/*

 * Copyright (c) 2015, 2016, 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.jvm;

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

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

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

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

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

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

import static com.sun.tools.javac.code.Kinds.Kind.MTH;

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

import static com.sun.tools.javac.jvm.ByteCodes.*;

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

import com.sun.tools.javac.jvm.Items.*;

import java.util.HashMap;

import java.util.Map;

/** This lowers the String concatenation to something that JVM can understand.

 *

 *  <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 abstract class StringConcat {

    /**

     * Maximum number of slots for String Concat call.

     * JDK's StringConcatFactory does not support more than that.

     */

    private static final int MAX_INDY_CONCAT_ARG_SLOTS = 200;

    private static final char TAG_ARG   = '\u0001';

    private static final char TAG_CONST = '\u0002';

    protected final Gen gen;

    protected final Symtab syms;

    protected final Names names;

    protected final TreeMaker make;

    protected final Types types;

    protected final Map<Type, Symbol> sbAppends;

    protected final Resolve rs;

    protected static final Context.Key<StringConcat> concatKey = new Context.Key<>();

    public static StringConcat instance(Context context) {

        StringConcat instance = context.get(concatKey);

        if (instance == null) {

            instance = makeConcat(context);

        }

        return instance;

    }

    private static StringConcat makeConcat(Context context) {

        Target target = Target.instance(context);

        String opt = Options.instance(context).get("stringConcat");

        if (target.hasStringConcatFactory()) {

            if (opt == null) {

                opt = "indyWithConstants";

            }

        } else {

            if (opt != null && !"inline".equals(opt)) {

                Assert.error("StringConcatFactory-based string concat is requested on a platform that does not support it.");

            }

            opt = "inline";

        }

        switch (opt) {

            case "inline":

                return new Inline(context);

            case "indy":

                return new IndyPlain(context);

            case "indyWithConstants":

                return new IndyConstants(context);

            default:

                Assert.error("Unknown stringConcat: " + opt);

                throw new IllegalStateException("Unknown stringConcat: " + opt);

        }

    }

    protected StringConcat(Context context) {

        context.put(concatKey, this);

        gen = Gen.instance(context);

        syms = Symtab.instance(context);

        types = Types.instance(context);

        names = Names.instance(context);

        make = TreeMaker.instance(context);

        rs = Resolve.instance(context);

        sbAppends = new HashMap<>();

    }

    public abstract Item makeConcat(JCTree.JCAssignOp tree);

    public abstract Item makeConcat(JCTree.JCBinary tree);

    protected List<JCTree> collectAll(JCTree tree) {

        return collect(tree, List.nil());

    }

    protected List<JCTree> collectAll(JCTree.JCExpression lhs, JCTree.JCExpression rhs) {

        return List.<JCTree>nil()

                .appendList(collectAll(lhs))

                .appendList(collectAll(rhs));

    }

    private List<JCTree> collect(JCTree tree, List<JCTree> res) {

        tree = TreeInfo.skipParens(tree);

        if (tree.hasTag(PLUS) && tree.type.constValue() == null) {

            JCTree.JCBinary op = (JCTree.JCBinary) tree;

            if (op.operator.kind == MTH && op.operator.opcode == string_add) {

                return res

                        .appendList(collect(op.lhs, res))

                        .appendList(collect(op.rhs, res));

            }

        }

        return res.append(tree);

    }

    /**

     * If the type is not accessible from current context, try to figure out the

     * sharpest accessible supertype.

     *

     * @param originalType type to sharpen

     * @return sharped type

     */

    Type sharpestAccessible(Type originalType) {

        if (originalType.hasTag(ARRAY)) {

            return types.makeArrayType(sharpestAccessible(types.elemtype(originalType)));

        }

        Type type = originalType;

        while (!rs.isAccessible(gen.getAttrEnv(), type.asElement())) {

            type = types.supertype(type);

        }

        return type;

    }

    /**

     * "Legacy" bytecode flavor: emit the StringBuilder.append chains for string

     * concatenation.

     */

    private static class Inline extends StringConcat {

        public Inline(Context context) {

            super(context);

        }

        @Override

        public Item makeConcat(JCTree.JCAssignOp tree) {

            // Generate code to make a string builder

            JCDiagnostic.DiagnosticPosition pos = tree.pos();

            // Create a string builder.

            newStringBuilder(tree);

            // Generate code for first string, possibly save one

            // copy under builder

            Item l = gen.genExpr(tree.lhs, tree.lhs.type);

            if (l.width() > 0) {

                gen.getCode().emitop0(dup_x1 + 3 * (l.width() - 1));

            }

            // Load first string and append to builder.

            l.load();

            appendString(tree.lhs);

            // Append all other strings to builder.

            List<JCTree> args = collectAll(tree.rhs);

            for (JCTree t : args) {

                gen.genExpr(t, t.type).load();

                appendString(t);

            }

            // Convert builder to string.

            builderToString(pos);

            return l;

        }

        @Override

        public Item makeConcat(JCTree.JCBinary tree) {

            JCDiagnostic.DiagnosticPosition pos = tree.pos();

            // Create a string builder.

            newStringBuilder(tree);

            // Append all strings to builder.

            List<JCTree> args = collectAll(tree);

            for (JCTree t : args) {

                gen.genExpr(t, t.type).load();

                appendString(t);

            }

            // Convert builder to string.

            builderToString(pos);

            return gen.getItems().makeStackItem(syms.stringType);

        }

        private JCDiagnostic.DiagnosticPosition newStringBuilder(JCTree tree) {

            JCDiagnostic.DiagnosticPosition pos = tree.pos();

            gen.getCode().emitop2(new_, gen.makeRef(pos, syms.stringBuilderType));

            gen.getCode().emitop0(dup);

            return pos;

        }

        private void appendString(JCTree tree) {

            Type t = tree.type.baseType();

            if (!t.isPrimitive() && t.tsym != syms.stringType.tsym) {

                t = syms.objectType;

            }

            Assert.checkNull(t.constValue());

            Symbol method = sbAppends.get(t);

            if (method == null) {

                method = rs.resolveInternalMethod(tree.pos(), gen.getAttrEnv(), syms.stringBuilderType, names.append, List.of(t), null);

                sbAppends.put(t, method);

            }

            gen.getItems().makeMemberItem(method, false).invoke();

        }

        private void builderToString(JCDiagnostic.DiagnosticPosition pos) {

        }

    }

    /**

     * Base class for indified concatenation bytecode flavors.

     */

    private static abstract class Indy extends StringConcat {

        public Indy(Context context) {

            super(context);

        }

        @Override

        public Item makeConcat(JCTree.JCAssignOp tree) {

            List<JCTree> args = collectAll(tree.lhs, tree.rhs);

            Item l = gen.genExpr(tree.lhs, tree.lhs.type);

            emit(args, tree.type, tree.pos());

            return l;

        }

        @Override

        public Item makeConcat(JCTree.JCBinary tree) {

            List<JCTree> args = collectAll(tree.lhs, tree.rhs);

            emit(args, tree.type, tree.pos());

            return gen.getItems().makeStackItem(syms.stringType);

        }

        protected abstract void emit(List<JCTree> args, Type type, JCDiagnostic.DiagnosticPosition pos);

        /** Peel the argument list into smaller chunks. */

        protected List<List<JCTree>> split(List<JCTree> args) {

            ListBuffer<List<JCTree>> splits = new ListBuffer<>();

            int slots = 0;

            // Need to peel, so that neither call has more than acceptable number

            // of slots for the arguments.

            ListBuffer<JCTree> cArgs = new ListBuffer<>();

            for (JCTree t : args) {

                int needSlots = (t.type.getTag() == LONG || t.type.getTag() == DOUBLE) ? 2 : 1;

                if (slots + needSlots >= MAX_INDY_CONCAT_ARG_SLOTS) {

                    splits.add(cArgs.toList());

                    cArgs.clear();

                    slots = 0;

                }

                cArgs.add(t);

                slots += needSlots;

            }

            // Flush the tail slice

            if (!cArgs.isEmpty()) {

                splits.add(cArgs.toList());

            }

            return splits.toList();

        }

    }

    /**

     * Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory,

     * without handling constants specially.

     *

     * We bypass empty strings, because they have no meaning at this level. This

     * captures the Java language trick to force String concat with e.g. ("" + int)-like

     * expression. Down here, we already know we are in String concat business, and do

     * not require these markers.

     */

    private static class IndyPlain extends Indy {

        public IndyPlain(Context context) {

            super(context);

        }

        /** Emit the indy concat for all these arguments, possibly peeling along the way */

        protected void emit(List<JCTree> args, Type type, JCDiagnostic.DiagnosticPosition pos) {

            List<List<JCTree>> split = split(args);

            for (List<JCTree> t : split) {

                Assert.check(!t.isEmpty(), "Arguments list is empty");

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

                for (JCTree arg : t) {

                    Object constVal = arg.type.constValue();

                    if ("".equals(constVal)) continue;

                    if (arg.type == syms.botType) {

                        dynamicArgs.add(types.boxedClass(syms.voidType).type);

                    } else {

                        dynamicArgs.add(sharpestAccessible(arg.type));

                    }

                    gen.genExpr(arg, arg.type).load();

                }

                doCall(type, pos, dynamicArgs.toList());

            }

            // More that one peel slice produced: concatenate the results

            if (split.size() > 1) {

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

                for (int c = 0; c < split.size(); c++) {

                    argTypes.append(syms.stringType);

                }

                doCall(type, pos, argTypes.toList());

            }

        }

        /** Produce the actual invokedynamic call to StringConcatFactory */

        private void doCall(Type type, JCDiagnostic.DiagnosticPosition pos, List<Type> dynamicArgTypes) {

            Type.MethodType indyType = new Type.MethodType(dynamicArgTypes,

                    type,

                    syms.methodClass);

            int prevPos = make.pos;

            try {

                make.at(pos);

                List<Type> bsm_staticArgs = List.of(syms.methodHandleLookupType,

                        syms.stringType,

                        syms.methodTypeType);

                Symbol bsm = rs.resolveInternalMethod(pos,

                        gen.getAttrEnv(),

                        syms.stringConcatFactory,

                        names.makeConcat,

                        bsm_staticArgs,

                        null);

                Symbol.DynamicMethodSymbol dynSym = new Symbol.DynamicMethodSymbol(names.makeConcat,

                        syms.noSymbol,

                        ClassFile.REF_invokeStatic,

                        (Symbol.MethodSymbol)bsm,

                        indyType,

                        List.nil().toArray());

                Items.Item item = gen.getItems().makeDynamicItem(dynSym);

                item.invoke();

            } finally {

                make.at(prevPos);

            }

        }

    }

    /**

     * Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory.

     * This code concatenates all known constants into the recipe, possibly escaping

     * some constants separately.

     *

     * We also bypass empty strings, because they have no meaning at this level. This

     * captures the Java language trick to force String concat with e.g. ("" + int)-like

     * expression. Down here, we already know we are in String concat business, and do

     * not require these markers.

     */

    private static final class IndyConstants extends Indy {

        public IndyConstants(Context context) {

            super(context);

        }

        @Override

        protected void emit(List<JCTree> args, Type type, JCDiagnostic.DiagnosticPosition pos) {

            List<List<JCTree>> split = split(args);

            for (List<JCTree> t : split) {

                Assert.check(!t.isEmpty(), "Arguments list is empty");

                StringBuilder recipe = new StringBuilder(t.size());

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

                ListBuffer<Object> staticArgs = new ListBuffer<>();

                for (JCTree arg : t) {

                    Object constVal = arg.type.constValue();

                    if ("".equals(constVal)) continue;

                    if (arg.type == syms.botType) {

                        // Concat the null into the recipe right away

                        recipe.append((String) null);

                    } else if (constVal != null) {

                        // Concat the String representation of the constant, except

                        // for the case it contains special tags, which requires us

                        // to expose it as detached constant.

                        String a = arg.type.stringValue();

                        if (a.indexOf(TAG_CONST) != -1 || a.indexOf(TAG_ARG) != -1) {

                            recipe.append(TAG_CONST);

                            staticArgs.add(a);

                        } else {

                            recipe.append(a);

                        }

                    } else {

                        // Ordinary arguments come through the dynamic arguments.

                        recipe.append(TAG_ARG);

                        dynamicArgs.add(sharpestAccessible(arg.type));

                        gen.genExpr(arg, arg.type).load();

                    }

                }

                doCall(type, pos, recipe.toString(), staticArgs.toList(), dynamicArgs.toList());

            }

            // More that one peel slice produced: concatenate the results

            // All arguments are assumed to be non-constant Strings.

            if (split.size() > 1) {

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

                StringBuilder recipe = new StringBuilder();

                for (int c = 0; c < split.size(); c++) {

                    argTypes.append(syms.stringType);

                    recipe.append(TAG_ARG);

                }

                doCall(type, pos, recipe.toString(), List.nil(), argTypes.toList());

            }

        }

        /** Produce the actual invokedynamic call to StringConcatFactory */

        private void doCall(Type type, JCDiagnostic.DiagnosticPosition pos, String recipe, List<Object> staticArgs, List<Type> dynamicArgTypes) {

            Type.MethodType indyType = new Type.MethodType(dynamicArgTypes,

                    type,

                    syms.methodClass);

            int prevPos = make.pos;

            try {

                make.at(pos);

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

                ListBuffer<Object> constants = new ListBuffer<>();

                for (Object t : staticArgs) {

                    constants.add(t);

                    constTypes.add(syms.stringType);

                }

                List<Type> bsm_staticArgs = List.of(syms.methodHandleLookupType,

                        syms.stringType,

                        syms.methodTypeType)

                        .append(syms.stringType)

                        .appendList(constTypes);

                Symbol bsm = rs.resolveInternalMethod(pos,

                        gen.getAttrEnv(),

                        syms.stringConcatFactory,

                        names.makeConcatWithConstants,

                        bsm_staticArgs,

                        null);

                Symbol.DynamicMethodSymbol dynSym = new Symbol.DynamicMethodSymbol(names.makeConcatWithConstants,

                        syms.noSymbol,

                        ClassFile.REF_invokeStatic,

                        (Symbol.MethodSymbol)bsm,

                        indyType,

                        List.<Object>of(recipe).appendList(constants).toArray());

                Items.Item item = gen.getItems().makeDynamicItem(dynSym);

                item.invoke();

            } finally {

                make.at(prevPos);

            }

        }

    }

}