package alien4cloud.webconfiguration;

import static com.codahale.metrics.MetricRegistry.name;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

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

import com.codahale.metrics.Counter;
import com.codahale.metrics.Meter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.Timer;
import com.codahale.metrics.servlet.AbstractInstrumentedFilter;
import lombok.extern.slf4j.Slf4j;

/**
 * {@link Filter} implementation which captures request information and a breakdown of the response
 * codes being returned.
 */
@Slf4j
public class MetricsFilter implements Filter {
    private static final String NAME_PREFIX = "responseCodes.";
    private static final int OK = 200;
    private static final int CREATED = 201;
    private static final int NO_CONTENT = 204;
    private static final int BAD_REQUEST = 400;
    private static final int NOT_FOUND = 404;
    private static final int SERVER_ERROR = 500;

    private final String otherMetricName;
    private final Map<Integer, String> meterNamesByStatusCode;

    // initialized after call of init method
    private ConcurrentMap<Integer, Meter> metersByStatusCode;
    private Meter otherMeter;
    private Counter activeRequests;
    private Timer requestTimer;

    /**
     * Creates a new instance of the filter.
     */
    public MetricsFilter(MetricRegistry metricsRegistry) {
        this.otherMetricName = NAME_PREFIX + "other";
        this.meterNamesByStatusCode = createMeterNamesByStatusCode();

        this.metersByStatusCode = new ConcurrentHashMap<Integer, Meter>(meterNamesByStatusCode.size());
        for (Entry<Integer, String> entry : meterNamesByStatusCode.entrySet()) {
            metersByStatusCode.put(entry.getKey(), metricsRegistry.meter(name(AbstractInstrumentedFilter.class, entry.getValue())));
        }
        this.otherMeter = metricsRegistry.meter(name(AbstractInstrumentedFilter.class, otherMetricName));
        this.activeRequests = metricsRegistry.counter(name(AbstractInstrumentedFilter.class, "activeRequests"));
        this.requestTimer = metricsRegistry.timer(name(AbstractInstrumentedFilter.class, "requests"));
        log.info("Metrics filter initialized.");
    }

    private static Map<Integer, String> createMeterNamesByStatusCode() {
        final Map<Integer, String> meterNamesByStatusCode = new HashMap<Integer, String>(6);
        meterNamesByStatusCode.put(OK, NAME_PREFIX + "ok");
        meterNamesByStatusCode.put(CREATED, NAME_PREFIX + "created");
        meterNamesByStatusCode.put(NO_CONTENT, NAME_PREFIX + "noContent");
        meterNamesByStatusCode.put(BAD_REQUEST, NAME_PREFIX + "badRequest");
        meterNamesByStatusCode.put(NOT_FOUND, NAME_PREFIX + "notFound");
        meterNamesByStatusCode.put(SERVER_ERROR, NAME_PREFIX + "serverError");
        return meterNamesByStatusCode;
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        final StatusExposingServletResponse wrappedResponse = new StatusExposingServletResponse((HttpServletResponse) response);
        activeRequests.inc();
        final Timer.Context context = requestTimer.time();
        try {
            chain.doFilter(request, wrappedResponse);
        } finally {
            context.stop();
            activeRequests.dec();
            markMeterForStatusCode(wrappedResponse.getStatus());
        }
    }

    private void markMeterForStatusCode(int status) {
        final Meter metric = metersByStatusCode.get(status);
        if (metric != null) {
            metric.mark();
        } else {
            otherMeter.mark();
        }
    }

    private static class StatusExposingServletResponse extends HttpServletResponseWrapper {
        // The Servlet spec says: calling setStatus is optional, if no status is set, the default is 200.
        private int httpStatus = 200;

        public StatusExposingServletResponse(HttpServletResponse response) {
            super(response);
        }

        @Override
        public void sendError(int sc) throws IOException {
            httpStatus = sc;
            super.sendError(sc);
        }

        @Override
        public void sendError(int sc, String msg) throws IOException {
            httpStatus = sc;
            super.sendError(sc, msg);
        }

        @Override
        public void setStatus(int sc) {
            httpStatus = sc;
            super.setStatus(sc);
        }

        public int getStatus() {
            return httpStatus;
        }
    }
}