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Spring HandlerInterceptorAdapter implementation.
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package com.github.kristofa.brave.spring;

import com.github.kristofa.brave.ServerSpan;
import com.github.kristofa.brave.ServerSpanThreadBinder;
import com.github.kristofa.brave.ServerTracer;
import com.github.kristofa.brave.http.BraveHttpHeaders;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import static com.github.kristofa.brave.IdConversion.convertToLong;

public class ServletHandlerInterceptor extends HandlerInterceptorAdapter {

    static final String HTTP_SERVER_SPAN_ATTRIBUTE = ServletHandlerInterceptor.class.getName() + ".server-span";
    private final ServerSpanThreadBinder serverThreadBinder;
    private final ServerTracer serverTracer;

    @Autowired
    public ServletHandlerInterceptor(final ServerTracer serverTracer, final ServerSpanThreadBinder serverThreadBinder) {
        this.serverTracer = serverTracer;
        this.serverThreadBinder = serverThreadBinder;
    }

    @Override
    public boolean preHandle(final HttpServletRequest request, final HttpServletResponse response, final Object handler) {
        beginTrace(request);

        return true;
    }

    @Override
    public void afterConcurrentHandlingStarted(final HttpServletRequest request, final HttpServletResponse response, final Object handler) {
        request.setAttribute(HTTP_SERVER_SPAN_ATTRIBUTE, serverThreadBinder.getCurrentServerSpan());
        serverTracer.clearCurrentSpan();
    }

    @Override
    public void afterCompletion(final HttpServletRequest request, final HttpServletResponse response, final Object handler, final Exception ex) {

        final ServerSpan span = (ServerSpan) request.getAttribute(HTTP_SERVER_SPAN_ATTRIBUTE);

        if (span != null) {
            serverThreadBinder.setCurrentSpan(span);
        }

        try {
            serverTracer.setServerSend();
        } finally {
            serverTracer.clearCurrentSpan();
        }
    }

    private void beginTrace(final HttpServletRequest request) {

        final String sampled = request.getHeader(BraveHttpHeaders.Sampled.getName());
        if (!Boolean.valueOf(sampled != null ? sampled : Boolean.TRUE.toString())) {
            serverTracer.setStateNoTracing();
            return;
        }

        updateServerState(request);

        serverTracer.setServerReceived();
    }

    private void updateServerState(final HttpServletRequest request) {
        final String traceId = request.getHeader(BraveHttpHeaders.TraceId.getName());
        final String spanId = request.getHeader(BraveHttpHeaders.SpanId.getName());
        final String spanName = request.getMethod();

        if (traceId != null && spanId != null) {
            final String parentSpanId = request.getHeader(BraveHttpHeaders.ParentSpanId.getName());
            serverTracer.setStateCurrentTrace(convertToLong(traceId), convertToLong(spanId),
                                              parentSpanId != null ? convertToLong(parentSpanId) : null, spanName);
        } else {
            serverTracer.setStateUnknown(spanName);
        }
        serverTracer.submitBinaryAnnotation("http.uri", request.getRequestURI());
    }

}