settled-reach/client/tests/test_step_canvas_annotation_layer.gd

## T-1182 tests: StepCanvasAnnotationLayer — the unscaled screen-space
## sibling's world->screen placement math (course polylines, settlement
## markers) and course visibility/terminus handling. Draw-call correctness
## itself needs a live render pass (this cluster's existing "state-level is
## fine" allowance, per test_atlas_descend_entry.gd's own precedent) — these
## tests pin the FRAME state (_world_to_local, _cell_center_world_m) a draw
## call would read from, without requiring a SubViewport.
class_name TestStepCanvasAnnotationLayer
extends GdUnitTestSuite

const StepCanvasTransport := preload("res://ui/implant/apps/atlas/step_canvas/step_canvas_transport.gd")


func test_set_frame_stores_the_frame_and_triggers_no_crash_on_draw() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var canvas := {
		"width": 4,
		"height": 4,
		"courses": [],
		"settlement_id": [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
	}
	layer.set_frame(canvas, Vector2(1000.0, 2000.0), "District", Vector2i(4, 4), 0.0)
	# No assertion beyond "did not crash" — set_frame()/queue_redraw() with a
	# well-formed empty-feature canvas is the baseline no-op path every
	# richer test below builds on.
	assert_object(layer).is_not_null()


func test_clear_frame_drops_the_held_canvas() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	layer.set_frame({"width": 1, "height": 1, "courses": []}, Vector2.ZERO, "Chunk", Vector2i(1, 1), 0.0)
	layer.clear_frame()
	assert_that(layer._canvas).is_null()


## _cell_center_world_m() is the inverse of step_canvas.rs's own per-cell
## placement (center_world_m + (col - half_w) * step_m) — a settlement id
## read from cell (col, row) must map back to the world point that cell was
## actually derived at.
## The invariant that survives the D-255 extent inversion, the viewport's
## aspect ratio, AND panning: **half the SHORT axis is half a rung cell.**
##
## Post-inversion the pitch is derived from the canvas rather than fixed per
## rung, so no literal spacing belongs in this test. Two things it must NOT
## assert, both of which an earlier version got wrong:
##
##  - *"the corner is half a district away"* holds only on a SQUARE canvas.
##    A real widescreen canvas spans one cell on its short axis and ~1.78 on
##    its long one, so the corner is half a district on one axis only.
##  - The canvas is one district **wide**; it is not sitting **on** a
##    district. It is a free-floating window centred wherever the player has
##    panned, with no relationship between its edges and any district
##    boundary — zoom is stepped, pan is continuous (D-255 premise 3).
##    A rung names a scale, the way a paper map says 1:25,000; it does not
##    name a cell you are inside.
func test_cell_center_world_m_short_axis_spans_exactly_one_rung_cell() -> void:
	var cell_m: float = StepCanvasTransport.RUNG_EXTENT_M["District"]
	# Landscape, portrait and square — the short axis is chosen by size, never
	# by which axis happens to be the width.
	for extent in [Vector2i(8, 4), Vector2i(4, 8), Vector2i(6, 6)]:
		var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
		add_child(layer)
		layer.set_frame(
			{"width": extent.x, "height": extent.y, "courses": []},
			Vector2.ZERO,
			"District",
			extent,
			0.0
		)
		var corner: Vector2 = layer._cell_center_world_m(0, 0)
		# On the SHORT axis, the edge sits half a rung cell from centre.
		var short_axis_offset: float = absf(corner.y if extent.y <= extent.x else corner.x)
		assert_float(short_axis_offset).override_failure_message(
			"%s: short-axis edge is %f m from centre, want half a District (%f)"
			% [extent, short_axis_offset, cell_m * 0.5]
		).is_equal_approx(cell_m * 0.5, 0.001)
		# And the centre cell is the world centre, whatever the shape. Note the
		# centre is (width/2, height/2) — NOT the same index on both axes once
		# the canvas is not square.
		assert_that(layer._cell_center_world_m(extent.x / 2, extent.y / 2)).is_equal(Vector2.ZERO)


## Panning does not align the canvas to anything — the frame's world centre is
## wherever the player stopped, and every cell offset is measured from it. A
## centre deliberately off any round boundary guards against a future change
## quietly snapping the canvas to the rung's own lattice, which would make pan
## step instead of slide.
func test_cell_center_world_m_is_independent_of_grid_alignment() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var ragged := Vector2(1_234_567.0, -987_654.0)  # deliberately unaligned
	layer.set_frame(
		{"width": 4, "height": 4, "courses": []}, ragged, "District", Vector2i(4, 4), 0.0
	)
	assert_that(layer._cell_center_world_m(2, 2)).override_failure_message(
		"the centre cell must be the frame's world centre exactly — no snapping"
	).is_equal(ragged)


func test_cell_center_world_m_offsets_by_the_frames_world_center() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	layer.set_frame(
		{"width": 2, "height": 2, "courses": []},
		Vector2(10_000.0, 20_000.0),
		"Chunk",
		Vector2i(2, 2),
		0.0
	)
	# half_w = half_h = 1; spacing = CHUNK_M / short axis = 64/2 = 32 post-
	# inversion. Cell (1,1) -> center + (1-1)*32 = center either way — this
	# asserts the centre cell lands on the centre, not the pitch itself.
	assert_that(layer._cell_center_world_m(1, 1)).is_equal(Vector2(10_000.0, 20_000.0))


## _world_to_local() delegates to StepCanvasTransport.world_m_to_canvas_local
## with the layer's OWN held frame — this pins that the layer actually reads
## its stored _world_center/_rung/_extent_cells, not stale defaults.
func test_world_to_local_uses_the_held_frame() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var world_center := Vector2(5_000.0, -3_000.0)
	var extent := Vector2i(32, 32)
	layer.set_frame({"width": 32, "height": 32, "courses": []}, world_center, "Quarter", extent, 0.0)

	var expected: Vector2 = StepCanvasTransport.world_m_to_canvas_local(
		world_center, world_center, "Quarter", extent, 0.0
	)
	assert_that(layer._world_to_local(world_center)).is_equal_approx(expected, Vector2(0.01, 0.01))


# -----------------------------------------------------------------------
# T-1175 seeded item 2 — source-taper ribbon geometry
# -----------------------------------------------------------------------


## A straight 5-point course (evenly spaced, 10px apart along +X) — the
## simplest case for pinning the arc-length taper ramp: cumulative length
## at vertex i is exactly i*10, total 40, so the taper window
## (TAPER_ARC_FRACTION * 40 = 6px) falls strictly inside the first segment.
func _straight_course_points(spacing_px: float = 10.0) -> PackedVector2Array:
	var pts := PackedVector2Array()
	for i in range(5):
		pts.append(Vector2(float(i) * spacing_px, 0.0))
	return pts


## Vertex 0 (the source, cumulative length 0) gets the hairline minimum
## width, never the class's full width — this is the taper's whole point.
## _head_widths_by_arc_length() is handed the HEAD span only (post PR #207
## finding 4's ribbon/polyline split) — this test exercises it directly on
## a short head span (the first two points), which is what
## _split_course_at_arc_length() would hand it for this same course.
func test_head_widths_by_arc_length_starts_at_the_taper_minimum() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var head := PackedVector2Array([Vector2(0.0, 0.0), Vector2(6.0, 0.0)])
	var widths: PackedFloat32Array = layer._head_widths_by_arc_length(head, 2.4)
	assert_float(widths[0]).is_equal_approx(StepCanvasAnnotationLayer.TAPER_MIN_WIDTH_PX, 0.001)


## The head's own LAST vertex always ramps to exactly full_width — that's
## the butt-joint contract _draw_tapered_course() relies on to hand off to
## the AA polyline tail at identical width.
func test_head_widths_by_arc_length_ends_at_full_width() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var head := PackedVector2Array([Vector2(0.0, 0.0), Vector2(3.0, 0.0), Vector2(6.0, 0.0)])
	var widths: PackedFloat32Array = layer._head_widths_by_arc_length(head, 2.4)
	assert_float(widths[2]).is_equal_approx(2.4, 0.001)


## The ramp is monotonically non-decreasing from source to the head's last
## vertex — no "wobble" where a later vertex is narrower than an earlier one.
func test_head_widths_by_arc_length_is_monotonic() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var head := _straight_course_points(1.0)
	var widths: PackedFloat32Array = layer._head_widths_by_arc_length(head, 2.4)
	for i in range(1, widths.size()):
		assert_float(widths[i]).is_greater_equal(widths[i - 1])


## A degenerate two-point head where both points coincide (zero-length)
## must not divide by zero — every vertex falls back to full width rather
## than crashing or producing NaN.
func test_head_widths_by_arc_length_handles_a_degenerate_zero_length_span() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var head := PackedVector2Array([Vector2(5.0, 5.0), Vector2(5.0, 5.0)])
	var widths: PackedFloat32Array = layer._head_widths_by_arc_length(head, 2.4)
	assert_float(widths[0]).is_equal_approx(2.4, 0.001)
	assert_float(widths[1]).is_equal_approx(2.4, 0.001)


# -----------------------------------------------------------------------
# PR #207 finding 4 — head/tail split (the AA-hybrid seam)
# -----------------------------------------------------------------------


## The split point lands EXACTLY at TAPER_ARC_FRACTION of the total arc
## length, interpolated within the straddling segment — not snapped to the
## nearest existing vertex (see _split_course_at_arc_length()'s own doc for
## why interpolation, not snapping, is required).
func test_split_course_at_arc_length_interpolates_the_exact_fraction() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	# Total length 40 (4 segments of 10px); taper fraction 0.15 -> split at
	# arc-length 6, which is 60% of the way through the FIRST segment
	# (0 -> 10), i.e. at x=6.
	var pts := _straight_course_points()
	var split: Array = layer._split_course_at_arc_length(pts, StepCanvasAnnotationLayer.TAPER_ARC_FRACTION)
	var head: PackedVector2Array = split[0]
	var tail: PackedVector2Array = split[1]
	assert_vector(head[head.size() - 1]).is_equal_approx(Vector2(6.0, 0.0), Vector2(0.001, 0.001))
	assert_vector(tail[0]).is_equal_approx(Vector2(6.0, 0.0), Vector2(0.001, 0.001))


## The head and tail share their boundary point EXACTLY (the butt-joint
## contract) — no gap, no overlap.
func test_split_course_at_arc_length_head_and_tail_share_the_boundary_point() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := _straight_course_points()
	var split: Array = layer._split_course_at_arc_length(pts, StepCanvasAnnotationLayer.TAPER_ARC_FRACTION)
	var head: PackedVector2Array = split[0]
	var tail: PackedVector2Array = split[1]
	assert_vector(head[head.size() - 1]).is_equal(tail[0])


## `_split_course_at_arc_length()` is a generic arc-length splitter (the
## `t_fraction` parameter is not hardwired to TAPER_ARC_FRACTION) — when the
## requested fraction covers the WHOLE course (t_fraction >= 1.0, "the taper
## window would run past the mouth"), there is no meaningful post-split
## span: the whole course is the head, tail is empty. TAPER_ARC_FRACTION
## itself (0.15) can never trigger this branch for a real course (any
## positive-length course has SOME arc beyond 15% of itself) — this pins
## the branch directly via an out-of-the-ordinary fraction, the same way a
## unit test for a generic clamp function exercises both ends of its range
## regardless of what the one real call site happens to pass.
func test_split_course_at_arc_length_returns_empty_tail_when_fraction_covers_the_whole_course() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := PackedVector2Array([Vector2(0.0, 0.0), Vector2(1.0, 0.0)])
	var split: Array = layer._split_course_at_arc_length(pts, 1.0)
	var head: PackedVector2Array = split[0]
	var tail: PackedVector2Array = split[1]
	assert_int(tail.size()).is_equal(0)
	assert_int(head.size()).is_equal(pts.size())


## The real call site's fraction (TAPER_ARC_FRACTION, 0.15) DOES still split
## even a very short two-point course — the split point just lands close to
## the source rather than at the mouth, and both head and tail are
## non-empty. This is the behavior _draw_tapered_course() actually relies
## on for a minimal two-point interior-source course.
func test_split_course_at_arc_length_still_splits_a_short_two_point_course() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := PackedVector2Array([Vector2(0.0, 0.0), Vector2(1.0, 0.0)])
	var split: Array = layer._split_course_at_arc_length(pts, StepCanvasAnnotationLayer.TAPER_ARC_FRACTION)
	var head: PackedVector2Array = split[0]
	var tail: PackedVector2Array = split[1]
	assert_int(head.size()).is_equal(2)
	assert_int(tail.size()).is_equal(2)
	assert_vector(head[head.size() - 1]).is_equal_approx(Vector2(0.15, 0.0), Vector2(0.001, 0.001))


## A degenerate (zero-length, coincident-point) course must not divide by
## zero in the split math — falls back to "whole course is the head".
func test_split_course_at_arc_length_handles_a_degenerate_zero_length_course() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := PackedVector2Array([Vector2(5.0, 5.0), Vector2(5.0, 5.0)])
	var split: Array = layer._split_course_at_arc_length(pts, StepCanvasAnnotationLayer.TAPER_ARC_FRACTION)
	var tail: PackedVector2Array = split[1]
	assert_int(tail.size()).is_equal(0)


# -----------------------------------------------------------------------
# PR #207 findings 2/3 — mitred offset (perpendicular width at bends,
# clamped against self-intersection at hairpins)
# -----------------------------------------------------------------------


## A perpendicular offset at any point along a straight horizontal course
## points along +/-Y, never +/-X — the ribbon must widen ACROSS the flow
## direction, not along it. On a straight run theta=0, so the mitred offset
## reduces to the plain half-width (no widening).
func test_mitred_offset_is_perpendicular_on_a_straight_course() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := _straight_course_points()
	var offset: Vector2 = layer._mitred_offset(pts, 2, 1.0)
	assert_float(offset.x).is_equal_approx(0.0, 0.001)
	assert_float(absf(offset.y)).is_equal_approx(1.0, 0.001)


## Finding 3 (Hoshe) — at a 90-degree bend, the mitred offset LENGTH is
## half_w / cos(45deg) = half_w * sqrt(2) ~= 1.414 * half_w, which projects
## back to exactly half_w perpendicular to EACH adjacent segment (the true
## width the old averaged-unit-normal joint under-widened by cos(theta/2),
## a 29% pinch). Course: (0,0) -> (10,0) -> (10,10) — a clean right-angle
## turn at the middle vertex.
func test_mitred_offset_at_a_90_degree_bend_restores_perpendicular_width() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var pts := PackedVector2Array([Vector2(0.0, 0.0), Vector2(10.0, 0.0), Vector2(10.0, 10.0)])
	var half_w := 1.0
	var offset: Vector2 = layer._mitred_offset(pts, 1, half_w)
	# The offset's projection onto EITHER adjacent segment's own unit
	# normal must equal half_w (the true perpendicular width on both
	# faces of the bend) — not the offset's raw length (which is longer,
	# by design, along the bisector).
	var incoming_normal := Vector2(0.0, 1.0)  # normal to the (0,0)->(10,0) segment
	var outgoing_normal := Vector2(1.0, 0.0)  # normal to the (10,0)->(10,10) segment
	assert_float(absf(offset.dot(incoming_normal))).is_equal_approx(half_w, 0.01)
	assert_float(absf(offset.dot(outgoing_normal))).is_equal_approx(half_w, 0.01)


## Finding 2 (Hoshe) — a tight hairpin (turn radius below half-width) must
## not produce a self-intersecting bowtie: the mitre offset is clamped to
## HAIRPIN_SEGMENT_FACTOR of the SHORTER adjacent segment length. Course
## with a very short middle segment (length 1) and a near-180-degree turn
## back on itself — an unclamped mitre would blow the offset length far
## past that short segment.
func test_mitred_offset_clamps_at_a_tight_hairpin() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	# (0,0) -> (1,0) -> (0, 0.01): a near-reversal at vertex 1, short
	# adjacent segments (length 1 and ~1).
	var pts := PackedVector2Array([Vector2(0.0, 0.0), Vector2(1.0, 0.0), Vector2(0.0, 0.01)])
	var half_w := 1.0
	var offset: Vector2 = layer._mitred_offset(pts, 1, half_w)
	var shortest_segment := minf(pts[1].distance_to(pts[0]), pts[2].distance_to(pts[1]))
	assert_float(offset.length()).is_less_equal(
		shortest_segment * StepCanvasAnnotationLayer.HAIRPIN_SEGMENT_FACTOR + 0.001
	)


## The ribbon polygon for an n-point head span has exactly 2n vertices (n on
## each side) — this pins the "side-A then side-B reversed" construction
## produces a closed strip outline with no dropped or duplicated vertex.
func test_head_widths_output_size_matches_head_point_count() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var head := PackedVector2Array([Vector2(0, 0), Vector2(2, 0), Vector2(4, 0), Vector2(6, 0)])
	var widths: PackedFloat32Array = layer._head_widths_by_arc_length(head, 2.4)
	assert_int(widths.size()).is_equal(head.size())


# -----------------------------------------------------------------------
# PR #207 finding 1 — crop-edge false-headwater detection gate
# -----------------------------------------------------------------------


## An interior source (well inside the canvas bounds) IS a true source —
## tapering fires.
func test_is_true_source_in_canvas_true_for_an_interior_point() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	# District spacing 2048m, extent 4x4 -> half-extent 4096m on each axis.
	layer.set_frame({"width": 4, "height": 4, "courses": []}, Vector2(1000.0, 2000.0), "District", Vector2i(4, 4), 0.0)
	assert_bool(layer._is_true_source_in_canvas(Vector2(1000.0, 2000.0))).is_true()


## A point beyond the canvas's own declared bounds is the one-station crop
## overhang (`crop_course_to_window`'s `lo = first_in.saturating_sub(1)`),
## not a true source — no taper.
func test_is_true_source_in_canvas_false_for_a_point_outside_the_bounds() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	layer.set_frame({"width": 4, "height": 4, "courses": []}, Vector2(1000.0, 2000.0), "District", Vector2i(4, 4), 0.0)
	# Half-extent is 4096m; world center + 5000m on X is well outside.
	assert_bool(layer._is_true_source_in_canvas(Vector2(1000.0 + 5000.0, 2000.0))).is_false()


## A source sitting exactly at the boundary (within CROP_EDGE_EPSILON_M)
## behaves conservatively — treated as OUTSIDE (no taper), per the ruling.
func test_is_true_source_in_canvas_is_conservative_at_the_exact_boundary() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	layer.set_frame({"width": 4, "height": 4, "courses": []}, Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	# Half-extent is 4096m exactly. A point AT the boundary (x=4096) is
	# within epsilon of the edge -> conservatively NOT a true source.
	assert_bool(layer._is_true_source_in_canvas(Vector2(4096.0, 0.0))).is_false()


## A null/malformed point (defensive — the caller already guards this via
## screen_pts.size() < 2) is conservatively NOT a true source.
func test_is_true_source_in_canvas_false_for_null() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	layer.set_frame({"width": 4, "height": 4, "courses": []}, Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	assert_bool(layer._is_true_source_in_canvas(null)).is_false()


## Godot only allows draw_*() calls INSIDE an active `_draw()`/NOTIFICATION_
## DRAW context (calling `_draw_tapered_course()` directly, outside that
## context, is a Godot Runtime Error, not a code bug) — so the "does not
## crash" smoke check for the taper=false/true routing goes through the SAME
## public entry every other "no crash" test in this suite already uses:
## `set_frame()` + `queue_redraw()` (matches
## `test_set_frame_stores_the_frame_and_triggers_no_crash_on_draw`'s own
## established pattern). This end-to-end path exercises
## `_draw_one_course()`'s routing decision (`_is_true_source_in_canvas()` ->
## `_draw_tapered_course()`'s `taper` argument) for real, without requiring
## a SubViewport or an explicit live-render await — matching this suite's
## own stated "pin the frame state, not pixels" scope. A crop-passthrough
## course (source point OUTSIDE the canvas bounds) exercises the taper=false
## flat-polyline path.
func test_set_frame_with_a_crop_passthrough_course_does_not_crash() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var canvas := {
		"width": 4,
		"height": 4,
		# world_center (0,0), District extent 4x4 -> half-extent 4096m. A
		# source at x=-9000 is well outside the canvas bounds — the crop
		# overhang case (finding 1).
		"courses": [{"class": 2, "points": [[-9000, 0], [0, 0], [10, 0]], "terminus": ""}],
	}
	layer.set_frame(canvas, Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	assert_object(layer).is_not_null()


## An interior-source course (source point inside the canvas bounds)
## exercises the taper=true ribbon-head + polyline-tail hybrid path.
func test_set_frame_with_an_interior_source_course_does_not_crash() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var canvas := {
		"width": 4,
		"height": 4,
		"courses": [{"class": 2, "points": [[0, 0], [500, 0], [1000, 0], [1500, 0]], "terminus": "Mouth"}],
	}
	layer.set_frame(canvas, Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	assert_object(layer).is_not_null()

# -----------------------------------------------------------------------
# D-261 — rivers as cartographic strokes
# -----------------------------------------------------------------------


func _canvas_with_courses(courses: Array) -> Dictionary:
	return {"width": 4, "height": 4, "courses": courses}


## A server "course" is an EDGE of the river network — the stretch between two
## confluences — not a river. Culling per course therefore culls per SEGMENT,
## and a long river assembled from many short edges vanishes entirely. Measured
## on Ferrath's Global canvas before chaining: 375 courses, 180 surviving the
## water clip, ZERO surviving the length cull. After chaining: 5 rivers.
func test_edges_chain_into_one_river_before_the_length_cull() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	# Three collinear edges, each meeting the next end-to-end. Sized so each
	# is individually UNDER the cull and the chain is comfortably over it.
	# At District with a 4x4 canvas the pitch is 512 m/gridunit and 2 px per
	# gridunit, i.e. 256 m per screen px — so the 15 px floor is 3,840 m.
	# 1,500 m per edge: 5.9 px alone (culled), 17.6 px chained (kept).
	var step: float = 1500.0
	var edges: Array = []
	for i in range(3):
		edges.append(
			{
				"class": 2,
				"points": [
					[float(i) * step, 0.0],
					[float(i + 1) * step, 0.0],
				],
			}
		)
	layer.set_frame(_canvas_with_courses(edges), Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	assert_int(layer.get_drawn_course_count()).override_failure_message(
		"three end-to-end edges must chain into ONE river, not be culled as three segments"
	).is_equal(1)


## The cull itself: a river too short to read as a line is not drawn at all,
## rather than drawn as a speck. 5 px wide by 5 px long is a square.
func test_a_river_shorter_than_the_stroke_reads_is_not_drawn() -> void:
	var layer: StepCanvasAnnotationLayer = auto_free(StepCanvasAnnotationLayer.new())
	add_child(layer)
	var tiny: Array = [{"class": 2, "points": [[0.0, 0.0], [0.001, 0.0]]}]
	layer.set_frame(_canvas_with_courses(tiny), Vector2.ZERO, "District", Vector2i(4, 4), 0.0)
	assert_int(layer.get_drawn_course_count()).override_failure_message(
		"a sub-threshold river must be dropped, not drawn as a speck"
	).is_equal(0)


## The stroke is a fixed screen-space width at every rung (D-261) — the
## per-class ladder is deliberately flattened until T-1238 restores a
## size-varying width.
func test_stroke_width_is_one_fixed_value() -> void:
	assert_float(StepCanvasAnnotationLayer.COURSE_WIDTH_PX).is_equal_approx(5.0, 0.001)
	assert_float(StepCanvasAnnotationLayer.MIN_COURSE_LENGTH_PX).override_failure_message(
		"the cull must DERIVE from the stroke (3x) so it self-corrects if the width changes"
	).is_equal_approx(StepCanvasAnnotationLayer.COURSE_WIDTH_PX * 3.0, 0.001)