nsContainerEnumerator.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*

  A simple cursor that enumerates the elements of an RDF container
  (RDF:Bag, RDF:Seq, or RDF:Alt).

  Caveats
  -------

  1. This uses an implementation-specific detail to determine the
     index of the last element in the container; specifically, the RDF
     utilities maintain a counter attribute on the container that
     holds the numeric value of the next value that is to be
     assigned. So, this cursor will bust if you use it with a bag that
     hasn't been created using the RDF utility routines.

 */

#include "nscore.h"
#include "nsCOMPtr.h"
#include "nsIRDFContainerUtils.h"
#include "nsIRDFDataSource.h"
#include "nsIRDFNode.h"
#include "nsIRDFService.h"
#include "nsIServiceManager.h"
#include "nsRDFCID.h"
#include "nsString.h"
#include "nsXPIDLString.h"
#include "prlog.h"
#include "rdf.h"
#include "rdfutil.h"

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

static NS_DEFINE_CID(kRDFServiceCID,        NS_RDFSERVICE_CID);
static NS_DEFINE_CID(kRDFContainerUtilsCID, NS_RDFCONTAINERUTILS_CID);

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

class ContainerEnumeratorImpl : public nsISimpleEnumerator {
private:
    // pseudo-constants
    static nsrefcnt              gRefCnt;
    static nsIRDFResource*       kRDF_nextVal;
    static nsIRDFContainerUtils* gRDFC;

    nsCOMPtr<nsIRDFDataSource>      mDataSource;
    nsCOMPtr<nsIRDFResource>        mContainer;
    nsCOMPtr<nsIRDFResource>        mOrdinalProperty;

    nsCOMPtr<nsISimpleEnumerator>   mCurrent;
    nsCOMPtr<nsIRDFNode>            mResult;
    int32_t mNextIndex;

public:
    ContainerEnumeratorImpl(nsIRDFDataSource* ds, nsIRDFResource* container);
    virtual ~ContainerEnumeratorImpl();

    nsresult Init();

    NS_DECL_ISUPPORTS
    NS_DECL_NSISIMPLEENUMERATOR
};

nsrefcnt              ContainerEnumeratorImpl::gRefCnt;
nsIRDFResource*       ContainerEnumeratorImpl::kRDF_nextVal;
nsIRDFContainerUtils* ContainerEnumeratorImpl::gRDFC;


ContainerEnumeratorImpl::ContainerEnumeratorImpl(nsIRDFDataSource* aDataSource,
                                                 nsIRDFResource* aContainer)
    : mDataSource(aDataSource),
      mContainer(aContainer),
      mNextIndex(1)
{
}

nsresult
ContainerEnumeratorImpl::Init()
{
    if (gRefCnt++ == 0) {
        nsresult rv;
        nsCOMPtr<nsIRDFService> rdf = do_GetService(kRDFServiceCID);
        NS_ASSERTION(rdf != nullptr, "unable to acquire resource manager");
        if (! rdf)
            return NS_ERROR_FAILURE;

        rv = rdf->GetResource(NS_LITERAL_CSTRING(RDF_NAMESPACE_URI "nextVal"), &kRDF_nextVal);
        NS_ASSERTION(NS_SUCCEEDED(rv), "unable to get resource");
        if (NS_FAILED(rv)) return rv;

        rv = CallGetService(kRDFContainerUtilsCID, &gRDFC);
        if (NS_FAILED(rv)) return rv;
    }

    return NS_OK;
}


ContainerEnumeratorImpl::~ContainerEnumeratorImpl()
{
    if (--gRefCnt == 0) {
        NS_IF_RELEASE(kRDF_nextVal);
        NS_IF_RELEASE(gRDFC);
    }
}

NS_IMPL_ISUPPORTS1(ContainerEnumeratorImpl, nsISimpleEnumerator)


NS_IMETHODIMP
ContainerEnumeratorImpl::HasMoreElements(bool* aResult)
{
    NS_PRECONDITION(aResult != nullptr, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    nsresult rv;

    // If we've already queued up a next value, then we know there are more elements.
    if (mResult) {
        *aResult = true;
        return NS_OK;
    }

    // Otherwise, we need to grovel

    // Figure out the upper bound so we'll know when we're done. Since it's
    // possible that we're targeting a composite datasource, we'll need to
    // "GetTargets()" and take the maximum value of "nextVal" to know the
    // upper bound.
    //
    // Remember that since nextVal is the next index that we'd assign
    // to an element in a container, it's *one more* than count of
    // elements in the container.
    int32_t max = 0;

    nsCOMPtr<nsISimpleEnumerator> targets;
    rv = mDataSource->GetTargets(mContainer, kRDF_nextVal, true, getter_AddRefs(targets));
    if (NS_FAILED(rv)) return rv;

    while (1) {
        bool hasmore;
        targets->HasMoreElements(&hasmore);
        if (! hasmore)
            break;

        nsCOMPtr<nsISupports> isupports;
        targets->GetNext(getter_AddRefs(isupports));

        nsCOMPtr<nsIRDFLiteral> nextValLiteral = do_QueryInterface(isupports);
        if (! nextValLiteral)
             continue;

         const PRUnichar *nextValStr;
         nextValLiteral->GetValueConst(&nextValStr);
		 
         nsresult err;
         int32_t nextVal = nsAutoString(nextValStr).ToInteger(&err);

         if (nextVal > max)
             max = nextVal;
    }

    // Now pre-fetch our next value into mResult.
    while (mCurrent || mNextIndex < max) {

        // If mCurrent has been depleted, then conjure up a new one
        if (! mCurrent) {
            rv = gRDFC->IndexToOrdinalResource(mNextIndex, getter_AddRefs(mOrdinalProperty));
            if (NS_FAILED(rv)) return rv;

            rv = mDataSource->GetTargets(mContainer, mOrdinalProperty, true, getter_AddRefs(mCurrent));
            if (NS_FAILED(rv)) return rv;

            ++mNextIndex;
        }

        if (mCurrent) {
            bool hasMore;
            rv = mCurrent->HasMoreElements(&hasMore);
            if (NS_FAILED(rv)) return rv;

            // Is the current enumerator depleted? If so, iterate to
            // the next index.
            if (! hasMore) {
                mCurrent = nullptr;
                continue;
            }

            // "Peek" ahead and pull out the next target.
            nsCOMPtr<nsISupports> result;
            rv = mCurrent->GetNext(getter_AddRefs(result));
            if (NS_FAILED(rv)) return rv;

            mResult = do_QueryInterface(result, &rv);
            if (NS_FAILED(rv)) return rv;

            *aResult = true;
            return NS_OK;
        }
    }

    // If we get here, we ran out of elements. The cursor is empty.
    *aResult = false;
    return NS_OK;
}


NS_IMETHODIMP
ContainerEnumeratorImpl::GetNext(nsISupports** aResult)
{
    nsresult rv;

    bool hasMore;
    rv = HasMoreElements(&hasMore);
    if (NS_FAILED(rv)) return rv;

    if (! hasMore)
        return NS_ERROR_UNEXPECTED;

    NS_ADDREF(*aResult = mResult);
    mResult = nullptr;

    return NS_OK;
}


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

nsresult
NS_NewContainerEnumerator(nsIRDFDataSource* aDataSource,
                          nsIRDFResource* aContainer,
                          nsISimpleEnumerator** aResult)
{
    NS_PRECONDITION(aDataSource != nullptr, "null ptr");
    if (! aDataSource)
        return NS_ERROR_NULL_POINTER;

    NS_PRECONDITION(aContainer != nullptr, "null ptr");
    if (! aContainer)
        return NS_ERROR_NULL_POINTER;

    NS_PRECONDITION(aResult != nullptr, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    ContainerEnumeratorImpl* result = new ContainerEnumeratorImpl(aDataSource, aContainer);
    if (! result)
        return NS_ERROR_OUT_OF_MEMORY;

    NS_ADDREF(result);

    nsresult rv = result->Init();
    if (NS_FAILED(rv))
        NS_RELEASE(result);

    *aResult = result;
    return rv;
}