import bpy
import mathutils
import queue
import importlib
import os
import re
# import time # for debugging performance

# then import dependencies for our addon
if "Font" in locals():
    importlib.reload(Font)
else:
    from .common import Font

if "utils" in locals():
    importlib.reload(utils)
else:
    from .common import utils

execution_queue = queue.Queue()

# This function can safely be called in another thread.
# The function will be executed when the timer runs the next time.
def run_in_main_thread(function):
    execution_queue.put(function)

def execute_queued_functions():
    while not execution_queue.empty():
        function = execution_queue.get()
        function()
    return 1.0

def apply_all_transforms(obj):
    mb = obj.matrix_basis
    if hasattr(obj.data, "transform"):
        obj.data.transform(mb)
    for c in obj.children:
        c.matrix_local = mb @ c.matrix_local
    obj.matrix_basis.identity()

def get_parent_collection_names(collection, parent_names):
  for parent_collection in bpy.data.collections:
    if collection.name in parent_collection.children.keys():
      parent_names.append(parent_collection.name)
      get_parent_collection_names(parent_collection, parent_names)
      return

# Ensure it's a curve object
# TODO: no raising, please
def get_curve_length(curve_obj, resolution = -1):
    total_length = 0

    curve = curve_obj.data

    # Loop through all splines in the curve
    for spline in curve.splines:
        total_length = total_length + spline.calc_length(resolution=resolution)
    
    return total_length

def get_curve_line_lengths(curve_obj, resolution = -1):
    lengths = []
    for spline in curve_obj.data.splines:
        lengths.append(spline.calc_length(resolution=resolution))
    return lengths

def get_next_line_advance(curve_obj, current_advance, previous_glyph_advance, resolution = -1):
    curve_line_lengths = get_curve_line_lengths(curve_obj, resolution)
    total_length = 0
    for cll in curve_line_lengths:
        total_length += cll
        if current_advance - previous_glyph_advance < total_length:
            return total_length
    return current_advance

def calc_point_on_bezier(bezier_point_1, bezier_point_2, t):
    p1 = bezier_point_1.co
    h1 = bezier_point_1.handle_right
    p2 = bezier_point_2.co
    h2 = bezier_point_2.handle_left
    return ((1 - t)**3) * p1 + (3 * t * (1 - t)**2) * h1 + (3 * (t**2) * (1 - t)) * h2 + (t**3) * p2

# same in slightly more lines
# result is equal, performance minimally better perhaps?
# def calc_point_on_bezier(bezier_point_1, bezier_point_2, ratio):
    # startPoint = bezier_point_1.co
    # controlPoint1 = bezier_point_1.handle_right
    # controlPoint2 = bezier_point_2.handle_left
    # endPoint = bezier_point_2.co

    # remainder = 1 - ratio
    # ratioSquared = ratio * ratio
    # remainderSquared = remainder * remainder
    # startPointMultiplier = remainderSquared * remainder
    # controlPoint1Multiplier = remainderSquared * ratio * 3
    # controlPoint2Multiplier = ratioSquared * remainder * 3
    # endPointMultiplier = ratioSquared * ratio

    # return startPoint * startPointMultiplier + controlPoint1 * controlPoint1Multiplier + controlPoint2 * controlPoint2Multiplier + endPoint * endPointMultiplier


def calc_tangent_on_bezier(bezier_point_1, bezier_point_2, t):
    p1 = bezier_point_1.co
    h1 = bezier_point_1.handle_right
    p2 = bezier_point_2.co
    h2 = bezier_point_2.handle_left
    return (
            (-3 * (1 - t)**2) * p1 + (-6 * t * (1 - t) + 3 * (1 - t)**2) * h1 +
            (-3 * (t**2) + 6 * t * (1 - t)) * h2 + (3 * t**2) * p2
            ).normalized()

from math import radians, sqrt, pi, acos

def align_rotations_auto_pivot(mask, input_rotations, vectors, factors, local_main_axis):
    output_rotations = [mathutils.Matrix().to_3x3() for _ in range(len(input_rotations))]

    for i in mask:
        vector = mathutils.Vector(vectors[i]).normalized()
        input_rotation = mathutils.Euler(input_rotations[i])

        if vector.length < 1e-6:
            output_rotations[i] = input_rotation.to_matrix()
            continue

        old_rotation = input_rotation.to_matrix()
        old_axis = (old_rotation @ local_main_axis).normalized()
        new_axis = vector
        # rotation_axis = (-(old_axis) + new_axis).normalized()
        rotation_axis = old_axis.cross(new_axis).normalized()

        if rotation_axis.length < 1e-6:
            # Vectors are linearly dependent, fallback to another axis
            rotation_axis = (old_axis + mathutils.Matrix().to_3x3().col[2]).normalized()
            
            if rotation_axis.length < 1e-6:
                # This is now guaranteed to not be zero
                rotation_axis = (-(old_axis) + mathutils.Matrix().to_3x3().col[1]).normalized()

        # full_angle = radians(sqrt((4 * pow(input_rotation.to_quaternion().dot(mathutils.Quaternion(vectors[i].normalized())), 2) - 3)))
        # dot = old_axis.dot(new_axis)
        # normalized_diff = (old_axis - new_axis).normalized()
        # full_angle = acos(min((old_axis * new_axis + normalized_diff.dot(2)).length, 1))
        full_angle = old_axis.angle(new_axis)
        angle = factors[i] * full_angle

        rotation = mathutils.Quaternion(rotation_axis, angle).to_matrix()
        new_rotation_matrix = old_rotation @ rotation
        output_rotations[i] = new_rotation_matrix

    return [mat.to_4x4() for mat in output_rotations]

def calc_bezier_length(bezier_point_1, bezier_point_2, resolution=20):
    step = 1/resolution
    previous_p = bezier_point_1.co
    length = 0
    for i in range(-1, resolution):
        t = (i + 1) * step
        p = calc_point_on_bezier(bezier_point_1, bezier_point_2, t)
        length += (p - previous_p).length
        previous_p = p
    return length

def calc_point_on_bezier_spline(bezier_spline_obj,
                                distance,
                                output_tangent = False,
                                resolution_factor = 1.0):
    # what's the point of just one point
    # assert len(bezier_spline_obj.bezier_points) >= 2
    # however, maybe let's have it not crash and do this
    if len(bezier_spline_obj.bezier_points) < 1:
        print("butils::calc_point_on_bezier_spline: whoops, no points. panicking. return 0,0,0")
        if output_tangent:
            return mathutils.Vector((0,0,0)), mathutils.Vector((1,0,0))
        else:
            return mathutils.Vector((0,0,0))
    if len(bezier_spline_obj.bezier_points) == 1:
        p = bezier_spline_obj.bezier_points[0]
        travel = (p.handle_left - p.co).normalized() * distance
        if output_tangent:
            tangent = mathutils.Vector((1,0,0))
            return travel, tangent
        else:
            return travel
    
    if distance <= 0:
        p = bezier_spline_obj.bezier_points[0]
        travel = (p.co - p.handle_left).normalized() * distance
        location = p.co + travel
        if output_tangent:
            p2 = bezier_spline_obj.bezier_points[1]
            tangent = calc_tangent_on_bezier(p, p2, 0)
            return location, tangent
        else:
            return location

    beziers = []
    lengths = []
    total_length = 0
    n_bezier_points = len(bezier_spline_obj.bezier_points)
    for i in range(0, len(bezier_spline_obj.bezier_points) - 1):
       bezier = [ bezier_spline_obj.bezier_points[i],
                  bezier_spline_obj.bezier_points[i + 1] ]
       length = calc_bezier_length(bezier[0],
                                   bezier[1],
                                   int(bezier_spline_obj.resolution_u * resolution_factor))
       total_length += length
       beziers.append(bezier)
       lengths.append(length)
       # if total_length > distance:
           # break

    iterated_distance = 0
    for i in range(0, len(beziers)):
        if iterated_distance + lengths[i] > distance:
            distance_on_bezier = (distance - iterated_distance)
            d = distance_on_bezier / lengths[i]
            # print(f"i: {i}, d: {d}, distance_on_bezier: {distance_on_bezier}, distance: {distance}")
            location = calc_point_on_bezier(beziers[i][0],
                                            beziers[i][1],
                                            d)
            if output_tangent:
                tangent = calc_tangent_on_bezier(beziers[i][0],
                                                 beziers[i][1],
                                                 d)
                return location, tangent
            else:
                return location
        iterated_distance += lengths[i]
    # if we are here, the point is outside the spline
    last_i = len(beziers) - 1
    p = beziers[last_i][1]
    travel = (p.handle_right - p.co).normalized() * (distance - total_length)
    location = p.co + travel
    if output_tangent:
        tangent = calc_tangent_on_bezier(beziers[last_i][0],
                                         p,
                                         1)
        return location, tangent
    else:
        return location


def calc_point_on_bezier_curve(bezier_curve_obj,
                               distance,
                               output_tangent = False,
                               resolution_factor = 1.0):
    curve = bezier_curve_obj.data

    # Loop through all splines in the curve
    total_length = 0
    for i, spline in enumerate(curve.splines):
        resolution = int(spline.resolution_u * resolution_factor)
        length = spline.calc_length(resolution=resolution)
        if total_length + length > distance or i == len(curve.splines) - 1:
            return calc_point_on_bezier_spline(spline,
                                               (distance - total_length),
                                               output_tangent,
                                               resolution_factor)
        total_length += length

    # TODO: can this fail?


# def get_objects_by_name(name, startswith="", endswith=""):
    # return [obj for obj in bpy.context.scene.objects if obj.name.startswith(startswith) and if obj.name.endswith(endswith)]

def find_objects_by_name(
        objects,
        equals="",
        contains="",
        startswith="",
        endswith=""):
    # handle equals
    if equals != "":
        index = objects.find(equals)
        if index >= 0:
            return [objects[index]]
        return []
    # handle others is more permissive
    return [obj for obj in objects if obj.name.startswith(startswith) and obj.name.endswith(endswith) and obj.name.find(contains) >= 0]

def find_objects_by_custom_property(
        objects,
        property_name="",
        property_value=""):
    return [obj for obj in objects if property_name in obj and obj[property_name] == property_value]

def turn_collection_hierarchy_into_path(obj):
    parent_collection = obj.users_collection[0]
    parent_names      = []
    parent_names.append(parent_collection.name)
    get_parent_collection_names(parent_collection, parent_names)
    parent_names.reverse()
    return '\\'.join(parent_names)

def find_font_object(fontcollection, font_name):
    fonts = find_objects_by_custom_property(fontcollection.objects,
                                            "is_font",
                                            True)
    for font in fonts:
        if font["font_name"] == font_name and font.parent == None:
            return font
    return None

def find_font_face_object(font_obj, face_name):
    faces = find_objects_by_custom_property(font_obj.children,
                                            "is_face",
                                            True)
    for face in faces:
        if face["face_name"] == face_name:
            return face
    return None

def move_in_fontcollection(obj, fontcollection, allow_duplicates=False):

    # parent nesting structure
    # the font object
    font_obj = find_font_object(fontcollection,
                                obj["font_name"])
    if font_obj == None:
        font_obj = bpy.data.objects.new(obj["font_name"], None)
        font_obj.empty_display_type = 'PLAIN_AXES'
        fontcollection.objects.link(font_obj)

    # ensure custom properties are set
    font_obj["font_name"] = obj["font_name"]
    font_obj["is_font"] = True

    # the face object as a child of font object
    face_obj = find_font_face_object(font_obj,
                                     obj["face_name"])
    if face_obj == None:
        face_obj = bpy.data.objects.new(obj["face_name"], None)
        face_obj.empty_display_type = 'PLAIN_AXES'
        face_obj["is_face"] = True
        fontcollection.objects.link(face_obj)

    # ensure custom properties are set
    face_obj["face_name"] = obj["face_name"]
    face_obj["font_name"] = obj["font_name"]

    if face_obj.parent != font_obj:
        face_obj.parent = font_obj

    # create glyphs if it does not exist
    glyphs_objs = find_objects_by_name(face_obj.children, startswith="glyphs")
    if len(glyphs_objs) <= 0:
        glyphs_obj = bpy.data.objects.new("glyphs", None)
        glyphs_obj.empty_display_type = 'PLAIN_AXES'
        fontcollection.objects.link(glyphs_obj)
        glyphs_obj.parent = face_obj
    elif len(glyphs_objs) > 1:
        print(f"found more glyphs objects than expected")

    # now it must exist
    glyphs_obj = find_objects_by_name(face_obj.children, startswith="glyphs")[0]
    glyphs_obj["face_name"] = obj["face_name"]
    glyphs_obj["font_name"] = obj["font_name"]

    def get_hash(o):
        return hash(tuple(tuple(v.co) for v in o.data.vertices ))

    for other_obj in find_objects_by_custom_property(glyphs_obj.children, "glyph", obj["glyph"]):
        if get_hash(other_obj) == get_hash(obj) and not allow_duplicates:
            return other_obj

    # and now parent it!
    if obj.parent != glyphs_obj:
        obj.parent = glyphs_obj

    for c in obj.users_collection:
        c.objects.unlink(obj)
    if fontcollection.objects.find(obj.name) < 0:
        fontcollection.objects.link(obj)

    return obj

def load_font_from_filepath(filepath):
    if not filepath.endswith(".glb") and not filepath.endswith(".gltf"):
        ShowMessageBox(f"{bl_info['name']} Font loading error", 'ERROR', f"Filepath({filepath}) is not a *.glb or *.gltf file")
        return False

    font3d_data = bpy.context.scene.font3d_data
    allObjectsBefore = []
    for ob in bpy.data.objects:
        allObjectsBefore.append(ob.name)

    bpy.ops.import_scene.gltf(filepath=filepath)

    fontcollection = bpy.data.collections.get("Font3D")
    if fontcollection is None:
        fontcollection = bpy.data.collections.new("Font3D")

    remove_list = []
    all_objects = []
    for o in bpy.data.objects:
        all_objects.append(o)
    for o in all_objects:
        if o.name not in allObjectsBefore:
            # must be new
            if ("glyph" in o.keys()
                    and "face_name" in o.keys()
                    and "font_name" in o.keys()
                    and not ("type" in o.keys() and o["type"] == "metrics")
                    and not is_metrics_object(o)
                    ):
                glyph_id = o["glyph"]
                font_name = o["font_name"]
                face_name = o["face_name"]
                glyph_obj = move_in_fontcollection(
                                o,
                                fontcollection)
                Font.add_glyph(
                        font_name,
                        face_name,
                        glyph_id,
                        glyph_obj)
                for c in o.children:
                    if is_metrics_object(c):
                        add_metrics_obj_from_bound_box(glyph_obj,
                                                       bound_box_as_array(c.bound_box))
                if glyph_obj != o:
                    remove_list.append(o)

                found = False
                for f in font3d_data.available_fonts.values():
                    if f.font_name == font_name:
                        found = True
                        break
                if not found:
                    f = font3d_data.available_fonts.add()
                    f.font_name = font_name
                    print(f"{__name__} added {font_name}")
            else:
                remove_list.append(o)
    for o in remove_list:
        bpy.data.objects.remove(o, do_unlink=True)
    print(f"{__name__}: loaded fonts")

def getPreferences(context):
    preferences = context.preferences
    return preferences.addons['font3d'].preferences

# clear available fonts
def clear_available_fonts():
    bpy.context.scene.font3d_data.available_fonts.clear()

def load_available_fonts():
    preferences = getPreferences(bpy.context)

    currentObjects = []
    for ob in bpy.data.objects:
        currentObjects.append(ob.name)

    print(f"assets folder: {preferences.assets_dir}")
    font_dir = f"{preferences.assets_dir}/fonts"
    for file in os.listdir(font_dir):
        if file.endswith(".glb") or file.endswith(".gltf"):
            font_path = os.path.join(font_dir, file)
            load_font_from_filepath(font_path)

def ShowMessageBox(title = "Message Box", icon = 'INFO', message=""):

    """Show a simple message box

    taken from `Link here <https://blender.stackexchange.com/questions/169844/multi-line-text-box-with-popup-menu>`_

    :param title: The title shown in the message top bar
    :type title: str
    :param icon: The icon to be shown in the message top bar
    :type icon: str
    :param message: lines of text to display, a.k.a. the message
    :type message: str or (str, str, ..)
    
    TIP: Check `Link blender icons <https://docs.blender.org/api/current/bpy_types_enum_items/icon_items.html>`_ for icons you can use
    TIP: Or even better, check `Link this addons <https://docs.blender.org/manual/en/latest/addons/development/icon_viewer.html>`_ to also see the icons.
    
    usage:
    .. code-block:: python
       myLines=("line 1","line 2","line 3")
       butils.ShowMessageBox(message=myLines)

    or:
    .. code-block:: python
       butils.ShowMessageBox(title="",message=("AAAAAH","NOOOOO"),icon=)
       
    """
    myLines=message
    def draw(self, context):
        if isinstance(myLines, str):
            self.layout.label(text=myLines)
        elif hasattr(myLines, "__iter__"):
            for n in myLines:
                self.layout.label(text=n)
    bpy.context.window_manager.popup_menu(draw, title = title, icon = icon)

def completely_delete_objects(objs):
    context_override = bpy.context.copy()
    context_override["selected_objects"] = list(objs)
    with bpy.context.temp_override(**context_override):
        bpy.ops.object.delete()

    # remove deleted objects
    # this is necessary
    for g in objs:
        if type(g) != type(None):
            try:
                bpy.data.objects.remove(g, do_unlink=True)
            except ReferenceError as e:
                # not important
                pass

def is_mesh(o):
    return type(o.data) == bpy.types.Mesh

def is_metrics_object(o):
    return (re.match("[\w]*_metrics$", o.name) != None or re.match("[\w]*_metrics.[\d]{3}$", o.name) != None) and is_mesh(o)

def is_glyph(o):
    try:
        return type(o.parent) is not type(None) \
                and "glyphs" in o.parent.name \
                and is_mesh(o) \
                and not is_metrics_object(o)
    except ReferenceError as e:
        return False

# blender bound_box vertices
# 
# 3------7.    
# |`.    | `.     +y
# |  `2------6     |
# |   |  |   |     |
# 0---|--4.  |     +--- +x
#  `. |    `.|      `.  
#    `1------5        `+z

def get_glyph_advance(glyph_obj):
    for c in glyph_obj.children:
        if is_metrics_object(c):
            return abs(c.bound_box[4][0] - c.bound_box[0][0])
    return abs(glyph_obj.bound_box[4][0] - glyph_obj.bound_box[0][0])

def set_text_on_curve(text_properties):
    # starttime = time.perf_counter_ns()
    mom = text_properties.text_object
    if mom.type != "CURVE":
        return False

    regenerate = False
    glyph_objects = []
    for i, g in enumerate(text_properties.glyphs):
        glyph_objects.append(g.glyph_object)

        # check if perhaps one glyph was deleted
        if (type(g.glyph_object) == type(None)
                or type(g.glyph_object.parent) == type(None)
                or g.glyph_object.parent.users_collection != g.glyph_object.users_collection):
            regenerate = True
        if len(text_properties.text) > i and g.glyph_id != text_properties.text[i]:
            regenerate = True

    if len(text_properties.text) != len(text_properties.glyphs):
        regenerate = True

    # if we regenerate.... delete objects
    if regenerate:
        completely_delete_objects(glyph_objects)
        # context_override = bpy.context.copy()
        # context_override["selected_objects"] = list(glyph_objects)
        # with bpy.context.temp_override(**context_override):
            # bpy.ops.object.delete()

        # # remove deleted objects
        # # this is necessary
        # for g in glyph_objects:
            # if type(g) != type(None):
                # bpy.data.objects.remove(g, do_unlink=True)

        text_properties.glyphs.clear()

#TODO: fix selection with context_override
    previous_selection = bpy.context.selected_objects
    bpy.ops.object.select_all(action='DESELECT')
    selected_objects = []

    curve_length = get_curve_length(mom)
    advance = 0
    glyph_advance = 0
    is_command = False
    for i, c in enumerate(text_properties.text):
        if c == '\\':
            is_command = True
            continue
        if is_command:
            if c == 'n':
                next_line_advance = get_next_line_advance(mom, advance, glyph_advance)
                if advance == next_line_advance:
                    # self.report({'INFO'}, f"would like to add new line for {text_properties.text} please")
                    print(f"would like to add new line for {text_properties.text} please")
                    # TODO: add a new line
                advance = next_line_advance
                continue
            is_command = False
        glyph_id = c

        glyph = Font.get_glyph(text_properties.font_name,
                               text_properties.font_face,
                               glyph_id)

        if glyph == None:
            # self.report({'ERROR'}, f"Glyph not found for {font_name} {font_face} {glyph_id}")
            print(f"Glyph not found for {text_properties.font_name} {text_properties.font_face} {glyph_id}")
            continue

        ob = None
        if regenerate:
            ob = bpy.data.objects.new(f"{glyph_id}", glyph.data)
            ob['linked_textobject'] = text_properties.text_id
        else:
            ob = text_properties.glyphs[i]['glyph_object']

        distribution_type = 'CALCULATE'
        if distribution_type == 'FOLLOW_PATH':
            ob.constraints.new(type='FOLLOW_PATH')
            ob.constraints["Follow Path"].target = mom
            ob.constraints["Follow Path"].use_fixed_location = True
            ob.constraints["Follow Path"].offset_factor = advance / curve_length
            ob.constraints["Follow Path"].use_curve_follow = True
            ob.constraints["Follow Path"].forward_axis = "FORWARD_X"
            ob.constraints["Follow Path"].up_axis = "UP_Y"
        elif distribution_type == 'CALCULATE':
            location, tangent = calc_point_on_bezier_curve(mom, advance, True)
            ob.location = mom.matrix_world @ (location + text_properties.translation)
            if not text_properties.ignore_orientation:
                mask = [0]
                input_rotations = [mathutils.Vector((0.0, 0.0, 0.0))]
                vectors = [tangent]
                factors = [1.0]
                local_main_axis = mathutils.Vector((1.0, 0.0, 0.0))
                motor = align_rotations_auto_pivot(mask,
                                                   input_rotations,
                                                   vectors,
                                                   factors,
                                                   local_main_axis)
                if ob.rotation_mode != 'QUATERNION':
                    ob.rotation_mode = 'QUATERNION'
                q = mathutils.Quaternion()
                q.rotate(text_properties.orientation)
                ob.rotation_quaternion = (mom.matrix_world @ motor[0] @ q.to_matrix().to_4x4()).to_quaternion()
            else:
                q = mathutils.Quaternion()
                q.rotate(text_properties.orientation)
                ob.rotation_quaternion = q
                # ob.rotation_quaternion = (mom.matrix_world @ q.to_matrix().to_4x4()).to_quaternion()

        scalor = 0.001 * text_properties.font_size

        glyph_advance = get_glyph_advance(glyph) * scalor + text_properties.letter_spacing

        # now we need to compensate for curvature
        # otherwise letters will be closer together the curvier the bezier is
        # this could be done more efficiently, but whatever
        curve_compensation = 0
        if text_properties.compensate_curvature:
            previous_location = calc_point_on_bezier_curve(mom, advance, False)
            new_location = calc_point_on_bezier_curve(mom, advance + glyph_advance, False)
            while (previous_location - new_location).length > glyph_advance:
                curve_compensation = curve_compensation - glyph_advance * 0.01
                new_location = calc_point_on_bezier_curve(mom, advance + glyph_advance + curve_compensation, False)
            while (previous_location - new_location).length < glyph_advance:
                curve_compensation = curve_compensation + glyph_advance * 0.01
                new_location = calc_point_on_bezier_curve(mom, advance + glyph_advance + curve_compensation, False)

        ob.scale = (scalor, scalor, scalor)

        advance = advance + glyph_advance + curve_compensation

        if regenerate:
            mom.users_collection[0].objects.link(ob)
            glyph_data = text_properties.glyphs.add()
            glyph_data.glyph_id = glyph_id
            glyph_data.glyph_object = ob
            glyph_data.letter_spacing = 0
            ob.select_set(True)
    
    if regenerate:
        mom.select_set(True)
        bpy.context.view_layer.objects.active = mom
        bpy.ops.object.parent_set(type='OBJECT')

    # endtime = time.perf_counter_ns()
    # elapsedtime = endtime - starttime

    return True

# blender bound_box vertices
# 
# 3------7.    
# |`.    | `.       +y
# |  `2------6  -z   |
# |   |  |   |    `. |
# 0---|--4.  |      `+--- +x
#  `. |    `.| 
#    `1------5 

def add_metrics_obj_from_bound_box(glyph, bound_box=None):
    mesh = bpy.data.meshes.new(f"{glyph.name}_metrics")  # add the new mesh
    obj = bpy.data.objects.new(mesh.name, mesh)
    obj["font_name"] = glyph["font_name"]
    obj["face_name"] = glyph["face_name"]
    obj["glyph"] = glyph["glyph"]
    obj["type"] = "metrics"
    col = glyph.users_collection[0]
    col.objects.link(obj)
    # bpy.context.view_layer.objects.active = obj
    obj.parent = glyph

    if type(bound_box) == type(None):
        bound_box = glyph.bound_box
    
    verts = [bound_box[0],
             bound_box[1],
             bound_box[2],
             bound_box[3],
             bound_box[4],
             bound_box[5],
             bound_box[6],
             bound_box[7],
             ]
    edges = [[0,1],[1,2],[2,3],[3,0],
             [0,4],[1,5],[2,6],[3,7],
             [4,5],[5,6],[6,7],[7,4],
             ]
    faces = []
    
    mesh.from_pydata(verts, edges, faces)

def add_faces_to_metrics(obj):
    mesh = bpy.data.meshes.new(f"{obj.name}")  # add the new mesh
    bound_box = bound_box_as_array(obj.bound_box)
    verts = [bound_box[0],
             bound_box[1],
             bound_box[2],
             bound_box[3],
             bound_box[4],
             bound_box[5],
             bound_box[6],
             bound_box[7],
             ]
    edges = [[0,1],[1,2],[2,3],[3,0],
             [0,4],[1,5],[2,6],[3,7],
             [4,5],[5,6],[6,7],[7,4],
             ]
    faces = [
                [0,1,2], [2,3,0],
                [2,6,7], [7,3,2],
                [6,5,4], [4,7,6],
                [4,5,1], [0,4,1],
                [1,5,6], [1,6,2],
                [4,0,7], [7,0,3],
            ]

    mesh.from_pydata(verts, edges, faces)

    old_mesh = obj.data
    obj.data = mesh
    bpy.data.meshes.remove(old_mesh)

def remove_faces_from_metrics(obj):
    mesh = bpy.data.meshes.new(f"{obj.name}")  # add the new mesh
    bound_box = bound_box_as_array(obj.bound_box)
    verts = [bound_box[0],
             bound_box[1],
             bound_box[2],
             bound_box[3],
             bound_box[4],
             bound_box[5],
             bound_box[6],
             bound_box[7],
             ]
    edges = [[0,1],[1,2],[2,3],[3,0],
             [0,4],[1,5],[2,6],[3,7],
             [4,5],[5,6],[6,7],[7,4],
             ]
    faces = [
            ]

    mesh.from_pydata(verts, edges, faces)

    old_mesh = obj.data
    obj.data = mesh
    bpy.data.meshes.remove(old_mesh)

# duplicate
# def remove_metrics_from_selection():
    # for o in bpy.context.selected_objects:
        # is_possibly_glyph = is_mesh(o)
        # if is_possibly_glyph:
            # metrics = []
            # for c in o.children:
                # if is_metrics_object(c):
                    # metrics.append(c)
            # completely_delete_objects(metrics)

def get_max_bound_box(bb_1, bb_2 = None):
    if type(bb_2) == type(None):
        bb_2 = bb_1
    x_max = max(bb_1[4][0], bb_2[4][0])
    x_min = min(bb_1[0][0], bb_2[0][0])
    y_max = max(bb_1[3][1], bb_2[3][1]) 
    y_min = min(bb_1[0][1], bb_2[0][1]) 
    z_max = max(bb_1[1][2], bb_2[1][2])
    z_min = min(bb_1[0][2], bb_2[0][2])
    return [
            mathutils.Vector((x_min, y_min, z_min)),
            mathutils.Vector((x_min, y_min, z_max)),
            mathutils.Vector((x_min, y_max, z_max)),
            mathutils.Vector((x_min, y_max, z_min)),

            mathutils.Vector((x_max, y_min, z_min)),
            mathutils.Vector((x_max, y_min, z_max)),
            mathutils.Vector((x_max, y_max, z_max)),
            mathutils.Vector((x_max, y_max, z_min)),
            ]

# blender bound_box vertices
# 
# 3------7.    
# |`.    | `.     +y
# |  `2------6     |
# |   |  |   |     |
# 0---|--4.  |     +--- +x
#  `. |    `.|      `.  
#    `1------5        `+z

# why not [ [0] * 3 ] * 8
# https://stackoverflow.com/questions/2397141/how-to-initialize-a-two-dimensional-array-list-of-lists-if-not-using-numpy-in
def bound_box_as_array(bound_box):
    array = [ [0] * 3 for i in range(8) ]
    for i in range(0, len(bound_box)):
        for j in range(0, len(bound_box[i])):
            array[i][j] = bound_box[i][j]
    return array

##
# @brief get_metrics_bound_box 
#        generates a metrics bounding box
#        where x-width comes from bb
#        and y-height + z-depth from bb_uebermetrics
#
# @param bb
# @param bb_uebermetrics
#
# @return metrics
def get_metrics_bound_box(bb, bb_uebermetrics):
    metrics = [[0] * 3] * 8
    # hurrays
    if type(bb_uebermetrics) == bpy.types.bpy_prop_array:
        metrics = bound_box_as_array(bb_uebermetrics)
    else:
        metrics = bb_uebermetrics.copy()
    metrics[0][0] = bb[0][0]
    metrics[1][0] = bb[1][0]
    metrics[2][0] = bb[2][0]
    metrics[3][0] = bb[3][0]
    metrics[4][0] = bb[4][0]
    metrics[5][0] = bb[5][0]
    metrics[6][0] = bb[6][0]
    metrics[7][0] = bb[7][0]
    return metrics

def add_default_metrics_to_objects(objects=None, overwrite_existing=False):
    if type(objects) == type(None):
        objects=bpy.context.selected_objects
    targets = []
    reference_bound_box = None
    for o in objects:
        is_possibly_glyph = is_glyph(o)
        if is_possibly_glyph:
            metrics = []
            for c in o.children:
                if is_metrics_object(c):
                    metrics.append(c)

            if len(metrics) == 0:
                targets.append(o)
                reference_bound_box = get_max_bound_box(o.bound_box, reference_bound_box)
            elif len(metrics) >= 0 and overwrite_existing:
                completely_delete_objects(metrics)
                targets.append(o)
                reference_bound_box = get_max_bound_box(o.bound_box, reference_bound_box)
            else:
                for m in metrics:
                    reference_bound_box = get_max_bound_box(m.bound_box, reference_bound_box)
    for t in targets:
        bound_box = get_metrics_bound_box(t.bound_box, reference_bound_box)
        add_metrics_obj_from_bound_box(t, bound_box)

def remove_metrics_from_objects(objects=None):
    if type(objects) == type(None):
        objects=bpy.context.selected_objects
    metrics = []
    for o in objects:
        for c in o.children:
            if is_metrics_object(c):
                metrics.append(c)
    completely_delete_objects(metrics)

def align_metrics_of_objects_to_active_object(objects=None):
    if type(objects) == type(None):
        objects=bpy.context.selected_objects
        if len(objects) == 0:
            return "no objects selected"

    # define the reference_bound_box
    reference_bound_box = None
    if type(bpy.context.active_object) == type(None):
        return "no active_object, but align_to_active_object is True"
    for c in bpy.context.active_object.children:
        if is_metrics_object(c):
            reference_bound_box = bound_box_as_array(c.bound_box)
            break
    if type(reference_bound_box) == type(None):
        if not is_mesh(bpy.context.active_object):
            return "active_object is not a mesh and does not have a metrics child"
        reference_bound_box = bound_box_as_array(bpy.context.active_object.bound_box)

    # do it
    for o in objects:
        is_possibly_glyph = is_glyph(o)
        if is_possibly_glyph:
            metrics = []
            for c in o.children:
                if is_metrics_object(c):
                    metrics.append(c)

            bb = None
            if len(metrics) == 0:
                bb = get_metrics_bound_box(o.bound_box,
                                           reference_bound_box)
            else:
                bb = get_metrics_bound_box(metrics[0].bound_box,
                                           reference_bound_box)
            if len(metrics) > 0:
                completely_delete_objects(metrics)
            
            add_metrics_obj_from_bound_box(o, bb)
    return ""

def align_metrics_of_objects(objects=None):
    if type(objects) == type(None):
        objects=bpy.context.selected_objects
        if len(objects) == 0:
            return "no objects selected"

    targets = []
    reference_bound_box = None
    for o in objects:
        is_possibly_glyph = is_glyph(o)
        if is_possibly_glyph:
            metrics = []
            for c in o.children:
                if is_metrics_object(c):
                    metrics.append(c)

            if len(metrics) == 0:
                reference_bound_box = get_max_bound_box(o.bound_box,
                                                        reference_bound_box)
            elif len(metrics) > 0:
                reference_bound_box = get_max_bound_box(metrics[0].bound_box,
                                                        reference_bound_box)
            targets.append(o)
    for t in targets:
        metrics = []
        for c in t.children:
            if is_metrics_object(c):
                metrics.append(c)
        bound_box = None
        if len(metrics) == 0:
            bound_box = get_metrics_bound_box(t.bound_box,
                                              reference_bound_box)
        else:
            bound_box = get_metrics_bound_box(metrics[0].bound_box,
                                              reference_bound_box)
            completely_delete_objects(metrics)
        
        add_metrics_obj_from_bound_box(t, bound_box)
    return ""