"""JWT Profile for OAuth 2.0 implementations (RFC 7523, RFC 9068).

This module implements JWT-related OAuth 2.0 profiles for secure token handling,
including JWT client assertions and JWT access token profiles.

RFC 7523: JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication
and Authorization Grants
https://datatracker.ietf.org/doc/html/rfc7523

RFC 9068: JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens
https://datatracker.ietf.org/doc/html/rfc9068

Key Features:
- JWT client authentication (RFC 7523)
- JWT authorization grants (RFC 7523)
- JWT access token format (RFC 9068)
- Claims validation and verification
- Signature verification and key management

JWT Client Authentication Use Cases:
- High-security environments requiring cryptographic authentication
- Distributed systems with pre-shared keys or certificates
- Service-to-service authentication
- Environments where client secrets are not practical

JWT Access Token Benefits:
- Self-contained tokens with embedded claims
- Cryptographic integrity protection
- Reduced database lookups for token validation
- Standardized claim format across services
"""

import base64
import json
from typing import Any

from pydantic import BaseModel


def get_claims(jwt_token: str) -> dict[str, Any]:
    """Extract all claims from a JWT token payload without verification.

    This utility extracts all claims from a JWT token's payload without
    performing signature verification. Useful for operational purposes
    like extracting specific claims for token exchange requests.

    Args:
        jwt_token: JWT token string (without Bearer prefix)

    Returns:
        Dictionary of all claims in the JWT payload

    Raises:
        ValueError: If token is malformed or cannot be decoded

    Note:
        This function does NOT verify the token signature. It's intended
        for extracting claims from trusted tokens for operational purposes.

    Example:
        >>> token = "eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.eyJjbGllbnRfaWQiOiJhYmMxMjMiLCJzdWIiOiJ1c2VyMTIzIn0.signature"
        >>> claims = get_claims(token)
        >>> print(claims)  # {"client_id": "abc123", "sub": "user123"}
    """
    try:
        # JWT tokens have 3 parts separated by dots: header.payload.signature
        parts = jwt_token.split('.')
        if len(parts) != 3:
            raise ValueError("Invalid JWT token format - expected 3 parts separated by dots")

        payload_b64 = parts[1]

        # Add padding if needed for base64 decoding
        padding = len(payload_b64) % 4
        if padding:
            payload_b64 += '=' * (4 - padding)

        try:
            payload_bytes = base64.urlsafe_b64decode(payload_b64)
            payload = json.loads(payload_bytes.decode('utf-8'))
        except (json.JSONDecodeError, UnicodeDecodeError) as e:
            raise ValueError(f"Failed to decode JWT payload: {e}") from e

        # Return the full claims dictionary
        return payload if isinstance(payload, dict) else {}

    except ValueError:
        raise
    except Exception as e:
        raise ValueError(f"Failed to extract claims from JWT token: {e}") from e


class JWTClientAssertion:
    """JWT Client Assertion utilities for RFC 7523.

    Implements JWT-based client authentication as an alternative to
    client secrets for OAuth 2.0 token requests.

    Reference: https://datatracker.ietf.org/doc/html/rfc7523#section-3
    """

    # Standard assertion type for JWT client authentication
    ASSERTION_TYPE = "urn:ietf:params:oauth:client-assertion-type:jwt-bearer"

    @staticmethod
    def create_assertion(
        client_id: str,
        audience: str,
        issuer: str,
        subject: str | None = None,
        expiration_seconds: int = 300,
        additional_claims: dict[str, Any] | None = None,
        private_key: str | None = None,
        algorithm: str = "RS256",
    ) -> str:
        """Create a JWT client assertion for authentication.

        Args:
            client_id: OAuth 2.0 client identifier
            audience: Token endpoint URL (aud claim)
            issuer: JWT issuer (iss claim)
            subject: JWT subject (sub claim), defaults to client_id
            expiration_seconds: Token lifetime in seconds
            additional_claims: Extra claims to include in JWT
            private_key: Private key for signing (PEM format)
            algorithm: Signing algorithm (RS256, ES256, etc.)

        Returns:
            Signed JWT assertion string

        Reference: https://datatracker.ietf.org/doc/html/rfc7523#section-3
        """
        # Implementation placeholder
        raise NotImplementedError("JWT client assertion creation not yet implemented")

    @staticmethod
    def verify_assertion(
        assertion: str,
        expected_audience: str,
        public_key: str | None = None,
        clock_skew_seconds: int = 30,
    ) -> dict[str, Any]:
        """Verify a JWT client assertion.

        Args:
            assertion: JWT assertion to verify
            expected_audience: Expected audience claim value
            public_key: Public key for verification (PEM format)
            clock_skew_seconds: Allowable clock skew for time-based claims

        Returns:
            Verified JWT payload claims

        Raises:
            OAuthInvalidTokenError: If JWT is invalid or verification fails
        """
        # Implementation placeholder
        raise NotImplementedError(
            "JWT client assertion verification not yet implemented"
        )


class JWTAccessToken(BaseModel):
    """JWT Access Token profile implementing RFC 9068.

    Defines the standard claims and structure for JWT-formatted access tokens
    as specified in RFC 9068.

    Reference: https://datatracker.ietf.org/doc/html/rfc9068#section-2
    """

    # Standard JWT claims (RFC 7519)
    iss: str  # Issuer
    sub: str  # Subject
    aud: str | list[str]  # Audience
    exp: int  # Expiration time
    iat: int  # Issued at
    jti: str | None = None  # JWT ID

    # OAuth 2.0 specific claims (RFC 9068)
    client_id: str  # OAuth 2.0 client identifier
    scope: str | None = None  # Space-separated scopes

    # Optional authorization details
    authorization_details: list[dict[str, Any]] | None = None


class JWTAccessTokenHandler:
    """Handler for JWT Access Tokens implementing RFC 9068.

    Provides utilities for creating, parsing, and validating JWT access tokens
    according to the standardized profile defined in RFC 9068.

    Reference: https://datatracker.ietf.org/doc/html/rfc9068

    Example:
        handler = JWTAccessTokenHandler(
            issuer="https://auth.example.com",
            private_key=private_key_pem,
            algorithm="RS256"
        )

        # Create a JWT access token
        jwt_token = handler.create_access_token(
            subject="user123",
            client_id="client456",
            audience="https://api.example.com",
            scope="read:data write:data",
            expires_in=3600
        )

        # Parse and validate a JWT access token
        claims = handler.parse_access_token(jwt_token)
        print(f"Token for client: {claims.client_id}")
        print(f"Token scopes: {claims.scope}")
    """

    def __init__(
        self, issuer: str, private_key: str | None = None, algorithm: str = "RS256"
    ):
        """Initialize the JWT access token handler.

        Args:
            issuer: Token issuer identifier
            private_key: Private key for signing tokens (PEM format)
            algorithm: JWT signing algorithm
        """
        # Implementation placeholder
        pass

    def create_access_token(
        self,
        subject: str,
        client_id: str,
        audience: str | list[str],
        scope: str | None = None,
        expires_in: int = 3600,
        additional_claims: dict[str, Any] | None = None,
    ) -> str:
        """Create a JWT access token.

        Args:
            subject: Token subject (typically user ID)
            client_id: OAuth 2.0 client identifier
            audience: Token audience (resource server URLs)
            scope: Space-separated OAuth 2.0 scopes
            expires_in: Token lifetime in seconds
            additional_claims: Extra claims to include

        Returns:
            Signed JWT access token string

        Reference: https://datatracker.ietf.org/doc/html/rfc9068#section-2
        """
        # Implementation placeholder
        raise NotImplementedError("JWT access token creation not yet implemented")

    def parse_access_token(
        self,
        jwt_token: str,
        verify_signature: bool = True,
        public_key: str | None = None,
    ) -> JWTAccessToken:
        """Parse and validate a JWT access token.

        Args:
            jwt_token: JWT access token string
            verify_signature: Whether to verify JWT signature
            public_key: Public key for verification (PEM format)

        Returns:
            Parsed JWT access token claims

        Raises:
            OAuthInvalidTokenError: If JWT is malformed or verification fails

        Reference: https://datatracker.ietf.org/doc/html/rfc9068#section-3
        """
        # Implementation placeholder
        raise NotImplementedError("JWT access token parsing not yet implemented")


class JWTAccessTokenValidator:
    """JWT Access Token validation per RFC 9068.

    Validates JWT access tokens according to the structured format
    and security requirements defined in RFC 9068.

    Reference: https://datatracker.ietf.org/doc/html/rfc9068
    """

    def __init__(self, issuer: str, audience: str, public_key: str | None = None):
        """Initialize JWT access token validator.

        Args:
            issuer: Expected token issuer (iss claim)
            audience: Expected token audience (aud claim)
            public_key: Public key for signature verification (PEM format)
        """
        # Implementation placeholder
        pass

    def validate_token(
        self,
        jwt_token: str,
        required_scope: str | None = None,
        clock_skew_seconds: int = 30,
    ) -> dict[str, Any]:
        """Validate a JWT access token.

        Performs comprehensive validation including:
        - Signature verification
        - Expiration check
        - Issuer/audience validation
        - Scope validation (if required)
        - Token structure compliance with RFC 9068

        Args:
            jwt_token: JWT access token to validate
            required_scope: Required OAuth 2.0 scope (optional)
            clock_skew_seconds: Allowable clock skew for exp/iat claims

        Returns:
            Validated token claims

        Raises:
            OAuthInvalidTokenError: If token is invalid or expired
            OAuthInvalidScopeError: If required scope is not present

        Reference: https://datatracker.ietf.org/doc/html/rfc9068#section-3
        """
        # Implementation placeholder
        raise NotImplementedError("JWT access token validation not yet implemented")
