package ca.uhn.fhir.rest.server;

/*
 * #%L
 * HAPI FHIR - Core Library
 * %%
 * Copyright (C) 2014 - 2017 University Health Network
 * %%
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * #L%
 */

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;

/**
 * Determines the server's base using the incoming request
 */
public class IncomingRequestAddressStrategy implements IServerAddressStrategy {

	private String myServletPath;

	@Override
	public String determineServerBase(ServletContext theServletContext, HttpServletRequest theRequest) {
		String requestFullPath = StringUtils.defaultString(theRequest.getRequestURI());

		String servletPath;
		if (myServletPath != null) {
			servletPath = myServletPath;
		} else {
			servletPath = StringUtils.defaultString(theRequest.getServletPath());
		}

		StringBuffer requestUrl = theRequest.getRequestURL();
		String servletContextPath = StringUtils.defaultString(theRequest.getContextPath());

		String requestPath = requestFullPath.substring(servletContextPath.length() + servletPath.length());
		if (requestPath.length() > 0 && requestPath.charAt(0) == '/') {
			requestPath = requestPath.substring(1);
		}

		int startOfPath = requestUrl.indexOf("//");
		int requestUrlLength = requestUrl.length();

		if (startOfPath != -1 && (startOfPath + 2) < requestUrlLength) {
			startOfPath = requestUrl.indexOf("/", startOfPath + 2);
		}
		if (startOfPath == -1) {
			startOfPath = 0;
		}

		int contextIndex;
		if (servletPath.length() == 0 || servletPath.equals("/")) {
			if (requestPath.length() == 0) {
				contextIndex = requestUrlLength;
			} else {
				contextIndex = requestUrl.indexOf(requestPath, startOfPath);
			}
		} else {
			//servletContextPath can start with servletPath 
			contextIndex = requestUrl.indexOf(servletPath + "/", startOfPath);
			if (contextIndex == -1) {
				contextIndex = requestUrl.indexOf(servletPath, startOfPath);
			}
		}

		String fhirServerBase;
		int length = contextIndex + servletPath.length();
		if (length > requestUrlLength) {
			length = requestUrlLength;
		}
		fhirServerBase = requestUrl.substring(0, length);
		return fhirServerBase;
	}

	/**
	 * If set to a non-null value (default is <code>null</code>), this address strategy assumes that the FHIR endpoint is deployed to the given servlet path within the context. This is useful in some
	 * deployments where it isn't obvious to the servlet which part of the path is actually the root path to reach the servlet.
	 * <p>
	 * Example values could be:
	 * <ul>
	 * <li>null</li>
	 * <li>/</li>
	 * <li>/base</li>
	 * </ul>
	 * </p>
	 * <p>
	 * <b>Wildcards are not supported!</b>
	 * </p>
	 */
	public void setServletPath(String theServletPath) {
		myServletPath = theServletPath;
	}

	/**
	 * Determines the servlet's context path.
	 * 
	 * This is here to try and deal with the wide variation in servers and what they return.
	 * 
	 * getServletContext().getContextPath() is supposed to return the path to the specific servlet we are deployed as but it's not available everywhere. On some servers getServletContext() can return
	 * null (old Jetty seems to suffer from this, see hapi-fhir-base-test-mindeps-server) and on other old servers (Servlet 2.4) getServletContext().getContextPath() doesn't even exist.
	 * 
	 * theRequest.getContextPath() returns the context for the specific incoming request. It should be available everywhere, but it's likely to be less predicable if there are multiple servlet mappings
	 * pointing to the same servlet, so we don't favour it. This is possibly not the best strategy (maybe we should just always use theRequest.getContextPath()?) but so far people seem happy with this
	 * behavour across a wide variety of platforms.
	 * 
	 * If you are having troubles on a given platform/configuration and want to suggest a change or even report incompatibility here, we'd love to hear about it.
	 */
	public static String determineServletContextPath(HttpServletRequest theRequest, RestfulServer server) {
		String retVal;
		if (server.getServletContext() != null) {
			if (server.getServletContext().getMajorVersion() >= 3 || (server.getServletContext().getMajorVersion() > 2 && server.getServletContext().getMinorVersion() >= 5)) {
				retVal = server.getServletContext().getContextPath();
			} else {
				retVal = theRequest.getContextPath();
			}
		} else {
			retVal = theRequest.getContextPath();
		}
		retVal = StringUtils.defaultString(retVal);
		return retVal;
	}

}