// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.security.tool.crypto;

import com.yahoo.security.SealedSharedKey;
import com.yahoo.security.SecretSharedKey;
import com.yahoo.security.SharedKeyGenerator;
import com.yahoo.security.SharedKeyResealingSession;
import com.yahoo.vespa.security.tool.CliUtils;
import com.yahoo.vespa.security.tool.Tool;
import com.yahoo.vespa.security.tool.ToolDescription;
import com.yahoo.vespa.security.tool.ToolInvocation;
import org.apache.commons.cli.Option;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Optional;

import static com.yahoo.vespa.security.tool.crypto.ToolUtils.NO_INTERACTIVE_OPTION;
import static com.yahoo.vespa.security.tool.crypto.ToolUtils.PRIVATE_KEY_DIR_OPTION;
import static com.yahoo.vespa.security.tool.crypto.ToolUtils.PRIVATE_KEY_FILE_OPTION;

/**
 * Tooling for decrypting a file using a private key that corresponds to the public key used
 * to originally encrypt the file.
 *
 * Uses the opaque token abstraction from {@link SharedKeyGenerator}.
 *
 * @author vekterli
 */
public class DecryptTool implements Tool {

    static final String OUTPUT_FILE_OPTION      = "output-file";
    static final String EXPECTED_KEY_ID_OPTION  = "expected-key-id";
    static final String ZSTD_DECOMPRESS_OPTION  = "zstd-decompress";
    static final String TOKEN_OPTION            = "token";
    static final String RESEAL_REQUEST          = "reseal-request";

    private static final List<Option> OPTIONS = List.of(
            Option.builder("o")
                    .longOpt(OUTPUT_FILE_OPTION)
                    .hasArg(true)
                    .required(false)
                    .desc("Output file for decrypted plaintext. Specify '-' (without the " +
                          "quotes) to write plaintext to STDOUT instead of a file.")
                    .build(),
            Option.builder("k")
                    .longOpt(PRIVATE_KEY_FILE_OPTION)
                    .hasArg(true)
                    .required(false)
                    .desc("Private key file in Base58 encoded format")
                    .build(),
            Option.builder("d")
                    .longOpt(PRIVATE_KEY_DIR_OPTION)
                    .hasArg(true)
                    .required(false)
                    .desc("Private key file directory used for automatically looking up " +
                          "private keys based on the key ID specified as part of a token.")
                    .build(),
            Option.builder()
                    .longOpt(NO_INTERACTIVE_OPTION)
                    .hasArg(false)
                    .required(false)
                    .desc("Never ask for private key interactively if no private key file or " +
                          "directory is provided, even if process is running in a console")
                    .build(),
            Option.builder("e")
                    .longOpt(EXPECTED_KEY_ID_OPTION)
                    .hasArg(true)
                    .required(false)
                    .desc("Expected key ID in token. If this is not provided, the key ID is not verified.")
                    .build(),
            Option.builder("z")
                    .longOpt(ZSTD_DECOMPRESS_OPTION)
                    .hasArg(false)
                    .required(false)
                    .desc("Decrypted data will be transparently Zstd-decompressed before being output.")
                    .build(),
            Option.builder("t")
                    .longOpt(TOKEN_OPTION)
                    .hasArg(true)
                    .required(false)
                    .desc("Token generated when the input file was encrypted")
                    .build(),
            Option.builder("r")
                    .longOpt(RESEAL_REQUEST)
                    .hasArg(false)
                    .required(false)
                    .desc("Delegate private key decryption via an interactive resealing session")
                    .build());

    @Override
    public String name() {
        return "decrypt";
    }

    @Override
    public ToolDescription description() {
        return new ToolDescription(
                "<encrypted file> <options>",
                "Decrypts a file using a provided token and a secret private key. The file must " +
                "previously have been encrypted using the public key component of the given private key.\n\n" +
                "To decrypt the contents of STDIN, specify an input file of '-' (without the quotes).",
                "Note: this is a BETA tool version; its interface may be changed at any time",
                OPTIONS);
    }

    @Override
    public int invoke(ToolInvocation invocation) {
        try {
            var arguments    = invocation.arguments();
            var leftoverArgs = arguments.getArgs();
            if (leftoverArgs.length != 1) {
                throw new IllegalArgumentException("Expected exactly 1 file argument to decrypt");
            }
            var inputArg    = leftoverArgs[0];
            var maybeKeyId  = Optional.ofNullable(arguments.getOptionValue(EXPECTED_KEY_ID_OPTION));
            var outputArg   = CliUtils.optionOrThrow(arguments, OUTPUT_FILE_OPTION);
            var tokenString = CliUtils.optionOrThrow(arguments, TOKEN_OPTION);
            var sealedSharedKey = SealedSharedKey.fromTokenString(tokenString.strip());
            ToolUtils.verifyExpectedKeyId(sealedSharedKey, maybeKeyId);

            var secret = arguments.hasOption(RESEAL_REQUEST)
                    ? secretFromInteractiveResealing(invocation, inputArg, outputArg, sealedSharedKey)
                    : secretFromPrivateKey(invocation, inputArg, outputArg, sealedSharedKey);

            var cipher     = secret.makeDecryptionCipher();
            boolean unZstd = arguments.hasOption(ZSTD_DECOMPRESS_OPTION);

            try (var inStream  = CliUtils.inputStreamFromFileOrStream(inputArg, invocation.stdIn());
                 var outStream = CliUtils.outputStreamToFileOrStream(outputArg, invocation.stdOut())) {
                CipherUtils.streamDecrypt(inStream, outStream, cipher, unZstd);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return 0;
    }

    private static SecretSharedKey secretFromPrivateKey(ToolInvocation invocation, String inputArg, String outputArg, SealedSharedKey sealedSharedKey) throws IOException {
        var privateKey = ToolUtils.resolvePrivateKeyFromInvocation(invocation, sealedSharedKey.keyId(),
                                                                   !CliUtils.useStdIo(inputArg) && !CliUtils.useStdIo(outputArg));
        return SharedKeyGenerator.fromSealedKey(sealedSharedKey, privateKey);
    }

    private static SecretSharedKey secretFromInteractiveResealing(ToolInvocation invocation, String inputArg,
                                                                  String outputArg, SealedSharedKey sealedSharedKey) throws IOException {
        if (CliUtils.useStdIo(outputArg) || CliUtils.useStdIo(inputArg)) {
            throw new IllegalArgumentException("Interactive token resealing not available with redirected I/O");
        }
        var session = SharedKeyResealingSession.newEphemeralSession();
        var req     = session.resealingRequestFor(sealedSharedKey);

        invocation.stdOut().format("\nInteractive token resealing request:\n\n%s\n\n", req.toSerializedString());
        invocation.stdOut().format("Paste response and hit return: ");

        try (var reader = new BufferedReader(new InputStreamReader(invocation.stdIn()))) {
            var serializedRes = reader.readLine().strip();
            if (serializedRes.isEmpty()) {
                throw new IllegalArgumentException("Empty response; aborting");
            }
            var res = SharedKeyResealingSession.ResealingResponse.fromSerializedString(serializedRes);
            return session.openResealingResponse(res);
        }
    }
}