public IEnumerable <GeoLocation> GetNearbyAreas()
{
foreach (var zipCode in ZipCodes.GetProximityList(ZipCode))
{
yield return(new GeoLocation(zipCode));
}
}
public static async Task RunOrchestrator(
[OrchestrationTrigger] IDurableOrchestrationContext context)
{
var(userId, location) = context.GetInput <(string, int)>();
var userEntity = new EntityId(nameof(UserEntity), userId);
// first, update the user information to advertise the location.
await context.CallEntityAsync(userEntity, nameof(UserEntity.SetLocation), location);
// next, try to match this user with
// someone who has already advertised their location in a nearby region
var nearbyRegions = ZipCodes.GetProximityList(location);
foreach (var region in nearbyRegions)
{
var regionProxy = context.CreateEntityProxy <IRegionEntity>(region.ToString());
string[] candidates = await(userId.StartsWith("R") ? regionProxy.GetAvailableDrivers() : regionProxy.GetAvailableRiders());
foreach (var candidate in candidates)
{
if (await TryFinalizeMatch(userId, candidate, context))
{
return;
}
}
}
// we could not find a match.
// we will just wait until someone else finds us.
}
public static async Task <bool> TryFinalizeMatch(string initiator, string candidate, IDurableOrchestrationContext context)
{
var initiatorEntity = new EntityId(nameof(UserEntity), initiator);
var candidateEntity = new EntityId(nameof(UserEntity), candidate);
// Check if both users are still available and close enough.
// To prevent race conditions, we do this in a critical section
// that locks both users.
using (await context.LockAsync(initiatorEntity, candidateEntity))
{
var initiatorProxy = context.CreateEntityProxy <IUserEntity>(initiatorEntity);
var candidateProxy = context.CreateEntityProxy <IUserEntity>(candidateEntity);
var initiatorInfo = await initiatorProxy.GetState();
var candidateInfo = await candidateProxy.GetState();
if (initiatorInfo.Location == null)
{
// initiator is no longer trying to find a match! No need to keep trying.
return(true);
}
if (candidateInfo.Location == null ||
!ZipCodes.GetProximityList(initiatorInfo.Location.Value).Contains(candidateInfo.Location.Value))
{
// candidate is no longer eligible
return(false);
}
// match was successful. Create a new ride.
var driver = initiator.StartsWith("D") ? initiatorInfo : candidateInfo;
var rider = initiator.StartsWith("R") ? initiatorInfo : candidateInfo;
var rideInfo = new RideInfo()
{
RideId = context.NewGuid(),
DriverId = driver.UserId,
DriverLocation = driver.Location.Value,
RiderId = rider.UserId,
RiderLocation = rider.Location.Value,
};
// assign both users to the new ride.
// (this is happening within the critical section)
await Task.WhenAll(initiatorProxy.SetRide(rideInfo), candidateProxy.SetRide(rideInfo));
return(true);
}
}