"""OAuth 2.0 Bearer Token Usage implementation (RFC 6750).

This module implements the OAuth 2.0 Bearer Token Usage specification which
describes how to use bearer tokens in HTTP requests to access protected resources.

RFC 6750: The OAuth 2.0 Authorization Framework: Bearer Token Usage
https://datatracker.ietf.org/doc/html/rfc6750

Key Features:
- Bearer token transmission methods (Authorization header, form body, query parameter)
- Token validation utilities
- Error response handling
- Security considerations implementation
- WWW-Authenticate header parsing

Transmission Methods:
1. Authorization Request Header Field (RECOMMENDED)
2. Form-Encoded Body Parameter
3. URI Query Parameter (NOT RECOMMENDED - for legacy support only)

Security Considerations:
- TLS/SSL required for all bearer token transmissions
- Token confidentiality and integrity protection
- Proper error handling without token leakage
- Cache control headers for token responses
"""

import re

from pydantic import BaseModel


# Standalone utility functions for interface proposal compliance
def extract_bearer_token(authorization_header: str | None) -> str | None:
    """Extract bearer token from Authorization header.

    Args:
        authorization_header: Authorization header value

    Returns:
        Bearer token or None if not found/invalid
    """
    if not authorization_header:
        return None

    parts = authorization_header.split()
    if len(parts) == 2 and parts[0].lower() == "bearer":
        return parts[1]
    return None


def validate_bearer_format(token: str) -> bool:
    """Validate bearer token format per RFC 6750.

    Args:
        token: Token to validate

    Returns:
        True if format is valid
    """
    if not token or not isinstance(token, str):
        return False
    # Basic format validation - token should not contain whitespace
    return (
        " " not in token
        and "\t" not in token
        and "\n" not in token
        and "\r" not in token
    )


def create_auth_header(token: str) -> str:
    """Create Authorization header with bearer token.

    Args:
        token: Bearer token string

    Returns:
        Formatted Authorization header value

    Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.1

    Example:
        >>> create_auth_header("eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...")
        'Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...'
    """
    if not token:
        raise ValueError("Token cannot be empty")
    return f"Bearer {token}"


class BearerTokenError(BaseModel):
    """Bearer token error response as defined in RFC 6750 Section 3.1.

    Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-3.1
    """

    error: str
    error_description: str | None = None
    error_uri: str | None = None
    scope: str | None = None


class BearerTokenErrors:
    """Standard bearer token error codes from RFC 6750 Section 3.1.

    Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-3.1
    """

    INVALID_REQUEST = "invalid_request"
    INVALID_TOKEN = "invalid_token"
    INSUFFICIENT_SCOPE = "insufficient_scope"


class BearerToken:
    """Utilities for OAuth 2.0 Bearer Token handling per RFC 6750.

    Provides methods for extracting, validating, and formatting bearer tokens
    according to the OAuth 2.0 Bearer Token Usage specification.

    Reference: https://datatracker.ietf.org/doc/html/rfc6750

    Example:
        # Extract token from Authorization header
        auth_header = "Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9..."
        token = BearerToken.extract_from_header(auth_header)

        # Validate token format
        if BearerToken.is_valid_format(token):
            print("Token format is valid")

        # Create Authorization header
        header = BearerToken.create_auth_header(token)
        # Returns: "Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9..."
    """

    # Bearer token pattern per RFC 6750 Section 2.1
    # b64token = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" ) *"="
    TOKEN_PATTERN = re.compile(r"^[A-Za-z0-9\-._~+/]+=*$")

    @staticmethod
    def extract_from_header(authorization_header: str) -> str | None:
        """Extract bearer token from Authorization header.

        Implements RFC 6750 Section 2.1 - Authorization Request Header Field.

        Args:
            authorization_header: HTTP Authorization header value

        Returns:
            Bearer token string or None if not found/invalid

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.1
        """
        # Implementation placeholder
        raise NotImplementedError("Bearer token header extraction not yet implemented")

    @staticmethod
    def extract_from_form_body(form_data: dict[str, str]) -> str | None:
        """Extract bearer token from form-encoded body parameter.

        Implements RFC 6750 Section 2.2 - Form-Encoded Body Parameter.

        Args:
            form_data: Form-encoded request body data

        Returns:
            Bearer token string or None if not found

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.2
        """
        # Implementation placeholder
        raise NotImplementedError("Bearer token form extraction not yet implemented")

    @staticmethod
    def extract_from_query_params(query_params: dict[str, str]) -> str | None:
        """Extract bearer token from URI query parameter.

        Implements RFC 6750 Section 2.3 - URI Query Parameter.

        WARNING: This method is NOT RECOMMENDED due to security concerns.
        Use only for legacy compatibility when other methods are not feasible.

        Args:
            query_params: URI query parameters

        Returns:
            Bearer token string or None if not found

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.3
        """
        # Implementation placeholder
        raise NotImplementedError("Bearer token query extraction not yet implemented")

    @staticmethod
    def is_valid_format(token: str) -> bool:
        """Validate bearer token format per RFC 6750.

        Checks if token conforms to the b64token ABNF rule defined in RFC 6750.

        Args:
            token: Bearer token string to validate

        Returns:
            True if token format is valid, False otherwise

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.1
        """
        # Implementation placeholder
        raise NotImplementedError("Bearer token format validation not yet implemented")

    @staticmethod
    def create_auth_header(token: str) -> str:
        """Create Authorization header with bearer token.

        Args:
            token: Bearer token string

        Returns:
            Formatted Authorization header value

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2.1
        """
        # Implementation placeholder
        raise NotImplementedError("Authorization header creation not yet implemented")

    @staticmethod
    def create_www_authenticate_header(
        realm: str | None = None,
        scope: str | None = None,
        error: str | None = None,
        error_description: str | None = None,
        error_uri: str | None = None,
    ) -> str:
        """Create WWW-Authenticate header for bearer token challenges.

        Used in 401 Unauthorized responses to indicate bearer token authentication
        is required and provide error details if applicable.

        Args:
            realm: Protection realm (optional)
            scope: Required OAuth 2.0 scopes
            error: Error code (invalid_token, invalid_request, insufficient_scope)
            error_description: Human-readable error description
            error_uri: URI for additional error information

        Returns:
            WWW-Authenticate header value

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-3
        """
        # Implementation placeholder
        raise NotImplementedError(
            "WWW-Authenticate header creation not yet implemented"
        )


class BearerTokenValidator:
    """Bearer token format and transmission validator per RFC 6750.

    Provides utilities to validate bearer token format and proper transmission
    according to the security requirements in RFC 6750.

    Reference: https://datatracker.ietf.org/doc/html/rfc6750
    """

    @staticmethod
    def extract_token_from_request(
        headers: dict[str, str],
        form_data: dict[str, str] | None = None,
        query_params: dict[str, str] | None = None,
        allow_query_param: bool = False,
    ) -> str | None:
        """Extract bearer token from HTTP request using RFC 6750 methods.

        Tries extraction methods in order of preference:
        1. Authorization header (RECOMMENDED)
        2. Form-encoded body parameter
        3. URI query parameter (if explicitly allowed)

        Args:
            headers: HTTP request headers
            form_data: Form-encoded body parameters
            query_params: URI query parameters
            allow_query_param: Whether to allow query parameter method (NOT RECOMMENDED)

        Returns:
            Extracted bearer token or None if not found

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2
        """
        # Implementation placeholder
        raise NotImplementedError("Bearer token extraction not yet implemented")

    @staticmethod
    def validate_token_transmission(
        headers: dict[str, str],
        form_data: dict[str, str] | None = None,
        query_params: dict[str, str] | None = None,
    ) -> tuple[bool, str | None]:
        """Validate that token is transmitted via exactly one method.

        RFC 6750 Section 2 requires that bearer tokens be transmitted using
        exactly one of the defined methods to prevent ambiguity.

        Args:
            headers: HTTP request headers
            form_data: Form-encoded body parameters
            query_params: URI query parameters

        Returns:
            Tuple of (is_valid, error_message)

        Reference: https://datatracker.ietf.org/doc/html/rfc6750#section-2
        """
        # Implementation placeholder
        raise NotImplementedError("Token transmission validation not yet implemented")
