From 5f3e7ff0c704e8ec9b518379c0208d466916cd09 Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Tue, 3 Mar 2026 14:27:17 +0100
Subject: [PATCH 1/2] new logic to replace an incompatbile waypoint and
 instrument problem with a general problem instead

---
 .../make_realistic/problems/simulator.py       | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/virtualship/make_realistic/problems/simulator.py b/src/virtualship/make_realistic/problems/simulator.py
index ee206e9a..dcffbbff 100644
--- a/src/virtualship/make_realistic/problems/simulator.py
+++ b/src/virtualship/make_realistic/problems/simulator.py
@@ -181,8 +181,26 @@ def select_problems(
                 else:
                     if available_idxs:
                         wp_select = random.choice(available_idxs)
+
+                        # fmt: off
+                        # check waypoint actually deploys the instrument associated with the problem...if not, replace it with a general (non-instrument related) problem
+                        # rather than a different waypoint, because it's possible no applicable waypoint is still available
+                        wp_instruments = self.expedition.schedule.waypoints[wp_select].instrument
+                        if isinstance(problem, InstrumentProblem) and problem.instrument_type not in wp_instruments:
+                            available_general = [p for p in GENERAL_PROBLEMS if not p.pre_departure and p not in selected_problems]
+
+                            if not available_general:
+                                unassigned_problems.append(problem)
+                                continue
+
+                            replacement = random.choice(available_general)
+                            problem_idx = selected_problems.index(problem)
+                            selected_problems[problem_idx] = replacement
+                        # fmt: on
+
                         waypoint_idxs.append(wp_select)
                         available_idxs.remove(wp_select)  # each waypoint only used once
+
                     else:
                         unassigned_problems.append(
                             problem

From 10fc1d9e202c6da4862f207c10e77f4806f535a5 Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Tue, 3 Mar 2026 14:27:37 +0100
Subject: [PATCH 2/2] update tests

---
 .../make_realistic/problems/test_simulator.py | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/tests/make_realistic/problems/test_simulator.py b/tests/make_realistic/problems/test_simulator.py
index 6a3f5558..ccd1de18 100644
--- a/tests/make_realistic/problems/test_simulator.py
+++ b/tests/make_realistic/problems/test_simulator.py
@@ -267,3 +267,54 @@ def test_post_expedition_report(tmp_path):
         assert problem.message in content, (
             "Problem messages in report should match those of selected problems."
         )
+
+
+def test_instrument_problems_only_selected_when_instruments_present(tmp_path):
+    expedition = _make_simple_expedition(num_waypoints=3, no_instruments=True)
+    instruments_in_expedition = expedition.get_instruments()
+    assert len(instruments_in_expedition) == 0, "Expedition should have no instruments"
+
+    simulator = ProblemSimulator(expedition, str(tmp_path))
+    problems = simulator.select_problems(
+        instruments_in_expedition, difficulty_level="hard"
+    )
+
+    has_instrument_problems = any(
+        isinstance(cls, InstrumentProblem) for cls in problems["problem_class"]
+    )
+    assert not has_instrument_problems, (
+        "Should not select instrument problems when no instruments are present"
+    )
+
+
+def test_instrument_not_present_doesnt_select_instrument_problem(tmp_path):
+    expedition = _make_simple_expedition(num_waypoints=3, no_instruments=True)
+
+    # prescribe instruments at waypoints, for this test case each should only be present at one waypoint
+    expedition.schedule.waypoints[0].instrument = [InstrumentType.CTD]
+    expedition.schedule.waypoints[1].instrument = [
+        InstrumentType.ARGO_FLOAT,
+        InstrumentType.DRIFTER,
+    ]
+
+    instruments_in_expedition = expedition.get_instruments()
+    simulator = ProblemSimulator(expedition, str(tmp_path))
+
+    # run many iterations of randomly selecting problems and check that if an instrument problem is selected, the associated instrument is actually present at the selected waypoint
+    for _ in range(int(1e4)):
+        problems = simulator.select_problems(
+            instruments_in_expedition, difficulty_level="hard"
+        )
+
+        for problem, wp_i in zip(
+            problems["problem_class"], problems["waypoint_i"], strict=False
+        ):
+            if isinstance(problem, InstrumentProblem):
+                wp_instruments = expedition.schedule.waypoints[wp_i].instrument
+                assert problem.instrument_type in wp_instruments, (
+                    "Instrument problem should only be selected if the instrument is present at the selected waypoint"
+                )
+
+            # any incompatible waypoint x instrument problem combinations should have been replaced by a general problem
+            else:
+                assert isinstance(problem, GeneralProblem)