import hashlib
from pathlib import Path
from .config import MAX_PDF_BYTES
from .schema import Document, Page


def read_document(name, data, models):
    if Path(name).suffix.lower() != '.pdf':
        raise ValueError('Upload a PDF. Save other document formats as PDF first.')
    if not data or len(data) > MAX_PDF_BYTES:
        raise ValueError('Upload a non-empty PDF smaller than 40 MB.')
    if b'%PDF-' not in data[:1024]:
        raise ValueError('This file does not appear to be a PDF.')
    extracted = models.extract_pdf(name, data)
    pages = [Page(number=p.number, original=p.original, english=p.english,
                  language=p.language, method='Gemini PDF extraction', reviewed=False,
                  warnings=p.warnings) for p in extracted]
    if not pages or not any(p.english.strip() for p in pages):
        raise ValueError('No readable text was found. Upload a clearer, unlocked PDF.')
    return Document(id=hashlib.sha256(data + b'.pdf').hexdigest()[:12],
                    name=Path(name).name, pages=pages)


def split_text(text, limit=1000):
    """Retained for Sarvam translation; never discards characters."""
    while text:
        end = min(len(text), limit)
        if end < len(text):
            cut = max(text.rfind('\n', limit // 2, end), text.rfind('. ', limit // 2, end),
                      text.rfind(' ', limit // 2, end))
            if cut > 0:
                end = cut + 1
        yield text[:end]
        text = text[end:]