Fix probability_rates mismatch with local_mut_regions in generate_var…

neat/read_simulator/utils/bed_func.py

@@ -21,30 +21,29 @@
 
 def intersect_regions(mutation_regions: list, block_tuple: tuple[int, int], default_value: float) -> list:
     """
+    Clips each mutation region to the block window and returns only the overlapping
+    sub-intervals, preserving each region's mutation rate.
+
     Our assumption here is that mutation regions is a continuous list, such that
     for each region, the end of the previous region is the start of the next region,
     and there are no gaps. This should be true of anything generated from parse_beds, but
     needs some tests to verify
     """
     ret_list = []
     block_start, block_end = block_tuple
-    for i in range(len(mutation_regions)):
-        region = mutation_regions[i]
-        if region[0] <= block_start < region[1]:
-            # We found the first region covering the block
-            if block_end <= region[1]:
-                # If the block spans the entire region, we have a special case
-                ret_list.append((block_start, block_end, region[2]))
-                # nothing more to do
-                return ret_list
-            ret_list.append((block_start, region[1], region[2]))
-        elif region[0] <= block_end < region[1]:
-            # We found the last region covering the block
-            ret_list.append((region[0], block_end, region[2]))
-            # nothing more to do
-            return ret_list
-    # If we haven't returned yet, then we did not find the end in our mutations list
-    ret_list.append((mutation_regions[-1][1], block_end, default_value))
+    for region in mutation_regions:
+        overlap_start = max(region[0], block_start)
+        overlap_end = min(region[1], block_end)
+        if overlap_start < overlap_end:
+            ret_list.append((overlap_start, overlap_end, region[2]))
+
+    if not ret_list:
+        # Block is entirely outside all provided regions
+        ret_list.append((block_start, block_end, default_value))
+    elif ret_list[-1][1] < block_end:
+        # Block extends past the last region; fill the tail with the default rate
+        ret_list.append((ret_list[-1][1], block_end, default_value))
+
     return ret_list
 
 def parse_beds(options: Options, ref_keys_counts: dict) -> list:

neat/read_simulator/utils/generate_variants.py

@@ -77,8 +77,9 @@ def generate_variants(
             for variant in input_variants.contig_variants[variant_location]:
                 return_variants.add_variant(variant)
 
-    # pase out the mutation rates
-    mutation_rates = np.array([x[2] for x in mutation_rate_regions])
+    # pase out the mutation rates; substitute None with the model average
+    mutation_rates = np.array([x[2] if x[2] is not None else mutation_model.avg_mut_rate
+                               for x in mutation_rate_regions])
 
     # Trying to use a random window to keep memory under control. May need to adjust this number.
     max_window_size = 1000
@@ -114,13 +115,12 @@ def generate_variants(
     # _LOG.info(f'Planning to add {how_many_mutations} mutations. The final number may be less.')
 
     while how_many_mutations > 0:
-        # Pick a region based on the mutation rates
-        # (default is one rate for the whole chromosome, so this will be trivial in that case
-        # for this selection, we'll normalize the mutation rates
-        probability_rates = mutation_rates / sum(mutation_rates)
         # We need to intersect our chosen mutation region with our block
         local_mut_regions = bed_func.intersect_regions(mutation_rate_regions, (ref_start, ref_start + len(reference)), options.mutation_rate)
         # For no input mutation regions bed, this will return the entire sequence.
+        # Build probability weights from the intersected regions so the lengths always match.
+        local_rates = np.array([r[2] if r[2] is not None else mutation_model.avg_mut_rate for r in local_mut_regions])
+        probability_rates = local_rates / sum(local_rates)
         mut_region = options.rng.choice(a=local_mut_regions, p=probability_rates)
         mut_region_offset = (int(mut_region[0]-ref_start), int(mut_region[1]-ref_start), mut_region[2])
 

tests/test_read_simulator/test_generate_variants.py

@@ -0,0 +1,209 @@
+"""
+Regression tests for the probability_rates / local_mut_regions mismatch and
+the intersect_regions algorithm fix.
+
+Both fixed on branch fix/generate-variants-probability-rates-mismatch.
+
+Root cause (two related bugs):
+
+1. intersect_regions dropped all "middle" mutation regions (those fully
+   contained within the block) and appended a zero-length fallback when
+   block_end == last_region_end, returning M items instead of N.
+
+2. generate_variants built probability_rates from the original N-item
+   mutation_rate_regions list, then called rng.choice(a=local_mut_regions,
+   p=probability_rates) where len(local_mut_regions) == M.  When M != N
+   (always true for N >= 3 in practice) this raised:
+       ValueError: 'a' and 'p' must have same length
+
+Fixes:
+    intersect_regions — rewritten using overlap arithmetic so every region
+        that intersects the block is included and the tail fallback only fires
+        when the block genuinely extends past all regions.
+
+    generate_variants — probability_rates now derived from local_mut_regions
+        (after the intersect) so lengths always match; None rates are
+        substituted with mutation_model.avg_mut_rate.
+
+Note: the single-region case and basic generate_variants behaviour are already
+covered on the feature/claude-assisted-tests branch (28 tests).  Tests here
+cover only the multi-region and None-rate scenarios that were broken.
+"""
+import pytest
+from Bio.Seq import Seq
+from Bio.SeqRecord import SeqRecord
+
+from neat.models import MutationModel
+from neat.read_simulator.utils.bed_func import intersect_regions
+from neat.read_simulator.utils.generate_variants import generate_variants
+from neat.read_simulator.utils.options import Options
+from neat.variants import ContigVariants
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _make_ref(length: int = 400) -> SeqRecord:
+    seq = "ACGT" * (length // 4)
+    return SeqRecord(Seq(seq), id="chr1", name="chr1", description="")
+
+
+def _make_opts(seed: int = 0, min_mutations: int = 1) -> Options:
+    opts = Options(rng_seed=seed)
+    opts.ploidy = 2
+    opts.min_mutations = min_mutations
+    opts.mutation_rate = None
+    opts.mutation_bed = None
+    return opts
+
+
+def _run_gv(regions, ref=None, seed=0, min_mutations=1):
+    if ref is None:
+        ref = _make_ref()
+    opts = _make_opts(seed=seed, min_mutations=min_mutations)
+    model = MutationModel()
+    model.rng = opts.rng
+    return generate_variants(
+        reference=ref,
+        ref_start=0,
+        mutation_rate_regions=regions,
+        input_variants=ContigVariants(),
+        mutation_model=model,
+        options=opts,
+        max_qual_score=40,
+    )
+
+
+# ===========================================================================
+# intersect_regions — regression for the algorithm rewrite
+# ===========================================================================
+
+def test_intersect_three_regions_all_included():
+    """
+    Three regions spanning the block exactly — all three must appear in output.
+    The old algorithm dropped the middle region and returned only 2 items.
+    """
+    regions = [(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)]
+    result = intersect_regions(regions, (0, 400), 0.0)
+    assert len(result) == 3
+    assert result[0] == (0, 133, 0.01)
+    assert result[1] == (133, 266, 0.02)
+    assert result[2] == (266, 400, 0.05)
+
+
+def test_intersect_four_regions_all_included():
+    """Four regions, block exactly spans all — all four returned."""
+    regions = [(0, 100, 0.01), (100, 200, 0.02), (200, 300, 0.03), (300, 400, 0.05)]
+    result = intersect_regions(regions, (0, 400), 0.0)
+    assert len(result) == 4
+
+
+def test_intersect_block_end_equals_last_region_end_no_fallback():
+    """
+    When block_end == last region end the old code appended a zero-length
+    fallback (last_end, block_end, default).  The new code must NOT add it.
+    """
+    regions = [(0, 200, 0.01), (200, 400, 0.05)]
+    result = intersect_regions(regions, (0, 400), 0.0)
+    # No zero-length entry
+    assert all(r[0] < r[1] for r in result)
+
+
+def test_intersect_block_partially_overlaps_middle_region():
+    """Block (150, 350) overlaps parts of all three input regions."""
+    regions = [(0, 200, 0.01), (200, 300, 0.02), (300, 400, 0.05)]
+    result = intersect_regions(regions, (150, 350), 0.0)
+    assert (150, 200, 0.01) in result
+    assert (200, 300, 0.02) in result
+    assert (300, 350, 0.05) in result
+
+
+def test_intersect_result_is_contiguous():
+    """Output sub-intervals must be contiguous (each end == next start)."""
+    regions = [(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)]
+    result = intersect_regions(regions, (0, 400), 0.0)
+    for i in range(len(result) - 1):
+        assert result[i][1] == result[i + 1][0]
+
+
+def test_intersect_result_covers_full_block():
+    """First item starts at block_start, last item ends at block_end."""
+    regions = [(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)]
+    result = intersect_regions(regions, (0, 400), 0.0)
+    assert result[0][0] == 0
+    assert result[-1][1] == 400
+
+
+def test_intersect_block_outside_all_regions_returns_default():
+    """Block with no overlap with any region → single fallback entry."""
+    regions = [(0, 100, 0.01), (100, 200, 0.05)]
+    result = intersect_regions(regions, (300, 500), 0.99)
+    assert result == [(300, 500, 0.99)]
+
+
+# ===========================================================================
+# generate_variants — crash regression with multiple mutation rate regions
+# ===========================================================================
+
+def test_three_mut_regions_no_crash():
+    """
+    Primary crash regression: 3 mutation rate regions over a 400 bp reference.
+
+    Before the fix:
+        intersect_regions returned 2 items; probability_rates had 3 →
+        ValueError: 'a' and 'p' must have same length
+    """
+    result = _run_gv([(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)])
+    assert isinstance(result, ContigVariants)
+
+
+def test_two_mut_regions_no_crash():
+    """Two regions — was silently broken (zero-length fallback as second region)."""
+    result = _run_gv([(0, 200, 0.01), (200, 400, 0.05)])
+    assert isinstance(result, ContigVariants)
+
+
+def test_four_mut_regions_no_crash():
+    """Four regions — more aggressively exercises the fix."""
+    result = _run_gv([(0, 100, 0.01), (100, 200, 0.02), (200, 300, 0.03), (300, 400, 0.05)])
+    assert isinstance(result, ContigVariants)
+
+
+def test_none_rate_region_no_crash():
+    """
+    None rate (from recalibrate_mutation_regions when no BED rate exists) is
+    replaced by avg_mut_rate before building probability_rates.
+    """
+    result = _run_gv([(0, 200, None), (200, 400, 0.02)])
+    assert isinstance(result, ContigVariants)
+
+
+def test_all_none_rates_no_crash():
+    """All None rates fall back entirely to avg_mut_rate."""
+    result = _run_gv([(0, 200, None), (200, 400, None)])
+    assert isinstance(result, ContigVariants)
+
+
+def test_three_regions_produces_variants():
+    """Multi-region run still generates at least the requested minimum mutations."""
+    result = _run_gv([(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)],
+                     min_mutations=5)
+    assert len(result.variant_locations) >= 1
+
+
+def test_multi_region_variant_positions_in_bounds():
+    """All variant positions fall within the reference after the fix."""
+    ref = _make_ref(400)
+    result = _run_gv([(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)],
+                     ref=ref, min_mutations=5)
+    for loc in result.variant_locations:
+        assert 0 <= loc < len(ref)
+
+
+def test_multi_region_reproducible_with_same_seed():
+    """Same seed produces identical variant locations with multiple regions."""
+    regions = [(0, 133, 0.01), (133, 266, 0.02), (266, 400, 0.05)]
+    r1 = _run_gv(regions, seed=7, min_mutations=5)
+    r2 = _run_gv(regions, seed=7, min_mutations=5)
+    assert r1.variant_locations == r2.variant_locations