/****************************************************************************
 * Copyright (c) 2022-2025 Imixs Software Solutions GmbH and others.
 * https://www.imixs.com
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * https://www.eclipse.org/legal/epl-2.0
 *
 * This Source Code may also be made available under the terms of the
 * GNU General Public License, version 2 or later (GPL-2.0-or-later),
 * which is available at https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
 ****************************************************************************/
package ai.dynamixs.cognition;

import java.time.Instant;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.imixs.workflow.exceptions.PluginException;
import org.imixs.workflow.faces.data.WorkflowEvent;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.event.Observes;
import jakarta.interceptor.Interceptor;

/**
 * The CognitoLockHandler is an application scoped CDI bean that holds a list of
 * workitem uniqueIds currently in edit mode. This caching mechanism is used by
 * the {@code CognitoEventService} to avoid optimistic lock exceptions.
 * <p>
 * The IDs are stored in the lock cache. The CognitoEventService looks up an ID
 * in this cache before updating a workitem in a safe way.
 * <p>
 * It may happen that a user switches into edit mode
 * ({@link WorkflowEvent#DOCUMENT_CHANGED}) without updating the workitem. For
 * this reason a locked ID will be released after {@value #LOCK_TIMEOUT_SECONDS}
 * seconds automatically.
 * <p>
 * <strong>Thread Safety:</strong> This implementation uses a
 * {@link ConcurrentHashMap} to ensure thread-safe operations in a
 * multi-user-environment where the same workitem can be opened by different
 * users in parallel.
 *
 * @author rsoika
 * @version 1.0
 */
@ApplicationScoped
public class CognitoLockHandler {

    private static final Logger logger = Logger.getLogger(CognitoLockHandler.class.getName());

    /**
     * Lock timeout in seconds. After this duration, a lock is considered stale and
     * will be automatically released.
     */
    public static final long LOCK_TIMEOUT_SECONDS = 120;

    /**
     * Thread-safe cache storing workitem uniqueIds mapped to their lock timestamp.
     * The timestamp is used to determine if a lock has expired.
     */
    private final Map<String, Instant> lockCache = new ConcurrentHashMap<>();

    /**
     * WorkflowEvent listener that manages the lock cache based on document
     * lifecycle events.
     * <p>
     * <ul>
     * <li>{@link WorkflowEvent#DOCUMENT_CHANGED}: Adds the workitem's uniqueID to
     * the lock cache (lock operation)</li>
     * <li>{@link WorkflowEvent#DOCUMENT_AFTER_SAVE}: Removes the workitem's
     * uniqueID from the lock cache (unlock operation)</li>
     * </ul>
     * <p>
     * This observer is executed with {@link Interceptor.Priority#LIBRARY_BEFORE}
     * priority to ensure it runs before other observers.
     *
     * @param workflowEvent the workflow event containing the workitem and event
     *                      type
     * @throws PluginException if an error occurs during event processing
     */
    public void onWorkflowEvent(@Observes WorkflowEvent workflowEvent)
            throws PluginException {

        int eventType = workflowEvent.getEventType();
        String uniqueId = extractUniqueId(workflowEvent);

        if (uniqueId == null || uniqueId.isEmpty()) {
            logger.log(Level.FINE, "Skipping lock operation - workitem has no uniqueId");
            return;
        }

        // Lock the workitem when user enters edit mode
        if (WorkflowEvent.WORKITEM_CHANGED == eventType) {
            lock(uniqueId);
            logger.log(Level.INFO, "Workitem locked: uniqueId={0}, active locks={1}",
                    new Object[] { uniqueId, lockCache.size() });
        }

        // Unlock the workitem after successful save
        if (WorkflowEvent.WORKITEM_AFTER_PROCESS == eventType) {
            boolean wasLocked = unlock(uniqueId);
            if (wasLocked) {
                logger.log(Level.INFO, "Workitem unlocked after process: uniqueId={0}, remaining locks={1}",
                        new Object[] { uniqueId, lockCache.size() });
            } else {
                logger.log(Level.INFO, "Workitem was not locked (possibly expired): uniqueId={0}",
                        uniqueId);
            }
        }
    }

    /**
     * Checks if the given workitem uniqueID is currently locked (in edit mode).
     * <p>
     * This method also performs cleanup of stale locks. If the lock for the given
     * ID has exceeded the timeout ({@value #LOCK_TIMEOUT_SECONDS} seconds), it will
     * be automatically removed and this method returns {@code false}.
     *
     * @param id the unique identifier of the workitem to check
     * @return {@code true} if the workitem is currently locked and the lock has not
     *         expired, {@code false} otherwise
     */
    public boolean isLocked(String id) {
        if (id == null || id.isEmpty()) {
            logger.log(Level.FINE, "isLocked called with null or empty id - returning false");
            return false;
        }

        Instant lockTimestamp = lockCache.get(id);

        if (lockTimestamp == null) {
            logger.log(Level.FINE, "Workitem not locked: uniqueId={0}", id);
            return false;
        }

        // Check if lock has expired
        if (isLockExpired(lockTimestamp)) {
            logger.log(Level.INFO, "Lock expired and removed: uniqueId={0}, locked since={1}",
                    new Object[] { id, lockTimestamp });
            lockCache.remove(id);
            return false;
        }

        long lockedSeconds = java.time.Duration.between(lockTimestamp, Instant.now()).getSeconds();
        logger.log(Level.FINE, "Workitem is locked: uniqueId={0}, locked for {1}s",
                new Object[] { id, lockedSeconds });
        return true;
    }

    /**
     * Adds a workitem uniqueID to the lock cache with the current timestamp.
     * <p>
     * If the ID is already in the cache, the timestamp will be updated (lock
     * refresh).
     *
     * @param id the unique identifier of the workitem to lock
     */
    public void lock(String id) {
        if (id == null || id.isEmpty()) {
            logger.log(Level.WARNING, "Attempted to lock with null or empty id - operation ignored");
            return;
        }

        Instant previousLock = lockCache.put(id, Instant.now());

        if (previousLock != null) {
            logger.log(Level.FINE, "Lock refreshed: uniqueId={0}, previous lock from={1}",
                    new Object[] { id, previousLock });
        } else {
            logger.log(Level.FINE, "New lock created: uniqueId={0}", id);
        }

        // Opportunistic cleanup of expired locks
        cleanupExpiredLocks();
    }

    /**
     * Removes a workitem uniqueID from the lock cache.
     *
     * @param id the unique identifier of the workitem to unlock
     * @return {@code true} if the workitem was locked and is now unlocked,
     *         {@code false} if the workitem was not locked
     */
    public boolean unlock(String id) {
        if (id == null || id.isEmpty()) {
            logger.log(Level.WARNING, "Attempted to unlock with null or empty id - operation ignored");
            return false;
        }

        Instant removed = lockCache.remove(id);

        if (removed != null) {
            long lockedDuration = java.time.Duration.between(removed, Instant.now()).getSeconds();
            logger.log(Level.FINE, "Lock removed: uniqueId={0}, was locked for {1}s",
                    new Object[] { id, lockedDuration });
            return true;
        }

        return false;
    }

    /**
     * Returns the current number of active locks in the cache.
     * <p>
     * <strong>Note:</strong> This count may include expired locks that have not yet
     * been cleaned up.
     *
     * @return the number of entries in the lock cache
     */
    public int getLockCount() {
        return lockCache.size();
    }

    /**
     * Removes all expired locks from the cache.
     * <p>
     * This method is called opportunistically during lock operations to prevent
     * unbounded cache growth.
     */
    public void cleanupExpiredLocks() {
        int initialSize = lockCache.size();

        lockCache.entrySet().removeIf(entry -> {
            boolean expired = isLockExpired(entry.getValue());
            if (expired) {
                logger.log(Level.FINE, "Cleaning up expired lock: uniqueId={0}, locked since={1}",
                        new Object[] { entry.getKey(), entry.getValue() });
            }
            return expired;
        });

        int removed = initialSize - lockCache.size();
        if (removed > 0) {
            logger.log(Level.INFO, "Expired locks cleanup completed: removed={0}, remaining={1}",
                    new Object[] { removed, lockCache.size() });
        }
    }

    /**
     * Checks if a lock timestamp has exceeded the timeout threshold.
     *
     * @param lockTimestamp the timestamp when the lock was created
     * @return {@code true} if the lock is expired, {@code false} otherwise
     */
    private boolean isLockExpired(Instant lockTimestamp) {
        return lockTimestamp.plusSeconds(LOCK_TIMEOUT_SECONDS).isBefore(Instant.now());
    }

    /**
     * Extracts the uniqueId from the workitem contained in the workflow event.
     *
     * @param workflowEvent the workflow event
     * @return the uniqueId of the workitem, or {@code null} if not available
     */
    private String extractUniqueId(WorkflowEvent workflowEvent) {
        if (workflowEvent == null || workflowEvent.getWorkitem() == null) {
            logger.log(Level.WARNING, "WorkflowEvent or workitem is null - cannot extract uniqueId");
            return null;
        }

        String uniqueId = workflowEvent.getWorkitem().getUniqueID();

        if (uniqueId == null || uniqueId.isEmpty()) {
            logger.log(Level.FINE, "Workitem has no uniqueId (possibly a new document)");
        }

        return uniqueId;
    }
}