/*
 * Copyright (C) 2009-2010, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.http.server.glue;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.regex.Pattern;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jgit.http.server.HttpServerText;

/**
 * Generic container filter to manage routing to different pipelines.
 * <p>
 * Callers can create and configure a new processing pipeline by using one of
 * the {@link #serve(String)} or {@link #serveRegex(String)} methods to allocate
 * a binder for a particular URL pattern.
 * <p>
 * Registered filters and servlets are initialized lazily, usually during the
 * first request. Once initialized the bindings in this servlet cannot be
 * modified without destroying the servlet and thereby destroying all registered
 * filters and servlets.
 */
public class MetaFilter implements Filter {
	static final String REGEX_GROUPS = "org.eclipse.jgit.http.server.glue.MetaServlet.serveRegex";

	private ServletContext servletContext;

	private final List<ServletBinderImpl> bindings;

	private volatile UrlPipeline[] pipelines;

	/**
	 * Empty filter with no bindings.
	 */
	public MetaFilter() {
		this.bindings = new ArrayList<>();
	}

	/**
	 * Construct a binding for a specific path.
	 *
	 * @param path
	 *            pattern to match.
	 * @return binder for the passed path.
	 */
	public ServletBinder serve(String path) {
		if (path.startsWith("*"))
			return register(new SuffixPipeline.Binder(path.substring(1)));
		throw new IllegalArgumentException(MessageFormat.format(HttpServerText
				.get().pathNotSupported, path));
	}

	/**
	 * Construct a binding for a regular expression.
	 *
	 * @param expression
	 *            the regular expression to pattern match the URL against.
	 * @return binder for the passed expression.
	 */
	public ServletBinder serveRegex(String expression) {
		return register(new RegexPipeline.Binder(expression));
	}

	/**
	 * Construct a binding for a regular expression.
	 *
	 * @param pattern
	 *            the regular expression to pattern match the URL against.
	 * @return binder for the passed expression.
	 */
	public ServletBinder serveRegex(Pattern pattern) {
		return register(new RegexPipeline.Binder(pattern));
	}

	/** {@inheritDoc} */
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		servletContext = filterConfig.getServletContext();
	}

	/** {@inheritDoc} */
	@Override
	public void destroy() {
		if (pipelines != null) {
			Set<Object> destroyed = newIdentitySet();
			for (UrlPipeline p : pipelines)
				p.destroy(destroyed);
			pipelines = null;
		}
	}

	private static Set<Object> newIdentitySet() {
		final Map<Object, Object> m = new IdentityHashMap<>();
		return new AbstractSet<Object>() {
			@Override
			public boolean add(Object o) {
				return m.put(o, o) == null;
			}

			@Override
			public boolean contains(Object o) {
				return m.containsKey(o);
			}

			@Override
			public Iterator<Object> iterator() {
				return m.keySet().iterator();
			}

			@Override
			public int size() {
				return m.size();
			}
		};
	}

	/** {@inheritDoc} */
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;
		UrlPipeline p = find(req);
		if (p != null)
			p.service(req, res);
		else
			chain.doFilter(req, res);
	}

	private UrlPipeline find(HttpServletRequest req) throws ServletException {
		for (UrlPipeline p : getPipelines())
			if (p.match(req))
				return p;
		return null;
	}

	private ServletBinder register(ServletBinderImpl b) {
		synchronized (bindings) {
			if (pipelines != null)
				throw new IllegalStateException(
						HttpServerText.get().servletAlreadyInitialized);
			bindings.add(b);
		}
		return register((ServletBinder) b);
	}

	/**
	 * Configure a newly created binder.
	 *
	 * @param b
	 *            the newly created binder.
	 * @return binder for the caller, potentially after adding one or more
	 *         filters into the pipeline.
	 */
	protected ServletBinder register(ServletBinder b) {
		return b;
	}

	private UrlPipeline[] getPipelines() throws ServletException {
		UrlPipeline[] r = pipelines;
		if (r == null) {
			synchronized (bindings) {
				r = pipelines;
				if (r == null) {
					r = createPipelines();
					pipelines = r;
				}
			}
		}
		return r;
	}

	private UrlPipeline[] createPipelines() throws ServletException {
		UrlPipeline[] array = new UrlPipeline[bindings.size()];

		for (int i = 0; i < bindings.size(); i++)
			array[i] = bindings.get(i).create();

		Set<Object> inited = newIdentitySet();
		for (UrlPipeline p : array)
			p.init(servletContext, inited);
		return array;
	}
}