/**
 * Copyright 2011 John DeRegnaucourt (jdereg@gmail.com)
 *
 * 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 hudson.util;

import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Test two objects for equivalence with a 'deep' comparison.  This will traverse 
 * the Object graph and perform either a field-by-field comparison on each
 * object (if no .equals() method has been overridden from Object), or it
 * will call the customized .equals() method if it exists.  This method will
 * allow object graphs loaded at different times (with different object ids)
 * to be reliably compared.  Object.equals() / Object.hashCode() rely on the
 * object's identity, which would not consider two equivalent objects necessarily
 * equals.  This allows graphs containing instances of Classes that did not
 * overide .equals() / .hashCode() to be compared.  For example, testing for
 * existence in a cache.  Relying on an object's identity will not locate an
 * equivalent object in a cache.<br/><br/>
 *
 * This method will handle cycles correctly, for example A->B->C->A.  Suppose a and
 * a' are two separate instances of A with the same values for all fields on
 * A, B, and C.  Then a.deepEquals(a') will return true.  It uses cycle detection
 * storing visited objects in a Set to prevent endless loops.
 *  
 * @author John DeRegnaucourt (jdereg@gmail.com)
 */
public class DeepEquals
{
    private static final Map<Class, Boolean> _customEquals = new ConcurrentHashMap<Class, Boolean>();
    private static final Map<Class, Boolean> _customHash = new ConcurrentHashMap<Class, Boolean>();
    private static final Map<Class, Collection<Field>> _reflectedFields = new ConcurrentHashMap<Class, Collection<Field>>();
    
    private static class DualKey
    {
        private final Object _key1;
        private final Object _key2;
        
        private DualKey(Object k1, Object k2)
        {
            _key1 = k1;
            _key2 = k2;
        }
        
        public boolean equals(Object other)
        {
            if (other == null)
            {
                return false;
            }
            
            if (!(other instanceof DualKey))
            {
                return false;
            }
            
            DualKey that = (DualKey) other;
            return _key1 == that._key1 && _key2 == that._key2;
        }
        
        public int hashCode()
        {
            int h1 = _key1 != null ? _key1.hashCode() : 0;
            int h2 = _key2 != null ? _key2.hashCode() : 0;
            return h1 + h2;
        }
    }

    /**
     * Compare two objects with a 'deep' comparison.  This will traverse the
     * Object graph and perform either a field-by-field comparison on each
     * object (if no .equals() method has been overridden from Object), or it
     * will call the customized .equals() method if it exists.  This method will
     * allow object graphs loaded at different times (with different object ids)
     * to be reliably compared.  Object.equals() / Object.hashCode() rely on the
     * object's identity, which would not consider to equivalent objects necessarily
     * equals.  This allows graphs containing instances of Classes that did no
     * overide .equals() / .hashCode() to be compared.  For example, testing for
     * existence in a cache.  Relying on an objects identity will not locate an
     * object in cache, yet relying on it being equivalent will.<br/><br/>
     *
     * This method will handle cycles correctly, for example A->B->C->A.  Suppose a and
     * a' are two separate instances of the A with the same values for all fields on
     * A, B, and C.  Then a.deepEquals(a') will return true.  It uses cycle detection
     * storing visited objects in a Set to prevent endless loops.
     * @param a Object one to compare
     * @param b Object two to compare
     * @return true if a is equivalent to b, false otherwise.  Equivalent means that
     * all field values of both subgraphs are the same, either at the field level
     * or via the respectively encountered overridden .equals() methods during
     * traversal.
     */
    public static boolean deepEquals(Object a, Object b)
    {
        Set visited = new HashSet<DualKey>();
        LinkedList<DualKey> stack = new LinkedList<DualKey>();
        stack.addFirst(new DualKey(a, b));

        while (!stack.isEmpty())
        {            
            DualKey dualKey = stack.removeFirst();        
            visited.add(dualKey);
            
            if (dualKey._key1 == dualKey._key2)
            {   // Same instance is always equal to itself.
                continue;
            }
            
            if (dualKey._key1 == null || dualKey._key2 == null)
            {   // If either one is null, not equal (both can't be null, due to above comparison).
                return false;
            }
                            
            if (!dualKey._key1.getClass().equals(dualKey._key2.getClass()))
            {   // Must be same class
                return false;
            }
            
            // Handle all [] types.  In order to be equal, the arrays must be the same 
            // length, be of the same type, be in the same order, and all elements within
            // the array must be deeply equivalent.
            if (dualKey._key1.getClass().isArray())
            {
                if (!compareArrays(dualKey._key1, dualKey._key2, stack, visited))
                {
                    return false;
                }
                continue;
            }
            
            // Special handle SortedSets because they are fast to compare because their
            // elements must be in the same order to be equivalent Sets.
            if (dualKey._key1 instanceof SortedSet)
            {
                if (!compareOrderedCollection((Collection) dualKey._key1, (Collection) dualKey._key2, stack, visited))
                {
                    return false;
                }
                continue;
            }
            
            // Handled unordered Sets.  This is a slightly more expensive comparison because order cannot
            // be assumed, a temporary Map must be created, however the comparison still runs in O(N) time.
            if (dualKey._key1 instanceof Set)
            {
                if (!compareUnorderedCollection((Collection) dualKey._key1, (Collection) dualKey._key2, stack, visited))
                {
                    return false;
                }
                continue;
            }
            
            // Check any Collection that is not a Set.  In these cases, element order
            // matters, therefore this comparison is faster than using unordered comparison.
            if (dualKey._key1 instanceof Collection)
            {
                if (!compareOrderedCollection((Collection) dualKey._key1, (Collection) dualKey._key2, stack, visited))
                {
                    return false;
                }                                
                continue;
            }
            
            // Compare two SortedMaps.  This takes advantage of the fact that these
            // Maps can be compared in O(N) time due to their ordering.
            if (dualKey._key1 instanceof SortedMap)
            {
                if (!compareSortedMap((SortedMap) dualKey._key1, (SortedMap) dualKey._key2, stack, visited))
                {
                    return false;
                }
                continue;
            }
            
            // Compare two Unordered Maps. This is a slightly more expensive comparison because
            // order cannot be assumed, therefore a temporary Map must be created, however the
            // comparison still runs in O(N) time.
            if (dualKey._key1 instanceof Map)
            {
                if (!compareUnorderedMap((Map) dualKey._key1, (Map) dualKey._key2, stack, visited))
                {
                    return false;
                }
                continue;
            }
            
            if (hasCustomEquals(dualKey._key1.getClass()))
            {
                if (!dualKey._key1.equals(dualKey._key2))
                {
                    return false;
                }
                continue;
            }        
            
            Collection<Field> fields = getDeepDeclaredFields(dualKey._key1.getClass());               
            
            for (Field field : fields)
            {
                try
                {
                    DualKey dk = new DualKey(field.get(dualKey._key1), field.get(dualKey._key2));
                    if (!visited.contains(dk))
                    {
                        stack.addFirst(dk);
                    }
                }
                catch (Exception ignored)
                { }
            }
        }

        return true;
    }

    /**
     * Deeply compare to Arrays []. Both arrays must be of the same type, same length, and all
     * elements within the arrays must be deeply equal in order to return true.
     * @param array1 [] type (Object[], String[], etc.)
     * @param array2 [] type (Object[], String[], etc.)
     * @param stack add items to compare to the Stack (Stack versus recursion)
     * @param visited Set of objects already compared (prevents cycles)
     * @return true if the two arrays are the same length and contain deeply equivalent items.
     */
    private static boolean compareArrays(Object array1, Object array2, LinkedList stack, Set visited)
    {
        // Same instance check already performed...

        int len = Array.getLength(array1);
        if (len != Array.getLength(array2))
        {
            return false;
        }

        for (int i = 0; i < len; i++)
        {
            DualKey dk = new DualKey(Array.get(array1, i), Array.get(array2, i));
            if (!visited.contains(dk))
            {   // push contents for further comparison
                stack.addFirst(dk);
            }
        }
        return true;
    }

    /**
     * Deeply compare two Collections that must be same length and in same order.
     * @param col1 First collection of items to compare
     * @param col2 Second collection of items to compare
     * @param stack add items to compare to the Stack (Stack versus recursion)
     * @param visited Set of objects already compared (prevents cycles)
     * value of 'true' indicates that the Collections may be equal, and the sets
     * items will be added to the Stack for further comparison.
     */
    private static boolean compareOrderedCollection(Collection col1, Collection col2, LinkedList stack, Set visited)
    {
        // Same instance check already performed...

        if (col1.size() != col2.size())
        {
            return false;
        }
                        
        Iterator i1 = col1.iterator();
        Iterator i2 = col2.iterator();
        
        while (i1.hasNext())
        {
            DualKey dk = new DualKey(i1.next(), i2.next());
            if (!visited.contains(dk))
            {   // push contents for further comparison
                stack.addFirst(dk);
            }
        }
        return true;
    }
        
    /**
     * Deeply compare the two sets referenced by dualKey.  This method attempts
     * to quickly determine inequality by length, then if lengths match, it
     * places one collection into a temporary Map by deepHashCode(), so that it
     * can walk the other collection and look for each item in the map, which
     * runs in O(N) time, rather than an O(N^2) lookup that would occur if each
     * item from collection one was scanned for in collection two.
     * @param col1 First collection of items to compare
     * @param col2 Second collection of items to compare
     * @param stack add items to compare to the Stack (Stack versus recursion)
     * @param visited Set containing items that have already been compared,
     * so as to prevent cycles.
     * @return boolean false if the Collections are for certain not equals. A
     * value of 'true' indicates that the Collections may be equal, and the sets
     * items will be added to the Stack for further comparison.
     */
    private static boolean compareUnorderedCollection(Collection col1, Collection col2, LinkedList stack, Set visited)
    {
        // Same instance check already performed...

        if (col1.size() != col2.size())
        {
            return false;
        }

        Map fastLookup = new HashMap();
        for (Object o : col2)
        {
            fastLookup.put(deepHashCode(o), o);
        }

        for (Object o : col1)
        {
            Object other = fastLookup.get(deepHashCode(o));
            if (other == null)
            {   // Item not even found in other Collection, no need to continue.
                return false;
            }

            DualKey dk = new DualKey(o, other);
            if (!visited.contains(dk))
            {   // Place items on 'stack' for further comparison.
                stack.addFirst(dk);
            }
        }
        return true;
    }

    /**
     * Deeply compare two SortedMap instances.  This method walks the Maps in order,
     * taking advantage of the fact that they Maps are SortedMaps.
     * @param map1 SortedMap one
     * @param map2 SortedMap two
     * @param stack add items to compare to the Stack (Stack versus recursion)
     * @param visited Set containing items that have already been compared, to prevent cycles.
     * @return false if the Maps are for certain not equals.  'true' indicates that 'on the surface' the maps
     * are equal, however, it will place the contents of the Maps on the stack for further comparisons.
     */
    private static boolean compareSortedMap(SortedMap map1, SortedMap map2, LinkedList stack, Set visited)
    {
        // Same instance check already performed...

        if (map1.size() != map2.size())
        {
            return false;
        }

        Iterator i1 = map1.entrySet().iterator();
        Iterator i2 = map2.entrySet().iterator();

        while (i1.hasNext())
        {
            Map.Entry entry1 = (Map.Entry)i1.next();
            Map.Entry entry2 = (Map.Entry)i2.next();

            // Must split the Key and Value so that Map.Entry's equals() method is not used.
            DualKey dk = new DualKey(entry1.getKey(), entry2.getKey());
            if (!visited.contains(dk))
            {   // Push Keys for further comparison
                stack.addFirst(dk);
            }

            dk = new DualKey(entry1.getValue(), entry2.getValue());
            if (!visited.contains(dk))
            {   // Push values for further comparison
                stack.addFirst(dk);
            }
        }
        return true;
    }

    /**
     * Deeply compare two Map instances.  After quick short-circuit tests, this method
     * uses a temporary Map so that this method can run in O(N) time.
     * @param map1 Map one
     * @param map2 Map two
     * @param stack add items to compare to the Stack (Stack versus recursion)
     * @param visited Set containing items that have already been compared, to prevent cycles.
     * @return false if the Maps are for certain not equals.  'true' indicates that 'on the surface' the maps
     * are equal, however, it will place the contents of the Maps on the stack for further comparisons.
     */
    private static boolean compareUnorderedMap(Map map1, Map map2, LinkedList stack, Set visited)
    {
        // Same instance check already performed...

        if (map1.size() != map2.size())
        {
            return false;
        }

        Map fastLookup = new HashMap();

        for (Map.Entry entry : (Set<Map.Entry>)map2.entrySet())
        {
            fastLookup.put(deepHashCode(entry.getKey()), entry);
        }

        for (Map.Entry entry : (Set<Map.Entry>)map1.entrySet())
        {
            Map.Entry other = (Map.Entry)fastLookup.get(deepHashCode(entry.getKey()));
            if (other == null)
            {
                return false;
            }

            DualKey dk = new DualKey(entry.getKey(), other.getKey());
            if (!visited.contains(dk))
            {   // Push keys for further comparison
                stack.addFirst(dk);
            }

            dk = new DualKey(entry.getValue(), other.getValue());
            if (!visited.contains(dk))
            {   // Push values for further comparison
                stack.addFirst(dk);
            }
        }

        return true;
    }

    /**
     * Determine if the passed in class has a non-Object.equals() method.  This
     * method caches its results in static ConcurrentHashMap to benefit
     * execution performance.
     * @param c Class to check.
     * @return true, if the passed in Class has a .equals() method somewhere between
     * itself and just below Object in it's inheritance.
     */
    public static boolean hasCustomEquals(Class c)
    {        
        Class origClass = c;
        if (_customEquals.containsKey(c))
        {
            return _customEquals.get(c);
        }

        while (!Object.class.equals(c))
        {
            try
            {
                c.getDeclaredMethod("equals", Object.class);
                _customEquals.put(origClass, true);
                return true;
            }
            catch (Exception ignored) { }
            c = c.getSuperclass();
        }
        _customEquals.put(origClass, false);
        return false;
    }

    /**
     * Get a deterministic hashCode (int) value for an Object, regardless of
     * when it was created or where it was loaded into memory.  The problem
     * with java.lang.Object.hashCode() is that it essentially relies on
     * memory location of an object (what identity it was assigned), whereas
     * this method will produce the same hashCode for any object graph, regardless
     * of how many times it is created.<br/><br/>
     *
     * This method will handle cycles correctly (A->B->C->A).  In this case,
     * Starting with object A, B, or C would yield the same hashCode.  If an
     * object encountered (root, suboject, etc.) has a hashCode() method on it
     * (that is not Object.hashCode()), that hashCode() method will be called
     * and it will stop traversal on that branch.
     * @param obj Object who hashCode is desired.
     * @return the 'deep' hashCode value for the passed in object.
     */
    public static int deepHashCode(Object obj)
    {
        Set visited = new HashSet();
        LinkedList<Object> stack = new LinkedList<Object>();
        stack.addFirst(obj);
        int hash = 0;

        while (!stack.isEmpty())
        {
            obj = stack.removeFirst();
            if (obj == null || visited.contains(obj))
            {
                continue;
            }
            
            visited.add(obj);
            
            if (obj.getClass().isArray())
            {
                int len = Array.getLength(obj);
                for (int i = 0; i < len; i++)
                {        
                    stack.addFirst(Array.get(obj, i));
                }
                continue;
            }
                                    
            if (obj instanceof Collection)
            {      
                stack.addAll(0, (Collection)obj);
                continue;
            }
            
            if (obj instanceof Map)
            {
                stack.addAll(0, ((Map)obj).keySet());
                stack.addAll(0, ((Map)obj).values());
                continue;                
            }
            
            if (hasCustomHashCode(obj.getClass()))
            {   // A real hashCode() method exists, call it.
                hash += obj.hashCode();
                continue;
            }
                        
            Collection<Field> fields = getDeepDeclaredFields(obj.getClass());
            for (Field field : fields)
            {
                try
                {           
                    stack.addFirst(field.get(obj));
                }
                catch (Exception ignored) { }
            }
        }
        return hash;        
    }
        
    /**
     * Determine if the passed in class has a non-Object.hashCode() method.  This
     * method caches its results in static ConcurrentHashMap to benefit
     * execution performance.
     * @param c Class to check.
     * @return true, if the passed in Class has a .hashCode() method somewhere between
     * itself and just below Object in it's inheritance.
     */
    public static boolean hasCustomHashCode(Class c)
    {   
        Class origClass = c;
        if (_customHash.containsKey(c))
        {
            return _customHash.get(c);
        }
        
        while (!Object.class.equals(c))
        {
            try
            {
                c.getDeclaredMethod("hashCode");
                _customHash.put(origClass, true);
                return true;
            }
            catch (Exception ignored) { }
            c = c.getSuperclass();
        }
        _customHash.put(origClass, false);
        return false;
    }
    
    /**
     * Get all non static, non transient, fields of the passed in class.
     * The special this$ field is also not returned.  The result is cached
     * in a static ConcurrentHashMap to benefit execution performance.
     * @param c Class instance
     * @return Collection of only the fields in the passed in class
     * that would need further processing (reference fields).  This
     * makes field traversal on a class faster as it does not need to
     * continually process known fields like primitives.
     */
    public static Collection<Field> getDeepDeclaredFields(Class c)
    {
        if (_reflectedFields.containsKey(c))
        {
            return _reflectedFields.get(c);
        }
        Collection<Field> fields = new ArrayList<Field>();
        Class curr = c;
        
        while (curr != null)
        {
            try 
            {
                Field[] local = curr.getDeclaredFields();

                for (Field field : local)
                {
                    if (!field.isAccessible())
                    {
                        try 
                        {
                            field.setAccessible(true);
                        }
                        catch (Exception ignored) { }
                    }
                    
                    int modifiers = field.getModifiers();
                    if (!Modifier.isStatic(modifiers) && 
                        !field.getName().startsWith("this$") && 
                        !Modifier.isTransient(modifiers))
                    {   // speed up: do not count static fields, not go back up to enclosing object in nested case    
                        fields.add(field);
                    }                                      
                }               
            }
            catch (ThreadDeath t)
            {
                throw t;
            }
            catch (Throwable ignored)
            { }

            curr = curr.getSuperclass();
        }
        _reflectedFields.put(c, fields);
        return fields;
    }            
}