package net.i2p.crypto;

/*
 * free (adj.): unencumbered; not under the control of others
 * Written by jrandom in 2003 and released into the public domain 
 * with no warranty of any kind, either expressed or implied.  
 * It probably won't  make your computer catch on fire, or eat 
 * your children, but it might.  Use at your own risk.
 *
 */

import java.io.IOException;
import java.io.Writer;
import java.util.Set;

import net.i2p.I2PAppContext;
import net.i2p.data.PublicKey;
import net.i2p.data.SessionKey;
import net.i2p.data.SessionTag;

/**
 * Manage the session keys and session tags used for encryption and decryption.
 * This base implementation simply ignores sessions and acts as if everything is
 * unknown (and hence always forces a full ElGamal encryption for each message).
 * See TransientSessionKeyManager subclass which manages and persists keys and tags.
 *
 */
public class SessionKeyManager {

    /**
     *  A dummy SessionKeyManager for testing or for passing to
     *  ElGamalAESEngine.decrypt()
     *
     *  @since 0.9.14
     */
    public SessionKeyManager() {}

    /**
     *  A dummy SessionKeyManager for testing or for passing to
     *  ElGamalAESEngine.decrypt()
     *
     *  @param context unused
     *  @since public since 0.9.14; protected before that
     */
    public SessionKeyManager(I2PAppContext context) {}
    
    /**
     * Retrieve the session key currently associated with encryption to the target,
     * or null if a new session key should be generated.
     *
     * Warning - don't generate a new session if this returns null, it's racy, use getCurrentOrNewKey()
     */
    public SessionKey getCurrentKey(PublicKey target) {
        return null;
    }

    /**
     * Retrieve the session key currently associated with encryption to the target.
     * Generates a new session and session key if not previously exising.
     *
     * @return non-null
     * @since 0.9
     */
    public SessionKey getCurrentOrNewKey(PublicKey target) {
        return null;
    }

    /**
     * Associate a new session key with the specified target.  Metrics to determine
     * when to expire that key begin with this call.
     *
     * Racy if called after getCurrentKey() to check for a current session;
     * use getCurrentOrNewKey() in that case.
     */
    public void createSession(PublicKey target, SessionKey key) { // nop
    }

    /**
     * Generate a new session key and associate it with the specified target.  
     *
     * Racy if called after getCurrentKey() to check for a current session;
     * use getCurrentOrNewKey() in that case.
     */
    public SessionKey createSession(PublicKey target) {
        SessionKey key = KeyGenerator.getInstance().generateSessionKey();
        createSession(target, key);
        return key;
    }

    /**
     * Retrieve the next available session tag for identifying the use of the given
     * key when communicating with the target.  If this returns null, no tags are
     * available so ElG should be used with the given key (a new sessionKey should
     * NOT be used)
     *
     */
    public SessionTag consumeNextAvailableTag(PublicKey target, SessionKey key) {
        return null;
    }

    /**
     *  How many to send, IF we need to.
     *  @since 0.9.2
     */
    public int getTagsToSend() { return 0; };

    /**
     *  @since 0.9.2
     */
    public int getLowThreshold() { return 0; };

    /**
     *  @return true if we have less than the threshold or what we have is about to expire
     *  @since 0.9.2
     */
    public boolean shouldSendTags(PublicKey target, SessionKey key) {
        return shouldSendTags(target, key, getLowThreshold());
    }

    /**
     *  @return true if we have less than the threshold or what we have is about to expire
     *  @since 0.9.2
     */
    public boolean shouldSendTags(PublicKey target, SessionKey key, int lowThreshold) { return false; }

    /**
     * Determine (approximately) how many available session tags for the current target
     * have been confirmed and are available
     *
     */
    public int getAvailableTags(PublicKey target, SessionKey key) {
        return 0;
    }

    /**
     * Determine how long the available tags will be available for before expiring, in 
     * milliseconds
     */
    public long getAvailableTimeLeft(PublicKey target, SessionKey key) {
        return 0;
    }

    /**
     * Take note of the fact that the given sessionTags associated with the key for
     * encryption to the target have definitely been received at the target (aka call this
     * method after receiving an ack to a message delivering them)
     *
     */
    public TagSetHandle tagsDelivered(PublicKey target, SessionKey key, Set<SessionTag> sessionTags) { // nop
         return null;
    }

    /**
     * Mark all of the tags delivered to the target up to this point as invalid, since the peer
     * has failed to respond when they should have.  This call essentially lets the system recover
     * from corrupted tag sets and crashes
     *
     */
    public void failTags(PublicKey target) { // nop
    }

    /**
     * Accept the given tags and associate them with the given key for decryption,
     * with the default expiration.
     */
    public void tagsReceived(SessionKey key, Set<SessionTag> sessionTags) {}

    /**
     * Accept the given tags and associate them with the given key for decryption,
     * with specified expiration.
     *
     * @param sessionTags modifiable; NOT copied
     * @param expire time from now
     * @since 0.9.7
     */
    public void tagsReceived(SessionKey key, Set<SessionTag> sessionTags, long expire) {}

    /**
     * Determine if we have received a session key associated with the given session tag,
     * and if so, discard it (but keep track for frequent dups) and return the decryption
     * key it was received with (via tagsReceived(...)).  returns null if no session key
     * matches
     *
     */
    public SessionKey consumeTag(SessionTag tag) {
        return null;
    }

    /** 
     * Called when the system is closing down, instructing the session key manager to take 
     * whatever precautions are necessary (saving state, etc)
     *
     */
    public void shutdown() { // nop
    }

    public void renderStatusHTML(Writer out) throws IOException {}
    public void failTags(PublicKey target, SessionKey key, TagSetHandle ts) {}
    public void tagsAcked(PublicKey target, SessionKey key, TagSetHandle ts) {}
}
