// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
//
// SPDX-License-Identifier: Apache-2.0

package org.pgpainless.decryption_verification;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.bouncycastle.openpgp.PGPCompressedData;
import org.bouncycastle.openpgp.PGPEncryptedData;
import org.bouncycastle.openpgp.PGPEncryptedDataList;
import org.bouncycastle.openpgp.PGPException;
import org.bouncycastle.openpgp.PGPLiteralData;
import org.bouncycastle.openpgp.PGPObjectFactory;
import org.bouncycastle.openpgp.PGPOnePassSignatureList;
import org.bouncycastle.openpgp.PGPPBEEncryptedData;
import org.bouncycastle.openpgp.PGPPublicKeyEncryptedData;
import org.bouncycastle.openpgp.PGPUtil;
import org.pgpainless.implementation.ImplementationFactory;
import org.pgpainless.util.ArmorUtils;

/**
 * Inspect an OpenPGP message to determine IDs of its encryption keys or whether it is passphrase protected.
 */
public final class MessageInspector {

    public static class EncryptionInfo {
        private final List<Long> keyIds = new ArrayList<>();
        private boolean isPassphraseEncrypted = false;
        private boolean isSignedOnly = false;

        /**
         * Return a list of recipient key ids for whom the message is encrypted.
         * @return recipient key ids
         */
        public List<Long> getKeyIds() {
            return Collections.unmodifiableList(keyIds);
        }

        public boolean isPassphraseEncrypted() {
            return isPassphraseEncrypted;
        }

        /**
         * Return true, if the message is encrypted.
         *
         * @return true if encrypted
         */
        public boolean isEncrypted() {
            return isPassphraseEncrypted || !keyIds.isEmpty();
        }

        /**
         * Return true, if the message is not encrypted, but signed using {@link org.bouncycastle.openpgp.PGPOnePassSignature OnePassSignatures}.
         *
         * @return true if message is signed only
         */
        public boolean isSignedOnly() {
            return isSignedOnly;
        }
    }

    private MessageInspector() {

    }

    /**
     * Parses parts of the provided OpenPGP message in order to determine which keys were used to encrypt it.
     *
     * @param message OpenPGP message
     * @return encryption info
     *
     * @throws PGPException in case the message is broken
     * @throws IOException in case of an IO error
     */
    public static EncryptionInfo determineEncryptionInfoForMessage(String message) throws PGPException, IOException {
        @SuppressWarnings("CharsetObjectCanBeUsed")
        Charset charset = Charset.forName("UTF-8");
        return determineEncryptionInfoForMessage(new ByteArrayInputStream(message.getBytes(charset)));
    }

    /**
     * Parses parts of the provided OpenPGP message in order to determine which keys were used to encrypt it.
     * Note: This method does not rewind the passed in Stream, so you might need to take care of that yourselves.
     *
     * @param dataIn openpgp message
     * @return encryption information
     *
     * @throws IOException in case of an IO error
     * @throws PGPException if the message is broken
     */
    public static EncryptionInfo determineEncryptionInfoForMessage(InputStream dataIn) throws IOException, PGPException {
        InputStream decoded = ArmorUtils.getDecoderStream(dataIn);
        EncryptionInfo info = new EncryptionInfo();

        processMessage(decoded, info);

        return info;
    }

    private static void processMessage(InputStream dataIn, EncryptionInfo info) throws PGPException, IOException {
        PGPObjectFactory objectFactory = ImplementationFactory.getInstance().getPGPObjectFactory(dataIn);

        Object next;
        while ((next = objectFactory.nextObject()) != null) {
            if (next instanceof PGPOnePassSignatureList) {
                PGPOnePassSignatureList signatures = (PGPOnePassSignatureList) next;
                if (!signatures.isEmpty()) {
                    info.isSignedOnly = true;
                    return;
                }
            }

            if (next instanceof PGPEncryptedDataList) {
                PGPEncryptedDataList encryptedDataList = (PGPEncryptedDataList) next;
                for (PGPEncryptedData encryptedData : encryptedDataList) {
                    if (encryptedData instanceof PGPPublicKeyEncryptedData) {
                        PGPPublicKeyEncryptedData pubKeyEncryptedData = (PGPPublicKeyEncryptedData) encryptedData;
                        info.keyIds.add(pubKeyEncryptedData.getKeyID());
                    } else if (encryptedData instanceof PGPPBEEncryptedData) {
                        info.isPassphraseEncrypted = true;
                    }
                }
                // Data is encrypted, we cannot go deeper
                return;
            }

            if (next instanceof PGPCompressedData) {
                PGPCompressedData compressed = (PGPCompressedData) next;
                InputStream decompressed = compressed.getDataStream();
                InputStream decoded = PGPUtil.getDecoderStream(decompressed);
                objectFactory = ImplementationFactory.getInstance().getPGPObjectFactory(decoded);
            }

            if (next instanceof PGPLiteralData) {
                return;
            }
        }
    }
}