"""Open-ended GT2 (2GT) timing belt, straight, 2 mm pitch: length along X, centred on the origin, back of the belt up, teeth down on the XY plane. detail = "full": the teeth along the
length; tooth width is a proportion for looks, not for design (only the height and pitch are published). A belt over 500 mm carries teeth along 250 mm at each end, the middle at full
height: more teeth build too slowly for a belt. detail = "simple": a plain bar of the belt's overall height."""
import math

from steve import Model

width = 6  # mm Belt width
length = 300  # mm Belt length
detail = "full"  # full: teeth; simple: a plain bar

# Handson Technology, GT2 belt data sheet: 2 mm pitch, belt height 1.38 mm, tooth height 0.75 mm.
HEIGHT = 1.38
TOOTH_HEIGHT = 0.75
PITCH = 2.0
TOOTH_WIDTH = 1.2  # a proportion for looks
TOOTHED_LENGTH = 500  # mm: the most of a belt that carries drawn teeth

model = Model()
if detail == "simple":
    outline = [(-length / 2, 0), (length / 2, 0), (length / 2, HEIGHT), (-length / 2, HEIGHT)]
else:
    back = TOOTH_HEIGHT
    outline = [(-length / 2, back), (-length / 2, HEIGHT), (length / 2, HEIGHT), (length / 2, back)]
    count = int(length // PITCH)
    centres = [(i - (count - 1) / 2) * PITCH for i in range(count)]
    if length > TOOTHED_LENGTH:   # teeth at both ends, so an end view shows them
        kept = int(TOOTHED_LENGTH / 2 // PITCH)
        centres = centres[:kept] + centres[-kept:]
    for x in reversed(centres):
        half = TOOTH_WIDTH / 2
        outline += [(x + half, back), (x + half * 0.6, 0.0), (x - half * 0.6, 0.0), (x - half, back)]
with model.sketch("belt_sketch", on="XZ", name="Belt section") as sk:
    sk.polyline("outline", outline, closed=True)
model.extrude("belt", "belt_sketch", distance=width, both=True, name="Belt")
result = model.result()