"""PDF → Markdown。無文字層（掃描件）回報 needs_ocr 並跳過，不擅自呼叫 OCR。

可獨立執行：python tools/convert/from_pdf.py <file.pdf> [-o out.md] [--dry-run]
"""
import argparse
import pathlib

import fitz  # pymupdf

# ponytail: 掃描件偵測用「平均每頁字元數 < 25」的 naive heuristic，
# 混合型 PDF（部分頁掃描）會整份判為有文字層；升級路徑：逐頁判定 + 逐頁標記。
_MIN_CHARS_PER_PAGE = 25


def convert(src, assets_dir=None, md_dir=None):
    """回傳 (markdown, status)。status ∈ {'ok', 'needs_ocr'}。

    ponytail: 表格輸出為純文字行（不重建表格結構），升級路徑：page.find_tables()。
    """
    src = pathlib.Path(src)
    md_dir = pathlib.Path(md_dir) if md_dir else src.parent
    doc = fitz.open(str(src))
    pages = [page.get_text("text").strip() for page in doc]
    total = sum(len(p) for p in pages)
    if total < _MIN_CHARS_PER_PAGE * max(len(pages), 1):
        doc.close()
        return "", "needs_ocr"

    counter = 0
    blocks = []
    for i, page in enumerate(doc):
        blocks.append(f"<!-- page {i + 1} -->\n\n{pages[i]}")
        if assets_dir is None:
            continue
        for img in page.get_images(full=True):
            xref = img[0]
            pix = fitz.Pixmap(doc, xref)
            if pix.n > 4:  # CMYK 等 → 轉 RGB
                pix = fitz.Pixmap(fitz.csRGB, pix)
            counter += 1
            name = f"img{counter}.png"
            assets_dir.mkdir(parents=True, exist_ok=True)
            pix.save(str(assets_dir / name))
            rel = (assets_dir / name).relative_to(md_dir).as_posix()
            blocks.append(f"![{name}]({rel})")
    doc.close()
    return "\n\n".join(blocks), "ok"


def main(argv=None):
    ap = argparse.ArgumentParser(description=__doc__)
    ap.add_argument("src")
    ap.add_argument("-o", "--output")
    ap.add_argument("--dry-run", action="store_true")
    a = ap.parse_args(argv)
    if a.dry_run:
        md, status = convert(a.src)
        print(f"[dry-run] {a.src}: status={status}, {len(md)} chars")
        return
    out = pathlib.Path(a.output) if a.output else pathlib.Path(a.src).with_suffix(".md")
    md, status = convert(a.src, assets_dir=out.parent / f"{out.stem}-assets", md_dir=out.parent)
    if status == "needs_ocr":
        print(f"needs_ocr: {a.src} 無文字層，已跳過（不擅自 OCR）")
        raise SystemExit(2)
    out.write_text(md, encoding="utf-8")
    print(out)


if __name__ == "__main__":
    main()