// SPDX-FileCopyrightText: 2018 Paul Schaub <vanitasvitae@fsfe.org>
//
// SPDX-License-Identifier: Apache-2.0

package org.pgpainless.key;

import java.net.URI;
import java.net.URISyntaxException;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import javax.annotation.Nonnull;

import org.bouncycastle.openpgp.PGPKeyRing;
import org.bouncycastle.openpgp.PGPPublicKey;
import org.bouncycastle.openpgp.PGPPublicKeyRing;
import org.bouncycastle.openpgp.PGPSecretKey;
import org.bouncycastle.openpgp.PGPSecretKeyRing;
import org.bouncycastle.util.encoders.Hex;

/**
 * This class represents an hex encoded, uppercase OpenPGP v4 fingerprint.
 */
public class OpenPgpV4Fingerprint implements CharSequence, Comparable<OpenPgpV4Fingerprint> {

    public static final String SCHEME = "openpgp4fpr";

    private static final Charset utf8 = Charset.forName("UTF-8");
    private final String fingerprint;

    /**
     * Create an {@link OpenPgpV4Fingerprint}.
     * @see <a href="https://xmpp.org/extensions/xep-0373.html#annoucning-pubkey">
     *     XEP-0373 §4.1: The OpenPGP Public-Key Data Node about how to obtain the fingerprint</a>
     * @param fingerprint hexadecimal representation of the fingerprint.
     */
    public OpenPgpV4Fingerprint(@Nonnull String fingerprint) {
        String fp = fingerprint.replace(" ", "").trim().toUpperCase();
        if (!isValid(fp)) {
            throw new IllegalArgumentException("Fingerprint " + fingerprint +
                    " does not appear to be a valid OpenPGP v4 fingerprint.");
        }
        this.fingerprint = fp;
    }

    public OpenPgpV4Fingerprint(@Nonnull byte[] bytes) {
        this(new String(bytes, utf8));
    }

    public OpenPgpV4Fingerprint(@Nonnull PGPPublicKey key) {
        this(Hex.encode(key.getFingerprint()));
        if (key.getVersion() != 4) {
            throw new IllegalArgumentException("Key is not a v4 OpenPgp key.");
        }
    }

    public OpenPgpV4Fingerprint(@Nonnull PGPSecretKey key) {
        this(key.getPublicKey());
    }

    public OpenPgpV4Fingerprint(@Nonnull PGPPublicKeyRing ring) {
        this(ring.getPublicKey());
    }

    public OpenPgpV4Fingerprint(@Nonnull PGPSecretKeyRing ring) {
        this(ring.getPublicKey());
    }

    public OpenPgpV4Fingerprint(@Nonnull PGPKeyRing ring) {
        this(ring.getPublicKey());
    }

    /**
     * Check, whether the fingerprint consists of 40 valid hexadecimal characters.
     * @param fp fingerprint to check.
     * @return true if fingerprint is valid.
     */
    private static boolean isValid(@Nonnull String fp) {
        return fp.matches("[0-9A-F]{40}");
    }

    /**
     * Return the key id of the OpenPGP public key this {@link OpenPgpV4Fingerprint} belongs to.
     *
     * @see <a href="https://tools.ietf.org/html/rfc4880#section-12.2">
     *     RFC-4880 §12.2: Key IDs and Fingerprints</a>
     * @return key id
     */
    public long getKeyId() {
        byte[] bytes = Hex.decode(toString().getBytes(utf8));
        ByteBuffer buf = ByteBuffer.wrap(bytes);

        // We have to cast here in order to be compatible with java 8
        // https://github.com/eclipse/jetty.project/issues/3244
        ((Buffer) buf).position(12);

        return buf.getLong();
    }

    @Override
    public boolean equals(Object other) {
        if (other == null) {
            return false;
        }

        if (!(other instanceof CharSequence)) {
            return false;
        }

        return this.toString().equals(other.toString());
    }

    @Override
    public int hashCode() {
        return fingerprint.hashCode();
    }

    @Override
    public int length() {
        return fingerprint.length();
    }

    @Override
    public char charAt(int i) {
        return fingerprint.charAt(i);
    }

    @Override
    public CharSequence subSequence(int i, int i1) {
        return fingerprint.subSequence(i, i1);
    }

    @Override
    @Nonnull
    public String toString() {
        return fingerprint;
    }

    public String prettyPrint() {
        String fp = toString();
        StringBuilder pretty = new StringBuilder();
        for (int i = 0; i < 5; i++) {
            pretty.append(fp, i * 4, (i + 1) * 4).append(' ');
        }
        pretty.append(' ');
        for (int i = 5; i < 9; i++) {
            pretty.append(fp, i * 4, (i + 1) * 4).append(' ');
        }
        pretty.append(fp, 36, 40);
        return pretty.toString();
    }

    /**
     * Return the fingerprint as an openpgp4fpr {@link URI}.
     * An example would be 'openpgp4fpr:7F9116FEA90A5983936C7CFAA027DB2F3E1E118A'.
     *
     * @return openpgp4fpr fingerprint uri
     * @see <a href="https://metacode.biz/openpgp/openpgp4fpr">openpgp4fpr URI scheme</a>
     */
    public URI toUri() {
        try {
            return new URI(SCHEME, toString(), null);
        } catch (URISyntaxException e) {
            throw new AssertionError(e);
        }
    }

    /**
     * Convert a openpgp4fpr URI to an {@link OpenPgpV4Fingerprint}.
     *
     * @param uri {@link URI} with scheme 'openpgp4fpr'
     * @return fingerprint parsed from the uri
     * @see <a href="https://metacode.biz/openpgp/openpgp4fpr">openpgp4fpr URI scheme</a>
     */
    public static OpenPgpV4Fingerprint fromUri(URI uri) {
        if (!SCHEME.equals(uri.getScheme())) {
            throw new IllegalArgumentException("URI scheme MUST equal '" + SCHEME + "'");
        }
        return new OpenPgpV4Fingerprint(uri.getSchemeSpecificPart());
    }

    @Override
    public int compareTo(@Nonnull OpenPgpV4Fingerprint openPgpV4Fingerprint) {
        return fingerprint.compareTo(openPgpV4Fingerprint.fingerprint);
    }
}