/*

 * Copyright (c) 2011, 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

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 */

package java.lang.invoke;

import java.lang.annotation.*;

import java.lang.reflect.Method;

import java.util.Map;

import java.util.List;

import java.util.Arrays;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.concurrent.ConcurrentHashMap;

import sun.invoke.util.Wrapper;

import static java.lang.invoke.MethodHandleStatics.*;

import static java.lang.invoke.MethodHandleNatives.Constants.*;

import java.lang.reflect.Field;

import java.util.Objects;

/**

 * The symbolic, non-executable form of a method handle's invocation semantics.

 * It consists of a series of names.

 * The first N (N=arity) names are parameters,

 * while any remaining names are temporary values.

 * Each temporary specifies the application of a function to some arguments.

 * The functions are method handles, while the arguments are mixes of

 * constant values and local names.

 * The result of the lambda is defined as one of the names, often the last one.

 * <p>

 * Here is an approximate grammar:

 * <pre>

 * LambdaForm = "(" ArgName* ")=>{" TempName* Result "}"

 * ArgName = "a" N ":" T

 * TempName = "t" N ":" T "=" Function "(" Argument* ");"

 * Function = ConstantValue

 * Argument = NameRef | ConstantValue

 * Result = NameRef | "void"

 * NameRef = "a" N | "t" N

 * N = (any whole number)

 * T = "L" | "I" | "J" | "F" | "D" | "V"

 * </pre>

 * Names are numbered consecutively from left to right starting at zero.

 * (The letters are merely a taste of syntax sugar.)

 * Thus, the first temporary (if any) is always numbered N (where N=arity).

 * Every occurrence of a name reference in an argument list must refer to

 * a name previously defined within the same lambda.

 * A lambda has a void result if and only if its result index is -1.

 * If a temporary has the type "V", it cannot be the subject of a NameRef,

 * even though possesses a number.

 * Note that all reference types are erased to "L", which stands for {@code Object).

 * All subword types (boolean, byte, short, char) are erased to "I" which is {@code int}.

 * The other types stand for the usual primitive types.

 * <p>

 * Function invocation closely follows the static rules of the Java verifier.

 * Arguments and return values must exactly match when their "Name" types are

 * considered.

 * Conversions are allowed only if they do not change the erased type.

 * <ul>

 * <li>L = Object: casts are used freely to convert into and out of reference types

 * <li>I = int: subword types are forcibly narrowed when passed as arguments (see {@code explicitCastArguments})

 * <li>J = long: no implicit conversions

 * <li>F = float: no implicit conversions

 * <li>D = double: no implicit conversions

 * <li>V = void: a function result may be void if and only if its Name is of type "V"

 * </ul>

 * Although implicit conversions are not allowed, explicit ones can easily be

 * encoded by using temporary expressions which call type-transformed identity functions.

 * <p>

 * Examples:

 * <pre>

 * (a0:J)=>{ a0 }

 *     == identity(long)

 * (a0:I)=>{ t1:V = System.out#println(a0); void }

 *     == System.out#println(int)

 * (a0:L)=>{ t1:V = System.out#println(a0); a0 }

 *     == identity, with printing side-effect

 * (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0);

 *                 t3:L = BoundMethodHandle#target(a0);

 *                 t4:L = MethodHandle#invoke(t3, t2, a1); t4 }

 *     == general invoker for unary insertArgument combination

 * (a0:L, a1:L)=>{ t2:L = FilterMethodHandle#filter(a0);

 *                 t3:L = MethodHandle#invoke(t2, a1);

 *                 t4:L = FilterMethodHandle#target(a0);

 *                 t5:L = MethodHandle#invoke(t4, t3); t5 }

 *     == general invoker for unary filterArgument combination

 * (a0:L, a1:L)=>{ ...(same as previous example)...

 *                 t5:L = MethodHandle#invoke(t4, t3, a1); t5 }

 *     == general invoker for unary/unary foldArgument combination

 * (a0:L, a1:I)=>{ t2:I = identity(long).asType((int)->long)(a1); t2 }

 *     == invoker for identity method handle which performs i2l

 * (a0:L, a1:L)=>{ t2:L = BoundMethodHandle#argument(a0);

 *                 t3:L = Class#cast(t2,a1); t3 }

 *     == invoker for identity method handle which performs cast

 * </pre>

 * <p>

 * @author John Rose, JSR 292 EG

 */

class LambdaForm {

    final int arity;

    final int result;

    final Name[] names;

    final String debugName;

    MemberName vmentry;   // low-level behavior, or null if not yet prepared

    private boolean isCompiled;

    // Caches for common structural transforms:

    LambdaForm[] bindCache;

    public static final int VOID_RESULT = -1, LAST_RESULT = -2;

    LambdaForm(String debugName,

               int arity, Name[] names, int result) {

        assert(namesOK(arity, names));

        this.arity = arity;

        this.result = fixResult(result, names);

        this.names = names.clone();

        this.debugName = debugName;

        normalize();

    }

    LambdaForm(String debugName,

               int arity, Name[] names) {

        this(debugName,

             arity, names, LAST_RESULT);

    }

    LambdaForm(String debugName,

               Name[] formals, Name[] temps, Name result) {

        this(debugName,

             formals.length, buildNames(formals, temps, result), LAST_RESULT);

    }

    private static Name[] buildNames(Name[] formals, Name[] temps, Name result) {

        int arity = formals.length;

        int length = arity + temps.length + (result == null ? 0 : 1);

        Name[] names = Arrays.copyOf(formals, length);

        System.arraycopy(temps, 0, names, arity, temps.length);

        if (result != null)

            names[length - 1] = result;

        return names;

    }

    private LambdaForm(String sig) {

        // Make a blank lambda form, which returns a constant zero or null.

        // It is used as a template for managing the invocation of similar forms that are non-empty.

        // Called only from getPreparedForm.

        assert(isValidSignature(sig));

        this.arity = signatureArity(sig);

        this.result = (signatureReturn(sig) == 'V' ? -1 : arity);

        this.names = buildEmptyNames(arity, sig);

        this.debugName = "LF.zero";

        assert(nameRefsAreLegal());

        assert(isEmpty());

        assert(sig.equals(basicTypeSignature()));

    }

    private static Name[] buildEmptyNames(int arity, String basicTypeSignature) {

        assert(isValidSignature(basicTypeSignature));

        int resultPos = arity + 1;  // skip '_'

        if (arity < 0 || basicTypeSignature.length() != resultPos+1)

            throw new IllegalArgumentException("bad arity for "+basicTypeSignature);

        int numRes = (basicTypeSignature.charAt(resultPos) == 'V' ? 0 : 1);

        Name[] names = arguments(numRes, basicTypeSignature.substring(0, arity));

        for (int i = 0; i < numRes; i++) {

            names[arity + i] = constantZero(arity + i, basicTypeSignature.charAt(resultPos + i));

        }

        return names;

    }

    private static int fixResult(int result, Name[] names) {

        if (result >= 0) {

            if (names[result].type == 'V')

                return -1;

        } else if (result == LAST_RESULT) {

            return names.length - 1;

        }

        return result;

    }

    private static boolean namesOK(int arity, Name[] names) {

        for (int i = 0; i < names.length; i++) {

            Name n = names[i];

            assert(n != null) : "n is null";

            if (i < arity)

                assert( n.isParam()) : n + " is not param at " + i;

            else

                assert(!n.isParam()) : n + " is param at " + i;

        }

        return true;

    }

    /** Renumber and/or replace params so that they are interned and canonically numbered. */

    private void normalize() {

        Name[] oldNames = null;

        int changesStart = 0;

        for (int i = 0; i < names.length; i++) {

            Name n = names[i];

            if (!n.initIndex(i)) {

                if (oldNames == null) {

                    oldNames = names.clone();

                    changesStart = i;

                }

                names[i] = n.cloneWithIndex(i);

            }

        }

        if (oldNames != null) {

            int startFixing = arity;

            if (startFixing <= changesStart)

                startFixing = changesStart+1;

            for (int i = startFixing; i < names.length; i++) {

                Name fixed = names[i].replaceNames(oldNames, names, changesStart, i);

                names[i] = fixed.newIndex(i);

            }

        }

        assert(nameRefsAreLegal());

        int maxInterned = Math.min(arity, INTERNED_ARGUMENT_LIMIT);

        boolean needIntern = false;

        for (int i = 0; i < maxInterned; i++) {

            Name n = names[i], n2 = internArgument(n);

            if (n != n2) {

                names[i] = n2;

                needIntern = true;

            }

        }

        if (needIntern) {

            for (int i = arity; i < names.length; i++) {

                names[i].internArguments();

            }

            assert(nameRefsAreLegal());

        }

    }

    /**

     * Check that all embedded Name references are localizable to this lambda,

     * and are properly ordered after their corresponding definitions.

     * <p>

     * Note that a Name can be local to multiple lambdas, as long as

     * it possesses the same index in each use site.

     * This allows Name references to be freely reused to construct

     * fresh lambdas, without confusion.

     */

    private boolean nameRefsAreLegal() {

        assert(arity >= 0 && arity <= names.length);

        assert(result >= -1 && result < names.length);

        // Do all names possess an index consistent with their local definition order?

        for (int i = 0; i < arity; i++) {

            Name n = names[i];

            assert(n.index() == i) : Arrays.asList(n.index(), i);

            assert(n.isParam());

        }

        // Also, do all local name references

        for (int i = arity; i < names.length; i++) {

            Name n = names[i];

            assert(n.index() == i);

            for (Object arg : n.arguments) {

                if (arg instanceof Name) {

                    Name n2 = (Name) arg;

                    int i2 = n2.index;

                    assert(0 <= i2 && i2 < names.length) : n.debugString() + ": 0 <= i2 && i2 < names.length: 0 <= " + i2 + " < " + names.length;

                    assert(names[i2] == n2) : Arrays.asList("-1-", i, "-2-", n.debugString(), "-3-", i2, "-4-", n2.debugString(), "-5-", names[i2].debugString(), "-6-", this);

                    assert(i2 < i);  // ref must come after def!

                }

            }

        }

        return true;

    }

    /** Invoke this form on the given arguments. */

    // final Object invoke(Object... args) throws Throwable {

    //     // NYI: fit this into the fast path?

    //     return interpretWithArguments(args);

    // }

    /** Report the return type. */

    char returnType() {

        if (result < 0)  return 'V';

        Name n = names[result];

        return n.type;

    }

    /** Report the N-th argument type. */

    char parameterType(int n) {

        assert(n < arity);

        return names[n].type;

    }

    /** Report the arity. */

    int arity() {

        return arity;

    }

    /** Return the method type corresponding to my basic type signature. */

    MethodType methodType() {

        return signatureType(basicTypeSignature());

    }

    /** Return ABC_Z, where the ABC are parameter type characters, and Z is the return type character. */

    final String basicTypeSignature() {

        StringBuilder buf = new StringBuilder(arity() + 3);

        for (int i = 0, a = arity(); i < a; i++)

            buf.append(parameterType(i));

        return buf.append('_').append(returnType()).toString();

    }

    static int signatureArity(String sig) {

        assert(isValidSignature(sig));

        return sig.indexOf('_');

    }

    static char signatureReturn(String sig) {

        return sig.charAt(signatureArity(sig)+1);

    }

    static boolean isValidSignature(String sig) {

        int arity = sig.indexOf('_');

        if (arity < 0)  return false;  // must be of the form *_*

        int siglen = sig.length();

        if (siglen != arity + 2)  return false;  // *_X

        for (int i = 0; i < siglen; i++) {

            if (i == arity)  continue;  // skip '_'

            char c = sig.charAt(i);

            if (c == 'V')

                return (i == siglen - 1 && arity == siglen - 2);

            if (ALL_TYPES.indexOf(c) < 0)  return false; // must be [LIJFD]

        }

        return true;  // [LIJFD]*_[LIJFDV]

    }

    static Class<?> typeClass(char t) {

        switch (t) {

        case 'I': return int.class;

        case 'J': return long.class;

        case 'F': return float.class;

        case 'D': return double.class;

        case 'L': return Object.class;

        case 'V': return void.class;

        default: assert false;

        }

        return null;

    }

    static MethodType signatureType(String sig) {

        Class<?>[] ptypes = new Class<?>[signatureArity(sig)];

        for (int i = 0; i < ptypes.length; i++)

            ptypes[i] = typeClass(sig.charAt(i));

        Class<?> rtype = typeClass(signatureReturn(sig));

        return MethodType.methodType(rtype, ptypes);

    }

    /*

     * Code generation issues:

     *

     * Compiled LFs should be reusable in general.

     * The biggest issue is how to decide when to pull a name into

     * the bytecode, versus loading a reified form from the MH data.

     *

     * For example, an asType wrapper may require execution of a cast

     * after a call to a MH.  The target type of the cast can be placed

     * as a constant in the LF itself.  This will force the cast type

     * to be compiled into the bytecodes and native code for the MH.

     * Or, the target type of the cast can be erased in the LF, and

     * loaded from the MH data.  (Later on, if the MH as a whole is

     * inlined, the data will flow into the inlined instance of the LF,

     * as a constant, and the end result will be an optimal cast.)

     *

     * This erasure of cast types can be done with any use of

     * reference types.  It can also be done with whole method

     * handles.  Erasing a method handle might leave behind

     * LF code that executes correctly for any MH of a given

     * type, and load the required MH from the enclosing MH's data.

     * Or, the erasure might even erase the expected MT.

     *

     * Also, for direct MHs, the MemberName of the target

     * could be erased, and loaded from the containing direct MH.

     * As a simple case, a LF for all int-valued non-static

     * field getters would perform a cast on its input argument

     * (to non-constant base type derived from the MemberName)

     * and load an integer value from the input object

     * (at a non-constant offset also derived from the MemberName).

     * Such MN-erased LFs would be inlinable back to optimized

     * code, whenever a constant enclosing DMH is available

     * to supply a constant MN from its data.

     *

     * The main problem here is to keep LFs reasonably generic,

     * while ensuring that hot spots will inline good instances.

     * "Reasonably generic" means that we don't end up with

     * repeated versions of bytecode or machine code that do

     * not differ in their optimized form.  Repeated versions

     * of machine would have the undesirable overheads of

     * (a) redundant compilation work and (b) extra I$ pressure.

     * To control repeated versions, we need to be ready to

     * erase details from LFs and move them into MH data,

     * whevener those details are not relevant to significant

     * optimization.  "Significant" means optimization of

     * code that is actually hot.

     *

     * Achieving this may require dynamic splitting of MHs, by replacing

     * a generic LF with a more specialized one, on the same MH,

     * if (a) the MH is frequently executed and (b) the MH cannot

     * be inlined into a containing caller, such as an invokedynamic.

     *

     * Compiled LFs that are no longer used should be GC-able.

     * If they contain non-BCP references, they should be properly

     * interlinked with the class loader(s) that their embedded types

     * depend on.  This probably means that reusable compiled LFs

     * will be tabulated (indexed) on relevant class loaders,

     * or else that the tables that cache them will have weak links.

     */

    /**

     * Make this LF directly executable, as part of a MethodHandle.

     * Invariant:  Every MH which is invoked must prepare its LF

     * before invocation.

     * (In principle, the JVM could do this very lazily,

     * as a sort of pre-invocation linkage step.)

     */

    public void prepare() {

        if (COMPILE_THRESHOLD == 0) {

            compileToBytecode();

        }

        if (this.vmentry != null) {

            // already prepared (e.g., a primitive DMH invoker form)

            return;

        }

        LambdaForm prep = getPreparedForm(basicTypeSignature());

        this.vmentry = prep.vmentry;

        // TO DO: Maybe add invokeGeneric, invokeWithArguments

    }

    /** Generate optimizable bytecode for this form. */

    MemberName compileToBytecode() {

        MethodType invokerType = methodType();

        assert(vmentry == null || vmentry.getMethodType().basicType().equals(invokerType));

        if (vmentry != null && isCompiled) {

            return vmentry;  // already compiled somehow

        }

        try {

            vmentry = InvokerBytecodeGenerator.generateCustomizedCode(this, invokerType);

            if (TRACE_INTERPRETER)

                traceInterpreter("compileToBytecode", this);

            isCompiled = true;

            return vmentry;

        } catch (Error | Exception ex) {

            throw newInternalError(this.toString(), ex);

        }

    }

    private static final ConcurrentHashMap<String,LambdaForm> PREPARED_FORMS;

    static {

        int   capacity   = 512;    // expect many distinct signatures over time

        float loadFactor = 0.75f;  // normal default

        int   writers    = 1;

        PREPARED_FORMS = new ConcurrentHashMap<>(capacity, loadFactor, writers);

    }

    private static Map<String,LambdaForm> computeInitialPreparedForms() {

        // Find all predefined invokers and associate them with canonical empty lambda forms.

        HashMap<String,LambdaForm> forms = new HashMap<>();

        for (MemberName m : MemberName.getFactory().getMethods(LambdaForm.class, false, null, null, null)) {

            if (!m.isStatic() || !m.isPackage())  continue;

            MethodType mt = m.getMethodType();

            if (mt.parameterCount() > 0 &&

                mt.parameterType(0) == MethodHandle.class &&

                m.getName().startsWith("interpret_")) {

                String sig = basicTypeSignature(mt);

                assert(m.getName().equals("interpret" + sig.substring(sig.indexOf('_'))));

                LambdaForm form = new LambdaForm(sig);

                form.vmentry = m;

                mt.form().setCachedLambdaForm(MethodTypeForm.LF_COUNTER, form);

                // FIXME: get rid of PREPARED_FORMS; use MethodTypeForm cache only

                forms.put(sig, form);

            }

        }

        //System.out.println("computeInitialPreparedForms => "+forms);

        return forms;

    }

    // Set this false to disable use of the interpret_L methods defined in this file.

    private static final boolean USE_PREDEFINED_INTERPRET_METHODS = true;

    // The following are predefined exact invokers.  The system must build

    // a separate invoker for each distinct signature.

    static Object interpret_L(MethodHandle mh) throws Throwable {

        Object[] av = {mh};

        String sig = null;

        assert(argumentTypesMatch(sig = "L_L", av));

        Object res = mh.form.interpretWithArguments(av);

        assert(returnTypesMatch(sig, av, res));

        return res;

    }

    static Object interpret_L(MethodHandle mh, Object x1) throws Throwable {

        Object[] av = {mh, x1};

        String sig = null;

        assert(argumentTypesMatch(sig = "LL_L", av));

        Object res = mh.form.interpretWithArguments(av);

        assert(returnTypesMatch(sig, av, res));

        return res;

    }

    static Object interpret_L(MethodHandle mh, Object x1, Object x2) throws Throwable {

        Object[] av = {mh, x1, x2};

        String sig = null;

        assert(argumentTypesMatch(sig = "LLL_L", av));

        Object res = mh.form.interpretWithArguments(av);

        assert(returnTypesMatch(sig, av, res));

        return res;

    }

    private static LambdaForm getPreparedForm(String sig) {

        MethodType mtype = signatureType(sig);

        //LambdaForm prep = PREPARED_FORMS.get(sig);

        LambdaForm prep =  mtype.form().cachedLambdaForm(MethodTypeForm.LF_INTERPRET);

        if (prep != null)  return prep;

        assert(isValidSignature(sig));