import mailbox
import email
from email.policy import default
from tqdm import tqdm
import numpy as np


def rolling_window(iterable, n):
    """Passes a rolling window over the iterable, yielding each n-length tuple.
    rolling_window(range(5), 3) -> (0, 1, 2), (1, 2, 3), (2, 3, 4)
    """
    it = iter(iterable)
    try:
        window = [next(it) for _ in range(n)]
        while True:
            yield tuple(window)
            window = window[1:] + [next(it)]
    except StopIteration:
        return


def read_mail_text(mbox_path):
    """
    Extract and concatenate all plaintext content from an mbox file.
    """
    texts = []
    mbox = mailbox.mbox(
        mbox_path,
        factory=lambda f: email.message_from_binary_file(f, policy=default)
    )
    for msg in tqdm(mbox):
        if msg.is_multipart():
            for part in msg.walk():
                if part.get_content_type() == "text/plain":
                    try:
                        text = part.get_content()
                        if text:
                            texts.append(text.strip())
                    except Exception:
                        pass
        else:
            if msg.get_content_type() == "text/plain":
                try:
                    text = msg.get_content()
                    if text:
                        texts.append(text.strip())
                except Exception:
                    pass
    return "\n\n".join(texts)


def join(tokens, punctuation=".,?!:;'\""):
    "Joins text, but does not give extra space before punctuation."
    tokens = [t if t in punctuation else ' ' + t for t in tokens]
    return ''.join(tokens).strip()


def softmax(x):
    "Convert a vector of scores (logits) into a probability distribution."
    e = np.exp(x - x.max())
    return e / e.sum()