"""C channel (U channel) of constant thickness with square corners, any size, thickness and length: the light channel
as step.parts' published models draw it.

Section: web `width` along X at the bottom, flanges `height` along Y (overall), thickness `thickness` throughout,
centred on the origin and extruded along +Z by `length`; the opening faces +Y.
"""
from steve import Model

width = 30  # mm Overall width (web)
height = 15  # mm Overall height (flanges)
thickness = 1.5  # mm Thickness
length = 1000  # mm Length
material = "unspecified"  # Material

# material choice: (STEVE material library id, appearance colour); the generic channels' models name no material
MATERIALS = {
    "unspecified": (None, None),
    "aluminum": ("aluminum-generic", "#cfd2d6"),
    "steel": ("steel-generic", "#7d8085"),
    "stainless-304": ("stainless-304", "#c9ccd0"),
}

if not (2 * thickness < width and thickness < height):
    raise ValueError("The thickness must leave an opening: 2 x thickness < width and thickness < height.")
x, y, t = width / 2, height / 2, thickness
material_id, colour = MATERIALS[material]

model = Model()
with model.sketch("section", on="XY", name="Section") as sk:
    sk.polyline("outline", [(-x, y), (-x, -y), (x, -y), (x, y), (x - t, y), (x - t, -y + t), (-x + t, -y + t),
                            (-x + t, y)])
model.extrude("channel", "section", distance=length, name="Channel")
if material_id:
    model.material(material_id, color=colour)
result = model.result()