/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */
package javassist.bytecode.analysis;

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

import javassist.CtClass;

MultiType represents an unresolved type. Whenever two Type instances are merged, if they share more than one super type (either an interface or a superclass), then a MultiType is used to represent the possible super types. The goal of a MultiType is to reduce the set of possible types down to a single resolved type. This is done by eliminating non-assignable types from the typeset when the MultiType is passed as an argument to Type.isAssignableFrom(Type), as well as removing non-intersecting types during a merge. Note: Currently the MultiType instance is reused as much as possible so that updates are visible from all frames. In addition, all MultiType merge paths are also updated. This is somewhat hackish, but it appears to handle most scenarios. 
Author:
Jason T. Greene/**
 * MultiType represents an unresolved type. Whenever two {@code Type}
 * instances are merged, if they share more than one super type (either an
 * interface or a superclass), then a {@code MultiType} is used to
 * represent the possible super types. The goal of a {@code MultiType}
 * is to reduce the set of possible types down to a single resolved type. This
 * is done by eliminating non-assignable types from the typeset when the
 * {@code MultiType} is passed as an argument to
 * {@link Type#isAssignableFrom(Type)}, as well as removing non-intersecting
 * types during a merge.
 *
 * Note: Currently the {@code MultiType} instance is reused as much
 * as possible so that updates are visible from all frames. In addition, all
 * {@code MultiType} merge paths are also updated. This is somewhat
 * hackish, but it appears to handle most scenarios.
 *
 * @author Jason T. Greene
 */

/* TODO - A better, but more involved, approach would be to track the instruction
 * offset that resulted in the creation of this type, and
 * whenever the typeset changes, to force a merge on that position. This
 * would require creating a new MultiType instance every time the typeset
 * changes, and somehow communicating assignment changes to the Analyzer
 */
public class MultiType extends Type {
    private Map<String,CtClass> interfaces;
    private Type resolved;
    private Type potentialClass;
    private MultiType mergeSource;
    private boolean changed = false;

    public MultiType(Map<String,CtClass> interfaces) {
        this(interfaces, null);
    }

    public MultiType(Map<String,CtClass> interfaces, Type potentialClass) {
        super(null);
        this.interfaces = interfaces;
        this.potentialClass = potentialClass;
    }

    
Gets the class that corresponds with this type. If this information
is not yet known, java.lang.Object will be returned.
/**
     * Gets the class that corresponds with this type. If this information
     * is not yet known, java.lang.Object will be returned.
     */
    @Override
    public CtClass getCtClass() {
        if (resolved != null)
            return resolved.getCtClass();

        return Type.OBJECT.getCtClass();
    }

    
Always returns null since this type is never used for an array.
/**
     * Always returns null since this type is never used for an array.
     */
    @Override
    public Type getComponent() {
        return null;
    }

    
Always returns 1, since this type is a reference.
/**
     * Always returns 1, since this type is a reference.
     */
    @Override
    public int getSize() {
        return 1;
    }

    
Always reutnrs false since this type is never used for an array
/**
     * Always reutnrs false since this type is never used for an array
     */
    @Override
    public boolean isArray() {
        return false;
    }

    
Returns true if the internal state has changed.
/**
     * Returns true if the internal state has changed.
     */
    @Override
    boolean popChanged() {
        boolean changed = this.changed;
        this.changed = false;
        return changed;
    }

    @Override
    public boolean isAssignableFrom(Type type) {
        throw new UnsupportedOperationException("Not implemented");
    }

    public boolean isAssignableTo(Type type) {
        if (resolved != null)
            return type.isAssignableFrom(resolved);

        if (Type.OBJECT.equals(type))
            return true;

        if (potentialClass != null && !type.isAssignableFrom(potentialClass))
            potentialClass = null;

        Map<String,CtClass> map = mergeMultiAndSingle(this, type);

        if (map.size() == 1 && potentialClass == null) {
            // Update previous merge paths to the same resolved type
            resolved = Type.get(map.values().iterator().next());
            propogateResolved();

            return true;
        }

        // Keep all previous merge paths up to date
        if (map.size() >= 1) {
            interfaces = map;
            propogateState();

            return true;
        }

        if (potentialClass != null) {
            resolved = potentialClass;
            propogateResolved();

            return true;
        }

        return false;
    }

    private void propogateState() {
        MultiType source = mergeSource;
        while (source != null) {
            source.interfaces = interfaces;
            source.potentialClass = potentialClass;
            source = source.mergeSource;
        }
    }

    private void propogateResolved() {
        MultiType source = mergeSource;
        while (source != null) {
            source.resolved = resolved;
            source = source.mergeSource;
        }
    }

    
Always returns true, since this type is always a reference.
Returns:
true/**
     * Always returns true, since this type is always a reference.
     *
     * @return true
     */
    @Override
    public boolean isReference() {
       return true;
    }

    private Map<String,CtClass> getAllMultiInterfaces(MultiType type) {
        Map<String,CtClass> map = new HashMap<String,CtClass>();

        for (CtClass intf:type.interfaces.values()) {
            map.put(intf.getName(), intf);
            getAllInterfaces(intf, map);
        }

        return map;
    }


    private Map<String,CtClass> mergeMultiInterfaces(MultiType type1, MultiType type2) {
        Map<String,CtClass> map1 = getAllMultiInterfaces(type1);
        Map<String,CtClass> map2 = getAllMultiInterfaces(type2);

        return findCommonInterfaces(map1, map2);
    }

    private Map<String,CtClass> mergeMultiAndSingle(MultiType multi, Type single) {
        Map<String,CtClass> map1 = getAllMultiInterfaces(multi);
        Map<String,CtClass> map2 = getAllInterfaces(single.getCtClass(), null);

        return findCommonInterfaces(map1, map2);
    }

    private boolean inMergeSource(MultiType source) {
        while (source != null) {
            if (source == this)
                return true;

            source = source.mergeSource;
        }

        return false;
    }

    @Override
    public Type merge(Type type) {
        if (this == type)
            return this;

        if (type == UNINIT)
            return this;

        if (type == BOGUS)
            return BOGUS;

        if (type == null)
            return this;

        if (resolved != null)
            return resolved.merge(type);

        if (potentialClass != null) {
            Type mergePotential = potentialClass.merge(type);
            if (! mergePotential.equals(potentialClass) || mergePotential.popChanged()) {
                potentialClass = Type.OBJECT.equals(mergePotential) ? null : mergePotential;
                changed = true;
            }
        }

        Map<String,CtClass> merged;

        if (type instanceof MultiType) {
            MultiType multi = (MultiType)type;

            if (multi.resolved != null) {
                merged = mergeMultiAndSingle(this, multi.resolved);
            } else {
                merged = mergeMultiInterfaces(multi, this);
                if (! inMergeSource(multi))
                    mergeSource = multi;
            }
        } else {
            merged = mergeMultiAndSingle(this, type);
        }

        // Keep all previous merge paths up to date
        if (merged.size() > 1 || (merged.size() == 1 && potentialClass != null)) {
            // Check for changes
            if (merged.size() != interfaces.size())
                changed = true;
            else if (changed == false)
                for (String key:merged.keySet())
                    if (!interfaces.containsKey(key))
                        changed = true;


            interfaces = merged;
            propogateState();

            return this;
        }

        if (merged.size() == 1)
            resolved = Type.get(merged.values().iterator().next());
        else if (potentialClass != null)
            resolved = potentialClass;
        else
            resolved = OBJECT;

        propogateResolved();

        return resolved;
    }

    @Override
    public int hashCode() {
        if (resolved != null)
            return resolved.hashCode();

        return interfaces.keySet().hashCode();
    }

    @Override
    public boolean equals(Object o) {
        if (! (o instanceof MultiType))
            return false;

        MultiType multi = (MultiType) o;
        if (resolved != null)
            return resolved.equals(multi.resolved);
        else if (multi.resolved != null)
            return false;

        return interfaces.keySet().equals(multi.interfaces.keySet());
    }

    @Override
    public String toString() {
        if (resolved != null)
            return resolved.toString();

        StringBuffer buffer = new StringBuffer("{");
        for (String key:interfaces.keySet())
            buffer.append(key).append(", ");
        if (potentialClass != null)
            buffer.append("*").append(potentialClass.toString());
        else
            buffer.setLength(buffer.length() - 2);
        buffer.append("}");
        return buffer.toString();
    }
}