"""Shared helpers that must stay importable outside Blender and Unreal.

Blender-side builders import `bpy` at module scope, so nothing in them can be unit
tested. Pure layout arithmetic lives here instead: the builders import it, and
`Tools/tests/` imports it without a 3D application.

Standard library only.
"""

from __future__ import annotations


def bay_centres(x0, x1, margin=0.9, bay=2.2):
    """Centres of equal bays across a frontage, inset by `margin` at each end.

    Used by the façade kit and the retail frontage so both use one rhythm. The count
    is the span divided by the bay module and rounded, so a 33 m frontage at a 2.2 m
    module gets 14 bays rather than one bay per 2.2 m of wall with a stub at the end.

    Returns [] when the margins consume the whole frontage.
    """
    span = (x1 - x0) - 2.0 * margin
    if span <= 0:
        return []
    count = max(1, int(round(span / bay)))
    step = span / count
    return [x0 + margin + step * (i + 0.5) for i in range(count)]