108 lines
4.5 KiB
C#
108 lines
4.5 KiB
C#
using MultiversalDiplomacy.Model;
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using MultiversalDiplomacy.Orders;
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namespace MultiversalDiplomacy.Adjudicate;
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/// <summary>
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/// Helper class encapsulating the convoy pathfindind code.
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/// </summary>
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public static class PathFinder
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{
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/// <summary>
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/// Determines if a convoy path exists for a move in a convoy order.
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/// </summary>
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public static bool ConvoyPathExists(World world, ConvoyOrder order)
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=> ConvoyPathExists(world, order.Target, order.Location, order.Season);
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/// <summary>
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/// Determines if a convoy path exists for a move order.
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/// </summary>
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public static bool ConvoyPathExists(World world, MoveOrder order)
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=> ConvoyPathExists(world, order.Unit, order.Location, order.Season);
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private static bool ConvoyPathExists(
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World world,
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Unit movingUnit,
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Location unitLocation,
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Season unitSeason)
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{
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// A convoy path exists between two locations if both are land locations in provinces that
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// also have coasts, and between those coasts there is a path of adjacent sea provinces
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// (not coastal) that are occupied by fleets. The move order is valid even if the fleets
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// belong to another power or were not given convoy orders; it will simply fail.
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IDictionary<(Location location, Season season), Unit> fleets = world.Units
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.Where(unit => unit.Type == UnitType.Fleet)
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.ToDictionary(unit => (unit.Location, unit.Season));
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// Verify that the origin is a coastal province.
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if (movingUnit.Location.Type != LocationType.Land) return false;
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IEnumerable<Location> originCoasts = movingUnit.Province.Locations
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.Where(location => location.Type == LocationType.Water);
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if (!originCoasts.Any()) return false;
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// Verify that the destination is a coastal province.
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if (unitLocation.Type != LocationType.Land) return false;
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IEnumerable<Location> destCoasts = unitLocation.Province.Locations
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.Where(location => location.Type == LocationType.Water);
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if (!destCoasts.Any()) return false;
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// Seed the to-visit set with the origin coasts. Coastal locations will be filtered out of
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// locations added to the to-visit set, but the logic will still work with these as
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// starting points.
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Queue<(Location location, Season season)> toVisit = new(
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originCoasts.Select(location => (location, unitSeason)));
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HashSet<(Location, Season)> visited = new();
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// Begin pathfinding.
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while (toVisit.Any())
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{
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// Visit the next point in the queue.
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(Location currentLocation, Season currentSeason) = toVisit.Dequeue();
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visited.Add((currentLocation, currentSeason));
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var adjacents = GetAdjacentPoints(currentLocation, currentSeason);
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foreach ((Location adjLocation, Season adjSeason) in adjacents)
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{
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// If the destination is adjacent, then a path exists.
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if (destCoasts.Contains(adjLocation) && unitSeason == adjSeason) return true;
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// If not, add this location to the to-visit set if it isn't a coast, has a fleet,
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// and hasn't already been visited.
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if (!adjLocation.Province.Locations.Any(l => l.Type == LocationType.Land)
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&& fleets.ContainsKey((adjLocation, adjSeason))
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&& !visited.Contains((adjLocation, adjSeason)))
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{
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toVisit.Enqueue((adjLocation, adjSeason));
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}
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}
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}
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// If the destination was never reached, then no path exists.
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return false;
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}
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private static List<(Location, Season)> GetAdjacentPoints(Location location, Season season)
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{
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List<(Location, Season)> adjacentPoints = new();
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List<Location> adjacentLocations = location.Adjacents.ToList();
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List<Season> adjacentSeasons = season.GetAdjacentSeasons().ToList();
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foreach (Location adjacentLocation in adjacentLocations)
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{
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adjacentPoints.Add((adjacentLocation, season));
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}
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foreach (Season adjacentSeason in adjacentSeasons)
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{
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adjacentPoints.Add((location, adjacentSeason));
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}
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foreach (Location adjacentLocation in adjacentLocations)
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{
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foreach (Season adjacentSeason in adjacentSeasons)
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{
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adjacentPoints.Add((adjacentLocation, adjacentSeason));
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}
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}
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return adjacentPoints;
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}
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} |