#!/usr/bin/env python3
"""Render Exercise Library visuals from an anatomical 3D rig.

A skeleton profile (skeleton.json: bone lengths incl. shoulder/pelvis widths
and feet, plus per-joint ROM) and a per-exercise motion script (motion.json:
key frames of anatomical joint angles - flexion/abduction/rotation measured
from neutral standing - a root anchor + trunk orientation, optional IK pins,
timing, and a camera) resolve through 3D forward kinematics and orthographic
projection into stick-figure frames. See SYSTEM.md for the format and the
visual language, kinematics.py for the math and conventions.

Outputs per exercise: frames/frame-N.svg, preview.gif (tweened, looping),
visual.svg (the primary frame). `--sheet` writes contact-sheet.png of every
key frame; `--demo` writes demo-sheet.png showing rig customizations (body
profiles, flipped camera, theme); `--orbit` writes orbit.gif per named
exercise (the camera sweeps 360 degrees while the motion loops). `--export`
instead bakes each motion down to the legacy planar schema consumed by the
in-app SwiftUI renderer. SVGs need no dependencies; GIFs/sheets need Pillow.
"""

import copy
import json
import math
import sys
from pathlib import Path

import kinematics as K

LIB = Path(__file__).parent
CANVAS = (320, 180)
GROUND_Y = 152

PALETTES = {
    "default": {
        "right": "#3a3f4b", "left": "#a9afba",
        "right_working": "#0d9488", "left_working": "#86cfc5",
        "ground": "#b9bec9", "legend_text": "#6b7180", "head_fill": "white",
        "equipment": "#c5cad4", "prop": "#6b7180",
    },
    "indigo": {
        "right": "#3a3f4b", "left": "#a9afba",
        "right_working": "#4f46e5", "left_working": "#a5b4fc",
        "ground": "#b9bec9", "legend_text": "#6b7180", "head_fill": "white",
        "equipment": "#c5cad4", "prop": "#6b7180",
    },
}
WIDTHS = {"near": 6, "far": 5, "spine": 6, "head": 6, "nose": 4}

# Draw order is by camera depth (far parts first, head always on top, filled
# opaque so overhead arms are occluded by the face). Depths are bucketed so
# side views stay stable; ties fall back to this fixed rank.
FIXED_RANK = {"arm_l": 0, "leg_l": 1, "spine": 2, "arm_r": 3, "leg_r": 4}
DEPTH_BUCKET = 3.0

PAIRS = (("arm_r", "arm_l"), ("leg_r", "leg_l"))

# Prop joint refs -> (limb, chain index): extremities are index 2, mid joints
# (elbows/knees) index 1, so equipment can ride either joint.
JOINT_LIMB = {
    "hand_r": ("arm_r", 2), "elbow_r": ("arm_r", 1),
    "hand_l": ("arm_l", 2), "elbow_l": ("arm_l", 1),
    "foot_r": ("leg_r", 2), "knee_r": ("leg_r", 1),
    "foot_l": ("leg_l", 2), "knee_l": ("leg_l", 1),
}


def profiles():
    return K.load_skeleton()["profiles"]


def dirv(deg):
    """Unit vector for a y-up angle, in y-down canvas coordinates."""
    r = math.radians(deg)
    return (math.cos(r), -math.sin(r))


def angle_of(a, b):
    """Y-up world angle of the canvas segment a->b."""
    return math.degrees(math.atan2(-(b[1] - a[1]), b[0] - a[0]))


# ------------------------------------------------------------------- solver

def mirror_frame(nf, width):
    """Mirror a normalized frame's canvas anchors for the flipped camera."""
    out = copy.deepcopy(nf)
    out["root"]["pos"][0] = width - out["root"]["pos"][0]
    out["pins"] = {k: [width - x, y] for k, (x, y) in out["pins"].items()}
    return out


def _chain_depth(pts):
    return sum(p[2] for p in pts) / len(pts)


def _bucket(depth):
    return round(depth / DEPTH_BUCKET)


def frame_geometry(nf, prof, cam, flipped=False):
    """Resolve one normalized frame into drawable 2D geometry.

    Returns (nf with IK-resolved angles and original pins, geo, order, shade):
    geo maps parts to canvas points, order is the depth-sorted draw order,
    shade maps each limb to "near"/"far" (near pair members draw dark and in
    front - the visual language; canvas-right wins depth ties in face-on
    views). The far member of each pair also gets the profile's readability
    offset, scaled by how side-on the view is, so overlapping limbs stay
    distinguishable in profile views.
    """
    p0 = K.pose(nf, prof, cam)
    shade, order_parts = {}, []
    for right, left in PAIRS:
        dr, dl = _chain_depth(p0["points"][right]), _chain_depth(p0["points"][left])
        if _bucket(dr) == _bucket(dl):
            ax_r = p0["points"][right][0][0]  # view x == canvas offset from anchor
            near = right if ax_r >= p0["points"][left][0][0] else left
        else:
            near = right if dr > dl else left
        shade[right] = "near" if near == right else "far"
        shade[left] = "near" if near == left else "far"

    fo = prof.get("farOffset", [6, 2])
    off = ((-fo[0] if flipped else fo[0]) * p0["k"], fo[1] * p0["k"])

    work = copy.deepcopy(nf)
    for limb, (_attach, _sigma, pin) in K.LIMBS.items():
        if shade[limb] == "far" and pin in work["pins"]:
            work["pins"][pin] = [work["pins"][pin][0] - off[0],
                                 work["pins"][pin][1] - off[1]]
    work, p = K.resolve(work, prof, cam)
    work["pins"] = dict(nf["pins"])  # keep authored pins; only angles resolved

    anchor = nf["root"]["pos"]

    def scr(v, limb_off=(0, 0)):
        return (anchor[0] + v[0] + limb_off[0], anchor[1] - v[1] + limb_off[1])

    pts = p["points"]
    pelvis, mid, neck_b = scr(pts["pelvis"]), scr(pts["mid"]), scr(pts["neckB"])
    geo = {"headR": prof["headR"], "head": scr(pts["head"]),
           "spine": [pelvis,
                     (2 * mid[0] - (pelvis[0] + neck_b[0]) / 2,
                      2 * mid[1] - (pelvis[1] + neck_b[1]) / 2),
                     neck_b]}
    depths = {"spine": _chain_depth([pts["pelvis"], pts["mid"], pts["neckB"]])}
    for limb in K.LIMBS:
        limb_off = off if shade[limb] == "far" else (0, 0)
        geo[limb] = [scr(v, limb_off) for v in pts[limb]]
        depths[limb] = _chain_depth(pts[limb])

    # The nose tick rides the head's anterior axis; it foreshortens naturally
    # and disappears when the face points at (or away from) the camera.
    nd = p["nose_dir"]
    mag = math.hypot(nd[0], nd[1])
    if mag > 0.3:
        ux, uy = nd[0] / mag, -nd[1] / mag
        hx, hy = geo["head"]
        r = prof["headR"]
        geo["nose"] = ((hx + ux * r, hy + uy * r),
                       (hx + ux * (r + 7 * mag), hy + uy * (r + 7 * mag)))

    order = sorted(depths, key=lambda part: (_bucket(depths[part]),
                                             FIXED_RANK[part])) + ["head"]
    return work, geo, order, shade


def ease(t):
    return 3 * t * t - 2 * t * t * t


def timeline(norms, fps=20):
    frames = []
    for i, kf in enumerate(norms):
        frames += [kf] * max(1, round(kf["hold"] * fps))
        nxt = norms[(i + 1) % len(norms)]
        steps = max(1, round(kf["tween"] * fps))
        frames += [K.lerp_frames(kf, nxt, ease(s / steps)) for s in range(1, steps)]
    return frames


# -------------------------------------------------------------------- props
# Equipment layer (see SYSTEM.md): `scene` shapes and `cable`s draw behind the
# figure in the recessive equipment gray; joint-attached items (`bar`,
# `dumbbell`, `pad`) draw over the limbs in the darker prop gray, following
# the resolved hand/foot positions frame by frame.

def flip_props(props, width):
    """Mirror the props horizontally, matching the flipped camera. Joint-
    attached props follow the mirrored limbs automatically; only fixed
    coordinates and world angles need mirroring."""
    def fx(p):
        return [width - p[0], p[1]]
    out = []
    for prop in props:
        p = json.loads(json.dumps(prop))
        if p["type"] == "scene":
            for s in p["shapes"]:
                if s["kind"] == "line":
                    s["pts"] = [fx(pt) for pt in s["pts"]]
                elif s["kind"] == "circle":
                    s["c"] = fx(s["c"])
                elif s["kind"] == "rect":
                    s["x"] = width - s["x"] - s["w"]
        elif p["type"] == "cable":
            p["from"] = fx(p["from"])
        elif p["type"] in ("bar", "pad") and "angle" in p:
            p["angle"] = 180 - p["angle"]
        out.append(p)
    return out


def joint_points(geo, ref):
    """Resolve a joint ref — `"hand_r"`, `"knee_l"`, or a midpoint list like
    `["knee_r", "foot_r"]` — to (point, unit direction of the bone ending at
    the first joint). None when the limb isn't drawn."""
    names = ref if isinstance(ref, list) else [ref]
    pts, direction = [], None
    for name in names:
        limb_name, idx = JOINT_LIMB[name]
        limb = geo.get(limb_name)
        if not limb:
            return None, None
        pts.append(limb[idx])
        if direction is None:
            a, b = limb[idx - 1], limb[idx]
            d = math.hypot(b[0] - a[0], b[1] - a[1]) or 1.0
            direction = ((b[0] - a[0]) / d, (b[1] - a[1]) / d)
    return ((sum(p[0] for p in pts) / len(pts),
             sum(p[1] for p in pts) / len(pts)), direction)


def resolve_props(props, geo):
    """Props -> drawable primitives for one frame: (background, foreground)."""
    bg, fg = [], []
    for p in props or []:
        t = p["type"]
        if t == "scene":
            for s in p["shapes"]:
                bg.append(dict(s, color=s.get("color", "equipment")))
        elif t == "cable":
            end, _ = joint_points(geo, p["to"])
            if end:
                bg.append({"kind": "line", "pts": [list(p["from"]), list(end)],
                           "w": p.get("w", 2), "color": "equipment"})
        elif t in ("bar", "dumbbell", "pad"):
            c, d = joint_points(geo, p["at"])
            if not c:
                continue
            if t == "bar" or "angle" in p:
                ux, uy = dirv(p.get("angle", 0))     # fixed world angle
            else:
                ux, uy = -d[1], d[0]                 # perpendicular to the lower bone
            h = p.get("halfLen", {"bar": 24, "dumbbell": 7, "pad": 8}[t])
            a = (c[0] - ux * h, c[1] - uy * h)
            b = (c[0] + ux * h, c[1] + uy * h)
            fg.append({"kind": "line", "pts": [a, b],
                       "w": p.get("w", {"bar": 4, "dumbbell": 3, "pad": 7}[t]),
                       "color": "prop"})
            plate = p.get("plateR", 4.5 if t == "dumbbell" else 0)
            if plate:
                for e in (a, b):
                    fg.append({"kind": "circle", "c": list(e), "r": plate,
                               "fill": True, "color": "prop"})
    return bg, fg


def svg_prims(prims, colors):
    lines = []
    for p in prims:
        color = colors[p["color"]]
        if p["kind"] == "line":
            d = "M " + " L ".join(f"{x:.1f} {y:.1f}" for x, y in p["pts"])
            lines.append(f'  <path d="{d}" stroke="{color}" stroke-width="{p.get("w", 4)}"'
                         f' stroke-linecap="round" stroke-linejoin="round"/>')
        elif p["kind"] == "circle":
            cx, cy = p["c"]
            if p.get("fill"):
                lines.append(f'  <circle cx="{cx:.1f}" cy="{cy:.1f}" r="{p["r"]}" fill="{color}"/>')
            else:
                lines.append(f'  <circle cx="{cx:.1f}" cy="{cy:.1f}" r="{p["r"]}"'
                             f' stroke="{color}" stroke-width="{p.get("w", 3)}"/>')
        elif p["kind"] == "rect":
            lines.append(f'  <rect x="{p["x"]}" y="{p["y"]}" width="{p["w"]}" height="{p["h"]}"'
                         f' rx="{p.get("r", 2)}" fill="{colors[p.get("color", "equipment")]}"/>')
    return lines


def draw_prims(d, prims, colors, scale):
    for p in prims:
        color = colors[p["color"]]
        if p["kind"] == "line":
            pts = [(x * scale, y * scale) for x, y in p["pts"]]
            w = p.get("w", 4) * scale
            d.line(pts, fill=color, width=w, joint="curve")
            for x, y in (pts[0], pts[-1]):
                d.ellipse([x - w / 2, y - w / 2, x + w / 2, y + w / 2], fill=color)
        elif p["kind"] == "circle":
            cx, cy = p["c"][0] * scale, p["c"][1] * scale
            r = p["r"] * scale
            if p.get("fill"):
                d.ellipse([cx - r, cy - r, cx + r, cy + r], fill=color)
            else:
                d.ellipse([cx - r, cy - r, cx + r, cy + r], outline=color,
                          width=p.get("w", 3) * scale)
        elif p["kind"] == "rect":
            x, y = p["x"] * scale, p["y"] * scale
            d.rounded_rectangle([x, y, x + p["w"] * scale, y + p["h"] * scale],
                                radius=p.get("r", 2) * scale, fill=color)


# ------------------------------------------------------------------- drawing

def part_style(part, working, colors, shade):
    """Near pair members draw in the dark ink, far members in the light one;
    the spine is always dark. Working parts swap ink for the accent teals."""
    tone = shade.get(part, "near")
    key = "right" if tone == "near" else "left"
    color = colors[f"{key}_working"] if part in working else colors[key]
    width = WIDTHS["spine"] if part == "spine" else WIDTHS[tone]
    return color, width


def quad_points(p0, ctrl, p2, n=24):
    pts = []
    for i in range(n + 1):
        t = i / n
        pts.append(((1 - t) ** 2 * p0[0] + 2 * (1 - t) * t * ctrl[0] + t ** 2 * p2[0],
                    (1 - t) ** 2 * p0[1] + 2 * (1 - t) * t * ctrl[1] + t ** 2 * p2[1]))
    return pts


def svg_for_frame(name, geo, order, shade, working, colors, props=None):
    bg, fg = resolve_props(props, geo)
    w, h = CANVAS
    parts = [f'<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 {w} {h}" fill="none">',
             f'  <title>{name}</title>',
             f'  <line x1="16" y1="{GROUND_Y + 4}" x2="{w - 16}" y2="{GROUND_Y + 4}"'
             f' stroke="{colors["ground"]}" stroke-width="3" stroke-linecap="round"/>']
    parts += svg_prims(bg, colors)
    for part in order:
        if part == "head":
            parts += svg_prims(fg, colors)
            hx, hy = geo["head"]
            parts.append(f'  <circle id="head" cx="{hx:.1f}" cy="{hy:.1f}" r="{geo["headR"]}"'
                         f' fill="{colors["head_fill"]}" stroke="{colors["right"]}" stroke-width="{WIDTHS["head"]}"/>')
            if "nose" in geo:
                (sx, sy), (ex, ey) = geo["nose"]
                parts.append(f'  <line id="nose" x1="{sx:.1f}" y1="{sy:.1f}" x2="{ex:.1f}" y2="{ey:.1f}"'
                             f' stroke="{colors["right"]}" stroke-width="{WIDTHS["nose"]}" stroke-linecap="round"/>')
            continue
        if part not in geo:
            continue
        color, width = part_style(part, working, colors, shade)
        if part == "spine":
            (ax, ay), (cx, cy), (bx, by) = geo["spine"]
            d = f"M {ax:.1f} {ay:.1f} Q {cx:.1f} {cy:.1f} {bx:.1f} {by:.1f}"
        else:
            d = "M " + " L ".join(f"{x:.1f} {y:.1f}" for x, y in geo[part])
        parts.append(f'  <path id="{part}" d="{d}" stroke="{color}" stroke-width="{width}"'
                     f' stroke-linecap="round" stroke-linejoin="round"/>')
    lx = w - 96
    parts.append(f'  <g font-family="-apple-system, Helvetica, sans-serif" font-size="11" fill="{colors["legend_text"]}">')
    parts.append(f'    <line x1="{lx}" y1="16" x2="{lx + 14}" y2="16" stroke="{colors["right"]}" stroke-width="4" stroke-linecap="round"/>')
    parts.append(f'    <text x="{lx + 19}" y="20">near</text>')
    parts.append(f'    <line x1="{lx + 49}" y1="16" x2="{lx + 63}" y2="16" stroke="{colors["left"]}" stroke-width="4" stroke-linecap="round"/>')
    parts.append(f'    <text x="{lx + 68}" y="20">far</text>')
    parts.append('  </g>')
    parts.append('</svg>')
    return "\n".join(parts) + "\n"


def draw_geo(geo, order, shade, working, colors, scale=2, font=None, props=None):
    from PIL import Image, ImageDraw

    bg, fg = resolve_props(props, geo)
    w, h = CANVAS[0] * scale, CANVAS[1] * scale
    img = Image.new("RGB", (w, h), "white")
    d = ImageDraw.Draw(img)

    def line(pts, color, width):
        pts = [(x * scale, y * scale) for x, y in pts]
        d.line(pts, fill=color, width=width * scale, joint="curve")
        r = width * scale / 2
        for x, y in (pts[0], pts[-1]):
            d.ellipse([x - r, y - r, x + r, y + r], fill=color)

    line([(16, GROUND_Y + 4), (CANVAS[0] - 16, GROUND_Y + 4)], colors["ground"], 3)
    draw_prims(d, bg, colors, scale)
    for part in order:
        if part == "head":
            draw_prims(d, fg, colors, scale)
            hx, hy = geo["head"]
            r, sw = geo["headR"] * scale, WIDTHS["head"] * scale
            d.ellipse([hx * scale - r, hy * scale - r, hx * scale + r, hy * scale + r],
                      fill=colors["head_fill"], outline=colors["right"], width=sw)
            if "nose" in geo:
                line(list(geo["nose"]), colors["right"], WIDTHS["nose"])
            continue
        if part not in geo:
            continue
        color, width = part_style(part, working, colors, shade)
        pts = quad_points(*geo["spine"]) if part == "spine" else geo[part]
        line(pts, color, width)

    lx = CANVAS[0] - 96
    line([(lx, 16), (lx + 14, 16)], colors["right"], 4)
    line([(lx + 49, 16), (lx + 63, 16)], colors["left"], 4)
    if font:
        d.text((lx * scale + 19 * scale, 16 * scale - 11 * scale / 2 - 2), "near",
               fill=colors["legend_text"], font=font)
        d.text((lx * scale + 68 * scale, 16 * scale - 11 * scale / 2 - 2), "far",
               fill=colors["legend_text"], font=font)
    return img.resize(CANVAS, Image.LANCZOS)


def legend_font(scale=2):
    from PIL import ImageFont
    try:
        return ImageFont.load_default(size=11 * scale)
    except TypeError:
        return ImageFont.load_default()


# --------------------------------------------------------------------- main

def load_motion(folder):
    return json.loads((folder / "motion.json").read_text())


def prepare(motion, figure="neutral", flip=False, strict=False):
    """Load a motion into (normalized frames, profile, camera yaw, props),
    validating each key frame against the skeleton's ROM."""
    skel = K.load_skeleton()
    prof = skel["profiles"][figure]
    cam = float(motion.get("camera", {}).get("yaw", 0.0)) + (180.0 if flip else 0.0)
    norms = [K.normalize_frame(kf) for kf in motion["frames"]]
    issues = []
    for i, nf in enumerate(norms, start=1):
        issues += K.validate_rom(nf, skel["joints"], f"frame {i}: ")
    if issues and strict:
        print(f"  {motion['name']}: ROM violations:")
        for msg in issues:
            print(f"    {msg}")
        sys.exit(1)
    if issues:
        print(f"  {motion['name']}: {len(issues)} ROM warning(s) — run --strict to list")
    props = motion.get("props", [])
    if flip:
        norms = [mirror_frame(nf, CANVAS[0]) for nf in norms]
        props = flip_props(props, CANVAS[0])
    return norms, prof, cam, props


def render_exercise(folder, figure="neutral", flip=False, strict=False):
    motion = load_motion(folder)
    working = set(motion.get("working", []))
    hide = set(motion.get("hide", []))
    norms, prof, cam, props = prepare(motion, figure, flip, strict)

    def geometry(nf):
        _, geo, order, shade = frame_geometry(nf, prof, cam, flip)
        for limb in hide:
            geo.pop(limb, None)
        return geo, order, shade

    resolved = []
    key_geos = []
    for nf in norms:
        out, geo, order, shade = frame_geometry(nf, prof, cam, flip)
        for limb in hide:
            geo.pop(limb, None)
        resolved.append(out)
        key_geos.append((geo, order, shade))

    frames_dir = folder / "frames"
    frames_dir.mkdir(exist_ok=True)
    for old in frames_dir.glob("frame-*.svg"):
        old.unlink()
    colors = PALETTES["default"]
    svgs = [svg_for_frame(motion["name"], geo, order, shade, working, colors, props)
            for geo, order, shade in key_geos]
    for i, svg in enumerate(svgs, start=1):
        (frames_dir / f"frame-{i}.svg").write_text(svg)
    (folder / "visual.svg").write_text(svgs[motion.get("primary", 1) - 1])

    try:
        font = legend_font()
        imgs = []
        for nf in timeline(resolved):
            geo, order, shade = geometry(nf)
            imgs.append(draw_geo(geo, order, shade, working, colors, font=font, props=props))
        imgs[0].save(folder / "preview.gif", save_all=True, append_images=imgs[1:],
                     duration=50, loop=0)
        print(f"  {motion['name']}: {len(svgs)} frames, preview.gif")
    except ImportError:
        print(f"  {motion['name']}: Pillow missing — SVGs written, preview.gif skipped")


def render_orbit(folder, figure="neutral"):
    """A full-turn demo: the camera sweeps 360 degrees while the motion loops.
    Scene props are view-locked billboards, so orbit shines on prop-free
    motions (bodyweight exercises)."""
    motion = load_motion(folder)
    working = set(motion.get("working", []))
    hide = set(motion.get("hide", []))
    norms, prof, cam, props = prepare(motion, figure)
    resolved = [frame_geometry(nf, prof, cam)[0] for nf in norms]
    font = legend_font()
    colors = PALETTES["default"]
    ticks = timeline(resolved)
    imgs = []
    for i, nf in enumerate(ticks):
        yaw = cam + 360.0 * i / len(ticks)
        _, geo, order, shade = frame_geometry(nf, prof, yaw)
        for limb in hide:
            geo.pop(limb, None)
        imgs.append(draw_geo(geo, order, shade, working, colors, font=font, props=props))
    imgs[0].save(folder / "orbit.gif", save_all=True, append_images=imgs[1:],
                 duration=50, loop=0)
    print(f"  {motion['name']}: orbit.gif ({len(imgs)} frames)")


def contact_sheet(folders, figure="neutral", out=None):
    font = legend_font()
    cells = []
    for folder in folders:
        motion = load_motion(folder)
        working, hide = set(motion.get("working", [])), set(motion.get("hide", []))
        norms, prof, cam, props = prepare(motion, figure)
        for i, nf in enumerate(norms, start=1):
            _, geo, order, shade = frame_geometry(nf, prof, cam)
            for limb in hide:
                geo.pop(limb, None)
            cells.append((f"{motion['name']} {i}/{len(norms)}",
                          draw_geo(geo, order, shade, working, PALETTES["default"],
                                   font=font, props=props)))
    save_sheet(cells, Path(out) if out else LIB / "contact-sheet.png")


def demo_sheet(folder):
    """One exercise's primary frame rendered five ways — the doors the rig
    opens: neutral / female / male profiles (same motion script, different
    proportions), the flipped camera, an alternate theme."""
    motion = load_motion(folder)
    working, hide = set(motion.get("working", [])), set(motion.get("hide", []))
    idx = motion.get("primary", 1) - 1
    font = legend_font()
    variants = [("neutral", "neutral", False, "default"),
                ("female profile", "female", False, "default"),
                ("male profile", "male", False, "default"),
                ("flipped camera", "neutral", True, "default"),
                ("themed (indigo)", "neutral", False, "indigo")]
    cells = []
    for label, figure, flip, palette in variants:
        norms, prof, cam, props = prepare(motion, figure, flip)
        _, geo, order, shade = frame_geometry(norms[idx], prof, cam, flip)
        for limb in hide:
            geo.pop(limb, None)
        cells.append((f"{motion['name']} — {label}",
                      draw_geo(geo, order, shade, working, PALETTES[palette],
                               font=font, props=props)))
    save_sheet(cells, LIB / "demo-sheet.png", cols=3)


def save_sheet(cells, path, cols=4):
    from PIL import Image, ImageDraw

    rows = (len(cells) + cols - 1) // cols
    cw, ch, cap = CANVAS[0], CANVAS[1], 22
    sheet = Image.new("RGB", (cols * (cw + 8) + 8, rows * (ch + cap + 8) + 8), "white")
    d = ImageDraw.Draw(sheet)
    for i, (label, img) in enumerate(cells):
        x, y = 8 + (i % cols) * (cw + 8), 8 + (i // cols) * (ch + cap + 8)
        sheet.paste(img, (x, y))
        d.text((x + 6, y + ch + 3), label, fill=PALETTES["default"]["right"])
    sheet.save(path)
    print(f"  {path.name} ({len(cells)} cells)")


# ------------------------------------------------------------------- export

def export_app_resources(folders):
    """Write the app's bundled copies: skeleton.json plus one
    `<Name>.motion.json` and one `<Name>.info.md` per library entry (unique
    basenames — Xcode copies resources flat). The in-app solver is a port of
    kinematics.py and consumes the same files; figure-fixtures.json in
    WorkoutsTests holds it to this pipeline's geometry."""
    out = LIB.parent / "Workouts" / "Resources" / "ExerciseMotions"
    out.mkdir(parents=True, exist_ok=True)
    (out / "skeleton.json").write_text((LIB / "skeleton.json").read_text())
    (out / "body.json").unlink(missing_ok=True)  # the legacy profile file
    for folder in folders:
        motion = load_motion(folder)
        (out / f"{motion['name']}.motion.json").write_text(
            (folder / "motion.json").read_text())
        print(f"  exported {motion['name']}.motion.json")
        info = folder / "info.md"
        if info.exists():
            (out / f"{motion['name']}.info.md").write_text(info.read_text())
            print(f"  exported {motion['name']}.info.md")
    print(f"  exported skeleton.json -> {out}")


def main():
    flags = [a for a in sys.argv[1:] if a.startswith("--")]
    names = [a for a in sys.argv[1:] if not a.startswith("--")]
    figure = "neutral"
    sheet = None            # False = off, None+flag = default path, str = custom path
    for f in flags:
        if f.startswith("--figure="):
            figure = f.split("=", 1)[1]
        elif f.startswith("--sheet"):
            sheet = f.split("=", 1)[1] if "=" in f else True
    folders = ([LIB / n for n in names] if names
               else sorted(p.parent for p in LIB.glob("*/motion.json")))
    if "--export" in flags:
        export_app_resources(folders)
        return
    if "--orbit" in flags:
        for folder in folders:
            render_orbit(folder, figure=figure)
        return
    for folder in folders:
        render_exercise(folder, figure=figure, flip="--flip" in flags,
                        strict="--strict" in flags)
    if sheet:
        contact_sheet(folders, figure=figure, out=None if sheet is True else sheet)
    if "--demo" in flags:
        demo_sheet(folders[0] if names else LIB / "Bird Dog")


if __name__ == "__main__":
    main()