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package zeroecho.core.err;

/**
 * Exception indicating that an algorithm does not support the requested role.
 *
 * <p>
 * This is thrown when a {@link zeroecho.core.CryptoAlgorithm} (or helpers such
 * as {@link zeroecho.core.CryptoAlgorithms}) is asked to create a context for a
 * {@link zeroecho.core.KeyUsage} that the algorithm never advertises. In other
 * words, the operation is unavailable regardless of the provided key or spec.
 * </p>
 *
 * <h2>When it is thrown</h2>
 * <ul>
 * <li>During
 * {@link zeroecho.sdk.ZeroEchoSession#createContext(String,
 * zeroecho.core.KeyUsage, java.security.Key,
 * zeroecho.core.spec.ContextSpec)}
 * after policy validation, if the resolved algorithm exposes no bindings for
 * the given role.</li>
 * <li>Directly from
 * {@link zeroecho.core.CryptoAlgorithm#createContext(zeroecho.core.KeyUsage,
 * java.security.Key, zeroecho.core.spec.ContextSpec)}
 * when no binding exists for the role.</li>
 * </ul>
 *
 * <p>
 * Contrast with {@link UnsupportedSpecException}, which means the role exists
 * but no binding accepts the supplied key/spec types.
 * </p>
 *
 * <h2>Example</h2> <pre>{@code
 * // Suppose "SHA-256" supports DIGEST only.
 * zeroecho.sdk.ZeroEchoSession session = new zeroecho.sdk.ZeroEchoSession();
 * try {
 *     // Asking for ENCRYPT on a digest algorithm will fail with UnsupportedRoleException.
 *     session.createContext("SHA-256", zeroecho.core.KeyUsage.ENCRYPT,
 *         zeroecho.core.NullKey.INSTANCE, null);
 * } catch (UnsupportedRoleException e) {
 *     // Handle: algorithm does not implement the ENCRYPT role.
 * }
 * }</pre>
 *
 * @since 1.0
 */
public class UnsupportedRoleException extends RuntimeException {
    private static final long serialVersionUID = 1653286859112182562L;

    /**
     * Creates a new exception with a detail message.
     *
     * @param m detail message describing the missing role for the algorithm
     */
    public UnsupportedRoleException(String m) {
        super(m);
    }
}
