/*
 * Copyright (C) 2008-2020, Juick
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.juick;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.juick.model.AnonymousUser;
import com.juick.model.User;
import com.juick.service.UserService;
import com.juick.service.activities.DeleteUserEvent;
import com.juick.util.DateFormattersHolder;
import com.juick.www.api.activity.model.Context;
import com.juick.www.api.activity.model.objects.Actor;
import com.juick.www.api.webfinger.model.Account;
import com.juick.www.api.webfinger.model.Link;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestClientException;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.UriComponentsBuilder;
import org.tomitribe.auth.signatures.Base64;
import org.tomitribe.auth.signatures.MissingRequiredHeaderException;
import org.tomitribe.auth.signatures.Signature;
import org.tomitribe.auth.signatures.Signer;
import org.tomitribe.auth.signatures.Verifier;
import rocks.xmpp.addr.Jid;

import javax.inject.Inject;
import java.io.IOException;
import java.net.URI;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SignatureException;
import java.time.Instant;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import static com.juick.www.api.activity.model.Context.ACTIVITY_MEDIA_TYPE;

public class SignatureManager {
    private static final Logger logger = LoggerFactory.getLogger("ActivityPub");
    @Inject
    private KeystoreManager keystoreManager;
    @Inject
    private ObjectMapper jsonMapper;
    @Inject
    private UserService userService;
    @Inject
    private RestTemplate apClient;
    @Inject
    private ApplicationEventPublisher applicationEventPublisher;

    public void post(Actor from, Actor to, Context data) throws IOException, NoSuchAlgorithmException {
        UriComponentsBuilder uriComponentsBuilder = UriComponentsBuilder.fromUriString(to.getInbox());
        URI inbox = uriComponentsBuilder.build().toUri();
        Instant now = Instant.now();
        String requestDate = DateFormattersHolder.getHttpDateFormatter().format(now);
        String host = inbox.getPort() > 0 ? String.format("%s:%d", inbox.getHost(), inbox.getPort()) : inbox.getHost();
        var finalContext = Context.build(data);
        var payload = jsonMapper.writeValueAsString(finalContext);
        final byte[] digest = MessageDigest.getInstance("SHA-256").digest(payload.getBytes()); // (1)
        final String digestHeader = "SHA-256=" + new String(Base64.encodeBase64(digest));
        String signatureString = addSignature(from, host, "POST", inbox.getPath(), requestDate, digestHeader);

        HttpHeaders requestHeaders = new HttpHeaders();
        requestHeaders.add("Content-Type", Context.ACTIVITYSTREAMS_PROFILE_MEDIA_TYPE);
        requestHeaders.add("Date", requestDate);
        requestHeaders.add("Host", host);
        requestHeaders.add("Digest", digestHeader);
        requestHeaders.add("Signature", signatureString);
        HttpEntity<String> request = new HttpEntity<>(payload, requestHeaders);
        logger.info("Sending context to {}: {}", to.getId(), payload);
        ResponseEntity<Void> response = apClient.postForEntity(inbox, request, Void.class);
        logger.info("Remote response: {}", response.getStatusCodeValue());
    }

    public String addSignature(Actor from, String host, String method, String path, String dateString,
            String digestHeader) throws IOException {
        return addSignature(from, host, method, path, dateString, digestHeader, keystoreManager);
    }

    public String addSignature(Actor from, String host, String method, String path, String dateString,
            String digestHeader, KeystoreManager keystoreManager) throws IOException {
        List<String> requiredHeaders = StringUtils.isEmpty(digestHeader)
                ? Arrays.asList("(request-target)", "host", "date")
                : Arrays.asList("(request-target)", "host", "date", "digest");
        Signature templateSignature = new Signature(from.getPublicKey().getId(), "rsa-sha256", null, requiredHeaders);
        Map<String, String> headers = new HashMap<>();
        headers.put("host", host);
        headers.put("date", dateString);
        if (StringUtils.isNotEmpty(digestHeader)) {
            headers.put("digest", digestHeader);
        }
        Signer signer = new Signer(keystoreManager.getPrivateKey(), templateSignature);
        Signature signature = signer.sign(method, path, headers);
        // remove "Signature: " from result
        return signature.toString().substring(10);
    }

    public User verifySignature(String method, String path, Map<String, String> headers) {
        String signatureString = headers.get("signature");
        Signature signature = Signature.fromString(signatureString);
        Optional<Context> context = getContext(
                UriComponentsBuilder.fromUriString(signature.getKeyId()).fragment(null).build().toUri());
        if (context.isPresent() && context.get() instanceof Actor) {
            Actor actor = (Actor) context.get();
            Key key = KeystoreManager.publicKeyOf(actor);
            if (key != null) {
                Verifier verifier = new Verifier(key, signature);
                try {
                    boolean result = verifier.verify(method, path, headers);
                    if (result) {
                        User user = new User();
                        user.setUri(URI.create(actor.getId()));
                        if (key.equals(keystoreManager.getPublicKey())) {
                            return userService.getUserByName(actor.getName());
                        }
                        if (actor.isSuspended()) {
                            logger.info("{} is suspended, deleting", actor.getId());
                            applicationEventPublisher.publishEvent(new DeleteUserEvent(this, actor.getId()));
                        }
                        return user;
                    } else {
                        return AnonymousUser.INSTANCE;
                    }
                } catch (NoSuchAlgorithmException | SignatureException | MissingRequiredHeaderException
                        | IOException e) {
                    logger.warn("Invalid signature {}: {}", signatureString, e.getMessage());
                }
            } else {
                logger.warn("Unknown actor");
            }
        } else {
            logger.warn("Unknown keyId");
        }
        return AnonymousUser.INSTANCE;
    }

    public Optional<Context> getContext(URI contextUri) {
        try {
            Context context = apClient.getForEntity(contextUri, Context.class).getBody();
            if (context == null) {
                logger.warn("Cannot identify {}", contextUri);
                return Optional.empty();
            }
            return Optional.of(context);
        } catch (Exception e) {
            logger.warn("REST Exception on {}: {}", contextUri, e.getMessage());
        }
        return Optional.empty();
    }

    public Optional<Context> discoverPerson(String acct) {
        Jid acctId = Jid.of(acct);
        URI resourceUri = UriComponentsBuilder.fromPath("/.well-known/webfinger").host(acctId.getDomain())
                .scheme("https").queryParam("resource", "acct:" + acct).build().toUri();
        HttpHeaders headers = new HttpHeaders();
        HttpEntity<Void> webfingerRequest = new HttpEntity<>(headers);
        try {
            ResponseEntity<Account> response = apClient.exchange(resourceUri, HttpMethod.GET, webfingerRequest,
                    Account.class);
            if (response.getStatusCode().is2xxSuccessful()) {
                Account acctData = response.getBody();
                if (acctData != null) {
                    for (Link l : acctData.links()) {
                        if (l.rel().equals("self") && l.type().equals(ACTIVITY_MEDIA_TYPE)) {
                            return getContext(URI.create(l.href()));
                        }
                    }
                }
            }
        } catch (RestClientException e) {
            logger.warn("Cannot discover person {}: {}", acct, e.getMessage());
            return Optional.empty();
        }
        return Optional.empty();
    }
}