"""
Deck-to-deck stairs from the Modular Stairs Kit (Quixel Megascans on Fab, asset wlombbzdw), already in the ship
file with its rust-free material (collection "06 KIT | Modular Stairs Kit (source)").

How the kit snaps (measured from the meshes, kit frame: +Y up the stair, Z up, floor at z 0):
  foot (SM_1, 2 treads, feet, loop rails)      at (0, 0, 0)
  flight i (SM_0, 6 treads, both handrails)     at (0, 1.3 i, 0.3 + 1.3 i)     stringers butt end to end, 45 degrees
  top plates (SM_5)                             at (0, 1.3 n, 0.3 + 1.3 n)     their flanges bolt to the landing's face
  landing face  y = 1.3 n + 0.213,  landing top  z = 0.3 + 1.3 n + 0.346
With n = 5 a stair climbs 7.146 m; it is scaled uniformly to the real height.
"""
import math

import bpy

N_FLIGHTS = 5
PERIOD = 1.3
Y_FACE = PERIOD * N_FLIGHTS + 0.213
Z_DECK = 0.3 + PERIOD * N_FLIGHTS + 0.346
X_MID = 0.0095                       # the kit's own centre line is 1 cm off its origin
RUN = Y_FACE + 0.461                 # toe of the foot to the landing face, kit units


def kit_mesh(i):
    return bpy.data.meshes["SM_wlombbzdw_%d" % i]


def kit_stair(name, coll, root, x_top, z_top, z_bot, direction, y_c):
    """direction +1: climbs toward +X, -1: toward -X. x_top = the face of the landing the stair arrives at.
    Returns (empty, children, scale)."""
    s = (z_top - z_bot) / Z_DECK
    e = bpy.data.objects.new(name, None)
    e.empty_display_type = "ARROWS"
    e.empty_display_size = 0.6
    coll.objects.link(e)
    e.parent = root
    e.rotation_euler = (0, 0, math.radians(-90.0 * direction))
    e.scale = (s, s, s)
    e.location = (x_top - direction * s * Y_FACE, y_c + direction * s * X_MID, z_bot)
    parts = [(1, "foot", (0.0, 0.0, 0.0))]
    for i in range(N_FLIGHTS):
        parts.append((0, "flight %d" % (i + 1), (0.0, PERIOD * i, 0.3 + PERIOD * i)))
    parts.append((5, "top plates", (0.0, PERIOD * N_FLIGHTS, 0.3 + PERIOD * N_FLIGHTS)))
    kids = []
    for mi, label, loc in parts:
        ob = bpy.data.objects.new("%s | %s" % (name, label), kit_mesh(mi))
        coll.objects.link(ob)
        ob.parent = e
        ob.location = loc
        kids.append(ob)
    return e, kids, s