/// <summary>
/// Attempt to read the page, with optional retry capabilities.
/// </summary>
/// <param name="offset"></param>
/// <param name="take"></param>
/// <returns></returns>
public virtual IObservable <PageReadResult <TItem> > ReadPage(int offset, int take)
{
var request = new PageReadRequest()
{
Offset = offset, Take = Math.Min(take, MaxPageSize)
};
return(this.ReadPage(request).RetryX((retryCount, ex) => OnErrorObservable(request, ex)));
}
/// <summary>
/// Enqueue a read
/// </summary>
/// <param name="pageReadRequest"></param>
/// <param name="replaceExisting"></param>
/// <returns></returns>
protected IObservable <PageReadResult <TItem> > EnqueueReadObservable(PageReadRequest pageReadRequest, bool replaceExisting = false)
{
return(Enqueue(() =>
{
var alignedStart = 0;
var alignedEnd = 0;
if (GetReadRange(pageReadRequest, replaceExisting, ref alignedStart, ref alignedEnd))
{
return _pageReader.ReadRangeObservable(alignedStart, alignedEnd).
ObserveOn(_updateScheduler).
Do(l => Total = l.Total).
Do(l => AddUpdate(l.Offset, l.Items, replaceExisting));
}
// no need to remotely read anything, just get on with it
return Observable.Return(new PageReadResult <TItem>(pageReadRequest.Offset, this.Total, null));
}
));
}
/// <summary>
/// Default exception factory, just fail.
/// </summary>
/// <param name="request"></param>
/// <param name="exception"></param>
/// <returns></returns>
protected static IObservable <bool> DefaultErrorObservable(PageReadRequest request, Exception exception)
{
return(Observable.Return(false));
}
/// <summary>
/// Upon an exception, invoke the appropriate exeception factory.
/// </summary>
/// <param name="request"></param>
/// <param name="exception"></param>
/// <returns></returns>
protected virtual IObservable <bool> OnErrorObservable(PageReadRequest request, Exception exception)
{
return(DefaultErrorObservable(request, exception));
}
/// <summary> /// Method that will be overridden for reading page page requests. /// </summary> /// <param name="pageReadRequest"></param> /// <returns></returns> protected abstract IObservable <PageReadResult <TItem> > ReadPage(PageReadRequest pageReadRequest);
protected override IObservable <PageReadResult <TItem> > ReadPage(PageReadRequest pageReadRequest)
{
return(_readChunkObservable(pageReadRequest));
}
/// <summary>
/// Upon an exception, invoke the appropriate exeception factory.
/// </summary>
/// <param name="request"></param>
/// <param name="exception"></param>
/// <returns></returns>
protected override IObservable <bool> OnErrorObservable(PageReadRequest request, Exception exception)
{
return(_exceptionObservable != null?_exceptionObservable(request, exception) : DefaultErrorObservable(request, exception));
}
/// <summary>
/// Calculate the read range given a specified count of a 'notional' list of existing read information.
/// </summary>
/// <typeparam name="TSource"></typeparam>
/// <param name="provider"></param>
/// <param name="pageReadRequest"></param>
/// <param name="currentCount"></param>
/// <param name="alignedStart"></param>
/// <param name="alignedEnd"></param>
/// <returns></returns>
public static bool CalcReadRange <TSource>(this BaseChangeSetProvider <TSource> provider, PageReadRequest pageReadRequest, int currentCount, ref int alignedStart, ref int alignedEnd)
{
var offset = pageReadRequest.Offset;
var take = pageReadRequest.Take;
var extremum = offset + take;
/*
* var anythingToRead = true;
*
* if (provider.Total.HasValue)
* {
* anythingToRead = (offset >= currentCount) || (offset + take > currentCount) && offset < provider.Total.Value;
* }
*
* if (anythingToRead)
* {
* // start from top
* alignedStart = provider.PageAlignedOffset(currentCount);
*
* // calculate the end
* alignedEnd = Math.Max(alignedStart + take, extremum);
*
* anythingToRead = alignedStart != alignedEnd;
* }
*/
var topEnd = int.MaxValue;
if (provider.Total.HasValue)
{
topEnd = provider.Total.Value;
}
var isAnythingToRead = offset + take <= topEnd && currentCount < offset + take;
if (isAnythingToRead)
{
alignedStart = currentCount;
var adjustedExtremum = Math.Min(extremum, topEnd);
alignedEnd = adjustedExtremum;
isAnythingToRead = alignedStart != alignedEnd;
}
return(isAnythingToRead);
//return anythingToRead;
}
/// <summary>
/// Read the data
/// </summary>
/// <param name="pageReadRequest"></param>
/// <returns></returns>
public IObservable <PageReadResult <TItem> > ReadPageObservable(PageReadRequest pageReadRequest)
{
Guard.NotNull(pageReadRequest);
return(EnqueueReadObservable(pageReadRequest));
}
/// <summary> /// Overloaded method used to calculate the range of reads required. /// </summary> /// <param name="pageReadRequest">Ther read request</param> /// <param name="forceReload">Should the data be always read?</param> /// <param name="alignedStart">output start of where data should be read from</param> /// <param name="alignedEnd">out put end of where data should be read up to</param> /// <returns>True if any data should infact be read.</returns> protected abstract bool GetReadRange(PageReadRequest pageReadRequest, bool forceReload, ref int alignedStart, ref int alignedEnd);
