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import bpy
from rigify import get_bone_data

# not used, defined for completeness
METARIG_NAMES = tuple()

def metarig_definition(obj, orig_bone_name):
    '''
    The bone given is the head, its parent is the body,
    # its only child the first of a chain with matching basenames.
    eg.
        body -> head -> neck_01 -> neck_02 -> neck_03.... etc
    '''
    arm = obj.data
    delta = arm.bones[orig_bone_name]
    children = delta.children
    
    if len(children) != 1:
        print("only 1 child supported for delta")
    
    bone_definition = [delta.name, children[0].name]
    
    return bone_definition

def main(obj, bone_definition, base_names):
    '''
    Use this bone to define a delta thats applied to its child in pose mode.
    '''
    
    mode_orig = obj.mode
    bpy.ops.object.mode_set(mode='OBJECT')
    
    delta_name, child_name = bone_definition
    
    delta_pbone = obj.pose.bones[delta_name]

    arm, child_pbone, child_bone = get_bone_data(obj, child_name)
    
    delta_phead = delta_pbone.head.copy()
    delta_ptail = delta_pbone.tail.copy()
    delta_pmatrix = delta_pbone.matrix.copy()
    
    child_phead = child_pbone.head.copy()
    child_ptail = child_pbone.tail.copy()
    child_pmatrix = child_pbone.matrix.copy()
    
    
    children = delta_pbone.children

    bpy.ops.object.mode_set(mode='EDIT')
    
    delta_ebone = arm.edit_bones[delta_name]
    child_ebone = arm.edit_bones[child_name]
    
    delta_head = delta_ebone.head.copy()
    delta_tail = delta_ebone.tail.copy()    
    
    # arm, parent_pbone, parent_bone = get_bone_data(obj, delta_name)
    child_head = child_ebone.head.copy()
    child_tail = child_ebone.tail.copy()
    
    arm.edit_bones.remove(delta_ebone)
    del delta_ebone # cant use this
    
    bpy.ops.object.mode_set(mode='OBJECT')
    
    
    # Move the child bone to the deltas location
    obj.animation_data_create()
    child_pbone = obj.pose.bones[child_name]
    
    # ------------------- drivers
    
    child_pbone.rotation_mode = 'XYZ'
    
    rot =  delta_pmatrix.invert().rotationPart() * child_pmatrix.rotationPart()
    rot = rot.invert().toEuler()
    
    fcurve_drivers = child_pbone.driver_add("rotation_euler", -1)
    for i, fcurve_driver in enumerate(fcurve_drivers):
        driver = fcurve_driver.driver
        driver.type = 'AVERAGE'
        #mod = fcurve_driver.modifiers.new('GENERATOR')
        mod = fcurve_driver.modifiers[0]
        mod.poly_order = 1
        mod.coefficients[0] = rot[i]
        mod.coefficients[1] = 0.0
    
    # tricky, find the transform to drive the bone to this location.
    delta_head_offset =  child_pmatrix.rotationPart() * (delta_phead - child_phead)
    
    fcurve_drivers = child_pbone.driver_add("location", -1)
    for i, fcurve_driver in enumerate(fcurve_drivers):
        driver = fcurve_driver.driver
        driver.type = 'AVERAGE'
        #mod = fcurve_driver.modifiers.new('GENERATOR')
        mod = fcurve_driver.modifiers[0]
        mod.poly_order = 1
        mod.coefficients[0] = delta_head_offset[i]
        mod.coefficients[1] = 0.0
    
    
    # arm, parent_pbone, parent_bone = get_bone_data(obj, delta_name)
    bpy.ops.object.mode_set(mode='EDIT')
    
    bpy.ops.object.mode_set(mode=mode_orig)

    # no blendeing
    return None