package model.pki;

import annotations.Assoc;
import model.asn1.ASN1Object;
import model.asn1.ObjectIdentifier;
import model.asn1.Tag;
import model.asn1.exceptions.ParseException;
import model.asn1.parsing.BytesReader;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.stream.Stream;

/**
 * Implements the following:
 * <pre>
 *   AlgorithmIdentifier{ALGORITHM:SupportedAlgorithms} ::= SEQUENCE {
 *       algorithm ALGORITHM.&id({SupportedAlgorithms}),
 *       parameters ALGORITHM.&Type({SupportedAlgorithms}{@algorithm}) OPTIONAL,
 *   ... }
 * </pre>
 */
public class AlgorithmIdentifier extends ASN1Object {
    /**
     * The type of that attribute. For example, <pre>1.2.840.113549.1.1.11</pre> is sha256WithRSAEncryption.
     */
    @Assoc(partOf = true)
    private final ObjectIdentifier type;

    /**
     * Additional parameters for that algorithm. Optional, and could be ASN.1 NULL or Java null (absent).
     * According to RFC8017$A.2, it should be NULL for a number of algorithms:
     * <pre>
     *     PKCS1Algorithms    ALGORITHM-IDENTIFIER ::= {
     *        { OID rsaEncryption                PARAMETERS NULL } |
     *        { OID md2WithRSAEncryption         PARAMETERS NULL } |
     *        { OID md5WithRSAEncryption         PARAMETERS NULL } |
     *        { OID sha1WithRSAEncryption        PARAMETERS NULL } |
     *        { OID sha224WithRSAEncryption      PARAMETERS NULL } |
     *        { OID sha256WithRSAEncryption      PARAMETERS NULL } |
     *        { OID sha384WithRSAEncryption      PARAMETERS NULL } |
     *        { OID sha512WithRSAEncryption      PARAMETERS NULL } |
     *        { OID sha512-224WithRSAEncryption  PARAMETERS NULL } |
     *        { OID sha512-256WithRSAEncryption  PARAMETERS NULL } |
     *        { OID id-RSAES-OAEP   PARAMETERS RSAES-OAEP-params } |
     *        PKCS1PSourceAlgorithms                               |
     *        { OID id-RSASSA-PSS   PARAMETERS RSASSA-PSS-params },
     *        ...  -- Allows for future expansion --
     *    }
     * </pre>
     */
    @Assoc(partOf = true, lowerBond = 0)
    private final ASN1Object parameters;

    /**
     * EFFECT: Init the object with tag, parentTag, type, and parameters. For tag and parentTag, see {@link ASN1Object}.
     * REQUIRES: The values must match the type. Type tag should be UNIVERSAL OID. Parameters nullable.
     */
    public AlgorithmIdentifier(Tag tag, Tag parentTag,
                               ObjectIdentifier type, ASN1Object parameters) {
        super(tag, parentTag);
        this.type = type;
        this.parameters = parameters;
    }

    /**
     * EFFECTS: Parse input DER. Parameters are not checked against the type.
     * Throws {@link ASN1Object} if invalid:
     * - Any fields missing
     * - Any fields having an incorrect tag (as seen in the ASN.1 definition)
     * - Any fields with encoding instructions that violate implicit / explicit encoding rules
     * - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
     * MODIFIES: this, encoded
     */
    public AlgorithmIdentifier(BytesReader encoded, boolean hasParentTag) throws ParseException {
        super(encoded, hasParentTag);
        int i = encoded.getIndex();
        this.type = new ObjectIdentifier(encoded, false);
        this.type.getTag().enforce(ObjectIdentifier.TAG);
        i = encoded.getIndex() - i;

        if (getLength() > i) {
            this.parameters = ASN1Object.parse(encoded, false);
        } else {
            this.parameters = null;
        }
    }

    /**
     * EFFECTS: Encode the fields into DER, in the order.
     */
    @Override
    public Byte[] encodeValueDER() {
        return Stream.of(Arrays.asList(type.encodeDER()),
                        parameters == null ? Collections.<Byte>emptyList() : Arrays.asList(parameters.encodeDER()))
                .flatMap(Collection::stream)
                .toArray(Byte[]::new);
    }

    public ObjectIdentifier getType() {
        return type;
    }

    public ASN1Object getParameters() {
        return parameters;
    }
}