import maya.cmds as cmds

# StartJointからEndJointに関連付けられているJointをListで取得
# Childが一つの想定なので骨が複数あるとおかしくなるかも。
def get_all_spline_joints(joint_list, parent_joint, last_joint):
    child = cmds.listRelatives(parent_joint, children=True, type="joint")
    joint_list.append(child[0])
    if child and last_joint not in child:
        get_all_spline_joints(joint_list, child[0], last_joint)
    else:
        return joint_list

# StretchySplineIKを自動作成するスクリプト
def create_stretchy_spline_ik(start_joint, end_joint, ik_name):
    
    spline_joints = [start_joint]
    get_all_spline_joints(spline_joints, start_joint, end_joint)
    
    # Spline IKの作成
    ik_handle, effector, curve = cmds.ikHandle(
        sj=start_joint,
        ee=end_joint,
        sol='ikSplineSolver',
        createCurve=True,
        numSpans=2,
        n=ik_name)
    
    curve_info = cmds.arclen(curve, ch=True)

    # ジョイントチェーンの初期長さを取得
    original_curve_length = cmds.getAttr(curve_info + ".arcLength")

    # スケールノードを作成
    mult_node = cmds.shadingNode('multiplyDivide', asUtility=True, n=ik_name + "_multDiv")
    cmds.setAttr(mult_node + ".operation", 2)  # Divide
    cmds.setAttr(mult_node + ".input2X", original_curve_length)

    # ノードを接続
    cmds.connectAttr(curve_info + ".arcLength", mult_node + ".input1X")
    
    for jnt in spline_joints:
        cmds.connectAttr(mult_node + ".outputX", jnt + ".scaleX")

    return ik_handle, curve

# CurveのControlPointにClusterを自動作成するスクリプト
def apply_clusters_to_curve(curve_name):
    curveCVs = cmds.ls('{0}.cv[:]'.format(curve_name), fl=True)
    for cv in curveCVs:
        cmds.cluster(cv)

# How To Use
selected_joints = cmds.ls(sl=True, flatten=True, type="joint")

start_joint = selected_joints[0]
end_joint = selected_joints[1]
ik_name = "{0}_splineIK".format(end_joint.split("_")[-1]) # ex: Character_LeftArm

ik_handle, curve = create_stretchy_spline_ik(start_joint, end_joint, ik_name)
apply_clusters_to_curve(curve)