#!/usr/bin/env python3
"""PDF nach Markdown konvertieren, Absätze gliedern und optional Bilder speichern."""

import argparse
import re
import sys
from pathlib import Path

import pymupdf4llm
from pymupdf4llm.ocr import tesseract_api


HEADING = re.compile(r"^\s{0,3}#{1,6}\s+\S")

# Satzzeichen, optional gefolgt von schließenden Anführungszeichen/Klammern.
SENTENCE_END = re.compile(r"""[.!?…]+[”’"'»›)\]]*$""")

FENCE = re.compile(r"^\s{0,3}(`{3,}|~{3,})")
LIST_ITEM = re.compile(r"^\s{0,3}(?:[-+*]|\d+[.)])\s+")
BLOCKQUOTE = re.compile(r"^\s{0,3}>\s?")
RULE = re.compile(r"^\s{0,3}(?:-\s*){3,}$|^\s{0,3}(?:\*\s*){3,}$")
IMAGE = re.compile(r"^\s*!\[.*?\]\(.*\)\s*$")

# Beispiel: **==> picture [426 x 480] intentionally omitted <==**
OMITTED_IMAGE = re.compile(
    r"^\s*(?:\*\*|__)?\s*==>\s*"
    r"(?:picture|image|bild)\b.*?"
    r"(?:intentionally omitted|omitted|ausgelassen)\s*"
    r"<==\s*(?:\*\*|__)?\s*$",
    re.IGNORECASE,
)

CONTENTS_TITLE = re.compile(
    r"^\s*(?:#{1,6}\s+)?"
    r"(?:inhaltsverzeichnis|inhalt|contents|table of contents)"
    r"\s*$",
    re.IGNORECASE,
)

TOC_WITH_PAGE = re.compile(
    r"^\s*(?:[-*]\s+)?\S.+?"
    r"(?:\.{2,}|\s{2,})"
    r"(?:\d+|[ivxlcdm]+)\s*$",
    re.IGNORECASE,
)

TOC_NUMBERED = re.compile(
    r"^\s*(?:[-*]\s+)?"
    r"(?:\d+(?:\.\d+)*\.?\s+|Kapitel\s+\d+\b|Chapter\s+\d+\b)"
    r".+",
    re.IGNORECASE,
)

HTML_BLOCK = re.compile(
    r"^\s*</?(?:table|tr|td|th|div|pre|p|h[1-6])\b",
    re.IGNORECASE,
)


def ends_sentence(text: str) -> bool:
    return bool(SENTENCE_END.search(text.rstrip()))


def is_other_structure(line: str) -> bool:
    """Markdown-Strukturen, die nicht zu Fließtext verbunden werden."""
    return bool(
        LIST_ITEM.match(line)
        or BLOCKQUOTE.match(line)
        or RULE.match(line)
        or IMAGE.match(line)
        or HTML_BLOCK.match(line)
        or line.lstrip().startswith("|")
        or line.startswith(("    ", "\t"))
    )


def normalize_markdown(markdown: str) -> str:
    result: list[str] = []
    paragraph: list[str] = []

    in_fence = False
    fence_char = ""
    fence_length = 0
    in_contents = False

    def blank_line() -> None:
        if result and result[-1] != "":
            result.append("")

    def flush_paragraph() -> None:
        if paragraph:
            result.append(" ".join(paragraph))
            paragraph.clear()

    def standalone(line: str) -> None:
        flush_paragraph()
        blank_line()
        result.append(line)
        result.append("")

    lines = markdown.replace("\r\n", "\n").replace("\r", "\n").split("\n")

    for original in lines:
        line = original.rstrip()
        marker = FENCE.match(line)

        if in_fence:
            result.append(line)
            if marker:
                token = marker.group(1)
                if token[0] == fence_char and len(token) >= fence_length:
                    in_fence = False
            continue

        if marker:
            flush_paragraph()
            blank_line()
            result.append(line)
            in_fence = True
            fence_char = marker.group(1)[0]
            fence_length = len(marker.group(1))
            continue

        if not line.strip():
            if paragraph and ends_sentence(paragraph[-1]):
                flush_paragraph()
                blank_line()
            elif not paragraph:
                blank_line()
            continue

        if CONTENTS_TITLE.match(line):
            standalone(line)
            in_contents = True
            continue

        if HEADING.match(line):
            standalone(line)
            in_contents = False
            continue

        if OMITTED_IMAGE.match(line):
            standalone(line)
            continue

        if TOC_WITH_PAGE.match(line):
            standalone(line)
            continue

        if in_contents and TOC_NUMBERED.match(line):
            standalone(line)
            continue

        if in_contents and ends_sentence(line):
            in_contents = False

        if is_other_structure(line):
            flush_paragraph()
            result.append(line)
            continue

        paragraph.append(line.strip())

    flush_paragraph()
    return "\n".join(result).strip() + "\n"


def make_image_links_relative(markdown: str, image_dir: Path) -> str:
    """Absolute Bildpfade durch Pfade relativ zur Markdown-Datei ersetzen."""
    absolute_dir = image_dir.resolve().as_posix()
    relative_dir = image_dir.name

    return markdown.replace(
        absolute_dir + "/",
        relative_dir + "/",
    )


def main() -> int:
    parser = argparse.ArgumentParser(
        description=(
            "PDF in Markdown umwandeln; Fließtext nach Satzenden gliedern "
            "und optional Grafiken speichern."
        )
    )
    parser.add_argument("pdf", type=Path, help="Eingabe-PDF")
    parser.add_argument(
        "markdown",
        type=Path,
        nargs="?",
        help="Ausgabe-Datei; Standard: gleicher Name mit .md",
    )
    parser.add_argument(
        "--ocr-language",
        default="deu",
        help="Tesseract-Sprachcode bei OCR (Standard: deu)",
    )
    parser.add_argument(
        "--no-ocr",
        action="store_true",
        help="OCR deaktivieren",
    )
    parser.add_argument(
        "--images",
        action="store_true",
        help="Grafiken speichern und in Markdown verlinken",
    )
    parser.add_argument(
        "--keep-headers",
        action="store_true",
        help="Wiederkehrende Seitenköpfe übernehmen",
    )
    parser.add_argument(
        "--keep-footers",
        action="store_true",
        help="Wiederkehrende Seitenfüße übernehmen",
    )
    args = parser.parse_args()

    source = args.pdf.expanduser()
    target = (args.markdown or source.with_suffix(".md")).expanduser()

    if not source.is_file():
        parser.error(f"Eingabedatei nicht gefunden: {source}")

    if source.resolve() == target.resolve():
        parser.error("Eingabe- und Ausgabedatei müssen verschieden sein.")

    image_dir = target.parent / f"{target.stem}_images"

    try:
        target.parent.mkdir(parents=True, exist_ok=True)

        if args.images:
            image_dir.mkdir(parents=True, exist_ok=True)

        markdown = pymupdf4llm.to_markdown(
            str(source),
            header=args.keep_headers,
            footer=args.keep_footers,
            use_ocr=not args.no_ocr,
            ocr_language=args.ocr_language,
            ocr_function=(
                tesseract_api.exec_ocr if not args.no_ocr else None
            ),
            write_images=args.images,
            image_path=str(image_dir.resolve()) if args.images else "",
            image_format="png",
        )

        if args.images:
            markdown = make_image_links_relative(markdown, image_dir)

        target.write_text(normalize_markdown(markdown), encoding="utf-8")

    except Exception as exc:
        print(f"Fehler bei der Konvertierung: {exc}", file=sys.stderr)
        return 1

    print(f"Markdown geschrieben: {target}")
    if args.images:
        print(f"Bilder gespeichert in: {image_dir}")

    return 0


if __name__ == "__main__":
    raise SystemExit(main())