// Copyright 2003-2005 Arthur van Hoff Rick Blair
// Licensed under Apache License version 2.0
// Original license LGPL

package javax.jmdns.impl;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.jmdns.impl.constants.DNSRecordClass;
import javax.jmdns.impl.constants.DNSRecordType;

/**
 * A table of DNS entries. This is a map table which can handle multiple entries with the same name.
 * <p/>
 * Storing multiple entries with the same name is implemented using a linked list. This is hidden from the user and can change in later implementation.
 * <p/>
 * Here's how to iterate over all entries:
 *
 * <pre>
 *       for (Iterator i=dnscache.allValues().iterator(); i.hasNext(); ) {
 *             DNSEntry entry = i.next();
 *             ...do something with entry...
 *       }
 * </pre>
 * <p/>
 * And here's how to iterate over all entries having a given name:
 *
 * <pre>
 *       for (Iterator i=dnscache.getDNSEntryList(name).iterator(); i.hasNext(); ) {
 *             DNSEntry entry = i.next();
 *           ...do something with entry...
 *       }
 * </pre>
 *
 * @author Arthur van Hoff, Werner Randelshofer, Rick Blair, Pierre Frisch
 */
public class DNSCache extends AbstractMap<String, List<? extends DNSEntry>> {

    // private static Logger logger = Logger.getLogger(DNSCache.class.getName());

    private transient Set<Map.Entry<String, List<? extends DNSEntry>>> _entrySet  = null;

    /**
     *
     */
    public static final DNSCache                                       EmptyCache = new _EmptyCache();

    static final class _EmptyCache extends DNSCache {

        /**
         * {@inheritDoc}
         */
        @Override
        public int size() {
            return 0;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean isEmpty() {
            return true;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean containsKey(Object key) {
            return false;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean containsValue(Object value) {
            return false;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public List<DNSEntry> get(Object key) {
            return null;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public Set<String> keySet() {
            return Collections.emptySet();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public Collection<List<? extends DNSEntry>> values() {
            return Collections.emptySet();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public Set<Map.Entry<String, List<? extends DNSEntry>>> entrySet() {
            return Collections.emptySet();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean equals(Object o) {
            return (o instanceof Map) && ((Map<?, ?>) o).size() == 0;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public List<? extends DNSEntry> put(String key, List<? extends DNSEntry> value) {
            return null;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int hashCode() {
            return 0;
        }

    }

    /**
     *
     */
    protected static class _CacheEntry extends Object implements Map.Entry<String, List<? extends DNSEntry>> {

        private List<? extends DNSEntry> _value;

        private String                   _key;

        /**
         * @param key
         * @param value
         */
        protected _CacheEntry(String key, List<? extends DNSEntry> value) {
            super();
            _key = (key != null ? key.trim().toLowerCase() : null);
            _value = value;
        }

        /**
         * @param entry
         */
        protected _CacheEntry(Map.Entry<String, List<? extends DNSEntry>> entry) {
            super();
            if (entry instanceof _CacheEntry) {
                _key = ((_CacheEntry) entry).getKey();
                _value = ((_CacheEntry) entry).getValue();
            }
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public String getKey() {
            return (_key != null ? _key : "");
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public List<? extends DNSEntry> getValue() {
            return _value;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public List<? extends DNSEntry> setValue(List<? extends DNSEntry> value) {
            List<? extends DNSEntry> oldValue = _value;
            _value = value;
            return oldValue;
        }

        /**
         * Returns <tt>true</tt> if this list contains no elements.
         *
         * @return <tt>true</tt> if this list contains no elements
         */
        public boolean isEmpty() {
            return this.getValue().isEmpty();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean equals(Object entry) {
            if (!(entry instanceof Map.Entry)) {
                return false;
            }
            return this.getKey().equals(((Map.Entry<?, ?>) entry).getKey()) && this.getValue().equals(((Map.Entry<?, ?>) entry).getValue());
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int hashCode() {
            return (_key == null ? 0 : _key.hashCode());
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public synchronized String toString() {
            StringBuffer aLog = new StringBuffer(200);
            aLog.append("\n\t\tname '");
            aLog.append(_key);
            aLog.append("' ");
            if ((_value != null) && (!_value.isEmpty())) {
                for (DNSEntry entry : _value) {
                    aLog.append("\n\t\t\t");
                    aLog.append(entry.toString());
                }
            } else {
                aLog.append(" no entries");
            }
            return aLog.toString();
        }
    }

    /**
     *
     */
    public DNSCache() {
        this(1024);
    }

    /**
     * @param map
     */
    public DNSCache(DNSCache map) {
        this(map != null ? map.size() : 1024);
        if (map != null) {
            this.putAll(map);
        }
    }

    /**
     * Create a table with a given initial size.
     *
     * @param initialCapacity
     */
    public DNSCache(int initialCapacity) {
        super();
        _entrySet = new HashSet<Map.Entry<String, List<? extends DNSEntry>>>(initialCapacity);
    }

    // ====================================================================
    // Map

    /*
     * (non-Javadoc)
     * @see java.util.AbstractMap#entrySet()
     */
    @Override
    public Set<Map.Entry<String, List<? extends DNSEntry>>> entrySet() {
        if (_entrySet == null) {
            _entrySet = new HashSet<Map.Entry<String, List<? extends DNSEntry>>>();
        }
        return _entrySet;
    }

    /**
     * @param key
     * @return map entry for the key
     */
    protected Map.Entry<String, List<? extends DNSEntry>> getEntry(String key) {
        String stringKey = (key != null ? key.trim().toLowerCase() : null);
        for (Map.Entry<String, List<? extends DNSEntry>> entry : this.entrySet()) {
            if (stringKey != null) {
                if (stringKey.equals(entry.getKey())) {
                    return entry;
                }
            } else {
                if (entry.getKey() == null) {
                    return entry;
                }
            }
        }
        return null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public List<? extends DNSEntry> put(String key, List<? extends DNSEntry> value) {
        synchronized (this) {
            List<? extends DNSEntry> oldValue = null;
            Map.Entry<String, List<? extends DNSEntry>> oldEntry = this.getEntry(key);
            if (oldEntry != null) {
                oldValue = oldEntry.setValue(value);
            } else {
                this.entrySet().add(new _CacheEntry(key, value));
            }
            return oldValue;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return new DNSCache(this);
    }

    // ====================================================================

    /**
     * Returns all entries in the cache
     *
     * @return all entries in the cache
     */
    public synchronized Collection<DNSEntry> allValues() {
        List<DNSEntry> allValues = new ArrayList<DNSEntry>();
        for (List<? extends DNSEntry> entry : this.values()) {
            if (entry != null) {
                allValues.addAll(entry);
            }
        }
        return allValues;
    }

    /**
     * Iterate only over items with matching name. Returns an list of DNSEntry or null. To retrieve all entries, one must iterate over this linked list.
     *
     * @param name
     * @return list of DNSEntries
     */
    public synchronized Collection<? extends DNSEntry> getDNSEntryList(String name) {
        Collection<? extends DNSEntry> entryList = this._getDNSEntryList(name);
        if (entryList != null) {
            entryList = new ArrayList<DNSEntry>(entryList);
        } else {
            entryList = Collections.emptyList();
        }
        return entryList;
    }

    private Collection<? extends DNSEntry> _getDNSEntryList(String name) {
        return this.get(name != null ? name.toLowerCase() : null);
    }

    /**
     * Get a matching DNS entry from the table (using isSameEntry). Returns the entry that was found.
     *
     * @param dnsEntry
     * @return DNSEntry
     */
    public synchronized DNSEntry getDNSEntry(DNSEntry dnsEntry) {
        DNSEntry result = null;
        if (dnsEntry != null) {
            Collection<? extends DNSEntry> entryList = this._getDNSEntryList(dnsEntry.getKey());
            if (entryList != null) {
                for (DNSEntry testDNSEntry : entryList) {
                    if (testDNSEntry.isSameEntry(dnsEntry)) {
                        result = testDNSEntry;
                        break;
                    }
                }
            }
        }
        return result;
    }

    /**
     * Get a matching DNS entry from the table.
     *
     * @param name
     * @param type
     * @param recordClass
     * @return DNSEntry
     */
    public synchronized DNSEntry getDNSEntry(String name, DNSRecordType type, DNSRecordClass recordClass) {
        DNSEntry result = null;
        Collection<? extends DNSEntry> entryList = this._getDNSEntryList(name);
        if (entryList != null) {
            for (DNSEntry testDNSEntry : entryList) {
                if (testDNSEntry.getRecordType().equals(type) && ((DNSRecordClass.CLASS_ANY == recordClass) || testDNSEntry.getRecordClass().equals(recordClass))) {
                    result = testDNSEntry;
                    break;
                }
            }
        }
        return result;
    }

    /**
     * Get all matching DNS entries from the table.
     *
     * @param name
     * @param type
     * @param recordClass
     * @return list of entries
     */
    public synchronized Collection<? extends DNSEntry> getDNSEntryList(String name, DNSRecordType type, DNSRecordClass recordClass) {
        Collection<? extends DNSEntry> entryList = this._getDNSEntryList(name);
        if (entryList != null) {
            entryList = new ArrayList<DNSEntry>(entryList);
            for (Iterator<? extends DNSEntry> i = entryList.iterator(); i.hasNext();) {
                DNSEntry testDNSEntry = i.next();
                if (!testDNSEntry.getRecordType().equals(type) || ((DNSRecordClass.CLASS_ANY != recordClass) && !testDNSEntry.getRecordClass().equals(recordClass))) {
                    i.remove();
                }
            }
        } else {
            entryList = Collections.emptyList();
        }
        return entryList;
    }

    /**
     * Adds an entry to the table.
     *
     * @param dnsEntry
     * @return true if the entry was added
     */
    public synchronized boolean addDNSEntry(final DNSEntry dnsEntry) {
        boolean result = false;
        if (dnsEntry != null) {
            Map.Entry<String, List<? extends DNSEntry>> oldEntry = this.getEntry(dnsEntry.getKey());

            List<DNSEntry> aNewValue = null;
            if (oldEntry != null) {
                aNewValue = new ArrayList<DNSEntry>(oldEntry.getValue());
            } else {
                aNewValue = new ArrayList<DNSEntry>();
            }
            aNewValue.add(dnsEntry);

            if (oldEntry != null) {
                oldEntry.setValue(aNewValue);
            } else {
                this.entrySet().add(new _CacheEntry(dnsEntry.getKey(), aNewValue));
            }
            // This is probably not very informative
            result = true;
        }
        return result;
    }

    /**
     * Removes a specific entry from the table. Returns true if the entry was found.
     *
     * @param dnsEntry
     * @return true if the entry was removed
     */
    public synchronized boolean removeDNSEntry(DNSEntry dnsEntry) {
        boolean result = false;
        if (dnsEntry != null) {
            Map.Entry<String, List<? extends DNSEntry>> existingEntry = this.getEntry(dnsEntry.getKey());
            if (existingEntry != null) {
                result = existingEntry.getValue().remove(dnsEntry);
                // If we just removed the last one we need to get rid of the entry
                if (existingEntry.getValue().isEmpty()) {
                    this.entrySet().remove(existingEntry);
                }
            }
        }
        return result;
    }

    /**
     * Replace an existing entry by a new one.<br/>
     * <b>Note:</b> the 2 entries must have the same key.
     *
     * @param newDNSEntry
     * @param existingDNSEntry
     * @return <code>true</code> if the entry has been replace, <code>false</code> otherwise.
     */
    public synchronized boolean replaceDNSEntry(DNSEntry newDNSEntry, DNSEntry existingDNSEntry) {
        boolean result = false;
        if ((newDNSEntry != null) && (existingDNSEntry != null) && (newDNSEntry.getKey().equals(existingDNSEntry.getKey()))) {
            Map.Entry<String, List<? extends DNSEntry>> oldEntry = this.getEntry(newDNSEntry.getKey());

            List<DNSEntry> aNewValue = null;
            if (oldEntry != null) {
                aNewValue = new ArrayList<DNSEntry>(oldEntry.getValue());
            } else {
                aNewValue = new ArrayList<DNSEntry>();
            }
            aNewValue.remove(existingDNSEntry);
            aNewValue.add(newDNSEntry);

            if (oldEntry != null) {
                oldEntry.setValue(aNewValue);
            } else {
                this.entrySet().add(new _CacheEntry(newDNSEntry.getKey(), aNewValue));
            }
            // This is probably not very informative
            result = true;
        }
        return result;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public synchronized String toString() {
        StringBuffer aLog = new StringBuffer(2000);
        aLog.append("\t---- cache ----");
        for (Map.Entry<String, List<? extends DNSEntry>> entry : this.entrySet()) {
            aLog.append("\n\t\t");
            aLog.append(entry.toString());
        }
        return aLog.toString();
    }

}