Build common interface for waypoint geometry constraints.

This is a replacement for the existing "zone geometry" classes that are
currently used for choosing locations for IP, hold, and join points.
The older approach required the author to define the methods for
choosing locations at a rather low level using shapely APIs to merge or
mask geometries. Debug UIs had to be defined manually which was a great
deal of work. Worse, those debug UIs were only useable for *successful*
waypoint placement. If there was a bug in the solver (which was pretty
much unavoidable during development or tuning), it wasn't possible to
use the debug UI.

This new system adds a (very simple) geometric constraint solver to
allow the author to describe the requirements for a waypoint at a high
level. Each waypoint type will define a waypoint solver that defines one
or more waypoint strategies which will be tried in order. For example,
the IP solver might have the following strategies:

1. Safe IP
2. Threat tolerant IP
3. Unsafe IP
4. Safe backtracking IP
5. Unsafe backtracking IP

We prefer those in the order defined, but the preferred strategies won't
always have a valid solution. When that happens, the next one is tried.

The strategies define the constraints for the waypoint location. For
example, the safe IP strategy could be defined as (in pseudo code):

* At least 5 NM away from the departure airfield
* Not farther from the departure airfield than the target is
* Within 10 NM and 45 NM of the target (doctrine dependent)
* Safe
* Within the permissible region, select the point nearest the departure
  airfield

When a solver fails to find a solution using any strategy, debug
information is automatically written in a GeoJSON format which can be
viewed on geojson.io.

Fixes dcs-liberation#3085.

game/flightplan/waypointsolver.py

@@ -0,0 +1,140 @@
+from __future__ import annotations
+
+import json
+from collections.abc import Iterator
+from pathlib import Path
+from typing import TYPE_CHECKING, Any
+
+from dcs import Point
+from dcs.mapping import Point as DcsPoint
+from dcs.terrain import Terrain
+from numpy import float64, array
+from numpy._typing import NDArray
+from shapely import transform, to_geojson
+from shapely.geometry.base import BaseGeometry
+
+if TYPE_CHECKING:
+    from .waypointstrategy import WaypointStrategy
+
+
+class NoSolutionsError(RuntimeError):
+    pass
+
+
+class WaypointSolver:
+    def __init__(self) -> None:
+        self.strategies: list[WaypointStrategy] = []
+        self.debug_output_directory: Path | None = None
+        self._terrain: Terrain | None = None
+
+    def add_strategy(self, strategy: WaypointStrategy) -> None:
+        self.strategies.append(strategy)
+
+    def set_debug_properties(self, path: Path, terrain: Terrain) -> None:
+        self.debug_output_directory = path
+        self._terrain = terrain
+
+    def to_geojson(self, geometry: BaseGeometry) -> dict[str, Any]:
+        if geometry.is_empty:
+            return json.loads(to_geojson(geometry))
+
+        assert self._terrain is not None
+        origin = DcsPoint(0, 0, self._terrain)
+
+        def xy_to_ll(points: NDArray[float64]) -> NDArray[float64]:
+            ll_points = []
+            for point in points:
+                p = origin.new_in_same_map(point[0], point[1])
+                latlng = p.latlng()
+                # Longitude is unintuitively first because it's the "X" coordinate:
+                # https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.1
+                ll_points.append([latlng.lng, latlng.lat])
+            return array(ll_points)
+
+        transformed = transform(geometry, xy_to_ll)
+        return json.loads(to_geojson(transformed))
+
+    def describe_metadata(self) -> dict[str, Any]:
+        return {}
+
+    def describe_inputs(self) -> Iterator[tuple[str, BaseGeometry]]:
+        yield from []
+
+    def describe_debug(self) -> dict[str, Any]:
+        assert self._terrain is not None
+        metadata = {"name": self.__class__.__name__, "terrain": self._terrain.name}
+        metadata.update(self.describe_metadata())
+        return {
+            "type": "FeatureCollection",
+            # The GeoJSON spec forbids us from adding a "properties" field to a feature
+            # collection, but it doesn't restrict us from adding our own custom fields.
+            # https://gis.stackexchange.com/a/209263
+            #
+            # It's possible that some consumers won't work with this, but we don't read
+            # collections directly with shapely and geojson.io is happy with it, so it
+            # works where we need it to.
+            "metadata": metadata,
+            "features": list(self.describe_features()),
+        }
+
+    def describe_features(self) -> Iterator[dict[str, Any]]:
+        for description, geometry in self.describe_inputs():
+            yield {
+                "type": "Feature",
+                "properties": {
+                    "description": description,
+                },
+                "geometry": self.to_geojson(geometry),
+            }
+
+    def dump_debug_info(self) -> None:
+        path = self.debug_output_directory
+        if path is None:
+            return
+
+        path.mkdir(exist_ok=True, parents=True)
+
+        inputs_path = path / "solver.json"
+        with inputs_path.open("w", encoding="utf-8") as inputs_file:
+            json.dump(self.describe_debug(), inputs_file)
+
+        features = list(self.describe_features())
+        for idx, strategy in enumerate(self.strategies):
+            strategy_path = path / f"{idx}.json"
+            with strategy_path.open("w", encoding="utf-8") as strategy_debug_file:
+                json.dump(
+                    {
+                        "type": "FeatureCollection",
+                        "metadata": {
+                            "name": strategy.__class__.__name__,
+                            "prerequisites": [
+                                p.describe_debug_info(self.to_geojson)
+                                for p in strategy.prerequisites
+                            ],
+                        },
+                        # Include the solver's features in the strategy feature
+                        # collection for easy copy/paste into geojson.io.
+                        "features": features
+                        + [
+                            d.to_geojson(self.to_geojson)
+                            for d in strategy.iter_debug_info()
+                        ],
+                    },
+                    strategy_debug_file,
+                )
+
+    def solve(self) -> Point:
+        if not self.strategies:
+            raise ValueError(
+                "WaypointSolver.solve() called before any strategies were added"
+            )
+
+        for strategy in self.strategies:
+            if (point := strategy.find()) is not None:
+                return point
+
+        self.dump_debug_info()
+        debug_details = "No debug output directory set"
+        if (debug_path := self.debug_output_directory) is not None:
+            debug_details = f"Debug details written to {debug_path}"
+        raise NoSolutionsError(f"No solutions found for waypoint. {debug_details}")