from __future__ import annotations

from dataclasses import dataclass
from typing import List, Tuple

import fitz  # PyMuPDF
from PIL import Image
import io

import pytesseract


@dataclass
class PageText:
    page_index: int  # 0-based
    extracted_text: str
    ocr_text: str
    used_ocr: bool


def _safe_text(s: str) -> str:
    return (s or "").replace("\x00", " ").strip()


def is_likely_scanned(extracted_text: str, min_text_chars_for_digital: int) -> bool:
    """
    Simple heuristic: if the native extracted text is too short, likely scanned.
    """
    t = _safe_text(extracted_text)
    return len(t) < min_text_chars_for_digital


def render_page_to_pil(doc: fitz.Document, page_index: int, dpi: int = 200) -> Image.Image:
    page = doc.load_page(page_index)
    zoom = dpi / 72.0
    mat = fitz.Matrix(zoom, zoom)
    pix = page.get_pixmap(matrix=mat, alpha=False)
    img = Image.open(io.BytesIO(pix.tobytes("png"))).convert("RGB")
    return img


def ocr_pil_image(img: Image.Image, lang: str = "eng") -> str:
    # You can also add config like "--psm 6" if needed.
    txt = pytesseract.image_to_string(img, lang=lang)
    return _safe_text(txt)


def extract_texts_from_pdf(
    pdf_path: str,
    dpi: int = 200,
    ocr_lang: str = "eng",
    min_text_chars_for_digital: int = 80,
) -> Tuple[List[PageText], int]:
    doc = fitz.open(pdf_path)
    page_count = doc.page_count
    results: List[PageText] = []

    for i in range(page_count):
        page = doc.load_page(i)
        extracted = _safe_text(page.get_text("text"))

        if is_likely_scanned(extracted, min_text_chars_for_digital):
            img = render_page_to_pil(doc, i, dpi=dpi)
            ocr_txt = ocr_pil_image(img, lang=ocr_lang)
            results.append(PageText(i, extracted_text=extracted, ocr_text=ocr_txt, used_ocr=True))
        else:
            results.append(PageText(i, extracted_text=extracted, ocr_text="", used_ocr=False))

    doc.close()
    return results, page_count


def render_pages_to_png_bytes(pdf_path: str, page_indices: List[int], dpi: int = 200) -> List[bytes]:
    doc = fitz.open(pdf_path)
    out: List[bytes] = []
    for p in page_indices:
        img = render_page_to_pil(doc, p, dpi=dpi)
        buf = io.BytesIO()
        img.save(buf, format="PNG")
        out.append(buf.getvalue())
    doc.close()
    return out