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package io.sentry.buffer;

import io.sentry.event.Event;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.*;
import java.util.Arrays;
import java.util.Iterator;

/**
 * Stores {@link Event} objects to a directory on the filesystem and allows
 * them to be flushed to Sentry (and deleted) at a later time.
 */
public class DiskBuffer implements Buffer {

    /**
     * File suffix added to all serialized event files.
     */
    public static final String FILE_SUFFIX = ".sentry-event";

    private static final Logger logger = LoggerFactory.getLogger(DiskBuffer.class);

    private int maxEvents;
    private final File bufferDir;

    /**
     * Construct an DiskBuffer which stores errors in the specified directory on disk.
     *
     * @param bufferDir File representing directory to store buffered Events in
     * @param maxEvents The maximum number of events to store offline
     */
    public DiskBuffer(File bufferDir, int maxEvents) {
        super();

        this.bufferDir = bufferDir;
        this.maxEvents = maxEvents;

        String errMsg = "Could not create or write to disk buffer dir: " + bufferDir.getAbsolutePath();
        try {
            bufferDir.mkdirs();
            if (!bufferDir.isDirectory() || !bufferDir.canWrite()) {
                throw new RuntimeException(errMsg);
            }
        } catch (Exception e) {
            throw new RuntimeException(errMsg, e);
        }

        logger.debug(Integer.toString(getNumStoredEvents())
            + " stored events found in dir: "
            + bufferDir.getAbsolutePath());
    }

    /**
     * Store a single event to the add directory. Java serialization is used and each
     * event is stored in a file named by its UUID.
     *
     * @param event Event to store in add directory
     */
    @Override
    public void add(Event event) {
        if (getNumStoredEvents() >= maxEvents) {
            logger.warn("Not adding Event because at least "
                + Integer.toString(maxEvents) + " events are already stored: " + event.getId());
            return;
        }

        File eventFile = new File(bufferDir.getAbsolutePath(), event.getId().toString() + FILE_SUFFIX);
        if (eventFile.exists()) {
            logger.trace("Not adding Event to offline storage because it already exists: "
                + eventFile.getAbsolutePath());
            return;
        } else {
            logger.debug("Adding Event to offline storage: " + eventFile.getAbsolutePath());
        }

        try (FileOutputStream fileOutputStream = new FileOutputStream(eventFile);
             ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream)) {
            objectOutputStream.writeObject(event);
        } catch (Exception e) {
            logger.error("Error writing Event to offline storage: " + event.getId(), e);
        }

        logger.debug(Integer.toString(getNumStoredEvents())
            + " stored events are now in dir: "
            + bufferDir.getAbsolutePath());
    }

    /**
     * Deletes a buffered {@link Event} from disk.
     *
     * @param event Event to delete from the disk.
     */
    @Override
    public void discard(Event event) {
        File eventFile = new File(bufferDir, event.getId().toString() + FILE_SUFFIX);
        if (eventFile.exists()) {
            logger.debug("Discarding Event from offline storage: " + eventFile.getAbsolutePath());
            if (!eventFile.delete()) {
                logger.warn("Failed to delete Event: " + eventFile.getAbsolutePath());
            }
        }
    }

    /**
     * Attempts to open and deserialize a single {@link Event} from a {@link File}.
     *
     * @param eventFile File to deserialize into an Event
     * @return Event from the File, or null
     */
    private Event fileToEvent(File eventFile) {
        Object eventObj;

        try (FileInputStream fileInputStream = new FileInputStream(new File(eventFile.getAbsolutePath()));
             ObjectInputStream ois = new ObjectInputStream(fileInputStream)) {
            eventObj = ois.readObject();
        } catch (FileNotFoundException e) {
            // event was deleted while we were iterating the array of files
            return null;
        } catch (Exception e) {
            logger.error("Error reading Event file: " + eventFile.getAbsolutePath(), e);
            if (!eventFile.delete()) {
                logger.warn("Failed to delete Event: " + eventFile.getAbsolutePath());
            }
            return null;
        }

        try {
            return (Event) eventObj;
        } catch (Exception e) {
            logger.error("Error casting Object to Event: " + eventFile.getAbsolutePath(), e);
            if (!eventFile.delete()) {
                logger.warn("Failed to delete Event: " + eventFile.getAbsolutePath());
            }
            return null;
        }
    }

    /**
     * Returns the next *valid* {@link Event} found in an Iterator of Files.
     *
     * @param files Iterator of Files to deserialize
     * @return The next Event found, or null if there are none
     */
    private Event getNextEvent(Iterator files) {
        while (files.hasNext()) {
            File file = files.next();

            // only consider files that end with FILE_SUFFIX
            if (!file.getAbsolutePath().endsWith(FILE_SUFFIX)) {
                continue;
            }

            Event event = fileToEvent(file);
            if (event != null) {
                return event;
            }
        }

        return null;
    }

    /**
     * Returns an Iterator of Events that are stored on disk at the point in time this method
     * is called. Note that files may not deserialize correctly, may be corrupted,
     * or may be missing on disk by the time we attempt to open them - so some care is taken to
     * only return valid {@link Event}s.
     *
     * If Events are written to disk after this Iterator is created they will not be returned
     * by this Iterator.
     *
     * @return Iterator of Events on disk
     */
    @Override
    public Iterator getEvents() {
        final Iterator files = Arrays.asList(bufferDir.listFiles()).iterator();

        return new Iterator() {
            private Event next = getNextEvent(files);

            @Override
            public boolean hasNext() {
                return next != null;
            }

            @Override
            public Event next() {
                Event toReturn = next;
                next = getNextEvent(files);
                return toReturn;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    private int getNumStoredEvents() {
        int count = 0;
        for (File file : bufferDir.listFiles()) {
            if (file.getAbsolutePath().endsWith(FILE_SUFFIX)) {
                count += 1;
            }
        }
        return count;
    }
}