/*
 * 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 java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.net.URI;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;

import javax.annotation.Nonnull;
import javax.inject.Inject;

import com.juick.model.Message;
import com.juick.model.Reaction;
import com.juick.model.Tag;
import com.juick.model.User;
import com.juick.service.MessagesService;
import com.juick.service.SocialService;
import com.juick.service.activities.ActivityListener;
import com.juick.service.activities.AnnounceEvent;
import com.juick.service.activities.DeleteMessageEvent;
import com.juick.service.activities.DeleteUserEvent;
import com.juick.service.activities.FollowEvent;
import com.juick.service.activities.UndoAnnounceEvent;
import com.juick.service.activities.UndoFollowEvent;
import com.juick.service.activities.UpdateEvent;
import com.juick.service.activities.UpdateUserEvent;
import com.juick.service.component.NotificationListener;
import com.juick.service.component.PingEvent;
import com.juick.service.component.SystemEvent;
import com.juick.util.HttpBadRequestException;
import com.juick.util.HttpUtils;
import com.juick.util.MessageUtils;
import com.juick.util.formatters.PlainTextFormatter;
import com.juick.www.api.SystemActivity.ActivityType;
import com.juick.www.api.activity.model.Context;
import com.juick.www.api.activity.model.activities.Accept;
import com.juick.www.api.activity.model.activities.Announce;
import com.juick.www.api.activity.model.activities.Create;
import com.juick.www.api.activity.model.activities.Delete;
import com.juick.www.api.activity.model.activities.Update;
import com.juick.www.api.activity.model.objects.Actor;
import com.juick.www.api.activity.model.objects.Hashtag;
import com.juick.www.api.activity.model.objects.Image;
import com.juick.www.api.activity.model.objects.Mention;
import com.juick.www.api.activity.model.objects.Note;
import io.pebbletemplates.pebble.PebbleEngine;
import io.pebbletemplates.pebble.template.PebbleTemplate;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.util.UriComponents;
import org.springframework.web.util.UriComponentsBuilder;

public class ActivityPubManager implements ActivityListener, NotificationListener {
    private static final Logger logger = LoggerFactory.getLogger("ActivityPub");
    @Inject
    private SignatureManager signatureManager;
    @Inject
    private SocialService socialService;
    @Inject
    private MessagesService messagesService;
    @Inject
    private PebbleEngine pebbleEngine;
    @Value("${ap_base_uri:http://localhost:8080/}")
    private String baseUri;

    @Override
    public void processFollowEvent(@Nonnull FollowEvent followEvent) {
        String acct = followEvent.getRequest().getObject().getId();
        logger.info("received follower request to {}", acct);
        User followedUser = socialService.getUserByAccountUri(acct);
        if (!followedUser.isAnonymous()) {
            // automatically accept follower requests
            Actor me = (Actor) signatureManager.getContext(URI.create(acct)).get();
            Actor follower = (Actor) signatureManager.getContext(URI.create(followEvent.getRequest().getActor())).get();
            Accept accept = new Accept();
            accept.setActor(me.getId());
            accept.setObject(followEvent.getRequest());
            try {
                signatureManager.post(me, follower, accept);
                socialService.addFollower(followedUser, follower.getId());
                logger.info("Follower added for {}", followedUser.getName());
            } catch (IOException | NoSuchAlgorithmException e) {
                logger.info("activitypub exception", e);
            }
        }
    }

    @Override
    public void undoFollowEvent(UndoFollowEvent event) {
        String actor = event.getActor();
        String me = event.getObject();
        logger.info("{} stopping to follow {}", actor, me);
        User followedUser = socialService.getUserByAccountUri(me);
        if (!followedUser.isAnonymous()) {
            socialService.removeFollower(followedUser, actor);
        }
    }

    @Override
    public void deleteUserEvent(DeleteUserEvent event) {
        String acct = event.getUserUri();
        logger.info("Deleting {} from followers", acct);
        socialService.removeAccount(acct);
    }

    @Override
    public void deleteMessageEvent(DeleteMessageEvent event) {
        Message msg = event.getMessage();
        User user = msg.getUser();
        String userUri = personUri(user);
        Note note = makeNote(msg);
        Actor me = (Actor) signatureManager.getContext(URI.create(userUri)).get();
        socialService.getFollowers(user).forEach(acct -> {
            try {
                Actor follower = (Actor) signatureManager.getContext(URI.create(acct)).orElseThrow();
                Delete delete = new Delete();
                delete.setId(note.getId());
                delete.setActor(me.getId());
                delete.setPublished(note.getPublished());
                delete.setObject(note);
                logger.info("Deletion to follower {}", follower.getId());
                signatureManager.post(me, follower, delete);
            } catch (NoSuchElementException e) {
                logger.warn("Unverified actor: {}", userUri);
            } catch (IOException | NoSuchAlgorithmException e) {
                logger.warn("activitypub exception", e);
            }
        });
    }

    @Override
    public void processAnnounceEvent(AnnounceEvent event) {
        UriComponents uriComponents = UriComponentsBuilder.fromUriString(event.getMessageUri()).build();
        List<String> segments = uriComponents.getPathSegments();
        if (segments.get(0).equals("n")) {
            String[] ids = segments.get(1).split("-", 2);
            if (ids.length == 2 && Integer.parseInt(ids[1]) == 0) {
                // only messages
                logger.info("{} recommends {}", event.getActorUri(), Integer.valueOf(ids[0]));
                messagesService.likeMessage(Integer.parseInt(ids[0]), 0, Reaction.LIKE, event.getActorUri());
            }
        }
    }

    @Override
    public void undoAnnounceEvent(UndoAnnounceEvent event) {
        UriComponents uriComponents = UriComponentsBuilder.fromUriString(event.getMessageUri()).build();
        List<String> segments = uriComponents.getPathSegments();
        if (segments.get(0).equals("n")) {
            String[] ids = segments.get(1).split("-", 2);
            if (ids.length == 2 && Integer.parseInt(ids[1]) == 0) {
                // only messages
                logger.info("{} stop recommending {}", event.getActorUri(), Integer.valueOf(ids[0]));
                messagesService.likeMessage(Integer.parseInt(ids[0]), 0, null, event.getActorUri());
            }
        }
    }

    @Override
    public void processUpdateEvent(UpdateEvent event) {
        String objectUri = event.getMessageUri();
        User user = event.getUser();
        String userUri = personUri(user);
        Actor me = (Actor) signatureManager.getContext(URI.create(userUri)).get();
        socialService.getFollowers(user).forEach(acct -> {  
            try {
                Actor follower = (Actor) signatureManager.getContext(URI.create(acct)).orElseThrow();
                Update update = new Update();
                update.setId(objectUri + "#update");
                update.setActor(me.getId());
                update.setObject(new Context(objectUri));
                logger.info("Update to follower {}", follower.getId());
                signatureManager.post(me, follower, update);
            } catch (NoSuchElementException e) {
                logger.warn("Person not verified: {}", acct);
            } catch (IOException | NoSuchAlgorithmException e) {
                logger.warn("activitypub exception", e);
            }
        });
    }

    @Override
    public void processSystemEvent(SystemEvent systemEvent) {
        ActivityType type = systemEvent.getActivity().getType();
        if (type.equals(ActivityType.message)) {
            processMessage(systemEvent.getActivity().getMessage());
        } else if (type.equals(ActivityType.like)) {
            processLike(systemEvent.getActivity().getFrom(), systemEvent.getActivity().getMessage());
        }
    }

    @Override
    public void processUpdateUserEvent(UpdateUserEvent event) {
        User user = event.getUser();
        String userUri = personUri(user);
        Actor me = (Actor) signatureManager.getContext(URI.create(userUri)).get();
        socialService.getFollowers(user).forEach(acct -> {  
            try {
                Actor follower = (Actor) signatureManager.getContext(URI.create(acct)).orElseThrow();
                Update update = new Update();
                update.setId(userUri + "#update");
                update.setActor(me.getId());
                update.setObject(new Context(userUri));
                logger.info("Update to follower {}", follower.getId());
                signatureManager.post(me, follower, update);
            } catch (NoSuchElementException e) {
                logger.warn("Person not verified: {}", acct);
            } catch (IOException | NoSuchAlgorithmException e) {
                logger.warn("activitypub exception", e);
            }
        });        
    }
    
    private void processMessage(Message msg) {
        if (MessageUtils.isPM(msg) || msg.isService()) {
            return;
        }
        User user = msg.getUser();
        String userUri = personUri(user);
        Note note = makeNote(msg);
        signatureManager.getContext(URI.create(userUri)).ifPresentOrElse((me) -> {
            Set<String> subscribers = new HashSet<>(socialService.getFollowers(user));
            if (MessageUtils.isReply(msg) && msg.getTo().getUri().toASCIIString().length() > 0) {
                String replier = msg.getTo().getUri().toASCIIString();
                subscribers.add(replier);
                List<String> cc = new ArrayList<>(note.getCc());
                cc.add(replier);
                note.setCc(cc);
            }
            subscribers.addAll(note.getCc());
            subscribers.forEach(acct -> {
                Optional<Context> context = signatureManager.getContext(URI.create(acct));
                if (context.isPresent() && context.get() instanceof Actor) {
                    Actor follower = (Actor) context.get();
                    Create create = new Create();
                    create.setId(note.getId());
                    create.setActor(me.getId());
                    create.setPublished(note.getPublished());
                    create.setObject(note);
                    try {
                        signatureManager.post((Actor)me, follower, create);
                    } catch (IOException | NoSuchAlgorithmException e) {
                        logger.warn("activitypub exception", e);
                    }
                } else {
                    logger.warn("Unhandled context: {}", acct);
                }
            });
        }, () -> {
            logger.warn("Context not found: {}", userUri);
        });
    }

    public String inboxUri() {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath("/api/inbox").toUriString();
    }

    public String outboxUri(User user) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/u/%s/blog/toc", user.getName())).toUriString();
    }

    public String personUri(User user) {
        if (user.getUri().toString().length() > 0) {
            return user.getUri().toASCIIString();
        }
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/u/%s", user.getName())).toUriString();
    }
    public String personWebUri(User user) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/%s/", user.getName())).toUriString();
    }

    public String followersUri(User user) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/u/%s/followers/toc", user.getName())).toUriString();
    }

    public String followingUri(User user) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/u/%s/following/toc", user.getName())).toUriString();
    }
    public String messageUri(Message msg) {
        return messageUri(msg.getMid(), msg.getRid());
    }
    public String messageUri(int mid, int rid) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        uri.replacePath(String.format("/n/%d-%d", mid, rid));
        return uri.toUriString();
    }
    public String tagUri(Tag tag) {
        UriComponentsBuilder uri = UriComponentsBuilder.fromUriString(baseUri);
        return uri.replacePath(String.format("/t/%s", tag.getName())).toUriString();
    }

    public String postId(String messageUri) {
        UriComponents uri = UriComponentsBuilder.fromUriString(messageUri).build();
        return uri.getPath().substring(uri.getPath().lastIndexOf('/') + 1).replace("-", "/");
    }

    public Note makeNote(Message msg) {
        Note note = new Note();
        note.setId(messageUri(msg));
        note.setUrl(PlainTextFormatter.formatUrl(msg));
        note.setAttributedTo(personUri(msg.getUser()));
        if (MessageUtils.isReply(msg)) {
            if (msg.getReplyToUri().toASCIIString().length() > 0) {
                note.setInReplyTo(msg.getReplyToUri().toASCIIString());
            } else {
                note.setInReplyTo(messageUri(msg.getMid(), msg.getReplyto()));
            }
        }
        if (MessageUtils.isPM(msg)) {
            note.setTo(Collections.singletonList(personUri(msg.getTo())));
        } else {
            note.setTo(Collections.singletonList(Context.ACTIVITYSTREAMS_PUBLIC));
            note.setCc(Collections.singletonList(followersUri(msg.getUser())));
        }
        note.setPublished(msg.getCreated());
        if (StringUtils.isNotBlank(msg.getAttachmentType())) {
            Image attachment = new Image();
            attachment.setId(msg.getAttachment().getMedium().getUrl());
            attachment.setUrl(msg.getAttachment().getMedium().getUrl());
            attachment.setMediaType(HttpUtils.mediaType(msg.getAttachmentType()));
            note.setAttachment(Collections.singletonList(attachment));
        }
        note.setTags(msg.getTags().stream().map(t -> new Hashtag(tagUri(t), t.getName())).collect(Collectors.toList()));
        if (msg.getReplyToUri() != null && msg.getReplyToUri().toASCIIString().length() > 0) {
            Optional<Context> noteContext = signatureManager.getContext(msg.getReplyToUri());
            if (noteContext.isPresent()) {
                Note activity = (Note) noteContext.get();
                Optional<Context> personContext = signatureManager.getContext(URI.create(activity.getAttributedTo()));
                if (personContext.isPresent()) {
                    Actor person = (Actor) personContext.get();
                    note.getTags().add(new Mention(person.getUrl(), person.getPreferredUsername()));
                    msg.getTo().setName(person.getPreferredUsername());
                    note.setInReplyTo(activity.getInReplyTo());
                }
            }
        } else if (MessageUtils.isReply(msg)) {
            note.getTags().add(new Mention(personWebUri(msg.getTo()), msg.getTo().getName()));
        }
        MessageUtils.getGlobalMentions(msg).forEach(m -> {
            // @user@server.tld -> user@server.tld
            Optional<Context> personContext = signatureManager.discoverPerson(m.substring(1));
            if (personContext.isPresent()) {
                Actor person = (Actor) personContext.get();
                note.getTags().add(new Mention(person.getUrl(), person.getPreferredUsername()));
                List<String> cc = new ArrayList<>(note.getCc());
                cc.add(person.getId());
                note.setCc(cc);
            }
        });
        note.setSensitive(MessageUtils.isSensitive(msg));
        if (msg.isHtml()) {
            note.setContent(msg.getText());
        } else {
            PebbleTemplate noteTemplate = pebbleEngine.getTemplate("layouts/note");
            Map<String, Object> context = new HashMap<>();
            context.put("msg", msg);
            context.put("baseUri", baseUri);
            try {
                Writer writer = new StringWriter();
                noteTemplate.evaluate(writer, context);
                note.setContent(writer.toString());
            } catch (IOException e) {
                logger.warn("template not rendered, falling back");
                note.setContent(MessageUtils.formatMessage(StringUtils.defaultString(msg.getText())));
            }
        }
        return note;
    }

    @Override
    public void processPingEvent(PingEvent pingEvent) {

    }

    private void processLike(User user, Message message) {
        Note note = makeNote(message);
        Announce announce = new Announce();
        announce.setId(note.getId() + "#announce-" + user.getName());
        announce.setActor(personUri(user));
        announce.setTo(Collections.singletonList(Context.ACTIVITYSTREAMS_PUBLIC));
        announce.setObject(note);
        signatureManager.getContext(URI.create(announce.getActor())).ifPresentOrElse((ctx) -> {
            if (ctx instanceof Actor) {
                socialService.getFollowers(user).forEach(acct -> {
                    var follower = signatureManager.getContext(URI.create(acct));
                    follower.ifPresentOrElse((person) -> {
                        if (person instanceof Actor) {
                            try {
                                logger.info("{} announcing {} to {}", user.getName(), message.getMid(), acct);
                                signatureManager.post((Actor) ctx, (Actor) person, announce);
                            } catch (IOException | NoSuchAlgorithmException e) {
                                logger.warn("activitypub exception", e);
                            }
                        } else {
                            logger.warn("Unhandled context: {}", acct);
                        }
                    }, () -> logger.warn("Follower not found: {}", acct));
                });
            } else {
                logger.warn("Unhandled context: {}", announce.getActor());
            }
        }, () -> {
            logger.warn("Context not found: {}", announce.getActor());
        });
    }
    public User actorToUser(URI uri) throws HttpBadRequestException {
        Actor person = (Actor) signatureManager.getContext(uri).orElseThrow(HttpBadRequestException::new);
        User user = new User();
        user.setUri(URI.create(person.getId()));
        user.setName(person.getPreferredUsername());
        if (person.getIcon() != null) {
            user.setAvatar(person.getIcon().getUrl());
        }
        return user;
    }
}