# Stage 6f: fold melt in the crotch box, normal-deviation detector.
# The mesh has only 3 boundary verts (00_welded closed the slits) — the remaining flap and
# dotted seam lines are welded CREASES: positions locally smooth, normals kinked. Detect
# verts whose normal deviates > ANG_THR from the 5-iter smoothed normal field, grow, melt.
#   blender --background --python 06f_fold_melt.py -- <in.blend> <out.blend>
import bpy, sys, time, math
import numpy as np

argv = sys.argv[sys.argv.index("--") + 1:]
BLEND, OUT = argv[0], argv[1]
t0 = time.time()

# optional box override: <bx> <z0> <z1> [ang_deg]
if len(argv) >= 5:
    BX, BZ0, BZ1 = float(argv[2]), float(argv[3]), float(argv[4])
    ANG_THR = math.radians(float(argv[5])) if len(argv) > 5 else math.radians(15.0)
else:
    BX, BZ0, BZ1 = 0.075, 0.340, 0.480
    ANG_THR = math.radians(15.0)
# navel stays: it is a real feature made of exactly the kind of kink this melts
NAVEL = lambda co: (np.abs(co[:, 0]) < 0.022) & (co[:, 2] > 0.495) & (co[:, 2] < 0.555) & (co[:, 1] < 0)
BOX = lambda co: (np.abs(co[:, 0]) < BX) & (co[:, 2] > BZ0) & (co[:, 2] < BZ1) & ~NAVEL(co)
MELT_ITERS = 150


def log(m):
    print(f"[fold {time.time()-t0:6.1f}s] {m}", flush=True)


bpy.ops.wm.open_mainfile(filepath=BLEND)
ob = max([o for o in bpy.data.objects if o.type == 'MESH'],
         key=lambda o: len(o.data.vertices))
me = ob.data
n_v = len(me.vertices)
co = np.empty(n_v * 3)
me.vertices.foreach_get("co", co)
co = co.reshape(-1, 3)
nrm = np.empty(n_v * 3)
me.vertices.foreach_get("normal", nrm)
nrm = nrm.reshape(-1, 3)

n_e = len(me.edges)
ev = np.empty(n_e * 2, dtype=np.int32)
me.edges.foreach_get("vertices", ev)
ev = ev.reshape(-1, 2)
order = np.concatenate([ev[:, 0], ev[:, 1]])
nbr = np.concatenate([ev[:, 1], ev[:, 0]])
srt = np.argsort(order, kind="stable")
o_s = order[srt]
n_s = nbr[srt]
ptr = np.searchsorted(o_s, np.arange(n_v + 1))
cnt = np.maximum(ptr[1:] - ptr[:-1], 1)

N = nrm.copy()
for _ in range(5):
    acc = np.zeros_like(N)
    np.add.at(acc, o_s, N[n_s])
    N = acc / cnt[:, None]
    N /= np.maximum(np.linalg.norm(N, axis=1, keepdims=True), 1e-12)
dot = np.clip((nrm * N).sum(axis=1), -1.0, 1.0)
ang = np.arccos(dot)

box = BOX(co)
hot = box & (ang > ANG_THR)
log(f"box {box.sum()}, folds {hot.sum()} (>{math.degrees(ANG_THR):.0f} deg)")
if hot.sum():
    hc = co[hot]
    log(f"fold cluster: x [{hc[:,0].min():+.4f}..{hc[:,0].max():+.4f}] "
        f"y [{hc[:,1].min():+.4f}..{hc[:,1].max():+.4f}] "
        f"z [{hc[:,2].min():+.4f}..{hc[:,2].max():+.4f}]")
    m = hot.copy()
    for _ in range(3):
        h = m[ev[:, 0]] | m[ev[:, 1]]
        m2 = m.copy()
        m2[ev[:, 0]] |= h
        m2[ev[:, 1]] |= h
        m = m2
    sidx = np.nonzero(m)[0]
    Q = co.copy()
    for _ in range(MELT_ITERS):
        acc = np.zeros_like(Q)
        np.add.at(acc, o_s, Q[n_s])
        mean = acc / cnt[:, None]
        Q[sidx] = 0.5 * Q[sidx] + 0.5 * mean[sidx]
    d = np.linalg.norm(Q - co, axis=1)
    log(f"melted {len(sidx)} fold verts, max move {d.max():.4f}")
    me.vertices.foreach_set("co", Q.reshape(-1))
    me.update()
    if me.has_custom_normals:
        vn = np.empty(n_v * 3, dtype=np.float32)
        me.vertices.foreach_get("normal", vn)
        me.normals_split_custom_set_from_vertices(vn.reshape(-1, 3))
else:
    log("no folds found")
bpy.context.preferences.filepaths.save_version = 0  # no .blend1 autosave
bpy.ops.wm.save_as_mainfile(filepath=OUT)
log(f"WROTE {OUT}")
print("FOLD_DONE")