/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software License
 * version 1.1, a copy of which has been included with this distribution in
 * the LICENSE file.
 */
package org.jivesoftware.util.log.util;

import java.io.PrintWriter;
import java.io.StringWriter;

/**
 * A set of utilities to inspect current stack frame.
 *
 * @author <a href="mailto:sylvain@apache.org">Sylvain Wallez</a>
 * @author <a href="mailto:stuart.roebuck@adolos.com">Stuart Roebuck</a>
 */
public final class StackIntrospector {
    /**
     * Hack to get the call stack as an array of classes. The
     * SecurityManager class provides it as a protected method, so
     * change it to public through a new method !
     */
    private final static class CallStack
            extends SecurityManager {
        /**
         * Returns the current execution stack as an array of classes.
         * The length of the array is the number of methods on the execution
         * stack. The element at index 0 is the class of the currently executing
         * method, the element at index 1 is the class of that method's caller,
         * and so on.
         */
        public Class[] get() {
            return getClassContext();
        }
    }

    ///Method to cache CallStack hack as needed
    private static CallStack c_callStack;

    /**
     * Private constructor to block instantiation.
     */
    private StackIntrospector() {
    }

    /**
     * Create Hack SecurityManager to get CallStack.
     *
     * @return the CallStack object
     * @throws SecurityException if an existing SecurityManager disallows construction
     *                           of another SecurityManager
     */
    private synchronized static CallStack getCallStack()
            throws SecurityException {
        if (null == c_callStack) {
            //Lazily create CallStack accessor as appropriate
            c_callStack = new CallStack();
        }

        return c_callStack;
    }

    /**
     * Find the caller of the passed in Class.
     * May return null if caller not found on execution stack
     *
     * @param clazz the Class to search for on stack to find caller of
     * @return the Class of object that called parrameter class
     * @throws SecurityException if an existing SecurityManager disallows construction
     *                           of another SecurityManager and thus blocks method results
     */
    public final static Class getCallerClass(final Class clazz)
            throws SecurityException {
        final Class[] stack = getCallStack().get();

        // Traverse the call stack in reverse order until we find clazz
        for (int i = stack.length - 1; i >= 0; i--) {
            if (clazz.isAssignableFrom(stack[i])) {
                // Found : the caller is the previous stack element
                return stack[i + 1];
            }
        }

        //Unable to locate class in call stack
        return null;
    }

    /**
     * Get the method path name for the method from which the LogEvent was
     * created, this includes the path name and the source filename and line
     * number if the source was compiled with debugging on.
     *
     * @return The method path name in the form "the.package.path.Method"
     */
    public final static String getCallerMethod(final Class clazz) {
        final String className = clazz.getName();

        //Extract stack into a StringBuffer
        final StringWriter sw = new StringWriter();
        final Throwable throwable = new Throwable();
        throwable.printStackTrace(new PrintWriter(sw, true));
        final StringBuffer buffer = sw.getBuffer();

        //Cache vars used in loop
        final StringBuffer line = new StringBuffer();
        final int length = buffer.length();

        //setup state
        boolean found = false;
        int state = 0;

        //parse line
        for (int i = 0; i < length; i++) {
            final char ch = buffer.charAt(i);

            switch (state) {
                case 0:
                    //Strip the first line from input
                    if ('\n' == ch) state = 1;
                    break;

                case 1:
                    //strip 't' from 'at'
                    if ('t' == ch) state = 2;
                    break;

                case 2:
                    //Strip space after 'at'
                    line.setLength(0);
                    state = 3;
                    break;

                case 3:
                    //accumulate all characters to end of line
                    if ('\n' != ch)
                        line.append(ch);
                    else {
                        //At this stage you have the line that looks like
                        //com.biz.SomeClass.someMethod(SomeClass.java:22)
                        final String method = line.toString();

                        ///Determine if line is a match for class
                        final boolean match = method.startsWith(className);
                        if (!found && match) {
                            //If this is the first time we cound class then
                            //set found to true and look for caller into class
                            found = true;
                        }
                        else if (found && !match) {
                            //We have now located caller of Clazz
                            return method;
                        }

                        //start parsing from start of line again
                        state = 1;
                    }
            }
        }

        return "";
    }

    /**
     * Return the current call stack as a String, starting with the first call
     * in the stack after a reference to the <code>clazz</code> class, and then
     * display <code>entries</code> entries.
     * <p/>
     * <p>This can be useful for debugging code to determine where calls to a
     * method are coming from.</p>
     *
     * @param clazz   the last class on the stack you are <i>not</i> interested in!
     * @param entries the number of stack lines to return.
     * @return The method path name in the form "the.package.path.Method"
     */
    public final static String getRecentStack(final Class clazz, int entries) {
        final String className = clazz.getName();

        //Extract stack into a StringBuffer
        final StringWriter sw = new StringWriter();
        final Throwable throwable = new Throwable();
        throwable.printStackTrace(new PrintWriter(sw, true));
        final StringBuffer buffer = sw.getBuffer();

        //Cache vars used in loop
        final StringBuffer line = new StringBuffer();
        final StringBuffer stack = new StringBuffer();
        final int length = buffer.length();

        //setup state
        boolean found = false;
        int state = 0;

        //parse line
        for (int i = 0; i < length; i++) {
            final char ch = buffer.charAt(i);

            switch (state) {
                case 0:
                    //Strip the first line from input
                    if ('\n' == ch) state = 1;
                    break;

                case 1:
                    //strip 't' from 'at'
                    if ('t' == ch) state = 2;
                    break;

                case 2:
                    //Strip space after 'at'
                    line.setLength(0);
                    state = 3;
                    break;

                case 3:
                    //accumulate all characters to end of line
                    if ('\n' != ch)
                        line.append(ch);
                    else {
                        //At this stage you have the line that looks like
                        //com.biz.SomeClass.someMethod(SomeClass.java:22)
                        final String method = line.toString();

                        ///Determine if line is a match for class
                        final boolean match = method.startsWith(className);
                        if (!found && match) {
                            //If this is the first time we cound class then
                            //set found to true and look for caller into class
                            found = true;
                        }
                        else if (found && !match) {
                            //We are looking at the callers of Clazz
                            stack.append(method);
                            entries--;
                            if (entries == 0) return stack.toString();
                            stack.append("\n");
                        }

                        //start parsing from start of line again
                        state = 1;
                    }
            }
        }

        return "";
    }
}