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 * distributed with this work for additional information        *
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 * to you under the Apache License, Version 2.0 (the            *
 * "License"); you may not use this file except in compliance   *
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package org.apache.james.webadmin.service;

import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.util.concurrent.ConcurrentLinkedDeque;

import javax.inject.Inject;

import org.apache.james.blob.api.BlobId;
import org.apache.james.blob.api.BlobStore;
import org.apache.james.blob.export.api.BlobExportMechanism;
import org.apache.james.blob.export.api.FileExtension;
import org.apache.james.core.Username;
import org.apache.james.mailbox.backup.MailboxBackup;
import org.apache.james.task.Task;
import org.apache.james.user.api.UsersRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.github.fge.lambdas.Throwing;
import com.google.common.collect.Lists;

import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

public class ExportService {

    public enum Stage {
        STARTING,
        ZIPPING,
        EXPORTING,
        COMPLETED,
    }

    public static class Progress {
        private final ConcurrentLinkedDeque stages;

        public Progress() {
            this.stages = new ConcurrentLinkedDeque<>(Lists.newArrayList(Stage.STARTING));
        }

        public Stage getStage() {
            return stages.getLast();
        }

        public void setStage(Stage stage) {
            this.stages.add(stage);
        }
    }

    private static final Logger LOGGER = LoggerFactory.getLogger(ExportService.class);
    private static final String EXPLANATION = "The backup of your mailboxes has been exported to you";
    private static final String FILE_PREFIX = "mailbox-backup-";

    private final MailboxBackup mailboxBackup;
    private final BlobStore blobStore;
    private final BlobExportMechanism blobExport;
    private final UsersRepository usersRepository;

    @Inject
    ExportService(MailboxBackup mailboxBackup, BlobStore blobStore, BlobExportMechanism blobExport, UsersRepository usersRepository) {
        this.mailboxBackup = mailboxBackup;
        this.blobStore = blobStore;
        this.blobExport = blobExport;
        this.usersRepository = usersRepository;
    }

    public Mono export(Progress progress, Username username) {
        return Mono.usingWhen(
            Mono.fromCallable(() -> zipMailboxesContent(progress, username)),
            inputStream -> export(progress, username, inputStream),
            this::closeResource,
            (inputStream, throwable) -> closeResource(inputStream),
            this::closeResource
        );
    }

    InputStream zipMailboxesContent(Progress progress, Username username) throws IOException {
        progress.setStage(Stage.ZIPPING);
        PipedOutputStream out = new PipedOutputStream();
        PipedInputStream in = new PipedInputStream(out);

        writeUserMailboxesContent(username, out)
            .subscribeOn(Schedulers.elastic())
            .subscribe();

        return in;
    }

    Mono export(Progress progress, Username username, InputStream inputStream) {
        return Mono.fromRunnable(() -> progress.setStage(Stage.EXPORTING))
            .then(Mono.usingWhen(
                blobStore.save(blobStore.getDefaultBucketName(), inputStream, BlobStore.StoragePolicy.LOW_COST),
                blobId -> export(username, blobId),
                this::deleteBlob)
            .doOnSuccess(any -> progress.setStage(Stage.COMPLETED))
            .thenReturn(Task.Result.COMPLETED)
            .onErrorResume(e -> {
                LOGGER.error("Error exporting mailboxes of user: {}", username.asString(), e);
                return Mono.just(Task.Result.PARTIAL);
            }));
    }

    private Mono export(Username username, BlobId blobId) {
        return Mono.fromRunnable(Throwing.runnable(() ->
            blobExport.blobId(blobId)
                .with(usersRepository.getMailAddressFor(username))
                .explanation(EXPLANATION)
                .filePrefix(FILE_PREFIX + username.asString() + "-")
                .fileExtension(FileExtension.ZIP)
                .export())
            .sneakyThrow());
    }

    private Mono deleteBlob(BlobId blobId) {
        return Mono.from(blobStore.delete(blobStore.getDefaultBucketName(), blobId))
            .onErrorResume(e -> {
                LOGGER.error("Error deleting Blob with blobId: {}", blobId.asString(), e);
                return Mono.empty();
            })
            .then();
    }

    private Mono writeUserMailboxesContent(Username username, PipedOutputStream out) {
        return Mono.usingWhen(
            Mono.fromCallable(() -> out),
            outputStream -> Mono.fromRunnable(Throwing.runnable(() -> mailboxBackup.backupAccount(username, outputStream))),
            this::closeResource,
            (outputStream, throwable) -> closeResource(outputStream)
                .doFinally(any -> LOGGER.error("Error while backing up mailboxes for user {}", username.asString(), throwable)),
            this::closeResource);
    }

    private Mono closeResource(Closeable resource) {
        return Mono.fromRunnable(() -> {
            try {
                resource.close();
            } catch (IOException e) {
                LOGGER.error("Error while closing resource", e);
            }
        });
    }
}