import os
import urllib.request
from pathlib import Path

import tokenizers
import tokenizers.processors

import log

MODELS_DIR = Path(p if (p := os.getenv("PROJECT")) else Path.cwd()) / "models"


def fetch_file(url: str, filepath: str) -> None:
    with urllib.request.urlopen(url) as response:
        with open(filepath, "wb") as out_file:
            while chunk := response.read(8192):
                out_file.write(chunk)


def t5() -> tuple[tokenizers.Tokenizer, int, int]:
    tokenizer_path = MODELS_DIR / "google-t5--t5-small"
    tokenizer_file = tokenizer_path / "tokenizer.json"
    if not tokenizer_file.exists():
        tokenizer_path.mkdir(parents=True, exist_ok=True)
        log.info(f"Tokenizer: downloading to {tokenizer_file}...")
        fetch_file("https://huggingface.co/google-t5/t5-small/resolve/main/tokenizer.json", str(tokenizer_file))
        log.info("Tokenizer: download complete.")
    tok = tokenizers.Tokenizer.from_file(str(tokenizer_file))
    tok.add_special_tokens(["<s>", "</s>", "<unk>"])
    bos_id = tok.token_to_id("<s>")
    eos_id = tok.token_to_id("</s>")
    tok.post_processor = tokenizers.processors.TemplateProcessing(
        single="<s> $A", pair=None, special_tokens=[("<s>", bos_id)]
    )
    return tok, bos_id, eos_id