package org.limewire.service;

import java.io.PrintStream;

/**
 * Forwards errors to an {@link ErrorCallback}. <code>ErrorService</code>
 * includes static methods to set and get the <code>ErrorCallback</code> class.
 */
public final class ErrorService {

    /**
     * The <tt>ErrorCallback</tt> instance that callbacks are sent to. As a
     * default the <tt>PrintStreamErrorCallback</tt> is set, which prints to
     * {@link System#out}.
     */
    private volatile static ErrorCallback _errorCallback = new PrintStreamErrorCallback(System.out);

    /**
     * Private constructor to ensure this class cannot be instantiated.
     */
    private ErrorService() {
    }

    /**
     * Sets the <tt>ErrorCallback</tt> class to use.
     */
    public static void setErrorCallback(ErrorCallback callback) {
        _errorCallback = callback;
    }

    /**
     * Gets the <code>ErrorCallback</code> currently in use.
     */
    public static ErrorCallback getErrorCallback() {
        return _errorCallback;
    }

    /**
     * Displays the error to the user.
     */
    public static void error(Throwable problem) {
        _errorCallback.error(problem);
    }

    /**
     * Displays the error to the user with a specific detail information.
     */
    public static void error(Throwable problem, String detail) {
        _errorCallback.error(problem, detail);
    }

    /**
     * Helper class that outputs the stack trace and the exception message to a
     * {@link PrintStream} and rethrows the exception as a
     * {@link RuntimeException}.
     */
    private static class PrintStreamErrorCallback implements ErrorCallback {

        private final PrintStream out;

        /**
         * Takes a {@link PrintStream} which is used for error output.
         */
        public PrintStreamErrorCallback(PrintStream out) {
            this.out = out;
        }

        /**
         * Implements the <code>ErrorCallback</code> interface. Prints the stack
         * trace for the given <code>Throwable</code> and rethrows the exception
         * as a {@link RuntimeException}.
         * 
         * @param t the <code>Throwable</code> to display
         */
        public void error(Throwable t) {
            t.printStackTrace(out);
            throw new RuntimeException(t.getMessage());
        }

        // inherit doc comment
        public void error(Throwable t, String msg) {
            t.printStackTrace(out);
            out.println(msg);
            throw new RuntimeException(t.getMessage());
        }
    }
}