package io.opentracing.contrib.spring.web.interceptor;

import io.opentracing.Span;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.method.HandlerMethod;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * SpanDecorator to decorate span at different stages in filter processing.
 *
 * @author Pavol Loffay
 */
public interface HandlerInterceptorSpanDecorator {

    /**
     * This is called in
     * {@link org.springframework.web.servlet.HandlerInterceptor#preHandle(HttpServletRequest, HttpServletResponse, Object)}.
     *
     * @param httpServletRequest request
     * @param handler handler
     * @param span current span
     */
    void onPreHandle(HttpServletRequest httpServletRequest, Object handler, Span span);

    /**
     * This is called in
     * {@link org.springframework.web.servlet.HandlerInterceptor#afterCompletion(HttpServletRequest, HttpServletResponse, Object, Exception)}
     *
     * @param httpServletRequest request
     * @param httpServletResponse response
     * @param handler handler
     * @param ex exception
     * @param span current span
     */
    void onAfterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object handler,
                           Exception ex, Span span);

    /**
     * This is called in
     * {@link org.springframework.web.servlet.AsyncHandlerInterceptor#afterConcurrentHandlingStarted(HttpServletRequest, HttpServletResponse, Object)}
     *
     * @param httpServletRequest request
     * @param httpServletResponse response
     * @param handler handler
     * @param span current span
     */
    void onAfterConcurrentHandlingStarted(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object handler,
                           Span span);

    /**
     * Decorator to record details about the handler as log events recorded on the span.
     */
    HandlerInterceptorSpanDecorator STANDARD_LOGS = new HandlerInterceptorSpanDecorator() {

        @Override
        public void onPreHandle(HttpServletRequest httpServletRequest, Object handler, Span span) {
            Map<String, Object> logs = new HashMap<>(3);
            logs.put("event", "preHandle");
            logs.put(HandlerUtils.HANDLER, handler);

            String metaData = HandlerUtils.className(handler);
            if (metaData != null) {
                logs.put(HandlerUtils.HANDLER_CLASS_NAME, metaData);
            }

            metaData = HandlerUtils.methodName(handler);
            if (metaData != null) {
                logs.put(HandlerUtils.HANDLER_METHOD_NAME, metaData);
            }

            span.log(logs);
        }

        @Override
        public void onAfterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
                                      Object handler, Exception ex, Span span) {
            Map<String, Object> logs = new HashMap<>(2);
            logs.put("event", "afterCompletion");
            logs.put(HandlerUtils.HANDLER, handler);
            span.log(logs);
        }

        @Override
        public void onAfterConcurrentHandlingStarted(HttpServletRequest httpServletRequest,
                HttpServletResponse httpServletResponse, Object handler, Span span) {
            Map<String, Object> logs = new HashMap<>(2);
            logs.put("event", "afterConcurrentHandlingStarted");
            logs.put(HandlerUtils.HANDLER, handler);
            span.log(logs);
        }
    };

    /**
     * Use the handler's method name as the span's operation name.
     */
    HandlerInterceptorSpanDecorator HANDLER_METHOD_OPERATION_NAME = new HandlerInterceptorSpanDecorator() {

        @Override
        public void onPreHandle(HttpServletRequest httpServletRequest, Object handler, Span span) {
            String metaData = HandlerUtils.methodName(handler);
            if (metaData != null) {
                span.setOperationName(metaData);
            }
        }

        @Override
        public void onAfterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
                                      Object handler, Exception ex, Span span) {
        }

        @Override
        public void onAfterConcurrentHandlingStarted(HttpServletRequest httpServletRequest,
                HttpServletResponse httpServletResponse, Object handler, Span span) {
        }
    };

    /**
     * Helper class for deriving tags/logs from handler object.
     */
    class HandlerUtils {
        private HandlerUtils() {}

        /**
         * Class name of a handler serving request
         */
        public static final String HANDLER_CLASS_NAME = "handler.class_simple_name";
        /**
         * Method name of handler serving request
         */
        public static final String HANDLER_METHOD_NAME = "handler.method_name";
        /**
         * Spring handler object
         */
        public static final String HANDLER = "handler";

        public static String className(Object handler) {
            return handler instanceof HandlerMethod ?
                    ((HandlerMethod) handler).getBeanType().getSimpleName() :
                    handler.getClass().getSimpleName() ;
        }

        public static String methodName(Object handler) {
            return handler instanceof HandlerMethod ?
                    ((HandlerMethod) handler).getMethod().getName() : null;
        }

        public static String requestMapping(Object handler) {
            String[] mappings = ((HandlerMethod) handler).getMethodAnnotation(RequestMapping.class).path();
            return Arrays.toString(mappings);
        }
    }
}
