private void AssertStringFieldIsMerged(ProgramInformationMergeFieldsFlags field, Action <TestProgramInformation> otherSourceFieldSetter, Func <IProgramInformation, string> informationFieldGetter)
{
var emptyInformation = new TestProgramInformation();
Assert.Null(informationFieldGetter(emptyInformation));
var otherInformationSource = new TestProgramInformation();
otherSourceFieldSetter(otherInformationSource);
Assert.NotNull(informationFieldGetter(otherInformationSource));
var mergedInformation = emptyInformation.Merge(field, new Tuple <IProgramInformation, ProgramInformationMergeFieldsFlags>(otherInformationSource, field));
var expectedValue = informationFieldGetter(otherInformationSource);
var actualValue = informationFieldGetter(mergedInformation);
Assert.Equal(expectedValue, actualValue);
}
/// <summary>
/// Merges the given IProgramInformation data to form a new, combined version of the information.
/// </summary>
/// <param name="programInformation">The "primary" source of information.</param>
/// <param name="fieldsToMerge">Identifies which fields to merge.</param>
/// <param name="otherSources">The other information sources to merge, and how to merge them. See Remarks.</param>
/// <returns>The merged program information.</returns>
/// <remarks>Each of the additional information sources in the merge will be combined with the primary. The newly
/// merged information is initialized using the data from <paramref name="programInformation"/>. The
/// other sources should be ordered such that the first entry is the "most important" and the final entry the
/// "least important". Each entry also describes which fields it is allowed to override in the merge.
/// This is to offer a means of conflict resolution in situations arising from multiple sources containing
/// the same information and attempting to override the default. For example, consider the case in which
/// <paramref name="programInformation"/> and two entries are provided via <paramref name="otherSources"/>,
/// all three of which define a value for <see cref="IProgramInformation.Title"/>. Here are some ways in which
/// this can be configured:
/// <code>
/// fieldsToMerge = ProgramInformationMergeFieldsFlags.None;
/// </code>
/// In this case, the information in <paramref name="programInformation"/> will not be changed. A copy of the
/// data within it will be returned. Note, however, that the specific implementation of <see cref="IProgramInformation"/>
/// used to deliver the resulting data may be different than the original!
/// Now, consider this scenario:
/// <code>
/// fieldsToMerge = ProgramInformationMergeFieldsFlags.Title;
/// otherSources[0].Item2 = ProgramInformationMergeFieldsFlags.Title;
/// otherSources[1].Item2 = ProgramInformationMergeFieldsFlags.Title;
/// </code>
/// In this case, each entry allows 'Title' to be set. Because <paramref name="programInformation"/> is
/// treated as the highest priority, its value will be retained unless it is not set (in this case, a <c>null</c>
/// or empty string). So, if programInformation.Title has no value, but otherSources[0].Item1.Title does, then
/// the final result contains otherSources[0].Item1.Title, regardless of the value of otherSources[1].Item1.Title.
/// By carefully considering these flags, you can have a reasonably rich order-of-precedence defined for establishing
/// the data in the merged result.
/// </remarks>
/// <exception cref="System.ArgumentException">Thrown if unrecognized flags are provided in <paramref name="fieldsToMerge"/> or via <paramref name="otherSources"/>.</exception>
public static IProgramInformation Merge(this IProgramInformation programInformation, ProgramInformationMergeFieldsFlags fieldsToMerge, params Tuple <IProgramInformation, ProgramInformationMergeFieldsFlags>[] otherSources)
{
// Grr.... PCLs (at least in .NET 4.0) don't support Enum.GetValues()
var flagsToProcess = new[] { ProgramInformationMergeFieldsFlags.Title, ProgramInformationMergeFieldsFlags.Vendor, ProgramInformationMergeFieldsFlags.Year, ProgramInformationMergeFieldsFlags.Features, ProgramInformationMergeFieldsFlags.ShortName, ProgramInformationMergeFieldsFlags.Crcs };
var unknownFlagsForMerge = otherSources.Select(s => s.Item2).Concat(new[] { fieldsToMerge }).Except(flagsToProcess).Except(new[] { ProgramInformationMergeFieldsFlags.None, ProgramInformationMergeFieldsFlags.All });
if (unknownFlagsForMerge.Any())
{
var unknownFlags = unknownFlagsForMerge.Aggregate((all, flag) => all | flag);
throw new ArgumentException(string.Format(Resources.Strings.ProgramInformation_InvalidFieldFormat, unknownFlags));
}
var mergedProgramInformation = new UserSpecifiedProgramInformation(programInformation);
var mergedPriorityFlags = fieldsToMerge; // accumulates if a "higher priority" info has already claimed a field
foreach (var otherSource in otherSources)
{
var otherInformation = otherSource.Item1;
var updateFlags = otherSource.Item2;
foreach (var flag in flagsToProcess)
{
if (updateFlags.HasFlag(flag))
{
switch (flag)
{
case ProgramInformationMergeFieldsFlags.Title:
if (string.IsNullOrEmpty(mergedProgramInformation.Title) || !mergedPriorityFlags.HasFlag(flag))
{
mergedProgramInformation.Title = otherInformation.Title;
if (!string.IsNullOrEmpty(mergedProgramInformation.Title))
{
mergedPriorityFlags |= flag;
}
}
break;
case ProgramInformationMergeFieldsFlags.Vendor:
if (string.IsNullOrEmpty(mergedProgramInformation.Vendor) || !mergedPriorityFlags.HasFlag(flag))
{
mergedProgramInformation.Vendor = otherInformation.Vendor;
if (!string.IsNullOrEmpty(mergedProgramInformation.Vendor))
{
mergedPriorityFlags |= flag;
}
}
break;
case ProgramInformationMergeFieldsFlags.Year:
if (string.IsNullOrEmpty(mergedProgramInformation.Year) || !mergedPriorityFlags.HasFlag(flag))
{
mergedProgramInformation.Year = otherInformation.Year;
if (!string.IsNullOrEmpty(mergedProgramInformation.Year))
{
mergedPriorityFlags |= flag;
}
}
break;
case ProgramInformationMergeFieldsFlags.Features:
// This runs the risk of combining conflicting flags...
mergedProgramInformation.Features = ProgramFeatures.Combine(mergedProgramInformation.Features, otherInformation.Features);
mergedPriorityFlags |= flag;
break;
case ProgramInformationMergeFieldsFlags.ShortName:
if (string.IsNullOrEmpty(mergedProgramInformation.ShortName) || !mergedPriorityFlags.HasFlag(flag))
{
mergedProgramInformation.ShortName = otherInformation.ShortName;
if (!string.IsNullOrEmpty(mergedProgramInformation.ShortName))
{
mergedPriorityFlags |= flag;
}
}
break;
case ProgramInformationMergeFieldsFlags.Crcs:
var crcsToMerge = otherInformation.Crcs.Where(o => !mergedProgramInformation.Crcs.Any(m => m.Crc == o.Crc));
foreach (var crc in crcsToMerge)
{
mergedProgramInformation.AddCrc(crc.Crc, crc.Description, crc.Incompatibilities);
mergedPriorityFlags |= flag;
}
break;
}
}
}
}
return(mergedProgramInformation);
}