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#include "sqlcachedresult_p.h"

QT_BEGIN_NAMESPACE

/*
   SqlCachedResult is a convenience class for databases that only allow
   forward only fetching. It will cache all the results so we can iterate
   backwards over the results again.
   All you need to do is to inherit from SqlCachedResult and reimplement
   gotoNext(). gotoNext() will have a reference to the internal cache and
   will give you an index where you can start filling in your data. Special
   case: If the user actually wants a forward-only query, idx will be -1
   to indicate that we are not interested in the actual values.
*/

static const uint initial_cache_size = 128;

class SqlCachedResultPrivate
{
public:
    SqlCachedResultPrivate();
    bool canSeek(int i) const;
    inline int cacheCount() const;
    void init(int count, bool fo);
    void cleanup();
    int nextIndex();
    void revertLast();

    SqlCachedResult::ValueCache cache;
    int rowCacheEnd;
    int colCount;
    bool forwardOnly;
    bool atEnd;
};

SqlCachedResultPrivate::SqlCachedResultPrivate():
    rowCacheEnd(0), colCount(0), forwardOnly(false), atEnd(false)
{
}

void SqlCachedResultPrivate::cleanup()
{
    cache.clear();
    forwardOnly = false;
    atEnd = false;
    colCount = 0;
    rowCacheEnd = 0;
}

void SqlCachedResultPrivate::init(int count, bool fo)
{
    Q_ASSERT(count);
    cleanup();
    forwardOnly = fo;
    colCount = count;
    if (fo) {
        cache.resize(count);
        rowCacheEnd = count;
    } else {
        cache.resize(initial_cache_size * count);
    }
}

int SqlCachedResultPrivate::nextIndex()
{
    if (forwardOnly)
        return 0;
    int newIdx = rowCacheEnd;
    if (newIdx + colCount > cache.size())
        cache.resize(qMin(cache.size() * 2, cache.size() + 10000));
    rowCacheEnd += colCount;

    return newIdx;
}

bool SqlCachedResultPrivate::canSeek(int i) const
{
    if (forwardOnly || i < 0)
        return false;
    return rowCacheEnd >= (i + 1) * colCount;
}

void SqlCachedResultPrivate::revertLast()
{
    if (forwardOnly)
        return;
    rowCacheEnd -= colCount;
}

inline int SqlCachedResultPrivate::cacheCount() const
{
    Q_ASSERT(!forwardOnly);
    Q_ASSERT(colCount);
    return rowCacheEnd / colCount;
}

//////////////

SqlCachedResult::SqlCachedResult(const QSqlDriver * db): QSqlResult (db)
{
    d = new SqlCachedResultPrivate();
}

SqlCachedResult::~SqlCachedResult()
{
    delete d;
}

void SqlCachedResult::init(int colCount)
{
    d->init(colCount, isForwardOnly());
}

bool SqlCachedResult::fetch(int i)
{
    if ((!isActive()) || (i < 0))
        return false;
    if (at() == i)
        return true;
    if (d->forwardOnly) {
        // speed hack - do not copy values if not needed
        if (at() > i || at() == QSql::AfterLastRow)
            return false;
        while(at() < i - 1) {
            if (!gotoNext(d->cache, -1))
                return false;
            setAt(at() + 1);
        }
        if (!gotoNext(d->cache, 0))
            return false;
        setAt(at() + 1);
        return true;
    }
    if (d->canSeek(i)) {
        setAt(i);
        return true;
    }
    if (d->rowCacheEnd > 0)
        setAt(d->cacheCount());
    while (at() < i + 1) {
        if (!cacheNext()) {
            if (d->canSeek(i))
                break;
            return false;
        }
    }
    setAt(i);

    return true;
}

bool SqlCachedResult::fetchNext()
{
    if (d->canSeek(at() + 1)) {
        setAt(at() + 1);
        return true;
    }
    return cacheNext();
}

bool SqlCachedResult::fetchPrevious()
{
    return fetch(at() - 1);
}

bool SqlCachedResult::fetchFirst()
{
    if (d->forwardOnly && at() != QSql::BeforeFirstRow) {
        return false;
    }
    if (d->canSeek(0)) {
        setAt(0);
        return true;
    }
    return cacheNext();
}

bool SqlCachedResult::fetchLast()
{
    if (d->atEnd) {
        if (d->forwardOnly)
            return false;
        else
            return fetch(d->cacheCount() - 1);
    }

    int i = at();
    while (fetchNext())
        ++i; /* brute force */
    if (d->forwardOnly && at() == QSql::AfterLastRow) {
        setAt(i);
        return true;
    } else {
        return fetch(i);
    }
}

QVariant SqlCachedResult::data(int i)
{
    int idx = d->forwardOnly ? i : at() * d->colCount + i;
    if (i >= d->colCount || i < 0 || at() < 0 || idx >= d->rowCacheEnd)
        return QVariant();

    return d->cache.at(idx);
}

bool SqlCachedResult::isNull(int i)
{
    int idx = d->forwardOnly ? i : at() * d->colCount + i;
    if (i >= d->colCount || i < 0 || at() < 0 || idx >= d->rowCacheEnd)
        return true;

    return d->cache.at(idx).isNull();
}

void SqlCachedResult::cleanup()
{
    setAt(QSql::BeforeFirstRow);
    setActive(false);
    d->cleanup();
}

void SqlCachedResult::clearValues()
{
    setAt(QSql::BeforeFirstRow);
    d->rowCacheEnd = 0;
    d->atEnd = false;
}

bool SqlCachedResult::cacheNext()
{
    if (d->atEnd)
        return false;

    if(isForwardOnly()) {
        d->cache.clear();
        d->cache.resize(d->colCount);
    }

    if (!gotoNext(d->cache, d->nextIndex())) {
        d->revertLast();
        d->atEnd = true;
        return false;
    }
    setAt(at() + 1);
    return true;
}

int SqlCachedResult::colCount() const
{
    return d->colCount;
}

SqlCachedResult::ValueCache &SqlCachedResult::cache()
{
    return d->cache;
}

void SqlCachedResult::virtual_hook(int id, void *data)
{
    QSqlResult::virtual_hook(id, data);
}

void SqlCachedResult::detachFromResultSet()
{
    cleanup();
}

void SqlCachedResult::setNumericalPrecisionPolicy(QSql::NumericalPrecisionPolicy policy)
{
    QSqlResult::setNumericalPrecisionPolicy(policy);
    cleanup();
}

QT_END_NAMESPACE