/// <summary>
/// Selects the best action given the provided route context and list of candidate actions.
/// </summary>
/// <param name="context">The current <see cref="RouteContext">route context</see> to evaluate.</param>
/// <param name="candidates">The <see cref="IReadOnlyList{T}">read-only list</see> of candidate <see cref="ActionDescriptor">actions</see> to select from.</param>
/// <returns>The best candidate <see cref="ActionDescriptor">action</see> or <c>null</c> if no candidate matches.</returns>
public virtual ActionDescriptor SelectBestCandidate(RouteContext context, IReadOnlyList <ActionDescriptor> candidates)
{
Arg.NotNull(context, nameof(context));
Arg.NotNull(candidates, nameof(candidates));
var httpContext = context.HttpContext;
if ((context.Handler = VerifyRequestedApiVersionIsNotAmbiguous(httpContext, out var apiVersion)) != null)
{
return(null);
}
var matches = EvaluateActionConstraints(context, candidates);
var selectionContext = new ActionSelectionContext(httpContext, matches, apiVersion);
var finalMatches = SelectBestActions(selectionContext);
var properties = httpContext.ApiVersionProperties();
var selectionResult = properties.SelectionResult;
properties.ApiVersion = selectionContext.RequestedVersion;
selectionResult.AddCandidates(candidates);
if (finalMatches == null)
{
selectionResult.EndIteration();
return(null);
}
if (finalMatches.Count == 1)
{
var selectedAction = finalMatches[0];
// note: short-circuit if the api version policy has already been applied to the match
// and there are no other matches in a previous iteration which would take precendence
if (selectedAction.VersionPolicyIsApplied() && !selectionResult.HasMatchesInPreviousIterations)
{
httpContext.ApiVersionProperties().ApiVersion = selectionContext.RequestedVersion;
return(selectedAction);
}
}
if (finalMatches.Count > 0)
{
var routeData = new RouteData(context.RouteData);
var matchingActions = new MatchingActionSequence(finalMatches, routeData);
selectionResult.AddMatches(matchingActions);
selectionResult.TrySetBestMatch(matchingActions.BestMatch);
}
// note: even though we may have had a successful match, this method could be called multiple times. the final decision
// is made by the IApiVersionRoutePolicy. we return here to make sure all candidates have been considered at least once.
selectionResult.EndIteration();
return(null);
}
void AppendPossibleMatches(IReadOnlyList <ActionDescriptor> matches, RouteContext context, ActionSelectionResult result)
{
Contract.Requires(matches != null);
Contract.Requires(context != null);
Contract.Requires(result != null);
if (matches.Count == 0)
{
return;
}
var routeData = new RouteData(context.RouteData);
var matchingActions = new MatchingActionSequence(matches, routeData);
result.AddMatches(matchingActions);
result.TrySetBestMatch(matchingActions.BestMatch);
}
