# Copyright (c) Meta Platforms, Inc. and affiliates.

# All rights reserved.

# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.


import torch
from torch import optim as optim
import json


def get_num_layer_for_convnext_single(var_name, depths):
    """
    Each layer is assigned distinctive layer ids
    """
    if var_name.startswith("downsample_layers"):
        stage_id = int(var_name.split(".")[1])
        layer_id = sum(depths[:stage_id]) + 1
        return layer_id

    elif var_name.startswith("stages"):
        stage_id = int(var_name.split(".")[1])
        block_id = int(var_name.split(".")[2])
        layer_id = sum(depths[:stage_id]) + block_id + 1
        return layer_id

    else:
        return sum(depths) + 1


def get_num_layer_for_convnext(var_name):
    """
    Divide [3, 3, 27, 3] layers into 12 groups; each group is three
    consecutive blocks, including possible neighboring downsample layers;
    adapted from https://github.com/microsoft/unilm/blob/master/beit/optim_factory.py
    """
    num_max_layer = 12
    if var_name.startswith("downsample_layers"):
        stage_id = int(var_name.split(".")[1])
        if stage_id == 0:
            layer_id = 0
        elif stage_id == 1 or stage_id == 2:
            layer_id = stage_id + 1
        elif stage_id == 3:
            layer_id = 12
        return layer_id

    elif var_name.startswith("stages"):
        stage_id = int(var_name.split(".")[1])
        block_id = int(var_name.split(".")[2])
        if stage_id == 0 or stage_id == 1:
            layer_id = stage_id + 1
        elif stage_id == 2:
            layer_id = 3 + block_id // 3
        elif stage_id == 3:
            layer_id = 12
        return layer_id
    else:
        return num_max_layer + 1


class LayerDecayValueAssigner(object):
    def __init__(self, values, depths=[3, 3, 27, 3], layer_decay_type="single"):
        self.values = values
        self.depths = depths
        self.layer_decay_type = layer_decay_type

    def get_scale(self, layer_id):
        return self.values[layer_id]

    def get_layer_id(self, var_name):
        if self.layer_decay_type == "single":
            return get_num_layer_for_convnext_single(var_name, self.depths)
        else:
            return get_num_layer_for_convnext(var_name)


def get_parameter_groups(
    model, weight_decay=1e-5, skip_list=(), get_num_layer=None, get_layer_scale=None
):
    parameter_group_names = {}
    parameter_group_vars = {}

    for name, param in model.named_parameters():
        if not param.requires_grad:
            continue  # frozen weights
        if (
            len(param.shape) == 1
            or name.endswith(".bias")
            or name in skip_list
            or name.endswith(".gamma")
            or name.endswith(".beta")
        ):
            group_name = "no_decay"
            this_weight_decay = 0.0
        else:
            group_name = "decay"
            this_weight_decay = weight_decay
        if get_num_layer is not None:
            layer_id = get_num_layer(name)
            group_name = "layer_%d_%s" % (layer_id, group_name)
        else:
            layer_id = None

        if group_name not in parameter_group_names:
            if get_layer_scale is not None:
                scale = get_layer_scale(layer_id)
            else:
                scale = 1.0

            parameter_group_names[group_name] = {
                "weight_decay": this_weight_decay,
                "params": [],
                "lr_scale": scale,
            }
            parameter_group_vars[group_name] = {
                "weight_decay": this_weight_decay,
                "params": [],
                "lr_scale": scale,
            }

        parameter_group_vars[group_name]["params"].append(param)
        parameter_group_names[group_name]["params"].append(name)
    print("Param groups = %s" % json.dumps(parameter_group_names, indent=2))
    return list(parameter_group_vars.values())