/*
 * Copyright (c) 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * 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.
 *
 */
package io.helidon.metrics;

import org.hamcrest.Description;
import org.hamcrest.TypeSafeMatcher;

/**
 * Hamcrest Matcher for Metrics-related value checking.
 * <p>
 * Includes:
 * <ul>
 * <li>{@link #withinTolerance(java.lang.Number)} for checking within a range (tolerance) either side of an expected value</li>
 * </ul>
 */
class HelidonMetricsMatcher {

    static final Double VARIANCE = Double.valueOf(System.getProperty("helidon.histogram.tolerance", "0.001"));

    static TypeSafeMatcher<Number> withinTolerance(final Number expected) {
        return new TypeSafeMatcher<Number>() {
            @Override
            protected boolean matchesSafely(Number item) {
                return Math.abs(expected.doubleValue() - item.doubleValue()) <= expected.doubleValue() * VARIANCE;
            }

            @Override
            public void describeTo(Description description) {
                description.appendText("withinTolerance expected value in range [")
                        .appendValue(expected.doubleValue() * (1.0 - VARIANCE))
                        .appendText(", ")
                        .appendValue(expected.doubleValue() * (1.0 + VARIANCE))
                        .appendText("]");
            }
        };
    }
}
