/*

 * Copyright 1999-2008 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package com.sun.tools.javac.comp;

import com.sun.tools.javac.util.*;

import com.sun.tools.javac.util.List;

import com.sun.tools.javac.code.*;

import com.sun.tools.javac.code.Type.*;

import com.sun.tools.javac.util.JCDiagnostic;

import static com.sun.tools.javac.code.TypeTags.*;

/** Helper class for type parameter inference, used by the attribution phase.

 *

 *  <p><b>This is NOT part of any API supported by Sun Microsystems.  If

 *  you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class Infer {

    protected static final Context.Key<Infer> inferKey =

        new Context.Key<Infer>();

    /** A value for prototypes that admit any type, including polymorphic ones. */

    public static final Type anyPoly = new Type(NONE, null);

    Symtab syms;

    Types types;

    JCDiagnostic.Factory diags;

    public static Infer instance(Context context) {

        Infer instance = context.get(inferKey);

        if (instance == null)

            instance = new Infer(context);

        return instance;

    }

    protected Infer(Context context) {

        context.put(inferKey, this);

        syms = Symtab.instance(context);

        types = Types.instance(context);

        diags = JCDiagnostic.Factory.instance(context);

        ambiguousNoInstanceException =

            new NoInstanceException(true, diags);

        unambiguousNoInstanceException =

            new NoInstanceException(false, diags);

    }

    public static class NoInstanceException extends RuntimeException {

        private static final long serialVersionUID = 0;

        boolean isAmbiguous; // exist several incomparable best instances?

        JCDiagnostic diagnostic;

        JCDiagnostic.Factory diags;

        NoInstanceException(boolean isAmbiguous, JCDiagnostic.Factory diags) {

            this.diagnostic = null;

            this.isAmbiguous = isAmbiguous;

            this.diags = diags;

        }

        NoInstanceException setMessage(String key) {

            this.diagnostic = diags.fragment(key);

            return this;

        }

        NoInstanceException setMessage(String key, Object arg1) {

            this.diagnostic = diags.fragment(key, arg1);

            return this;

        }

        NoInstanceException setMessage(String key, Object arg1, Object arg2) {

            this.diagnostic = diags.fragment(key, arg1, arg2);

            return this;

        }

        NoInstanceException setMessage(String key, Object arg1, Object arg2, Object arg3) {

            this.diagnostic = diags.fragment(key, arg1, arg2, arg3);

            return this;

        }

        public JCDiagnostic getDiagnostic() {

            return diagnostic;

        }

    }

    private final NoInstanceException ambiguousNoInstanceException;

    private final NoInstanceException unambiguousNoInstanceException;

/***************************************************************************

 * Auxiliary type values and classes

 ***************************************************************************/

    /** A mapping that turns type variables into undetermined type variables.

     */

    Mapping fromTypeVarFun = new Mapping("fromTypeVarFun") {

            public Type apply(Type t) {

                if (t.tag == TYPEVAR) return new UndetVar(t);

                else return t.map(this);

            }

        };

    /** A mapping that returns its type argument with every UndetVar replaced

     *  by its `inst' field. Throws a NoInstanceException

     *  if this not possible because an `inst' field is null.

     */

    Mapping getInstFun = new Mapping("getInstFun") {

            public Type apply(Type t) {

                switch (t.tag) {

                case UNKNOWN:

                    throw ambiguousNoInstanceException

                        .setMessage("undetermined.type");

                case UNDETVAR:

                    UndetVar that = (UndetVar) t;

                    if (that.inst == null)

                        throw ambiguousNoInstanceException

                            .setMessage("type.variable.has.undetermined.type",

                                        that.qtype);

                    return apply(that.inst);

                default:

                    return t.map(this);

                }

            }

        };

/***************************************************************************

 * Mini/Maximization of UndetVars

 ***************************************************************************/

    /** Instantiate undetermined type variable to its minimal upper bound.

     *  Throw a NoInstanceException if this not possible.

     */

    void maximizeInst(UndetVar that, Warner warn) throws NoInstanceException {

        if (that.inst == null) {

            if (that.hibounds.isEmpty())

                that.inst = syms.objectType;

            else if (that.hibounds.tail.isEmpty())

                that.inst = that.hibounds.head;

            else {

                for (List<Type> bs = that.hibounds;

                     bs.nonEmpty() && that.inst == null;

                     bs = bs.tail) {

                    // System.out.println("hibounds = " + that.hibounds);//DEBUG

                    if (isSubClass(bs.head, that.hibounds))

                        that.inst = types.fromUnknownFun.apply(bs.head);

                }

                if (that.inst == null) {

                    int classCount = 0, interfaceCount = 0;

                    for (Type t : that.hibounds) {

                        if (t.tag == CLASS) {

                            if (t.isInterface())

                                interfaceCount++;

                            else

                                classCount++;

                        }

                    }

                    if ((that.hibounds.size() == classCount + interfaceCount) && classCount == 1)

                        that.inst = types.makeCompoundType(that.hibounds);

                }

                if (that.inst == null || !types.isSubtypeUnchecked(that.inst, that.hibounds, warn))

                    throw ambiguousNoInstanceException

                        .setMessage("no.unique.maximal.instance.exists",

                                    that.qtype, that.hibounds);

            }

        }

    }

    //where

        private boolean isSubClass(Type t, final List<Type> ts) {

            t = t.baseType();

            if (t.tag == TYPEVAR) {

                List<Type> bounds = types.getBounds((TypeVar)t);

                for (Type s : ts) {

                    if (!types.isSameType(t, s.baseType())) {

                        for (Type bound : bounds) {

                            if (!isSubClass(bound, List.of(s.baseType())))

                                return false;

                        }

                    }

                }

            } else {

                for (Type s : ts) {

                    if (!t.tsym.isSubClass(s.baseType().tsym, types))

                        return false;

                }

            }

            return true;

        }

    /** Instaniate undetermined type variable to the lub of all its lower bounds.

     *  Throw a NoInstanceException if this not possible.

     */

    void minimizeInst(UndetVar that, Warner warn) throws NoInstanceException {

        if (that.inst == null) {

            if (that.lobounds.isEmpty())

                that.inst = syms.botType;

            else if (that.lobounds.tail.isEmpty())

                that.inst = that.lobounds.head.isPrimitive() ? syms.errType : that.lobounds.head;

            else {

                that.inst = types.lub(that.lobounds);

            }

            if (that.inst == null || that.inst == syms.errType)

                    throw ambiguousNoInstanceException

                        .setMessage("no.unique.minimal.instance.exists",

                                    that.qtype, that.lobounds);

            // VGJ: sort of inlined maximizeInst() below.  Adding

            // bounds can cause lobounds that are above hibounds.

            if (that.hibounds.isEmpty())

                return;

            Type hb = null;

            if (that.hibounds.tail.isEmpty())

                hb = that.hibounds.head;

            else for (List<Type> bs = that.hibounds;

                      bs.nonEmpty() && hb == null;

                      bs = bs.tail) {

                if (isSubClass(bs.head, that.hibounds))

                    hb = types.fromUnknownFun.apply(bs.head);

            }

            if (hb == null ||

                !types.isSubtypeUnchecked(hb, that.hibounds, warn) ||

                !types.isSubtypeUnchecked(that.inst, hb, warn))

                throw ambiguousNoInstanceException;

        }

    }

/***************************************************************************

 * Exported Methods

 ***************************************************************************/

    /** Try to instantiate expression type `that' to given type `to'.

     *  If a maximal instantiation exists which makes this type

     *  a subtype of type `to', return the instantiated type.

     *  If no instantiation exists, or if several incomparable

     *  best instantiations exist throw a NoInstanceException.

     */

    public Type instantiateExpr(ForAll that,

                                Type to,

                                Warner warn) throws NoInstanceException {

        List<Type> undetvars = Type.map(that.tvars, fromTypeVarFun);

        for (List<Type> l = undetvars; l.nonEmpty(); l = l.tail) {

            UndetVar v = (UndetVar) l.head;

            ListBuffer<Type> hibounds = new ListBuffer<Type>();

            for (List<Type> l1 = types.getBounds((TypeVar) v.qtype); l1.nonEmpty(); l1 = l1.tail) {

                if (!l1.head.containsSome(that.tvars)) {

                    hibounds.append(l1.head);

                }

            }

            v.hibounds = hibounds.toList();

        }

        Type qtype1 = types.subst(that.qtype, that.tvars, undetvars);

        if (!types.isSubtype(qtype1, to)) {

            throw unambiguousNoInstanceException

                .setMessage("no.conforming.instance.exists",

                            that.tvars, that.qtype, to);

        }

        for (List<Type> l = undetvars; l.nonEmpty(); l = l.tail)

            maximizeInst((UndetVar) l.head, warn);

        // System.out.println(" = " + qtype1.map(getInstFun));//DEBUG

        // check bounds

        List<Type> targs = Type.map(undetvars, getInstFun);

        targs = types.subst(targs, that.tvars, targs);

        checkWithinBounds(that.tvars, targs, warn);

        return getInstFun.apply(qtype1);

    }

    /** Instantiate method type `mt' by finding instantiations of

     *  `tvars' so that method can be applied to `argtypes'.

     */

    public Type instantiateMethod(List<Type> tvars,

                                  MethodType mt,

                                  List<Type> argtypes,

                                  boolean allowBoxing,

                                  boolean useVarargs,

                                  Warner warn) throws NoInstanceException {

        //-System.err.println("instantiateMethod(" + tvars + ", " + mt + ", " + argtypes + ")"); //DEBUG

        List<Type> undetvars = Type.map(tvars, fromTypeVarFun);

        List<Type> formals = mt.argtypes;

        // instantiate all polymorphic argument types and

        // set up lower bounds constraints for undetvars

        Type varargsFormal = useVarargs ? formals.last() : null;

        while (argtypes.nonEmpty() && formals.head != varargsFormal) {

            Type ft = formals.head;

            Type at = argtypes.head.baseType();

            if (at.tag == FORALL)

                at = instantiateArg((ForAll) at, ft, tvars, warn);

            Type sft = types.subst(ft, tvars, undetvars);

            boolean works = allowBoxing

                ? types.isConvertible(at, sft, warn)

                : types.isSubtypeUnchecked(at, sft, warn);

            if (!works) {

                throw unambiguousNoInstanceException

                    .setMessage("no.conforming.assignment.exists",

                                tvars, at, ft);

            }

            formals = formals.tail;

            argtypes = argtypes.tail;

        }

        if (formals.head != varargsFormal || // not enough args

            !useVarargs && argtypes.nonEmpty()) { // too many args

            // argument lists differ in length

            throw unambiguousNoInstanceException

                .setMessage("arg.length.mismatch");

        }

        // for varargs arguments as well

        if (useVarargs) {

            Type elt = types.elemtype(varargsFormal);

            Type sft = types.subst(elt, tvars, undetvars);

            while (argtypes.nonEmpty()) {

                Type ft = sft;

                Type at = argtypes.head.baseType();

                if (at.tag == FORALL)

                    at = instantiateArg((ForAll) at, ft, tvars, warn);

                boolean works = types.isConvertible(at, sft, warn);

                if (!works) {

                    throw unambiguousNoInstanceException

                        .setMessage("no.conforming.assignment.exists",

                                    tvars, at, ft);

                }

                argtypes = argtypes.tail;

            }

        }

        // minimize as yet undetermined type variables

        for (Type t : undetvars)

            minimizeInst((UndetVar) t, warn);

        /** Type variables instantiated to bottom */

        ListBuffer<Type> restvars = new ListBuffer<Type>();

        /** Instantiated types or TypeVars if under-constrained */

        ListBuffer<Type> insttypes = new ListBuffer<Type>();

        /** Instantiated types or UndetVars if under-constrained */

        ListBuffer<Type> undettypes = new ListBuffer<Type>();

        for (Type t : undetvars) {

            UndetVar uv = (UndetVar)t;

            if (uv.inst.tag == BOT) {

                restvars.append(uv.qtype);

                insttypes.append(uv.qtype);

                undettypes.append(uv);

                uv.inst = null;

            } else {

                insttypes.append(uv.inst);

                undettypes.append(uv.inst);

            }

        }

        checkWithinBounds(tvars, undettypes.toList(), warn);

        if (!restvars.isEmpty()) {

            // if there are uninstantiated variables,

            // quantify result type with them

            mt = new MethodType(mt.argtypes,

                                new ForAll(restvars.toList(), mt.restype),

                                mt.thrown, syms.methodClass);

        }

        // return instantiated version of method type

        return types.subst(mt, tvars, insttypes.toList());

    }

    //where

        /** Try to instantiate argument type `that' to given type `to'.

         *  If this fails, try to insantiate `that' to `to' where

         *  every occurrence of a type variable in `tvars' is replaced

         *  by an unknown type.

         */

        private Type instantiateArg(ForAll that,

                                    Type to,

                                    List<Type> tvars,

                                    Warner warn) throws NoInstanceException {

            List<Type> targs;

            try {

                return instantiateExpr(that, to, warn);

            } catch (NoInstanceException ex) {

                Type to1 = to;

                for (List<Type> l = tvars; l.nonEmpty(); l = l.tail)

                    to1 = types.subst(to1, List.of(l.head), List.of(syms.unknownType));

                return instantiateExpr(that, to1, warn);

            }

        }

    /** check that type parameters are within their bounds.

     */

    private void checkWithinBounds(List<Type> tvars,

                                   List<Type> arguments,

                                   Warner warn)

        throws NoInstanceException {

        for (List<Type> tvs = tvars, args = arguments;

             tvs.nonEmpty();

             tvs = tvs.tail, args = args.tail) {

            if (args.head instanceof UndetVar) continue;

            List<Type> bounds = types.subst(types.getBounds((TypeVar)tvs.head), tvars, arguments);

            if (!types.isSubtypeUnchecked(args.head, bounds, warn))

                throw unambiguousNoInstanceException

                    .setMessage("inferred.do.not.conform.to.bounds",

                                arguments, tvars);

        }

    }

}