package com.temp.shared.utils;

import java.util.HashMap;
import java.util.Map;

public class Global {
    @SuppressWarnings("rawtypes")
    private static final Map INSTANCES_BY_CLASS = new HashMap();

    /**
     * Get the required instance associated with the klass.
     *
     * @param klass
     *            !null
     *
     * @throws IllegalStateException
     *             if there is currently nothing associated with the klass
     *
     * @return !null instance associated with the klass
     */
    public static <T> T get(Class<T> klass) throws IllegalStateException {
        T instance = getOptional(klass);
        if (instance != null) {
            return instance;
        }
        throw new IllegalStateException("No 'instance' associated with class: " + klass);
    }

    /**
     * Set/Replace/Clear the current instance associated with a class
     *
     * @param klass
     *            !null
     * @param instance
     *            if null then removes current instance associated with the
     *            class, if !null then sets / replaces the current instance
     *            associated with the class.
     *
     * @return the previous instance associated with klass.
     */
    public static <T> T set(Class<T> klass, T instance) {
        Assert.notNull("Class", klass);
        synchronized (INSTANCES_BY_CLASS) {
            if (instance == null) {
                return ObjectUtils.cast(INSTANCES_BY_CLASS.remove(klass));
            } else {
                return ObjectUtils.cast(put(klass, instance));
            }
        }
    }

    /**
     * Get the optional instance associated with the klass.
     *
     * @param klass
     *            !null
     *
     * @return instance associated with the klass or null
     */
    public static <T> T getOptional(Class<T> klass) {
        Assert.notNull("Class", klass);
        synchronized (INSTANCES_BY_CLASS) {
            return ObjectUtils.cast(INSTANCES_BY_CLASS.get(klass));
        }
    }

    @SuppressWarnings("unchecked")
    private static Object put(Object key, Object value) {
        return INSTANCES_BY_CLASS.put(key, value);
    }
}