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package org.wings.header;

import org.wings.SFrame;
import org.wings.session.SessionManager;
import org.wings.util.SessionLocal;

import java.util.*;

/**
 * A class to manage headers which should be appended to all frames within a wingS session.
 */
public final class SessionHeaders {

    protected static final SessionLocal INSTANCE = new SessionLocal() {
        @Override
        protected SessionHeaders initialValue() {
            return new SessionHeaders();
        }
    };

    protected final List headerList = new ArrayList<>();
    protected final Map linkCounts = new HashMap<>();

    /**
     * Session local manager class.
     */
    private SessionHeaders() {}

    /**
     * @return The session local instance of this class.
     */
    public static SessionHeaders getInstance() {
        return INSTANCE.get();
    }

    /**
     * @return The headers currently attached to all frames inside this wingS session.
     */
    public List getHeaders() {
        return Collections.unmodifiableList(headerList);
    }

    public void registerHeaders(List headers) {
        registerHeaders(headerList.size(), headers);
    }

    public void registerHeader(Header header) {
        registerHeader(headerList.size(), header);
    }
    
    public void registerHeaders(int index, List headers) {
        for (Header header : headers) {
            registerHeader(index++, header);
        }
    }
    
    public void registerHeader(int index, Header header) {
        if (header == null)
            throw new IllegalArgumentException("Header must not be null!");

        if (getLinkCount(header) == 0) {
            Set frames = SessionManager.getSession().getFrames();
            for (SFrame frame : frames) {
                (frame).addHeader(header);
            }
            headerList.add(index, header);
        }
        incrementLinkCount(header);
    }

    public void deregisterHeaders(List headers) {
        headers.forEach(this::deregisterHeader);
    }

    public void deregisterHeader(Header header) {
        if (header == null)
            throw new IllegalArgumentException("Header must not be null!");

        decrementLinkCount(header);

        if (getLinkCount(header) == 0) {
            Set frames = SessionManager.getSession().getFrames();
            for (SFrame frame : frames) {
                (frame).removeHeader(header);
            }
            headerList.remove(header);
        }
    }

    protected int getLinkCount(Header header) {
        Integer linkCount = linkCounts.get(header);
        if (linkCount == null) {
            return 0;
        } else {
            return linkCount;
        }
    }

    protected void incrementLinkCount(Header header) {
        linkCounts.put(header, getLinkCount(header) + 1);
    }

    protected void decrementLinkCount(Header header) {
        linkCounts.put(header, getLinkCount(header) > 0 ? getLinkCount(header) - 1 : 0);
    }

}