from typing import Any, Callable, Optional

import torch
import torch.distributed as dist
from transformers import PreTrainedTokenizer

from .base import Actor

try:
    from transformers.generation_logits_process import (
        LogitsProcessorList,
        TemperatureLogitsWarper,
        TopKLogitsWarper,
        TopPLogitsWarper,
    )
except ImportError:
    from transformers.generation import LogitsProcessorList, TemperatureLogitsWarper, TopKLogitsWarper, TopPLogitsWarper


def _prepare_logits_processor(
    top_k: Optional[int] = None, top_p: Optional[float] = None, temperature: Optional[float] = None
) -> LogitsProcessorList:
    processor_list = LogitsProcessorList()
    if temperature is not None and temperature != 1.0:
        processor_list.append(TemperatureLogitsWarper(temperature))
    if top_k is not None and top_k != 0:
        processor_list.append(TopKLogitsWarper(top_k))
    if top_p is not None and top_p < 1.0:
        processor_list.append(TopPLogitsWarper(top_p))
    return processor_list


def _is_sequence_finished(unfinished_sequences: torch.Tensor) -> bool:
    if dist.is_initialized() and dist.get_world_size() > 1:
        # consider DP
        unfinished_sequences = unfinished_sequences.clone()
        dist.all_reduce(unfinished_sequences)
    return unfinished_sequences.max() == 0


def _sample(
    model: Actor,
    input_ids: torch.Tensor,
    max_length: int,
    early_stopping: bool = False,
    eos_token_id: Optional[int] = None,
    pad_token_id: Optional[int] = None,
    top_k: Optional[int] = None,
    top_p: Optional[float] = None,
    temperature: Optional[float] = None,
    prepare_inputs_fn: Optional[Callable[[torch.Tensor, Any], dict]] = None,
    update_model_kwargs_fn: Optional[Callable[[dict, Any], dict]] = None,
    **model_kwargs,
) -> torch.Tensor:
    if input_ids.size(1) >= max_length:
        return input_ids

    logits_processor = _prepare_logits_processor(top_k, top_p, temperature)
    unfinished_sequences = input_ids.new(input_ids.shape[0]).fill_(1)

    for _ in range(input_ids.size(1), max_length):
        model_inputs = (
            prepare_inputs_fn(input_ids, **model_kwargs) if prepare_inputs_fn is not None else {"input_ids": input_ids}
        )
        outputs = model(**model_inputs)

        # NOTE: this is correct only in left padding mode
        next_token_logits = outputs["logits"][:, -1, :]
        next_token_logits = logits_processor(input_ids, next_token_logits)
        # sample
        probs = torch.softmax(next_token_logits, dim=-1, dtype=torch.float)
        next_tokens = torch.multinomial(probs, num_samples=1).squeeze(1)

        # finished sentences should have their next token be a padding token
        if eos_token_id is not None:
            assert pad_token_id is not None, "If `eos_token_id` is defined, make sure that `pad_token_id` is defined."
            next_tokens = next_tokens * unfinished_sequences + pad_token_id * (1 - unfinished_sequences)

        # update generated ids, model inputs for next step
        input_ids = torch.cat([input_ids, next_tokens[:, None]], dim=-1)
        if update_model_kwargs_fn is not None:
            model_kwargs = update_model_kwargs_fn(outputs, model_kwargs)

        # if eos_token was found in one sentence, set sentence to finished
        if eos_token_id is not None:
            unfinished_sequences = unfinished_sequences.mul((next_tokens != eos_token_id).long())

        # stop when each sentence is finished if early_stopping=True
        if early_stopping and _is_sequence_finished(unfinished_sequences):
            break

    return input_ids


@torch.no_grad()
def generate(
    model: Actor,
    input_ids: torch.Tensor,
    tokenizer: PreTrainedTokenizer,
    max_length: int,
    num_beams: int = 1,
    do_sample: bool = True,
    early_stopping: bool = False,
    top_k: Optional[int] = None,
    top_p: Optional[float] = None,
    temperature: Optional[float] = None,
    prepare_inputs_fn: Optional[Callable[[torch.Tensor, Any], dict]] = None,
    update_model_kwargs_fn: Optional[Callable[[dict, Any], dict]] = None,
    **model_kwargs,
) -> torch.Tensor:
    """Generate token sequence. The returned sequence is input_ids + generated_tokens.

    Args:
        model (nn.Module): model
        input_ids (torch.Tensor): input sequence
        max_length (int): max length of the returned sequence
        num_beams (int, optional): number of beams. Defaults to 1.
        do_sample (bool, optional): whether to do sample. Defaults to True.
        early_stopping (bool, optional): if True, the sequence length may be smaller than max_length due to finding eos. Defaults to False.
        top_k (Optional[int], optional): the number of highest probability vocabulary tokens to keep for top-k-filtering. Defaults to None.
        top_p (Optional[float], optional): If set to float < 1, only the smallest set of most probable tokens with probabilities that add up to top_p or higher are kept for generation. Defaults to None.
        temperature (Optional[float], optional): The value used to module the next token probabilities. Defaults to None.
        prepare_inputs_fn (Optional[Callable[[torch.Tensor, Any], dict]], optional): Function to preprocess model inputs. Arguments of this function should be input_ids and model_kwargs. Defaults to None.
        update_model_kwargs_fn (Optional[Callable[[dict, Any], dict]], optional): Function to update model_kwargs based on outputs. Arguments of this function should be outputs and model_kwargs. Defaults to None.
    """
    assert tokenizer.padding_side == "left", "Current generation only supports left padding."
    is_greedy_gen_mode = (num_beams == 1) and do_sample is False
    is_sample_gen_mode = (num_beams == 1) and do_sample is True
    is_beam_gen_mode = (num_beams > 1) and do_sample is False
    if is_greedy_gen_mode:
        # run greedy search
        raise NotImplementedError
    elif is_sample_gen_mode:
        # run sample
        return _sample(
            model,
            input_ids,
            max_length,
            early_stopping=early_stopping,
            eos_token_id=tokenizer.eos_token_id,
            pad_token_id=tokenizer.pad_token_id,
            top_k=top_k,
            top_p=top_p,
            temperature=temperature,
            prepare_inputs_fn=prepare_inputs_fn,
            update_model_kwargs_fn=update_model_kwargs_fn,
            **model_kwargs,
        )
    elif is_beam_gen_mode:
        raise NotImplementedError
    else:
        raise ValueError("Unsupported generation mode")
