/*

 * Copyright (c) 2012, Oracle and/or its affiliates. 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.  Oracle designates this

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

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.javac.comp;

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

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

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

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

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

import com.sun.tools.javac.comp.Attr.ResultInfo;

import com.sun.tools.javac.comp.Infer.InferenceContext;

import com.sun.tools.javac.comp.Resolve.MethodResolutionPhase;

import com.sun.tools.javac.tree.JCTree.*;

import javax.tools.JavaFileObject;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.Map;

import java.util.Queue;

import java.util.Set;

import java.util.WeakHashMap;

import static com.sun.tools.javac.code.TypeTag.DEFERRED;

import static com.sun.tools.javac.code.TypeTag.NONE;

import static com.sun.tools.javac.tree.JCTree.Tag.*;

/**

 * This is an helper class that is used to perform deferred type-analysis.

 * Each time a poly expression occurs in argument position, javac attributes it

 * with a temporary 'deferred type' that is checked (possibly multiple times)

 * against an expected formal type.

 *

 *  <p><b>This is NOT part of any supported API.

 *  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 DeferredAttr extends JCTree.Visitor {

    protected static final Context.Key<DeferredAttr> deferredAttrKey =

        new Context.Key<DeferredAttr>();

    final Attr attr;

    final Check chk;

    final Enter enter;

    final Infer infer;

    final Log log;

    final Symtab syms;

    final TreeMaker make;

    final Types types;

    public static DeferredAttr instance(Context context) {

        DeferredAttr instance = context.get(deferredAttrKey);

        if (instance == null)

            instance = new DeferredAttr(context);

        return instance;

    }

    protected DeferredAttr(Context context) {

        context.put(deferredAttrKey, this);

        attr = Attr.instance(context);

        chk = Check.instance(context);

        enter = Enter.instance(context);

        infer = Infer.instance(context);

        log = Log.instance(context);

        syms = Symtab.instance(context);

        make = TreeMaker.instance(context);

        types = Types.instance(context);

    }

    /**

     * This type represents a deferred type. A deferred type starts off with

     * no information on the underlying expression type. Such info needs to be

     * discovered through type-checking the deferred type against a target-type.

     * Every deferred type keeps a pointer to the AST node from which it originated.

     */

    public class DeferredType extends Type {

        public JCExpression tree;

        Env<AttrContext> env;

        AttrMode mode;

        SpeculativeCache speculativeCache;

        DeferredType(JCExpression tree, Env<AttrContext> env) {

            super(DEFERRED, null);

            this.tree = tree;

            this.env = env.dup(tree, env.info.dup());

            this.speculativeCache = new SpeculativeCache();

        }

        /**

         * A speculative cache is used to keep track of all overload resolution rounds

         * that triggered speculative attribution on a given deferred type. Each entry

         * stores a pointer to the speculative tree and the resolution phase in which the entry

         * has been added.

         */

        class SpeculativeCache {

            private Map<Symbol, List<Entry>> cache =

                    new WeakHashMap<Symbol, List<Entry>>();

            class Entry {

                JCTree speculativeTree;

                Resolve.MethodResolutionPhase phase;

                public Entry(JCTree speculativeTree, MethodResolutionPhase phase) {

                    this.speculativeTree = speculativeTree;

                    this.phase = phase;

                }

                boolean matches(Resolve.MethodResolutionPhase phase) {

                    return this.phase == phase;

                }

            }

            /**

             * Clone a speculative cache entry as a fresh entry associated

             * with a new method (this maybe required to fixup speculative cache

             * misses after Resolve.access())

             */

            void dupAllTo(Symbol from, Symbol to) {

                Assert.check(cache.get(to) == null);

                List<Entry> entries = cache.get(from);

                if (entries != null) {

                    cache.put(to, entries);

                }

            }

            /**

             * Retrieve a speculative cache entry corresponding to given symbol

             * and resolution phase

             */

            Entry get(Symbol msym, MethodResolutionPhase phase) {

                List<Entry> entries = cache.get(msym);

                if (entries == null) return null;

                for (Entry e : entries) {

                    if (e.matches(phase)) return e;

                }

                return null;

            }

            /**

             * Stores a speculative cache entry corresponding to given symbol

             * and resolution phase

             */

            void put(Symbol msym, JCTree speculativeTree, MethodResolutionPhase phase) {

                List<Entry> entries = cache.get(msym);

                if (entries == null) {

                    entries = List.nil();

                }

                cache.put(msym, entries.prepend(new Entry(speculativeTree, phase)));

            }

        }

        /**

         * Get the type that has been computed during a speculative attribution round

         */

        Type speculativeType(Symbol msym, MethodResolutionPhase phase) {

            SpeculativeCache.Entry e = speculativeCache.get(msym, phase);

            return e != null ? e.speculativeTree.type : Type.noType;

        }

        /**

         * Check a deferred type against a potential target-type. Depending on

         * the current attribution mode, a normal vs. speculative attribution

         * round is performed on the underlying AST node. There can be only one

         * speculative round for a given target method symbol; moreover, a normal

         * attribution round must follow one or more speculative rounds.

         */

        Type check(ResultInfo resultInfo) {

            DeferredAttrContext deferredAttrContext =

                    resultInfo.checkContext.deferredAttrContext();

            Assert.check(deferredAttrContext != emptyDeferredAttrContext);

            List<Type> stuckVars = stuckVars(tree, resultInfo);

            if (stuckVars.nonEmpty()) {

                deferredAttrContext.addDeferredAttrNode(this, resultInfo, stuckVars);

                return Type.noType;

            } else {

                try {

                    switch (deferredAttrContext.mode) {

                        case SPECULATIVE:

                            Assert.check(mode == null ||

                                    (mode == AttrMode.SPECULATIVE &&

                                    speculativeType(deferredAttrContext.msym, deferredAttrContext.phase).hasTag(NONE)));

                            JCTree speculativeTree = attribSpeculative(tree, env, resultInfo);

                            speculativeCache.put(deferredAttrContext.msym, speculativeTree, deferredAttrContext.phase);

                            return speculativeTree.type;

                        case CHECK:

                            Assert.check(mode == AttrMode.SPECULATIVE);

                            return attr.attribTree(tree, env, resultInfo);

                    }

                    Assert.error();

                    return null;

                } finally {

                    mode = deferredAttrContext.mode;

                }

            }

        }

    }

    /**

     * The 'mode' in which the deferred type is to be type-checked

     */

    public enum AttrMode {

        /**

         * A speculative type-checking round is used during overload resolution

         * mainly to generate constraints on inference variables. Side-effects

         * arising from type-checking the expression associated with the deferred

         * type are reversed after the speculative round finishes. This means the

         * expression tree will be left in a blank state.

         */

        SPECULATIVE,

        /**

         * This is the plain type-checking mode. Produces side-effects on the underlying AST node

         */

        CHECK;

    }

    /**

     * Routine that performs speculative type-checking; the input AST node is

     * cloned (to avoid side-effects cause by Attr) and compiler state is

     * restored after type-checking. All diagnostics (but critical ones) are

     * disabled during speculative type-checking.

     */

    JCTree attribSpeculative(JCTree tree, Env<AttrContext> env, ResultInfo resultInfo) {

        JCTree newTree = new TreeCopier<Object>(make).copy(tree);

        Env<AttrContext> speculativeEnv = env.dup(newTree, env.info.dup(env.info.scope.dupUnshared()));

        speculativeEnv.info.scope.owner = env.info.scope.owner;

        final JavaFileObject currentSource = log.currentSourceFile();

        try {

            attr.attribTree(newTree, speculativeEnv, resultInfo);

            unenterScanner.scan(newTree);

            return newTree;

        } catch (Abort ex) {

            //if some very bad condition occurred during deferred attribution

            //we should dump all errors before killing javac

            throw ex;

        } finally {

            unenterScanner.scan(newTree);

        }

    }

    //where

        protected TreeScanner unenterScanner = new TreeScanner() {

            @Override

            public void visitClassDef(JCClassDecl tree) {

                ClassSymbol csym = tree.sym;

                enter.typeEnvs.remove(csym);

                chk.compiled.remove(csym.flatname);

                syms.classes.remove(csym.flatname);

                super.visitClassDef(tree);

            }

        };

    /**

     * A deferred context is created on each method check. A deferred context is

     * used to keep track of information associated with the method check, such as

     * the symbol of the method being checked, the overload resolution phase,

     * the kind of attribution mode to be applied to deferred types and so forth.

     * As deferred types are processed (by the method check routine) stuck AST nodes

     * are added (as new deferred attribution nodes) to this context. The complete()

     * routine makes sure that all pending nodes are properly processed, by

     * progressively instantiating all inference variables on which one or more

     * deferred attribution node is stuck.

     */

    class DeferredAttrContext {

        /** attribution mode */

        final AttrMode mode;

        /** symbol of the method being checked */

        final Symbol msym;

        /** method resolution step */

        final Resolve.MethodResolutionPhase phase;

        /** inference context */

        final InferenceContext inferenceContext;

        /** list of deferred attribution nodes to be processed */

        ArrayList<DeferredAttrNode> deferredAttrNodes = new ArrayList<DeferredAttrNode>();

        DeferredAttrContext(AttrMode mode, Symbol msym, MethodResolutionPhase phase, InferenceContext inferenceContext) {

            this.mode = mode;

            this.msym = msym;

            this.phase = phase;

            this.inferenceContext = inferenceContext;

        }

        /**

         * Adds a node to the list of deferred attribution nodes - used by Resolve.rawCheckArgumentsApplicable

         * Nodes added this way act as 'roots' for the out-of-order method checking process.

         */

        void addDeferredAttrNode(final DeferredType dt, ResultInfo resultInfo, List<Type> stuckVars) {

            deferredAttrNodes.add(new DeferredAttrNode(dt, resultInfo, stuckVars));

        }

        /**

         * Incrementally process all nodes, by skipping 'stuck' nodes and attributing

         * 'unstuck' ones. If at any point no progress can be made (no 'unstuck' nodes)

         * some inference variable might get eagerly instantiated so that all nodes

         * can be type-checked.

         */

        void complete() {

            while (!deferredAttrNodes.isEmpty()) {

                Set<Type> stuckVars = new HashSet<Type>();

                boolean progress = false;

                //scan a defensive copy of the node list - this is because a deferred

                //attribution round can add new nodes to the list

                for (DeferredAttrNode deferredAttrNode : List.from(deferredAttrNodes)) {

                    if (!deferredAttrNode.isStuck()) {

                        deferredAttrNode.process();

                        deferredAttrNodes.remove(deferredAttrNode);

                        progress = true;

                    } else {

                        stuckVars.addAll(deferredAttrNode.stuckVars);

                    }

                }

                if (!progress) {

                    //remove all variables that have already been instantiated

                    //from the list of stuck variables

                    inferenceContext.solveAny(inferenceContext.freeVarsIn(List.from(stuckVars)), types, infer);

                    inferenceContext.notifyChange(types);

                }

            }

        }

        /**

         * Class representing a deferred attribution node. It keeps track of

         * a deferred type, along with the expected target type information.

         */

        class DeferredAttrNode implements Infer.InferenceContext.FreeTypeListener {

            /** underlying deferred type */

            DeferredType dt;

            /** underlying target type information */

            ResultInfo resultInfo;

            /** list of uninferred inference variables causing this node to be stuck */

            List<Type> stuckVars;

            DeferredAttrNode(DeferredType dt, ResultInfo resultInfo, List<Type> stuckVars) {

                this.dt = dt;

                this.resultInfo = resultInfo;

                this.stuckVars = stuckVars;

                if (!stuckVars.isEmpty()) {

                    resultInfo.checkContext.inferenceContext().addFreeTypeListener(stuckVars, this);

                }

            }

            @Override

            public void typesInferred(InferenceContext inferenceContext) {

                stuckVars = List.nil();

                resultInfo = resultInfo.dup(inferenceContext.asInstType(resultInfo.pt, types));

            }

            /**

             * is this node stuck?

             */

            boolean isStuck() {

                return stuckVars.nonEmpty();

            }

            /**

             * Process a deferred attribution node.

             * Invariant: a stuck node cannot be processed.

             */

            void process() {

                if (isStuck()) {

                    throw new IllegalStateException("Cannot process a stuck deferred node");

                }

                dt.check(resultInfo);

            }

        }

    }

    /** an empty deferred attribution context - all methods throw exceptions */

    final DeferredAttrContext emptyDeferredAttrContext =

            new DeferredAttrContext(null, null, null, null) {

                @Override

                void addDeferredAttrNode(DeferredType dt, ResultInfo ri, List<Type> stuckVars) {

                    Assert.error("Empty deferred context!");

                }

                @Override

                void complete() {

                    Assert.error("Empty deferred context!");

                }

            };

    /**

     * Map a list of types possibly containing one or more deferred types

     * into a list of ordinary types. Each deferred type D is mapped into a type T,

     * where T is computed by retrieving the type that has already been

     * computed for D during a previous deferred attribution round of the given kind.

     */

    class DeferredTypeMap extends Type.Mapping {

        DeferredAttrContext deferredAttrContext;

        protected DeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {

            super(String.format("deferredTypeMap[%s]", mode));

            this.deferredAttrContext = new DeferredAttrContext(mode, msym, phase, infer.emptyContext);

        }

        protected boolean validState(DeferredType dt) {

            return dt.mode != null &&

                    deferredAttrContext.mode.ordinal() <= dt.mode.ordinal();

        }

        @Override

        public Type apply(Type t) {

            if (!t.hasTag(DEFERRED)) {

                return t.map(this);

            } else {

                DeferredType dt = (DeferredType)t;

                Assert.check(validState(dt));

                return typeOf(dt);

            }

        }

        protected Type typeOf(DeferredType dt) {

            switch (deferredAttrContext.mode) {

                case CHECK:

                    return dt.tree.type == null ? Type.noType : dt.tree.type;

                case SPECULATIVE:

                    return dt.speculativeType(deferredAttrContext.msym, deferredAttrContext.phase);

            }

            Assert.error();

            return null;

        }

    }

    /**

     * Specialized recovery deferred mapping.

     * Each deferred type D is mapped into a type T, where T is computed either by

     * (i) retrieving the type that has already been computed for D during a previous

     * attribution round (as before), or (ii) by synthesizing a new type R for D

     * (the latter step is useful in a recovery scenario).

     */

    public class RecoveryDeferredTypeMap extends DeferredTypeMap {

        public RecoveryDeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {

            super(mode, msym, phase);

        }

        @Override

        protected Type typeOf(DeferredType dt) {

            Type owntype = super.typeOf(dt);

            return owntype.hasTag(NONE) ?

                        recover(dt) : owntype;

        }

        @Override

        protected boolean validState(DeferredType dt) {

            return true;

        }

        /**

         * Synthesize a type for a deferred type that hasn't been previously

         * reduced to an ordinary type. Functional deferred types and conditionals

         * are mapped to themselves, in order to have a richer diagnostic

         * representation. Remaining deferred types are attributed using

         * a default expected type (j.l.Object).

         */

        private Type recover(DeferredType dt) {

            dt.check(attr.new RecoveryInfo(deferredAttrContext));

            switch (TreeInfo.skipParens(dt.tree).getTag()) {

                case LAMBDA:

                case REFERENCE:

                case CONDEXPR:

                    //propagate those deferred types to the

                    //diagnostic formatter

                    return dt;

                default:

                    return super.apply(dt);

            }

        }

    }

    /**

     * Retrieves the list of inference variables that need to be inferred before

     * an AST node can be type-checked

     */

    @SuppressWarnings("fallthrough")

    List<Type> stuckVars(JCTree tree, ResultInfo resultInfo) {

        if (resultInfo.pt.hasTag(NONE) || resultInfo.pt.isErroneous()) {

            return List.nil();

        } else {

            StuckChecker sc = new StuckChecker(resultInfo);

            sc.scan(tree);

            return List.from(sc.stuckVars);

        }

    }

    /**