decoded,
        settings.secret_key,
        algorithm=settings.algorithm,
    )
    if not compare_digest(token, expected_token):
        raise TokenDecodeError("Token contents have been altered.")

    try:
        payload = _model_validate(TokenPayload, decoded)
    except ValidationError as exc:
        raise TokenDecodeError("Token payload validation failed") from exc

    if payload.type != expected_type:
        raise TokenTypeMismatchError(
            f"Expected a {expected_type} token but received '{payload.type}'."
        )

    return payload


def _model_validate(model: Type[TokenPayload], data: Dict[str, Any]) -> TokenPayload:
    if hasattr(model, "model_validate"):
        return model.model_validate(data)  # type: ignore[attr-defined]
    return model.parse_obj(data)  # type: ignore[attr-defined]


__all__ = [
    "JWTSettings",
    "TokenDecodeError",
    "TokenError",
    "TokenExpiredError",
    "TokenKind",
    "TokenPayload",
    "TokenTypeMismatchError",
    "create_access_token",
    "create_refresh_token",
    "decode_access_token",
    "decode_refresh_token",
    "hash_password",
    "password_context",
    "verify_password",
]