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** Copyright (C) 2016 The Qt Company Ltd.
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**
** This file is part of the QtQml module of the Qt Toolkit.
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** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
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** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 or any later version approved by the KDE Free
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****************************************************************************/
#include "qv4arraydata_p.h"
#include "qv4object_p.h"
#include "qv4functionobject_p.h"
#include <private/qv4mm_p.h>
#include "qv4runtime_p.h"
#include "qv4argumentsobject_p.h"
#include "qv4string_p.h"
#include "qv4jscall_p.h"

using namespace QV4;

DEFINE_MANAGED_VTABLE(ArrayData);

const ArrayVTable SimpleArrayData::static_vtbl =
{
    DEFINE_MANAGED_VTABLE_INT(SimpleArrayData, nullptr),
    Heap::ArrayData::Simple,
    SimpleArrayData::reallocate,
    SimpleArrayData::get,
    SimpleArrayData::put,
    SimpleArrayData::putArray,
    SimpleArrayData::del,
    SimpleArrayData::setAttribute,
    SimpleArrayData::push_front,
    SimpleArrayData::pop_front,
    SimpleArrayData::truncate,
    SimpleArrayData::length
};

const ArrayVTable SparseArrayData::static_vtbl =
{
    DEFINE_MANAGED_VTABLE_INT(SparseArrayData, nullptr),
    Heap::ArrayData::Sparse,
    SparseArrayData::reallocate,
    SparseArrayData::get,
    SparseArrayData::put,
    SparseArrayData::putArray,
    SparseArrayData::del,
    SparseArrayData::setAttribute,
    SparseArrayData::push_front,
    SparseArrayData::pop_front,
    SparseArrayData::truncate,
    SparseArrayData::length
};

Q_STATIC_ASSERT(sizeof(Heap::ArrayData) == sizeof(Heap::SimpleArrayData));
Q_STATIC_ASSERT(sizeof(Heap::ArrayData) == sizeof(Heap::SparseArrayData));

void Heap::ArrayData::markObjects(Heap::Base *base, MarkStack *stack)
{
    ArrayData *a = static_cast<ArrayData *>(base);
    a->values.mark(stack);
}


void ArrayData::realloc(Object *o, Type newType, uint requested, bool enforceAttributes)
{
    Scope scope(o->engine());
    Scoped<ArrayData> d(scope, o->arrayData());

    uint alloc = 8;
    uint toCopy = 0;
    uint offset = 0;

    if (d) {
        bool hasAttrs = d->attrs();
        enforceAttributes |= hasAttrs;

        if (requested <= d->alloc() && newType == d->type() && hasAttrs == enforceAttributes)
            return;
        if (alloc < d->alloc())
            alloc = d->alloc();

        if (d->type() < Heap::ArrayData::Sparse) {
            offset = d->d()->offset;
            toCopy = d->d()->values.size;
        } else {
            toCopy = d->alloc();
        }
        if (d->type() > newType)
            newType = d->type();
    }

    while (alloc < requested)
        alloc *= 2;
    size_t size = sizeof(Heap::ArrayData) + (alloc - 1)*sizeof(Value);
    if (enforceAttributes)
        size += alloc*sizeof(PropertyAttributes);

    Scoped<ArrayData> newData(scope);
    if (newType < Heap::ArrayData::Sparse) {
        Heap::SimpleArrayData *n = scope.engine->memoryManager->allocManaged<SimpleArrayData>(size);
        n->init();
        n->offset = 0;
        n->values.size = d ? d->d()->values.size : 0;
        newData = n;
    } else {
        Heap::SparseArrayData *n = scope.engine->memoryManager->allocManaged<SparseArrayData>(size);
        n->init();
        newData = n;
    }
    newData->setAlloc(alloc);
    newData->setType(newType);
    newData->setAttrs(enforceAttributes ? reinterpret_cast<PropertyAttributes *>(newData->d()->values.values + alloc) : nullptr);
    o->setArrayData(newData);

    if (d) {
        if (enforceAttributes) {
            if (d->attrs())
                memcpy(newData->attrs(), d->attrs(), sizeof(PropertyAttributes)*toCopy);
            else
                for (uint i = 0; i < toCopy; ++i)
                    newData->attrs()[i] = Attr_Data;
        }

        if (toCopy > d->d()->values.alloc - offset) {
            uint copyFromStart = toCopy - (d->d()->values.alloc - offset);
            // no write barrier required here
            memcpy(newData->d()->values.values + toCopy - copyFromStart, d->d()->values.values, sizeof(Value)*copyFromStart);
            toCopy -= copyFromStart;
        }
        // no write barrier required here
        memcpy(newData->d()->values.values, d->d()->values.values + offset, sizeof(Value)*toCopy);
    }

    if (newType != Heap::ArrayData::Sparse)
        return;

    Heap::SparseArrayData *sparse = static_cast<Heap::SparseArrayData *>(newData->d());

    Value *lastFree;
    if (d && d->type() == Heap::ArrayData::Sparse) {
        Heap::SparseArrayData *old = static_cast<Heap::SparseArrayData *>(d->d());
        sparse->sparse = old->sparse;
        old->sparse = nullptr;
        lastFree = &sparse->sparse->freeList;
    } else {
        sparse->sparse = new SparseArray;
        lastFree = &sparse->sparse->freeList;
        *lastFree = Encode(0);
        for (uint i = 0; i < toCopy; ++i) {
            if (!sparse->values[i].isEmpty()) {
                SparseArrayNode *n = sparse->sparse->insert(i);
                n->value = i;
            } else {
                *lastFree = Encode(i);
                sparse->values.values[i].setEmpty();
                lastFree = &sparse->values.values[i];
            }
        }
    }

    if (toCopy < sparse->values.alloc) {
        for (uint i = toCopy; i < sparse->values.alloc; ++i) {
            *lastFree = Encode(i);
            sparse->values.values[i].setEmpty();
            lastFree = &sparse->values.values[i];
        }
    }
    *lastFree = Encode(-1);

    Q_ASSERT(sparse->sparse->freeList.isInteger());
    // ### Could explicitly free the old data
}

Heap::ArrayData *SimpleArrayData::reallocate(Object *o, uint n, bool enforceAttributes)
{
    realloc(o, Heap::ArrayData::Simple, n, enforceAttributes);
    return o->arrayData();
}

void ArrayData::ensureAttributes(Object *o)
{
    if (o->arrayData() && o->arrayData()->attrs)
        return;

    ArrayData::realloc(o, Heap::ArrayData::Simple, 0, true);
}

ReturnedValue SimpleArrayData::get(const Heap::ArrayData *d, uint index)
{
    const Heap::SimpleArrayData *dd = static_cast<const Heap::SimpleArrayData *>(d);
    if (index >= dd->values.size)
        return Value::emptyValue().asReturnedValue();
    return dd->data(index).asReturnedValue();
}

bool SimpleArrayData::put(Object *o, uint index, const Value &value)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    Q_ASSERT(index >= dd->values.size || !dd->attrs || !dd->attrs[index].isAccessor());
    // ### honour attributes
    dd->setData(o->engine(), index, value);
    if (index >= dd->values.size) {
        if (dd->attrs)
            dd->attrs[index] = Attr_Data;
        dd->values.size = index + 1;
    }
    return true;
}

bool SimpleArrayData::del(Object *o, uint index)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    if (index >= dd->values.size)
        return true;

    if (!dd->attrs || dd->attrs[index].isConfigurable()) {
        dd->setData(o->engine(), index, Value::emptyValue());
        if (dd->attrs)
            dd->attrs[index] = Attr_Data;
        return true;
    }
    if (dd->data(index).isEmpty())
        return true;
    return false;
}

void SimpleArrayData::setAttribute(Object *o, uint index, PropertyAttributes attrs)
{
    o->arrayData()->attrs[index] = attrs;
}

void SimpleArrayData::push_front(Object *o, const Value *values, uint n)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    Q_ASSERT(!dd->attrs);
    if (dd->values.size + n > dd->values.alloc) {
        realloc(o, Heap::ArrayData::Simple, dd->values.size + n, false);
        Q_ASSERT(o->d()->arrayData->type == Heap::ArrayData::Simple);
        dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    }
    if (n <= dd->offset) {
        dd->offset -= n; // there is enough space left in front
    } else {
         // we need to wrap around, so:
        dd->offset = dd->values.alloc - // start at the back, but subtract:
                (n - dd->offset); // the number of items we can put in the free space at the start of the allocated array
    }
    dd->values.size += n;
    for (uint i = 0; i < n; ++i)
        dd->setData(o->engine(), i, values[i]);
}

ReturnedValue SimpleArrayData::pop_front(Object *o)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    Q_ASSERT(!dd->attrs);
    if (!dd->values.size)
        return Encode::undefined();

    ReturnedValue v = dd->data(0).isEmpty() ? Encode::undefined() : dd->data(0).asReturnedValue();
    dd->offset = (dd->offset + 1) % dd->values.alloc;
    --dd->values.size;
    return v;
}

uint SimpleArrayData::truncate(Object *o, uint newLen)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    if (dd->values.size < newLen)
        return newLen;

    if (!dd->attrs) {
        dd->values.size = newLen;
        return newLen;
    }

    while (dd->values.size > newLen) {
        if (!dd->data(dd->values.size - 1).isEmpty() && !dd->attrs[dd->values.size - 1].isConfigurable())
            return dd->values.size;
        --dd->values.size;
    }
    return dd->values.size;
}

uint SimpleArrayData::length(const Heap::ArrayData *d)
{
    return d->values.size;
}

bool SimpleArrayData::putArray(Object *o, uint index, const Value *values, uint n)
{
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    if (index + n > dd->values.alloc) {
        reallocate(o, index + n + 1, false);
        dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    }
    QV4::ExecutionEngine *e = o->engine();
    for (uint i = dd->values.size; i < index; ++i)
        dd->setData(e, i, Value::emptyValue());
    for (uint i = 0; i < n; ++i)
        dd->setData(e, index + i, values[i]);
    dd->values.size = qMax(dd->values.size, index + n);
    return true;
}

void SparseArrayData::free(Heap::ArrayData *d, uint idx)
{
    Q_ASSERT(d && d->type == Heap::ArrayData::Sparse);
    Value *v = d->values.values + idx;
    if (d->attrs && d->attrs[idx].isAccessor()) {
        // double slot, free both. Order is important, so we have a double slot for allocation again afterwards.
        v[1] = d->sparse->freeList;
        v[0] = Encode(idx + 1);
    } else {
        *v = d->sparse->freeList;
    }
    d->sparse->freeList = Encode(idx);
    if (d->attrs)
        d->attrs[idx].clear();
}

Heap::ArrayData *SparseArrayData::reallocate(Object *o, uint n, bool enforceAttributes)
{
    realloc(o, Heap::ArrayData::Sparse, n, enforceAttributes);
    return o->arrayData();
}

// double slots are required for accessor properties
uint SparseArrayData::allocate(Object *o, bool doubleSlot)
{
    Q_ASSERT(o->d()->arrayData->type == Heap::ArrayData::Sparse);
    Heap::SimpleArrayData *dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
    if (doubleSlot) {
        Value *last = &dd->sparse->freeList;
        while (1) {
            if (last->int_32() == -1) {
                reallocate(o, dd->values.alloc + 2, true);
                dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
                last = &dd->sparse->freeList;
                Q_ASSERT(last->int_32() != -1);
            }

            Q_ASSERT(dd->values[static_cast<uint>(last->int_32())].int_32() != last->int_32());
            if (dd->values[static_cast<uint>(last->int_32())].int_32() == last->int_32() + 1) {
                // found two slots in a row
                uint idx = static_cast<uint>(last->int_32());
                *last = Encode(dd->values[static_cast<uint>(last->int_32()) + 1].int_32());
                dd->attrs[idx] = Attr_Accessor;
                return idx;
            }
            last = &dd->values.values[last->int_32()];
        }
    } else {
        if (dd->sparse->freeList.int_32() == -1) {
            reallocate(o, dd->values.alloc + 1, false);
            dd = o->d()->arrayData.cast<Heap::SimpleArrayData>();
        }
        Q_ASSERT(dd->sparse->freeList.int_32() != -1);
        uint idx = static_cast<uint>(dd->sparse->freeList.int_32());
        dd->sparse->freeList = dd->values[idx];
        Q_ASSERT(dd->sparse->freeList.isInteger());
        if (dd->attrs)
            dd->attrs[idx] = Attr_Data;
        return idx;
    }
}

ReturnedValue SparseArrayData::get(const Heap::ArrayData *d, uint index)
{
    const Heap::SparseArrayData *s = static_cast<const Heap::SparseArrayData *>(d);
    index = s->mappedIndex(index);
    if (index == UINT_MAX)
        return Value::emptyValue().asReturnedValue();
    return s->values[index].asReturnedValue();
}

bool SparseArrayData::put(Object *o, uint index, const Value &value)
{
    if (value.isEmpty())
        return true;

    Heap::SparseArrayData *s = o->d()->arrayData.cast<Heap::SparseArrayData>();
    SparseArrayNode *n = s->sparse->insert(index);
    Q_ASSERT(n->value == UINT_MAX || !s->attrs || !s->attrs[n->value].isAccessor());
    if (n->value == UINT_MAX)
        n->value = allocate(o);
    s = o->d()->arrayData.cast<Heap::SparseArrayData>();
    s->setArrayData(o->engine(), n->value, value);
    if (s->attrs)
        s->attrs[n->value] = Attr_Data;
    return true;
}

bool SparseArrayData::del(Object *o, uint index)
{
    Heap::SparseArrayData *dd = o->d()->arrayData.cast<Heap::SparseArrayData>();

    SparseArrayNode *n = dd->sparse->findNode(index);
    if (!n)
        return true;

    uint pidx = n->value;
    Q_ASSERT(!dd->values[pidx].isEmpty());

    bool isAccessor = false;
    if (dd->attrs) {
        if (!dd->attrs[pidx].isConfigurable())
            return false;

        isAccessor = dd->attrs[pidx].isAccessor();
        dd->attrs[pidx] = Attr_Data;
    }

    if (isAccessor) {
        // free up both indices
        dd->values.values[pidx + 1] = dd->sparse->freeList;
        dd->values.values[pidx] = Encode(pidx + 1);
    } else {
        Q_ASSERT(dd->type == Heap::ArrayData::Sparse);
        dd->values.values[pidx] = dd->sparse->freeList;
    }

    dd->sparse->freeList = Encode(pidx);
    dd->sparse->erase(n);
    return true;
}

void SparseArrayData::setAttribute(Object *o, uint index, PropertyAttributes attrs)
{
    Heap::SparseArrayData *d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    SparseArrayNode *n = d->sparse->insert(index);
    if (n->value == UINT_MAX) {
        n->value = allocate(o, attrs.isAccessor());
        d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    }
    else if (attrs.isAccessor() != d->attrs[n->value].isAccessor()) {
        // need to convert the slot
        free(o->arrayData(), n->value);
        n->value = allocate(o, attrs.isAccessor());
        d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    }
    d->attrs[n->value] = attrs;
}

void SparseArrayData::push_front(Object *o, const Value *values, uint n)
{
    Heap::SparseArrayData *d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    Q_ASSERT(!d->attrs);
    for (int i = static_cast<int>(n) - 1; i >= 0; --i) {
        uint idx = allocate(o);
        d = o->d()->arrayData.cast<Heap::SparseArrayData>();
        d->setArrayData(o->engine(), idx, values[i]);
        d->sparse->push_front(idx);
    }
}

ReturnedValue SparseArrayData::pop_front(Object *o)
{
    Heap::SparseArrayData *d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    Q_ASSERT(!d->attrs);
    uint idx = d->sparse->pop_front();
    ReturnedValue v;
    if (idx != UINT_MAX) {
        v = d->values[idx].asReturnedValue();
        free(o->arrayData(), idx);
    } else {
        v = Encode::undefined();
    }
    return v;
}

uint SparseArrayData::truncate(Object *o, uint newLen)
{
    Heap::SparseArrayData *d = o->d()->arrayData.cast<Heap::SparseArrayData>();
    SparseArrayNode *begin = d->sparse->lowerBound(newLen);
    if (begin != d->sparse->end()) {
        SparseArrayNode *it = d->sparse->end()->previousNode();
        while (1) {
            if (d->attrs) {
                if (!d->attrs[it->value].isConfigurable()) {
                    newLen = it->key() + 1;
                    break;
                }
            }
            free(o->arrayData(), it->value);
            bool brk = (it == begin);
            SparseArrayNode *prev = it->previousNode();
            d->sparse->erase(it);
            if (brk)
                break;
            it = prev;
        }
    }
    return newLen;
}

uint SparseArrayData::length(const Heap::ArrayData *d)
{
    const Heap::SparseArrayData *dd = static_cast<const Heap::SparseArrayData *>(d);
    if (!dd->sparse)
        return 0;
    SparseArrayNode *n = dd->sparse->end();
    n = n->previousNode();
    return n ? n->key() + 1 : 0;
}

bool SparseArrayData::putArray(Object *o, uint index, const Value *values, uint n)
{
    for (uint i = 0; i < n; ++i)
        put(o, index + i, values[i]);
    return true;
}


uint ArrayData::append(Object *obj, ArrayObject *otherObj, uint n)
{
    Q_ASSERT(!obj->d()->arrayData || !obj->d()->arrayData->attrs);

    if (!n)
        return obj->getLength();

    Scope scope(obj->engine());
    Scoped<ArrayData> other(scope, otherObj->arrayData());

    if (other && other->isSparse())
        obj->initSparseArray();
    else
        obj->arrayCreate();

    uint oldSize = obj->getLength();

    if (!other || ArgumentsObject::isNonStrictArgumentsObject(otherObj)) {
        ScopedValue v(scope);
        for (uint i = 0; i < n; ++i)
            obj->arraySet(oldSize + i, (v = otherObj->get(i)));
    } else if (other->isSparse()) {
        Heap::SparseArrayData *os = static_cast<Heap::SparseArrayData *>(other->d());
        if (other->hasAttributes()) {
            ScopedValue v(scope);
            for (const SparseArrayNode *it = os->sparse->begin();
                 it != os->sparse->end(); it = it->nextNode()) {
                v = otherObj->getValue(os->values[it->value], other->d()->attrs[it->value]);
                obj->arraySet(oldSize + it->key(), v);
            }
        } else {
            for (const SparseArrayNode *it = other->d()->sparse->begin();
                 it != os->sparse->end(); it = it->nextNode())
                obj->arraySet(oldSize + it->key(), os->values[it->value]);
        }
    } else {
        Heap::SimpleArrayData *os = static_cast<Heap::SimpleArrayData *>(other->d());
        uint toCopy = n;
        uint chunk = toCopy;
        if (chunk > os->values.alloc - os->offset)
            chunk = os->values.alloc - os->offset;
        obj->arrayPut(oldSize, os->values.data() + os->offset, chunk);
        toCopy -= chunk;
        if (toCopy)
            obj->arrayPut(oldSize + chunk, os->values.data(), toCopy);
    }

    return oldSize + n;
}

void ArrayData::insert(Object *o, uint index, const Value *v, bool isAccessor)
{
    if (!isAccessor && o->d()->arrayData->type != Heap::ArrayData::Sparse) {
        Heap::SimpleArrayData *d = o->d()->arrayData.cast<Heap::SimpleArrayData>();
        if (index < 0x1000 || index < d->values.size + (d->values.size >> 2)) {
            if (index >= d->values.alloc) {
                o->arrayReserve(index + 1);
                d = o->d()->arrayData.cast<Heap::SimpleArrayData>();
            }
            if (index >= d->values.size) {
                // mark possible hole in the array
                for (uint i = d->values.size; i < index; ++i)
                    d->setData(o->engine(), i, Value::emptyValue());
                d->values.size = index + 1;
            }
            d->setData(o->engine(), index, *v);
            return;
        }
    }

    o->initSparseArray();
    Heap::SparseArrayData *s = o->d()->arrayData.cast<Heap::SparseArrayData>();
    SparseArrayNode *n = s->sparse->insert(index);
    if (n->value == UINT_MAX)
        n->value = SparseArrayData::allocate(o, isAccessor);
    s = o->d()->arrayData.cast<Heap::SparseArrayData>();
    s->setArrayData(o->engine(), n->value, *v);
    if (isAccessor)
        s->setArrayData(o->engine(), n->value + Object::SetterOffset, v[Object::SetterOffset]);
}


class ArrayElementLessThan
{
public:
    inline ArrayElementLessThan(ExecutionEngine *engine, const Value &comparefn)
        : m_engine(engine), m_comparefn(comparefn) {}

    bool operator()(Value v1, Value v2) const;

private:
    ExecutionEngine *m_engine;
    const Value &m_comparefn;
};


bool ArrayElementLessThan::operator()(Value v1, Value v2) const
{
    Scope scope(m_engine);

    if (v1.isUndefined() || v1.isEmpty())
        return false;
    if (v2.isUndefined() || v2.isEmpty())
        return true;
    ScopedFunctionObject o(scope, m_comparefn);
    if (o) {
        Scope scope(o->engine());
        ScopedValue result(scope);
        JSCallArguments jsCallData(scope, 2);
        jsCallData.args[0] = v1;
        jsCallData.args[1] = v2;
        result = o->call(jsCallData);
        if (scope.hasException())
            return false;

        return result->toNumber() < 0;
    }
    ScopedString p1s(scope, v1.toString(scope.engine));
    ScopedString p2s(scope, v2.toString(scope.engine));

    if (!p1s)
        return false;
    if (!p2s)
        return true;

    return p1s->toQString() < p2s->toQString();
}

template <typename RandomAccessIterator, typename LessThan>
void sortHelper(RandomAccessIterator start, RandomAccessIterator end, LessThan lessThan)
{
top:
    int span = int(end - start);
    if (span < 2)
        return;

    --end;
    RandomAccessIterator low = start, high = end - 1;
    RandomAccessIterator pivot = start + span / 2;

    if (lessThan(*end, *start))
        qSwap(*end, *start);
    if (span == 2)
        return;

    if (lessThan(*pivot, *start))
        qSwap(*pivot, *start);
    if (lessThan(*end, *pivot))
        qSwap(*end, *pivot);
    if (span == 3)
        return;

    qSwap(*pivot, *end);

    while (low < high) {
        while (low < high && lessThan(*low, *end))
            ++low;

        while (high > low && lessThan(*end, *high))
            --high;

        if (low < high) {
            qSwap(*low, *high);
            ++low;
            --high;
        } else {
            break;
        }
    }

    if (lessThan(*low, *end))
        ++low;

    qSwap(*end, *low);
    sortHelper(start, low, lessThan);

    start = low + 1;
    ++end;
    goto top;
}


void ArrayData::sort(ExecutionEngine *engine, Object *thisObject, const Value &comparefn, uint len)
{
    if (!len)
        return;

    Scope scope(engine);
    Scoped<ArrayData> arrayData(scope, thisObject->arrayData());

    if (!arrayData || !arrayData->length())
        return;

    if (!comparefn.isUndefined() && !comparefn.isFunctionObject()) {
        engine->throwTypeError();
        return;
    }

    // The spec says the sorting goes through a series of get,put and delete operations.
    // this implies that the attributes don't get sorted around.

    if (arrayData->type() == Heap::ArrayData::Sparse) {
        // since we sort anyway, we can simply iterate over the entries in the sparse
        // array and append them one by one to a regular one.
        Scoped<SparseArrayData> sparse(scope, static_cast<Heap::SparseArrayData *>(arrayData->d()));

        if (!sparse->sparse()->nEntries())
            return;

        thisObject->setArrayData(nullptr);
        ArrayData::realloc(thisObject, Heap::ArrayData::Simple, sparse->sparse()->nEntries(), sparse->attrs() ? true : false);
        Heap::SimpleArrayData *d = thisObject->d()->arrayData.cast<Heap::SimpleArrayData>();

        SparseArrayNode *n = sparse->sparse()->begin();
        uint i = 0;
        if (sparse->attrs()) {
            while (n != sparse->sparse()->end()) {
                if (n->value >= len)
                    break;

                PropertyAttributes a = sparse->attrs() ? sparse->attrs()[n->value] : Attr_Data;
                d->setData(engine, i, Value::fromReturnedValue(thisObject->getValue(sparse->arrayData()[n->value], a)));
                d->attrs[i] = a.isAccessor() ? Attr_Data : a;

                n = n->nextNode();
                ++i;
            }
        } else {
            while (n != sparse->sparse()->end()) {
                if (n->value >= len)
                    break;
                d->setData(engine, i, sparse->arrayData()[n->value]);
                n = n->nextNode();
                ++i;
            }
        }
        d->values.size = i;
        if (len > i)
            len = i;
        if (n != sparse->sparse()->end()) {
            // have some entries outside the sort range that we need to ignore when sorting
            thisObject->initSparseArray();
            while (n != sparse->sparse()->end()) {
                PropertyAttributes a = sparse->attrs() ? sparse->attrs()[n->value] : Attr_Data;
                thisObject->arraySet(n->value, reinterpret_cast<const Property *>(sparse->arrayData() + n->value), a);

                n = n->nextNode();
            }

        }
    } else {
        Heap::SimpleArrayData *d = thisObject->d()->arrayData.cast<Heap::SimpleArrayData>();
        if (len > d->values.size)
            len = d->values.size;

        // sort empty values to the end
        for (uint i = 0; i < len; i++) {
            if (d->data(i).isEmpty()) {
                while (--len > i)
                    if (!d->data(len).isEmpty())
                        break;
                Q_ASSERT(!d->attrs || !d->attrs[len].isAccessor());
                d->setData(engine, i, d->data(len));
                d->setData(engine, len, Value::emptyValue());
            }
        }

        if (!len)
            return;
    }


    ArrayElementLessThan lessThan(engine, static_cast<const FunctionObject &>(comparefn));

    const auto thisArrayData = thisObject->arrayData();
    uint startIndex = thisArrayData->mappedIndex(0);
    uint endIndex = thisArrayData->mappedIndex(len - 1) + 1;
    if (startIndex < endIndex) {
        // Values are contiguous. Sort right away.
        sortHelper(
                thisArrayData->values.values + startIndex,
                thisArrayData->values.values + endIndex,
                lessThan);
    } else {
        // Values wrap around the end of the allocation. Close the gap to form a contiguous array.
        // We're going to sort anyway. So we don't need to care about order.

        // ArrayElementLessThan sorts empty and undefined to the end of the array anyway, but we
        // probably shouldn't rely on the unused slots to be actually undefined or empty.

        const uint gap = startIndex - endIndex;
        const uint allocEnd = thisArrayData->values.alloc - 1;
        for (uint i = 0; i < gap; ++i) {
            const uint from = allocEnd - i;
            const uint to = endIndex + i;
            if (from < startIndex)
                break;

            std::swap(thisArrayData->values.values[from], thisArrayData->values.values[to]);
        }

        thisArrayData->offset = 0;
        sortHelper(thisArrayData->values.values, thisArrayData->values.values + len, lessThan);
    }

#ifdef CHECK_SPARSE_ARRAYS
    thisObject->initSparseArray();
#endif

}
