"""Stage 1, ingest: copy the original PDF into its book folder (never modify it), record its sha256,
find pages without a text layer and OCR only if there are any."""
import hashlib
import os
import re
import shutil
import subprocess

import bookio
import pdftext
import settings


def sha256(path):
    h = hashlib.sha256()
    with open(path, "rb") as f:
        for block in iter(lambda: f.read(1 << 20), b""):
            h.update(block)
    return h.hexdigest()


def find_title(pdf):
    out = subprocess.run(["pdfinfo", pdf], capture_output=True, text=True).stdout
    m = re.search(r"^Title:\s+(.+)$", out, re.M)
    return bookio.title_case(m.group(1).strip()) if m else ""


def find_author(unit_texts):
    """The author is the line 'By <Name>' on the first pages."""
    for text in unit_texts:
        m = re.search(r"^\s*By\s+([A-Z][A-Za-z.\- ]+?)\s*$", text, re.M)
        if m:
            return m.group(1).strip()
    return ""


def author_slug(author):
    """'Glenn Clark' -> 'clark-glenn' (surname first, last word taken as surname)."""
    parts = author.split()
    return bookio.slug(" ".join([parts[-1]] + parts[:-1])) if parts else "unknown"


def run(cfg, pdf, title=None, author=None):
    """Returns the book folder path."""
    pdf_units = pdftext.units(pdf)
    author = author or find_author([u["text"] for u in pdf_units[:6]])
    title = title or find_title(pdf)
    if not author or not title:
        raise SystemExit("could not find title/author in the PDF; pass --title and --author")
    book_dir = os.path.join(settings.resolve(cfg, "books_dir"), author_slug(author), bookio.slug(title))
    os.makedirs(book_dir, exist_ok=True)
    copy = os.path.join(book_dir, os.path.basename(pdf))
    if os.path.exists(copy) and sha256(copy) != sha256(pdf):
        raise SystemExit("a different file with this name is already in the book folder: " + copy)
    if not os.path.exists(copy):
        shutil.copyfile(pdf, copy)
    book = {}
    if os.path.exists(os.path.join(book_dir, "book.json")):
        book = bookio.read_book(book_dir)
    counts = pdftext.chars_per_page(copy)
    book.update({
        "title": title,
        "author": author,
        "source_pdf": os.path.basename(pdf),
        "sha256": sha256(copy),
        "pdf_pages": len(counts),
        "pages_without_text_layer": [i + 1 for i, c in enumerate(counts) if c < cfg["ocr"]["min_chars_per_page"]],
    })
    book.setdefault("coauthors", [])
    book.setdefault("publisher", "")
    book.setdefault("edition", "")
    book.setdefault("series", "")
    book.setdefault("summaries", {})
    bookio.write_book(book_dir, book)
    warnings = ocr_if_needed(cfg, book_dir, book)
    bookio.write_warnings(book_dir, "ingest", warnings)
    return book_dir


def work_pdf(cfg, book_dir, book):
    """The PDF text is read from: the OCR copy if one exists, else the untouched original."""
    ocr_pdf = os.path.join(settings.resolve(cfg, "work_dir"), os.path.basename(book_dir), "ocr.pdf")
    return ocr_pdf if os.path.exists(ocr_pdf) else os.path.join(book_dir, book["source_pdf"])


def ocr_if_needed(cfg, book_dir, book):
    """OCR a scratch copy (never the original) when pages lack a text layer. Returns warnings."""
    missing = book["pages_without_text_layer"]
    if not missing:
        return []
    where = "pdf pages " + ",".join(map(str, missing))
    if not cfg["ocr"]["enabled"]:
        return [("no-text-layer", where, "no text layer and OCR is disabled in settings")]
    if shutil.which("ocrmypdf") is None:
        return [("no-text-layer", where, "no text layer and ocrmypdf is not installed on this host; those pages have no text")]
    out_dir = os.path.join(settings.resolve(cfg, "work_dir"), os.path.basename(book_dir))
    os.makedirs(out_dir, exist_ok=True)
    out = os.path.join(out_dir, "ocr.pdf")
    src = os.path.join(book_dir, book["source_pdf"])
    r = subprocess.run(["ocrmypdf", "--skip-text", "-l", cfg["ocr"]["language"], src, out], capture_output=True, text=True)
    if r.returncode != 0:
        return [("ocr-failed", where, "ocrmypdf exit %d: %s" % (r.returncode, r.stderr.strip()[-300:]))]
    return [("ocr", where, "OCR applied to a scratch copy; original untouched")]