/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.painless;

import org.elasticsearch.core.Strings;
import org.elasticsearch.painless.api.ValueIterator;
import org.elasticsearch.painless.lookup.PainlessLookup;
import org.elasticsearch.painless.lookup.PainlessLookupUtility;
import org.elasticsearch.painless.lookup.PainlessMethod;
import org.elasticsearch.painless.symbol.FunctionTable;

import java.lang.invoke.CallSite;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.BitSet;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static org.elasticsearch.painless.lookup.PainlessLookupUtility.typeToCanonicalTypeName;

/**
 * Support for dynamic type (def).
 * <p>
 * Dynamic types can invoke methods, load/store fields, and be passed as parameters to operators without
 * compile-time type information.
 * <p>
 * Dynamic methods, loads, stores, and array/list/map load/stores involve locating the appropriate field
 * or method depending on the receiver's class. For these, we emit an {@code invokedynamic} instruction that,
 * for each new type encountered will query a corresponding {@code lookupXXX} method to retrieve the appropriate
 * method. In most cases, the {@code lookupXXX} methods here will only be called once for a given call site, because
 * caching ({@link DefBootstrap}) generally works: usually all objects at any call site will be consistently
 * the same type (or just a few types).  In extreme cases, if there is type explosion, they may be called every
 * single time, but simplicity is still more valuable than performance in this code.
 */
public final class Def {

    /** pointer to Map.get(Object) */
    private static final MethodHandle MAP_GET;
    /** pointer to Map.put(Object,Object) */
    private static final MethodHandle MAP_PUT;
    /** pointer to List.get(int) */
    private static final MethodHandle LIST_GET;
    /** pointer to List.set(int,Object) */
    private static final MethodHandle LIST_SET;
    /** pointer to new ObjectIterator(Iterable.iterator()) */
    private static final MethodHandle OBJECT_ITERATOR;
    /** pointer to {@link Def#mapIndexNormalize}. */
    private static final MethodHandle MAP_INDEX_NORMALIZE;
    /** pointer to {@link Def#listIndexNormalize}. */
    private static final MethodHandle LIST_INDEX_NORMALIZE;
    /** factory for arraylength MethodHandle (intrinsic) */
    private static final MethodHandle ARRAY_LENGTH;

    public static final Map<Class<?>, MethodHandle> DEF_TO_BOXED_TYPE_IMPLICIT_CAST;

    static {
        final MethodHandles.Lookup methodHandlesLookup = MethodHandles.lookup();

        try {
            MAP_GET = methodHandlesLookup.findVirtual(Map.class, "get", MethodType.methodType(Object.class, Object.class));
            MAP_PUT = methodHandlesLookup.findVirtual(Map.class, "put", MethodType.methodType(Object.class, Object.class, Object.class));
            LIST_GET = methodHandlesLookup.findVirtual(List.class, "get", MethodType.methodType(Object.class, int.class));
            LIST_SET = methodHandlesLookup.findVirtual(List.class, "set", MethodType.methodType(Object.class, int.class, Object.class));
            OBJECT_ITERATOR = MethodHandles.filterReturnValue(
                methodHandlesLookup.findVirtual(Iterable.class, "iterator", MethodType.methodType(Iterator.class)),
                methodHandlesLookup.findConstructor(ObjectIterator.class, MethodType.methodType(void.class, Iterator.class))
            );
            MAP_INDEX_NORMALIZE = methodHandlesLookup.findStatic(
                Def.class,
                "mapIndexNormalize",
                MethodType.methodType(Object.class, Map.class, Object.class)
            );
            LIST_INDEX_NORMALIZE = methodHandlesLookup.findStatic(
                Def.class,
                "listIndexNormalize",
                MethodType.methodType(int.class, List.class, int.class)
            );
            ARRAY_LENGTH = methodHandlesLookup.findStatic(
                MethodHandles.class,
                "arrayLength",
                MethodType.methodType(MethodHandle.class, Class.class)
            );
        } catch (ReflectiveOperationException roe) {
            throw new AssertionError(roe);
        }

        Map<Class<?>, MethodHandle> defToBoxedTypeImplicitCast = new HashMap<>();

        try {
            defToBoxedTypeImplicitCast.put(
                Byte.class,
                methodHandlesLookup.findStatic(Def.class, "defToByteImplicit", MethodType.methodType(Byte.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Short.class,
                methodHandlesLookup.findStatic(Def.class, "defToShortImplicit", MethodType.methodType(Short.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Character.class,
                methodHandlesLookup.findStatic(Def.class, "defToCharacterImplicit", MethodType.methodType(Character.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Integer.class,
                methodHandlesLookup.findStatic(Def.class, "defToIntegerImplicit", MethodType.methodType(Integer.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Long.class,
                methodHandlesLookup.findStatic(Def.class, "defToLongImplicit", MethodType.methodType(Long.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Float.class,
                methodHandlesLookup.findStatic(Def.class, "defToFloatImplicit", MethodType.methodType(Float.class, Object.class))
            );
            defToBoxedTypeImplicitCast.put(
                Double.class,
                methodHandlesLookup.findStatic(Def.class, "defToDoubleImplicit", MethodType.methodType(Double.class, Object.class))
            );
        } catch (NoSuchMethodException | IllegalAccessException exception) {
            throw new IllegalStateException(exception);
        }

        DEF_TO_BOXED_TYPE_IMPLICIT_CAST = Collections.unmodifiableMap(defToBoxedTypeImplicitCast);
    }

    /** Hack to rethrow unknown Exceptions from {@link MethodHandle#invokeExact}: */
    @SuppressWarnings("unchecked")
    static <T extends Throwable> void rethrow(Throwable t) throws T {
        throw (T) t;
    }

    /** Returns an array length getter MethodHandle for the given array type */
    static MethodHandle arrayLengthGetter(Class<?> arrayType) {
        try {
            return (MethodHandle) ARRAY_LENGTH.invokeExact(arrayType);
        } catch (Throwable t) {
            rethrow(t);
            throw new AssertionError(t);
        }
    }

    /**
     * Looks up handle for a dynamic method call, with lambda replacement
     * <p>
     * A dynamic method call for variable {@code x} of type {@code def} looks like:
     * {@code x.method(args...)}
     * <p>
     * This method traverses {@code recieverClass}'s class hierarchy (including interfaces)
     * until it finds a matching whitelisted method. If one is not found, it throws an exception.
     * Otherwise it returns a handle to the matching method.
     *
     * @param painlessLookup the whitelist
     * @param functions user defined functions and lambdas
     * @param constants available constants to be used if the method has the {@code InjectConstantAnnotation}
     * @param methodHandlesLookup caller's lookup
     * @param callSiteType callsite's type
     * @param receiverClass Class of the object to invoke the method on.
     * @param name Name of the method.
     * @param args bootstrap args passed to callsite
     * @return pointer to matching method to invoke. never returns null.
     * @throws IllegalArgumentException if no matching whitelisted method was found.
     * @throws Throwable if a method reference cannot be converted to an functional interface
     */
    static MethodHandle lookupMethod(
        PainlessLookup painlessLookup,
        FunctionTable functions,
        Map<String, Object> constants,
        MethodHandles.Lookup methodHandlesLookup,
        MethodType callSiteType,
        Class<?> receiverClass,
        String name,
        Object[] args
    ) throws Throwable {

        String recipeString = (String) args[0];
        int numArguments = callSiteType.parameterCount();
        // simple case: no lambdas
        if (recipeString.isEmpty()) {
            PainlessMethod painlessMethod = painlessLookup.lookupRuntimePainlessMethod(receiverClass, name, numArguments - 1);

            if (painlessMethod == null) {
                throw new IllegalArgumentException(
                    "dynamic method "
                        + "["
                        + typeToCanonicalTypeName(receiverClass)
                        + ", "
                        + name
                        + "/"
                        + (numArguments - 1)
                        + "] not found"
                );
            }

            MethodHandle handle = painlessMethod.methodHandle();
            Object[] injections = PainlessLookupUtility.buildInjections(painlessMethod, constants);

            if (injections.length > 0) {
                // method handle contains the "this" pointer so start injections at 1
                handle = MethodHandles.insertArguments(handle, 1, injections);
            }

            return handle;
        }

        // convert recipe string to a bitset for convenience (the code below should be refactored...)
        BitSet lambdaArgs = new BitSet(recipeString.length());
        for (int i = 0; i < recipeString.length(); i++) {
            lambdaArgs.set(recipeString.charAt(i));
        }

        // otherwise: first we have to compute the "real" arity. This is because we have extra arguments:
        // e.g. f(a, g(x), b, h(y), i()) looks like f(a, g, x, b, h, y, i).
        int arity = callSiteType.parameterCount() - 1;
        int upTo = 1;
        for (int i = 1; i < numArguments; i++) {
            if (lambdaArgs.get(i - 1)) {
                Def.Encoding signature = new Def.Encoding((String) args[upTo++]);
                arity -= signature.numCaptures;
                // arity in painlessLookup does not include 'this' reference
                if (signature.needsInstance) {
                    arity--;
                }
            }
        }

        // lookup the method with the proper arity, then we know everything (e.g. interface types of parameters).
        // based on these we can finally link any remaining lambdas that were deferred.
        PainlessMethod method = painlessLookup.lookupRuntimePainlessMethod(receiverClass, name, arity);

        if (method == null) {
            throw new IllegalArgumentException(
                "dynamic method [" + typeToCanonicalTypeName(receiverClass) + ", " + name + "/" + arity + "] not found"
            );
        }

        MethodHandle handle = method.methodHandle();
        Object[] injections = PainlessLookupUtility.buildInjections(method, constants);

        if (injections.length > 0) {
            // method handle contains the "this" pointer so start injections at 1
            handle = MethodHandles.insertArguments(handle, 1, injections);
        }

        int replaced = 0;
        upTo = 1;
        for (int i = 1; i < numArguments; i++) {
            // its a functional reference, replace the argument with an impl
            if (lambdaArgs.get(i - 1)) {
                Def.Encoding defEncoding = new Encoding((String) args[upTo++]);
                MethodHandle filter;
                Class<?> interfaceType = method.typeParameters().get(i - 1 - replaced - (defEncoding.needsInstance ? 1 : 0));
                if (defEncoding.isStatic) {
                    // the implementation is strongly typed, now that we know the interface type,
                    // we have everything.
                    filter = lookupReferenceInternal(
                        painlessLookup,
                        functions,
                        constants,
                        methodHandlesLookup,
                        interfaceType,
                        defEncoding.symbol,
                        defEncoding.methodName,
                        defEncoding.numCaptures,
                        defEncoding.needsInstance
                    );
                } else {
                    // the interface type is now known, but we need to get the implementation.
                    // this is dynamically based on the receiver type (and cached separately, underneath
                    // this cache). It won't blow up since we never nest here (just references)
                    Class<?>[] captures = new Class<?>[defEncoding.numCaptures];
                    for (int capture = 0; capture < captures.length; capture++) {
                        captures[capture] = callSiteType.parameterType(i + 1 + capture);
                    }
                    MethodType nestedType = MethodType.methodType(interfaceType, captures);
                    CallSite nested = DefBootstrap.bootstrap(
                        painlessLookup,
                        functions,
                        constants,
                        methodHandlesLookup,
                        defEncoding.methodName,
                        nestedType,
                        0,
                        DefBootstrap.REFERENCE,
                        PainlessLookupUtility.typeToCanonicalTypeName(interfaceType)
                    );
                    filter = nested.dynamicInvoker();
                }
                // the filter now ignores the signature (placeholder) on the stack
                filter = MethodHandles.dropArguments(filter, 0, String.class);
                handle = MethodHandles.collectArguments(handle, i - (defEncoding.needsInstance ? 1 : 0), filter);
                i += defEncoding.numCaptures;
                replaced += defEncoding.numCaptures;
            }
        }

        return handle;
    }

    /**
     * Returns an implementation of interfaceClass that calls receiverClass.name
     * <p>
     * This is just like LambdaMetaFactory, only with a dynamic type. The interface type is known,
     * so we simply need to lookup the matching implementation method based on receiver type.
     */
    static MethodHandle lookupReference(
        PainlessLookup painlessLookup,
        FunctionTable functions,
        Map<String, Object> constants,
        MethodHandles.Lookup methodHandlesLookup,
        String interfaceClass,
        Class<?> receiverClass,
        String name
    ) throws Throwable {

        Class<?> interfaceType = painlessLookup.canonicalTypeNameToType(interfaceClass);
        if (interfaceType == null) {
            throw new IllegalArgumentException("type [" + interfaceClass + "] not found");
        }
        PainlessMethod interfaceMethod = painlessLookup.lookupFunctionalInterfacePainlessMethod(interfaceType);
        if (interfaceMethod == null) {
            throw new IllegalArgumentException("Class [" + interfaceClass + "] is not a functional interface");
        }
        int arity = interfaceMethod.typeParameters().size();
        PainlessMethod implMethod = painlessLookup.lookupRuntimePainlessMethod(receiverClass, name, arity);
        if (implMethod == null) {
            throw new IllegalArgumentException(
                "dynamic method [" + typeToCanonicalTypeName(receiverClass) + ", " + name + "/" + arity + "] not found"
            );
        }

        return lookupReferenceInternal(
            painlessLookup,
            functions,
            constants,
            methodHandlesLookup,
            interfaceType,
            PainlessLookupUtility.typeToCanonicalTypeName(implMethod.targetClass()),
            implMethod.javaMethod().getName(),
            1,
            false
        );
    }

    /** Returns a method handle to an implementation of clazz, given method reference signature. */
    private static MethodHandle lookupReferenceInternal(
        PainlessLookup painlessLookup,
        FunctionTable functions,
        Map<String, Object> constants,
        MethodHandles.Lookup methodHandlesLookup,
        Class<?> clazz,
        String type,
        String call,
        int captures,
        boolean needsScriptInstance
    ) throws Throwable {

        final FunctionRef ref = FunctionRef.create(
            painlessLookup,
            functions,
            null,
            clazz,
            type,
            call,
            captures,
            constants,
            needsScriptInstance
        );
        Class<?>[] parameters = ref.factoryMethodParameters(needsScriptInstance ? methodHandlesLookup.lookupClass() : null);
        MethodType factoryMethodType = MethodType.methodType(clazz, parameters);
        final CallSite callSite = LambdaBootstrap.lambdaBootstrap(
            methodHandlesLookup,
            ref.interfaceMethodName,
            factoryMethodType,
            ref.interfaceMethodType,
            ref.delegateClassName,
            ref.delegateInvokeType,
            ref.delegateMethodName,
            ref.delegateMethodType,
            ref.isDelegateInterface ? 1 : 0,
            ref.isDelegateAugmented ? 1 : 0,
            ref.delegateInjections
        );
        return callSite.dynamicInvoker().asType(MethodType.methodType(clazz, parameters));
    }

    /**
     * Looks up handle for a dynamic field getter (field load)
     * <p>
     * A dynamic field load for variable {@code x} of type {@code def} looks like:
     * {@code y = x.field}
     * <p>
     * The following field loads are allowed:
     * <ul>
     *   <li>Whitelisted {@code field} from receiver's class or any superclasses.
     *   <li>Whitelisted method named {@code getField()} from receiver's class/superclasses/interfaces.
     *   <li>Whitelisted method named {@code isField()} from receiver's class/superclasses/interfaces.
     *   <li>The {@code length} field of an array.
     *   <li>The value corresponding to a map key named {@code field} when the receiver is a Map.
     *   <li>The value in a list at element {@code field} (integer) when the receiver is a List.
     * </ul>
     * <p>
     * This method traverses {@code recieverClass}'s class hierarchy (including interfaces)
     * until it finds a matching whitelisted getter. If one is not found, it throws an exception.
     * Otherwise it returns a handle to the matching getter.
     *
     * @param painlessLookup the whitelist
     * @param receiverClass Class of the object to retrieve the field from.
     * @param name Name of the field.
     * @return pointer to matching field. never returns null.
     * @throws IllegalArgumentException if no matching whitelisted field was found.
     */
    static MethodHandle lookupGetter(PainlessLookup painlessLookup, Class<?> receiverClass, String name) {
        // first try whitelist
        MethodHandle getter = painlessLookup.lookupRuntimeGetterMethodHandle(receiverClass, name);

        if (getter != null) {
            return getter;
        }

        // special case: arrays, maps, and lists
        if (receiverClass.isArray() && "length".equals(name)) {
            // arrays expose .length as a read-only getter
            return arrayLengthGetter(receiverClass);
        } else if (Map.class.isAssignableFrom(receiverClass)) {
            // maps allow access like mymap.key
            // wire 'key' as a parameter, its a constant in painless
            return MethodHandles.insertArguments(MAP_GET, 1, name);
        } else if (List.class.isAssignableFrom(receiverClass)) {
            // lists allow access like mylist.0
            // wire '0' (index) as a parameter, its a constant. this also avoids
            // parsing the same integer millions of times!
            try {
                int index = Integer.parseInt(name);
                return MethodHandles.insertArguments(LIST_GET, 1, index);
            } catch (NumberFormatException exception) {
                throw new IllegalArgumentException("Illegal list shortcut value [" + name + "].");
            }
        }

        throw new IllegalArgumentException("dynamic getter [" + typeToCanonicalTypeName(receiverClass) + ", " + name + "] not found");
    }

    /**
     * Looks up handle for a dynamic field setter (field store)
     * <p>
     * A dynamic field store for variable {@code x} of type {@code def} looks like:
     * {@code x.field = y}
     * <p>
     * The following field stores are allowed:
     * <ul>
     *   <li>Whitelisted {@code field} from receiver's class or any superclasses.
     *   <li>Whitelisted method named {@code setField()} from receiver's class/superclasses/interfaces.
     *   <li>The value corresponding to a map key named {@code field} when the receiver is a Map.
     *   <li>The value in a list at element {@code field} (integer) when the receiver is a List.
     * </ul>
     * <p>
     * This method traverses {@code recieverClass}'s class hierarchy (including interfaces)
     * until it finds a matching whitelisted setter. If one is not found, it throws an exception.
     * Otherwise it returns a handle to the matching setter.
     *
     * @param painlessLookup the whitelist
     * @param receiverClass Class of the object to retrieve the field from.
     * @param name Name of the field.
     * @return pointer to matching field. never returns null.
     * @throws IllegalArgumentException if no matching whitelisted field was found.
     */
    static MethodHandle lookupSetter(PainlessLookup painlessLookup, Class<?> receiverClass, String name) {
        // first try whitelist
        MethodHandle setter = painlessLookup.lookupRuntimeSetterMethodHandle(receiverClass, name);

        if (setter != null) {
            return setter;
        }

        // special case: maps, and lists
        if (Map.class.isAssignableFrom(receiverClass)) {
            // maps allow access like mymap.key
            // wire 'key' as a parameter, its a constant in painless
            return MethodHandles.insertArguments(MAP_PUT, 1, name);
        } else if (List.class.isAssignableFrom(receiverClass)) {
            // lists allow access like mylist.0
            // wire '0' (index) as a parameter, its a constant. this also avoids
            // parsing the same integer millions of times!
            try {
                int index = Integer.parseInt(name);
                return MethodHandles.insertArguments(LIST_SET, 1, index);
            } catch (final NumberFormatException exception) {
                throw new IllegalArgumentException("Illegal list shortcut value [" + name + "].");
            }
        }

        throw new IllegalArgumentException("dynamic setter [" + typeToCanonicalTypeName(receiverClass) + ", " + name + "] not found");
    }

    /**
     * Returns a method handle to normalize the index into an array. This is what makes lists and arrays stored in {@code def} support
     * negative offsets.
     * @param receiverClass Class of the array to store the value in
     * @return a MethodHandle that accepts the receiver as first argument, the index as second argument, and returns the normalized index
     *   to use with array loads and array stores
     */
    static MethodHandle lookupIndexNormalize(Class<?> receiverClass) {
        if (receiverClass.isArray()) {
            return ArrayIndexNormalizeHelper.arrayIndexNormalizer(receiverClass);
        } else if (Map.class.isAssignableFrom(receiverClass)) {
            // noop so that mymap[key] doesn't do funny things with negative keys
            return MAP_INDEX_NORMALIZE;
        } else if (List.class.isAssignableFrom(receiverClass)) {
            return LIST_INDEX_NORMALIZE;
        }
        throw new IllegalArgumentException(
            "Attempting to address a non-array-like type " + "[" + receiverClass.getCanonicalName() + "] as an array."
        );
    }

    /**
     * Returns a method handle to do an array store.
     * @param receiverClass Class of the array to store the value in
     * @return a MethodHandle that accepts the receiver as first argument, the index as second argument,
     *   and the value to set as 3rd argument. Return value is undefined and should be ignored.
     */
    static MethodHandle lookupArrayStore(Class<?> receiverClass) {
        if (receiverClass.isArray()) {
            return MethodHandles.arrayElementSetter(receiverClass);
        } else if (Map.class.isAssignableFrom(receiverClass)) {
            // maps allow access like mymap[key]
            return MAP_PUT;
        } else if (List.class.isAssignableFrom(receiverClass)) {
            return LIST_SET;
        }
        throw new IllegalArgumentException(
            "Attempting to address a non-array type " + "[" + receiverClass.getCanonicalName() + "] as an array."
        );
    }

    /**
     * Returns a method handle to do an array load.
     * @param receiverClass Class of the array to load the value from
     * @return a MethodHandle that accepts the receiver as first argument, the index as second argument.
     *   It returns the loaded value.
     */
    static MethodHandle lookupArrayLoad(Class<?> receiverClass) {
        if (receiverClass.isArray()) {
            return MethodHandles.arrayElementGetter(receiverClass);
        } else if (Map.class.isAssignableFrom(receiverClass)) {
            // maps allow access like mymap[key]
            return MAP_GET;
        } else if (List.class.isAssignableFrom(receiverClass)) {
            return LIST_GET;
        }
        throw new IllegalArgumentException(
            "Attempting to address a non-array type " + "[" + receiverClass.getCanonicalName() + "] as an array."
        );
    }

    private static ClassCastException castException(Class<?> sourceClass, Class<?> targetClass, Boolean implicit) {
        return new ClassCastException(
            Strings.format(
                "cannot %scast def [%s] to %s",
                implicit != null ? (implicit ? "implicitly " : "explicitly ") : "",
                PainlessLookupUtility.typeToUnboxedType(sourceClass).getCanonicalName(),
                targetClass.getCanonicalName()
            )
        );
    }

    private abstract static class BaseIterator<T> implements ValueIterator<T> {
        @Override
        public boolean nextBoolean() {
            Object next = next();
            try {
                return (boolean) next;
            } catch (ClassCastException e) {
                throw castException(next.getClass(), boolean.class, null);
            }
        }

        @Override
        public byte nextByte() {
            Object next = next();
            try {
                return ((Number) next).byteValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), byte.class, null);
            }
        }

        @Override
        public short nextShort() {
            Object next = next();
            try {
                return ((Number) next).shortValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), short.class, null);
            }
        }

        @Override
        public char nextChar() {
            Object next = next();
            try {
                return (char) next;
            } catch (ClassCastException e) {
                throw castException(next.getClass(), char.class, null);
            }
        }

        @Override
        public int nextInt() {
            Object next = next();
            try {
                return ((Number) next).intValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), int.class, null);
            }
        }

        @Override
        public long nextLong() {
            Object next = next();
            try {
                return ((Number) next).longValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), long.class, null);
            }
        }

        @Override
        public float nextFloat() {
            Object next = next();
            try {
                return ((Number) next).floatValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), float.class, null);
            }
        }

        @Override
        public double nextDouble() {
            Object next = next();
            try {
                return ((Number) next).doubleValue();
            } catch (ClassCastException e) {
                throw castException(next.getClass(), double.class, null);
            }
        }
    }

    private static class ObjectIterator<T> extends BaseIterator<T> {
        private final Iterator<T> iterator;

        ObjectIterator(Iterator<T> iterator) {
            this.iterator = iterator;
        }

        @Override
        public boolean hasNext() {
            return iterator.hasNext();
        }

        @Override
        public T next() {
            return iterator.next();
        }

        @Override
        public void remove() {
            iterator.remove();
        }

        @Override
        public void forEachRemaining(Consumer<? super T> action) {
            iterator.forEachRemaining(action);
        }
    }

    /** Helper class for isolating MethodHandles and methods to get iterators over arrays
     * (to emulate "enhanced for loop" using MethodHandles).
     */
    @SuppressWarnings("unused") // iterator() methods are are actually used, javac just does not know :)
    private static final class ArrayIteratorHelper {
        private static final MethodHandles.Lookup PRIVATE_METHOD_HANDLES_LOOKUP = MethodHandles.lookup();

        private static final Map<Class<?>, MethodHandle> ARRAY_TYPE_MH_MAPPING = Collections.unmodifiableMap(
            Stream.of(
                boolean[].class,
                byte[].class,
                short[].class,
                int[].class,
                long[].class,
                char[].class,
                float[].class,
                double[].class,
                Object[].class
            ).collect(Collectors.toMap(Function.identity(), type -> {
                try {
                    return PRIVATE_METHOD_HANDLES_LOOKUP.findStatic(
                        PRIVATE_METHOD_HANDLES_LOOKUP.lookupClass(),
                        "iterator",
                        MethodType.methodType(ValueIterator.class, type)
                    );
                } catch (ReflectiveOperationException e) {
                    throw new AssertionError(e);
                }
            }))
        );

        private static final MethodHandle OBJECT_ARRAY_MH = ARRAY_TYPE_MH_MAPPING.get(Object[].class);

        static ValueIterator<Boolean> iterator(final boolean[] array) {
            return new BaseIterator<Boolean>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public boolean nextBoolean() {
                    return array[index++];
                }

                @Override
                public Boolean next() {
                    return nextBoolean();
                }
            };
        }

        static ValueIterator<Byte> iterator(final byte[] array) {
            return new BaseIterator<Byte>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return array[index++];
                }

                @Override
                public short nextShort() {
                    return nextByte();
                }

                @Override
                public char nextChar() {
                    return (char) nextByte();
                }

                @Override
                public int nextInt() {
                    return nextByte();
                }

                @Override
                public long nextLong() {
                    return nextByte();
                }

                @Override
                public float nextFloat() {
                    return nextByte();
                }

                @Override
                public double nextDouble() {
                    return nextByte();
                }

                @Override
                public Byte next() {
                    return nextByte();
                }
            };
        }

        static ValueIterator<Short> iterator(final short[] array) {
            return new BaseIterator<Short>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextShort();
                }

                @Override
                public short nextShort() {
                    return array[index++];
                }

                @Override
                public char nextChar() {
                    return (char) nextShort();
                }

                @Override
                public int nextInt() {
                    return nextShort();
                }

                @Override
                public long nextLong() {
                    return nextShort();
                }

                @Override
                public float nextFloat() {
                    return nextShort();
                }

                @Override
                public double nextDouble() {
                    return nextShort();
                }

                @Override
                public Short next() {
                    return nextShort();
                }
            };
        }

        static ValueIterator<Integer> iterator(final int[] array) {
            return new BaseIterator<Integer>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextInt();
                }

                @Override
                public short nextShort() {
                    return (short) nextInt();
                }

                @Override
                public char nextChar() {
                    return (char) nextInt();
                }

                @Override
                public int nextInt() {
                    return array[index++];
                }

                @Override
                public long nextLong() {
                    return nextInt();
                }

                @Override
                public float nextFloat() {
                    return nextInt();
                }

                @Override
                public double nextDouble() {
                    return nextInt();
                }

                @Override
                public Integer next() {
                    return nextInt();
                }
            };
        }

        static ValueIterator<Long> iterator(final long[] array) {
            return new BaseIterator<Long>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextLong();
                }

                @Override
                public short nextShort() {
                    return (short) nextLong();
                }

                @Override
                public char nextChar() {
                    return (char) nextLong();
                }

                @Override
                public int nextInt() {
                    return (int) nextLong();
                }

                @Override
                public long nextLong() {
                    return array[index++];
                }

                @Override
                public float nextFloat() {
                    return nextLong();
                }

                @Override
                public double nextDouble() {
                    return nextLong();
                }

                @Override
                public Long next() {
                    return nextLong();
                }
            };
        }

        static ValueIterator<Character> iterator(final char[] array) {
            return new BaseIterator<Character>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextChar();
                }

                @Override
                public short nextShort() {
                    return (short) nextChar();
                }

                @Override
                public char nextChar() {
                    return array[index++];
                }

                @Override
                public int nextInt() {
                    return nextChar();
                }

                @Override
                public long nextLong() {
                    return nextChar();
                }

                @Override
                public float nextFloat() {
                    return nextChar();
                }

                @Override
                public double nextDouble() {
                    return nextChar();
                }

                @Override
                public Character next() {
                    return nextChar();
                }
            };
        }

        static ValueIterator<Float> iterator(final float[] array) {
            return new BaseIterator<Float>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextFloat();
                }

                @Override
                public short nextShort() {
                    return (short) nextFloat();
                }

                @Override
                public char nextChar() {
                    return (char) nextFloat();
                }

                @Override
                public int nextInt() {
                    return (int) nextFloat();
                }

                @Override
                public long nextLong() {
                    return (long) nextFloat();
                }

                @Override
                public float nextFloat() {
                    return array[index++];
                }

                @Override
                public double nextDouble() {
                    return nextFloat();
                }

                @Override
                public Float next() {
                    return nextFloat();
                }
            };
        }

        static ValueIterator<Double> iterator(final double[] array) {
            return new BaseIterator<Double>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public byte nextByte() {
                    return (byte) nextDouble();
                }

                @Override
                public short nextShort() {
                    return (short) nextDouble();
                }

                @Override
                public char nextChar() {
                    return (char) nextDouble();
                }

                @Override
                public int nextInt() {
                    return (int) nextDouble();
                }

                @Override
                public long nextLong() {
                    return (long) nextDouble();
                }

                @Override
                public float nextFloat() {
                    return (float) nextDouble();
                }

                @Override
                public double nextDouble() {
                    return array[index++];
                }

                @Override
                public Double next() {
                    return nextDouble();
                }
            };
        }

        static ValueIterator<Object> iterator(final Object[] array) {
            return new BaseIterator<Object>() {
                int index = 0;

                @Override
                public boolean hasNext() {
                    return index < array.length;
                }

                @Override
                public Object next() {
                    return array[index++];
                }
            };
        }

        static MethodHandle newIterator(Class<?> arrayType) {
            if (arrayType.isArray() == false) {
                throw new IllegalArgumentException("type must be an array");
            }
            MethodHandle iterator = ARRAY_TYPE_MH_MAPPING.get(arrayType);
            return iterator != null ? iterator : OBJECT_ARRAY_MH.asType(OBJECT_ARRAY_MH.type().changeParameterType(0, arrayType));
        }

        private ArrayIteratorHelper() {}
    }

    /**
     * Returns a method handle to do iteration (for enhanced for loop)
     * @param receiverClass Class of the array to load the value from
     * @return a MethodHandle that accepts the receiver as first argument, returns iterator
     */
    static MethodHandle lookupIterator(Class<?> receiverClass) {
        if (Iterable.class.isAssignableFrom(receiverClass)) {
            return OBJECT_ITERATOR;
        } else if (receiverClass.isArray()) {
            return ArrayIteratorHelper.newIterator(receiverClass);
        } else {
            throw new IllegalArgumentException("Cannot iterate over [" + receiverClass.getCanonicalName() + "]");
        }
    }

    // Conversion methods for def to primitive types.

    public static boolean defToboolean(final Object value) {
        if (value instanceof Boolean) {
            return (boolean) value;
        } else {
            throw castException(value.getClass(), boolean.class, null);
        }
    }

    public static byte defTobyteImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else {
            throw castException(value.getClass(), byte.class, true);
        }
    }

    public static short defToshortImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else if (value instanceof Short) {
            return (short) value;
        } else {
            throw castException(value.getClass(), short.class, true);
        }
    }

    public static char defTocharImplicit(final Object value) {
        if (value instanceof Character) {
            return (char) value;
        } else {
            throw castException(value.getClass(), char.class, true);
        }
    }

    public static int defTointImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else if (value instanceof Short) {
            return (short) value;
        } else if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Integer) {
            return (int) value;
        } else {
            throw castException(value.getClass(), int.class, true);
        }
    }

    public static long defTolongImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else if (value instanceof Short) {
            return (short) value;
        } else if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Integer) {
            return (int) value;
        } else if (value instanceof Long) {
            return (long) value;
        } else {
            throw castException(value.getClass(), long.class, true);
        }
    }

    public static float defTofloatImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else if (value instanceof Short) {
            return (short) value;
        } else if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Integer) {
            return (int) value;
        } else if (value instanceof Long) {
            return (long) value;
        } else if (value instanceof Float) {
            return (float) value;
        } else {
            throw castException(value.getClass(), float.class, true);
        }
    }

    public static double defTodoubleImplicit(final Object value) {
        if (value instanceof Byte) {
            return (byte) value;
        } else if (value instanceof Short) {
            return (short) value;
        } else if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Integer) {
            return (int) value;
        } else if (value instanceof Long) {
            return (long) value;
        } else if (value instanceof Float) {
            return (float) value;
        } else if (value instanceof Double) {
            return (double) value;
        } else {
            throw castException(value.getClass(), double.class, true);
        }
    }

    public static byte defTobyteExplicit(final Object value) {
        if (value instanceof Character) {
            return (byte) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).byteValue();
            } else {
                throw castException(value.getClass(), byte.class, false);
            }
    }

    public static short defToshortExplicit(final Object value) {
        if (value instanceof Character) {
            return (short) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).shortValue();
            } else {
                throw castException(value.getClass(), short.class, false);
            }
    }

    public static char defTocharExplicit(final Object value) {
        if (value instanceof String) {
            return Utility.StringTochar((String) value);
        } else if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return (char) ((Number) value).intValue();
            } else {
                throw castException(value.getClass(), char.class, false);
            }
    }

    public static int defTointExplicit(final Object value) {
        if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).intValue();
            } else {
                throw castException(value.getClass(), int.class, false);
            }
    }

    public static long defTolongExplicit(final Object value) {
        if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).longValue();
            } else {
                throw castException(value.getClass(), long.class, false);
            }
    }

    public static float defTofloatExplicit(final Object value) {
        if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).floatValue();
            } else {
                throw castException(value.getClass(), float.class, false);
            }
    }

    public static double defTodoubleExplicit(final Object value) {
        if (value instanceof Character) {
            return (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).doubleValue();
            } else {
                throw castException(value.getClass(), byte.class, false);
            }
    }

    // Conversion methods for def to boxed types.

    public static Boolean defToBoolean(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Boolean) {
            return (Boolean) value;
        } else {
            throw castException(value.getClass(), Boolean.class, false);
        }
    }

    public static Byte defToByteImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (Byte) value;
        } else {
            throw castException(value.getClass(), Byte.class, false);
        }
    }

    public static Short defToShortImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (short) (byte) value;
        } else if (value instanceof Short) {
            return (Short) value;
        } else {
            throw castException(value.getClass(), Short.class, false);
        }
    }

    public static Character defToCharacterImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (Character) value;
        } else {
            throw castException(value.getClass(), Character.class, false);
        }
    }

    public static Integer defToIntegerImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (int) (byte) value;
        } else if (value instanceof Short) {
            return (int) (short) value;
        } else if (value instanceof Character) {
            return (int) (char) value;
        } else if (value instanceof Integer) {
            return (Integer) value;
        } else {
            throw castException(value.getClass(), Integer.class, false);
        }
    }

    public static Long defToLongImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (long) (byte) value;
        } else if (value instanceof Short) {
            return (long) (short) value;
        } else if (value instanceof Character) {
            return (long) (char) value;
        } else if (value instanceof Integer) {
            return (long) (int) value;
        } else if (value instanceof Long) {
            return (Long) value;
        } else {
            throw castException(value.getClass(), Long.class, false);
        }
    }

    public static Float defToFloatImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (float) (byte) value;
        } else if (value instanceof Short) {
            return (float) (short) value;
        } else if (value instanceof Character) {
            return (float) (char) value;
        } else if (value instanceof Integer) {
            return (float) (int) value;
        } else if (value instanceof Long) {
            return (float) (long) value;
        } else if (value instanceof Float) {
            return (Float) value;
        } else {
            throw castException(value.getClass(), Float.class, false);
        }
    }

    public static Double defToDoubleImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Byte) {
            return (double) (byte) value;
        } else if (value instanceof Short) {
            return (double) (short) value;
        } else if (value instanceof Character) {
            return (double) (char) value;
        } else if (value instanceof Integer) {
            return (double) (int) value;
        } else if (value instanceof Long) {
            return (double) (long) value;
        } else if (value instanceof Float) {
            return (double) (float) value;
        } else if (value instanceof Double) {
            return (Double) value;
        } else {
            throw castException(value.getClass(), Double.class, false);
        }
    }

    public static Byte defToByteExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (byte) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).byteValue();
            } else {
                throw castException(value.getClass(), Byte.class, false);
            }
    }

    public static Short defToShortExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (short) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).shortValue();
            } else {
                throw castException(value.getClass(), Short.class, false);
            }
    }

    public static Character defToCharacterExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof String) {
            return Utility.StringTochar((String) value);
        } else if (value instanceof Character) {
            return (Character) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return (char) ((Number) value).intValue();
            } else {
                throw castException(value.getClass(), Character.class, false);
            }
    }

    public static Integer defToIntegerExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (int) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).intValue();
            } else {
                throw castException(value.getClass(), Integer.class, false);
            }
    }

    public static Long defToLongExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (long) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).longValue();
            } else {
                throw castException(value.getClass(), Long.class, false);
            }
    }

    public static Float defToFloatExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (float) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).floatValue();
            } else {
                throw castException(value.getClass(), Float.class, false);
            }
    }

    public static Double defToDoubleExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return (double) (char) value;
        } else if (value instanceof Byte
            || value instanceof Short
            || value instanceof Integer
            || value instanceof Long
            || value instanceof Float
            || value instanceof Double) {
                return ((Number) value).doubleValue();
            } else {
                throw castException(value.getClass(), Double.class, false);
            }
    }

    public static String defToStringImplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof String) {
            return (String) value;
        } else {
            throw castException(value.getClass(), String.class, true);
        }
    }

    public static String defToStringExplicit(final Object value) {
        if (value == null) {
            return null;
        } else if (value instanceof Character) {
            return Utility.charToString((char) value);
        } else if (value instanceof String) {
            return (String) value;
        } else {
            throw castException(value.getClass(), String.class, false);
        }
    }

    /**
     * "Normalizes" the index into a {@code Map} by making no change to the index.
     */
    public static Object mapIndexNormalize(final Map<?, ?> value, Object index) {
        return index;
    }

    /**
     * "Normalizes" the idnex into a {@code List} by flipping negative indexes around so they are "from the end" of the list.
     */
    public static int listIndexNormalize(final List<?> value, int index) {
        return index >= 0 ? index : value.size() + index;
    }

    /**
     * Methods to normalize array indices to support negative indices into arrays stored in {@code def}s.
     */
    @SuppressWarnings("unused") // normalizeIndex() methods are are actually used, javac just does not know :)
    private static final class ArrayIndexNormalizeHelper {
        private static final MethodHandles.Lookup PRIVATE_METHOD_HANDLES_LOOKUP = MethodHandles.lookup();

        private static final Map<Class<?>, MethodHandle> ARRAY_TYPE_MH_MAPPING = Collections.unmodifiableMap(
            Stream.of(
                boolean[].class,
                byte[].class,
                short[].class,
                int[].class,
                long[].class,
                char[].class,
                float[].class,
                double[].class,
                Object[].class
            ).collect(Collectors.toMap(Function.identity(), type -> {
                try {
                    return PRIVATE_METHOD_HANDLES_LOOKUP.findStatic(
                        PRIVATE_METHOD_HANDLES_LOOKUP.lookupClass(),
                        "normalizeIndex",
                        MethodType.methodType(int.class, type, int.class)
                    );
                } catch (ReflectiveOperationException e) {
                    throw new AssertionError(e);
                }
            }))
        );

        private static final MethodHandle OBJECT_ARRAY_MH = ARRAY_TYPE_MH_MAPPING.get(Object[].class);

        static int normalizeIndex(final boolean[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final byte[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final short[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final int[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final long[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final char[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final float[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final double[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static int normalizeIndex(final Object[] array, final int index) {
            return index >= 0 ? index : index + array.length;
        }

        static MethodHandle arrayIndexNormalizer(Class<?> arrayType) {
            if (arrayType.isArray() == false) {
                throw new IllegalArgumentException("type must be an array");
            }
            MethodHandle handle = ARRAY_TYPE_MH_MAPPING.get(arrayType);
            return handle != null ? handle : OBJECT_ARRAY_MH.asType(OBJECT_ARRAY_MH.type().changeParameterType(0, arrayType));
        }

        private ArrayIndexNormalizeHelper() {}
    }

    public static class Encoding {
        public final boolean isStatic;
        public final boolean needsInstance;
        public final String symbol;
        public final String methodName;
        public final int numCaptures;

        /**
         * Encoding is passed to invokedynamic to help DefBootstrap find the method.  invokedynamic can only take
         * "Class, java.lang.invoke.MethodHandle, java.lang.invoke.MethodType, String, int, long, float, or double" types to
         * help find the callsite, which is why this object is encoded as a String for indy.
         * See: https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#jvms-6.5.invokedynamic
         * */
        public final String encoding;

        private static final String FORMAT = "[SD][tf]symbol.methodName,numCaptures";

        public Encoding(boolean isStatic, boolean needsInstance, String symbol, String methodName, int numCaptures) {
            this.isStatic = isStatic;
            this.needsInstance = needsInstance;
            this.symbol = Objects.requireNonNull(symbol);
            this.methodName = Objects.requireNonNull(methodName);
            this.numCaptures = numCaptures;
            this.encoding = (isStatic ? "S" : "D") + (needsInstance ? "t" : "f") + symbol + "." + methodName + "," + numCaptures;

            if ("this".equals(symbol)) {
                if (isStatic == false) {
                    throw new IllegalArgumentException("Def.Encoding must be static if symbol is 'this', encoding [" + encoding + "]");
                }
            } else {
                if (needsInstance) {
                    throw new IllegalArgumentException(
                        "Def.Encoding symbol must be 'this', not [" + symbol + "] if needsInstance," + " encoding [" + encoding + "]"
                    );
                }
            }

            if (methodName.isEmpty()) {
                throw new IllegalArgumentException("methodName must be non-empty, encoding [" + encoding + "]");
            }
            if (numCaptures < 0) {
                throw new IllegalArgumentException(
                    "numCaptures must be non-negative, not [" + numCaptures + "]," + " encoding: [" + encoding + "]"
                );
            }
        }

        // Parsing constructor, does minimal validation to avoid extra work during runtime
        public Encoding(String encoding) {
            this.encoding = Objects.requireNonNull(encoding);
            if (encoding.length() < 6) {
                throw new IllegalArgumentException(
                    "Encoding too short. Minimum 6, given ["
                        + encoding.length()
                        + "],"
                        + " encoding: ["
                        + encoding
                        + "], format: "
                        + FORMAT
                        + ""
                );
            }

            // 'S' or 'D'
            this.isStatic = encoding.charAt(0) == 'S';

            // 't' or 'f'
            this.needsInstance = encoding.charAt(1) == 't';

            int dotIndex = encoding.lastIndexOf('.');
            if (dotIndex < 2) {
                throw new IllegalArgumentException(
                    "Invalid symbol, could not find '.' at expected position after index 1, instead found"
                        + " index ["
                        + dotIndex
                        + "], encoding: ["
                        + encoding
                        + "], format: "
                        + FORMAT
                );
            }

            this.symbol = encoding.substring(2, dotIndex);

            int commaIndex = encoding.indexOf(',');
            if (commaIndex <= dotIndex) {
                throw new IllegalArgumentException(
                    "Invalid symbol, could not find ',' at expected position after '.' at"
                        + " ["
                        + dotIndex
                        + "], instead found index ["
                        + commaIndex
                        + "], encoding: ["
                        + encoding
                        + "], format: "
                        + FORMAT
                );
            }

            this.methodName = encoding.substring(dotIndex + 1, commaIndex);

            if (commaIndex == encoding.length() - 1) {
                throw new IllegalArgumentException(
                    "Invalid symbol, could not find ',' at expected position, instead found"
                        + " index ["
                        + commaIndex
                        + "], encoding: ["
                        + encoding
                        + "], format: "
                        + FORMAT
                );
            }

            this.numCaptures = Integer.parseUnsignedInt(encoding.substring(commaIndex + 1));
        }

        @Override
        public String toString() {
            return encoding;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if ((o instanceof Encoding) == false) return false;
            Encoding encoding1 = (Encoding) o;
            return isStatic == encoding1.isStatic
                && needsInstance == encoding1.needsInstance
                && numCaptures == encoding1.numCaptures
                && Objects.equals(symbol, encoding1.symbol)
                && Objects.equals(methodName, encoding1.methodName)
                && Objects.equals(encoding, encoding1.encoding);
        }

        @Override
        public int hashCode() {
            return Objects.hash(isStatic, needsInstance, symbol, methodName, numCaptures, encoding);
        }
    }
}