import argparse
import re
from functools import partial
from pathlib import Path
from typing import Optional, Union

import nltk
import torch
from datasets import load_dataset
from transformers import AutoModelForSeq2SeqLM, AutoTokenizer

DEVICE = torch.device("cuda" if torch.cuda.is_available() else "cpu")


def to_lang_code(texts, lang_code, model, tokenizer, max_words=500):
    is_string = isinstance(texts, str)
    if is_string:
        texts = [texts]
    batch_size = len(texts)
    to_translate = []
    merges = []
    for index, text in enumerate(texts):
        # Split in sentences if too long
        merges.append(0)
        if text.count(" ") > max_words:
            sentences = nltk.sent_tokenize(text, "norwegian")
            text_to_translate = ""
            for sentence in sentences:
                spaces = (text_to_translate + " " + sentence).count(" ")
                if spaces >= max_words:
                    to_translate.append(text_to_translate.strip())
                    merges[-1] += 1
                else:
                    text_to_translate += sentence + " "
        else:
            to_translate.append(text)
    translated_texts = []
    # Split in batches for translation
    to_translate_batchs = [to_translate[i:i + batch_size] for i in range(0, len(to_translate), batch_size)]
    for to_translate_batch in to_translate_batchs:
        inputs = tokenizer(to_translate_batch, return_tensors="pt", padding=True, truncation=True).to(DEVICE)
        translated_tokens = model.generate(
            **inputs,
            forced_bos_token_id=tokenizer.lang_code_to_id[lang_code],
            max_length=int(len(inputs.tokens()) * 1.25)  # 25% more tokens for the translation just in case
        )
        translated_texts += tokenizer.batch_decode(translated_tokens, skip_special_tokens=True)
    # Merge outputs properly
    outputs = []
    for merge in merges:
        output = ""
        if merge:
            for i in range(len(outputs), len(outputs) + merge):
                output += translated_texts[i] + " "
            outputs.append(output.strip())
        else:
            outputs.append(translated_texts[len(outputs)].strip())
    return outputs[0] if is_string else outputs


def main(
    dataset_name: str,
    dataset_columns: Union[list, tuple],
    model_name: Optional[str]="facebook/nllb-200-3.3B",  # "facebook/nllb-200-distilled-600M"
    model_revision: Optional[str]=None,
    dataset_splits: Union[list, tuple]=("test", "validation", "train"),
    dataset_config: Optional[str]=None,
    dataset_revision: Optional[str]=None,
    source_lang: Optional[str]="eng_Latn",
    target_langs: Optional[Union[list, tuple]]=("nob_Latn", "nno_Latn"),
    batch_size: Optional[int]=24,
    output_dir: Optional[Path]=Path("./"),
) -> None:

    model = AutoModelForSeq2SeqLM.from_pretrained(model_name, use_auth_token=True, torch_dtype=torch.float32)
    model.to(DEVICE, torch.float32, True)
    tokenizer = AutoTokenizer.from_pretrained(
        model_name, revision=model_revision, use_auth_token=True, src_lang=source_lang,
    )

    ds = load_dataset(dataset_name, name=dataset_config, revision=dataset_revision)
    dss = {}
    for lang_code in target_langs:
        translate = partial(to_lang_code, lang_code=lang_code, model=model, tokenizer=tokenizer)
        dss[lang_code] = ds.map(
            lambda batch: {col: translate(batch[col]) for col in dataset_columns},
            batched=True,
            batch_size=batch_size,
            desc=f"Translating to {lang_code}",
        )
        lang_code_short = re.split(r"[-_ /]", lang_code)[0]
        dss[lang_code].save_to_disk(output_dir / lang_code_short, max_shard_size="1GB")
        for split in dataset_splits:
            json_filename = f"{lang_code_short}_{split}.json.tar.gz".lower()
            dss[lang_code][split].to_pandas().to_json(
                output_dir / lang_code_short / json_filename, orient='records', lines=True
            )



if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Translate datasets using Facebook's NLLB models")
    parser.add_argument('dataset_name')
    parser.add_argument('dataset_columns', help="Comma separated column names to translate")
    parser.add_argument('--dataset_splits', default="test,validation,train", help="Comma separated splits to translate")
    parser.add_argument('--dataset_config')
    parser.add_argument('--dataset_revision')
    parser.add_argument('--model_name', default="facebook/nllb-200-3.3B")
    parser.add_argument('--model_revision')
    parser.add_argument('--source_lang', default="eng_Latn")
    parser.add_argument('--target_langs', default="nob_Latn,nno_Latn", help="Comma separated target languages to translate to")
    parser.add_argument('--batch_size', '-bs', default=24, type=int, help='Number of inputs per batch for prediction')
    parser.add_argument('--output_dir', '-o', default="./", type=str)
    args = parser.parse_args()
    main(
        dataset_name=args.dataset_name,
        dataset_columns=args.dataset_columns.split(","),
        dataset_splits=args.dataset_splits.split(","),
        dataset_config=args.dataset_config,
        dataset_revision=args.dataset_revision,
        model_name=args.model_name,
        model_revision=args.model_revision,
        source_lang=args.source_lang,
        target_langs=args.target_langs.split(","),
        batch_size=args.batch_size,
        output_dir=Path(args.output_dir),
    )