# Copyright 2025 the LlamaFactory team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import math
from contextlib import nullcontext
from typing import TYPE_CHECKING

import torch
from transformers.integrations import is_deepspeed_zero3_enabled

from ...extras import logging


if TYPE_CHECKING:
    from transformers import PreTrainedModel, PreTrainedTokenizer


logger = logging.get_logger(__name__)


def _noisy_mean_initialization(embed_weight: "torch.Tensor", num_new_tokens: int) -> None:
    embedding_dim = embed_weight.size(1)
    avg_weight = embed_weight[:-num_new_tokens].mean(dim=0, keepdim=True)
    noise_weight = torch.empty_like(embed_weight[-num_new_tokens:])
    noise_weight.normal_(mean=0, std=(1.0 / math.sqrt(embedding_dim)))
    embed_weight[-num_new_tokens:] = avg_weight + noise_weight


def resize_embedding_layer(model: "PreTrainedModel", tokenizer: "PreTrainedTokenizer") -> None:
    r"""Resize token embeddings."""
    if is_deepspeed_zero3_enabled():
        import deepspeed  # type: ignore

        params = [model.get_input_embeddings().weight]
        if model.get_output_embeddings() is not None and not model.config.tie_word_embeddings:
            params.append(model.get_output_embeddings().weight)

        context_maybe_zero3 = deepspeed.zero.GatheredParameters(params, modifier_rank=0)
    else:
        context_maybe_zero3 = nullcontext()

    with context_maybe_zero3:
        current_embedding_size = model.get_input_embeddings().weight.size(0)

    if len(tokenizer) > current_embedding_size:
        if getattr(model, "quantization_method", None):
            raise ValueError("Cannot resize embedding layers of a quantized model.")

        if not isinstance(model.get_output_embeddings(), torch.nn.Linear):
            raise ValueError("Current model does not support resizing embedding layers.")

        model.resize_token_embeddings(len(tokenizer), pad_to_multiple_of=64)
        with context_maybe_zero3:
            new_embedding_size = model.get_input_embeddings().weight.size(0)
            num_new_tokens = new_embedding_size - current_embedding_size
            _noisy_mean_initialization(model.get_input_embeddings().weight.data, num_new_tokens)
            _noisy_mean_initialization(model.get_output_embeddings().weight.data, num_new_tokens)

        logger.info_rank0(f"Resized token embeddings from {current_embedding_size} to {new_embedding_size}.")
