#!/usr/bin/env python3
"""libgen.vg downloader (the box-verified flow, 2026-07-14).

Pipeline (curl engine — Python's DNS is flaky on this box, curl is not):
  search:  tools/lg.py "query"                    -> edition ids
  ed:      json.php?object=e&ids=E                 -> title/author/publisher/year + files{f_id, md5}
  f:       json.php?object=f&addkeys=*&ids=F       -> filesize, extension
  dl:      ads.php?md5=M (UA+cookie+referer)       -> card HTML with
          libgen.bz/get.php?md5=M&key=KEY          -> one-time download URL
          curl that (same cookie jar)              -> real bytes

Usage:
    tools/lgdl.py ed   <edition_id> [more_ids...]
    tools/lgdl.py dl   <file_id> <out_dir> <target_name>
    tools/lgdl.py md5  <file_id>

Verification on dl: final size must equal libgen filesize; magic-byte sniff
(fb2/pdf/epub/doc) must not be HTML. Card+key are re-fetched up to 3x.
Politeness: ~4s between libgen requests.
"""
import json, os, re, subprocess, sys, time

UA = ("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 "
      "(KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36")
BASE = "https://libgen.vg"
JAR = "/tmp/lgdl_cookies.txt"


def curl(url, out=None, referer=None, binary=False, timeout=240, tries=3, extra=None):
    cmd = ["curl", "-s", "--fail", "--max-time", str(timeout),
           "-c", JAR, "-b", JAR,
           "-H", "User-Agent: " + UA,
           "-H", "Accept: */*",
           "-H", "Accept-Language: ru,en;q=0.9",
           "-H", "Referer: " + (referer or BASE + "/"),
           "-L"]
    if extra:
        cmd += extra
    if out:
        cmd.append("-o")
        cmd.append(out)
    cmd.append(url)
    last = None
    for i in range(tries):
        p = subprocess.run(cmd, capture_output=True, timeout=timeout + 30)
        if p.returncode == 0:
            if out is None:
                data = p.stdout
                if not binary:
                    try:
                        data = data.decode("utf-8")
                    except UnicodeDecodeError:
                        data = data.decode("utf-8", "replace")
                return data
            return p.returncode
        last = p.returncode
        time.sleep(5 * (i + 1))
    raise RuntimeError(f"curl failed (code {last}) after {tries} tries: {url}")


def jget(path):
    return json.loads(curl(BASE + "/" + path))


def file_info(f_id):
    d = jget(f"json.php?object=f&addkeys=*&ids={f_id}")
    return d[str(f_id)]


def edition(e_id):
    d = jget(f"json.php?object=e&ids={e_id}")
    e = d[str(e_id)]
    files = []
    for rel, f in (e.get("files") or {}).items():
        fi = file_info(f["f_id"])
        time.sleep(1)
        files.append({
            "f_id": f["f_id"], "md5": f["md5"],
            "ext": fi.get("extension"), "size": int(fi.get("filesize") or 0),
        })
    e["files"] = files
    return e


def sniff(data: bytes) -> str:
    if data[:5] == b"<?xml" and b"FictionBook" in data[:500]:
        return "fb2"
    if data[:5] == b"%PDF-":
        return "pdf"
    if data[:4] == b"PK\x03\x04":
        return "epub/zip"
    if data[:8] == b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1":
        return "doc/ole"
    if data[:8] in (b"AT&TFORM", b"AT&ToC\01", b"AT&ToC\02"):
        return "djvu"
    if b"<html" in data[:2000].lower():
        return "HTML-ERROR"
    return "unknown"


def download(f_id, out_dir, name, tries=16):
    fi = file_info(f_id)
    md5, size, ext = fi["md5"], int(fi.get("filesize") or 0), fi.get("extension") or "bin"
    if not name.lower().endswith("." + ext.lower()):
        name = f"{name}.{ext}"
    os.makedirs(out_dir, exist_ok=True)
    out = os.path.join(out_dir, name)
    stall = 0
    for t in range(1, tries + 1):
        card = None
        for c in range(5):  # card fetch with backoff (libgen DB is flaky)
            try:
                card = curl(f"{BASE}/ads.php?md5={md5}",
                            referer=f"{BASE}/file.php?id={f_id}", tries=1)
                break
            except RuntimeError:
                time.sleep(8 * (c + 1))
        if card is None:
            print(f"  try {t}: card fetch failed 5x — back off harder")
            time.sleep(30)
            continue
        m = re.search(r'(https?://[^"\']*get\.php\?md5=' + md5 + r'&key=[^"\']+)', card)
        if not m:
            print(f"  try {t}: no get.php link in card ({len(card)}b) — retry")
            time.sleep(4)
            continue
        url = m.group(1)
        tmp = out + ".part"
        prev = os.path.getsize(tmp) if os.path.exists(tmp) else 0
        try:
            rc = curl(url, out=tmp, referer=f"{BASE}/ads.php?md5={md5}", binary=True,
                      timeout=3600,
                      # abort hung connections: <500B/s for 300s
                      extra=["-C", "-", "--speed-time", "300", "--speed-limit", "500"])
        except RuntimeError as e:
            print(f"  try {t}: fetch error ({e}) — back off")
            time.sleep(45)
            continue
        cur = os.path.getsize(tmp) if os.path.exists(tmp) else 0
        # resume-hang detection: two consecutive zero-progress resumes at the
        # same offset => this CDN offset is wedged; wipe and start fresh
        if 0 < prev == cur:
            stall += 1
            if stall >= 2:
                print(f"  try {t}: resume stalled 2x at {prev}b — wiping part, fresh start")
                os.remove(tmp)
                stall = 0
                cur = 0
        else:
            stall = 0
        data = open(tmp, "rb").read()
        kind = sniff(data)
        ok_size = (size == 0) or (len(data) == size)
        print(f"  try {t}: {len(data)}b (expected {size}) kind={kind}")
        if kind == "HTML-ERROR":
            os.remove(tmp)
        if kind == "HTML-ERROR" or not ok_size:
            time.sleep(4)
            continue
        os.replace(tmp, out)
        print(f"  OK -> {out} ({len(data)}b, {kind})")
        return out
    print(f"  FAILED after {tries} tries: file_id={f_id} md5={md5}")
    return None


def main():
    if len(sys.argv) < 2:
        sys.exit(__doc__)
    cmd = sys.argv[1]
    if cmd == "ed":
        for e_id in sys.argv[2:]:
            e = edition(e_id)
            keep = {k: e[k] for k in ("title", "title_add", "author", "publisher",
                                      "year", "pages", "series_name", "libgen_topic") if e.get(k)}
            print(f"[{e_id}] {json.dumps(keep, ensure_ascii=False)}")
            for f in e["files"]:
                print(f"    f_id={f['f_id']} {f['size']:>10}b {f['ext']:<6} md5={f['md5']}")
            time.sleep(1)
    elif cmd == "dl":
        f_id, out_dir, name = sys.argv[2], sys.argv[3], sys.argv[4]
        download(f_id, out_dir, name)
    elif cmd == "md5":
        print(file_info(sys.argv[2])["md5"])
    else:
        sys.exit(__doc__)


if __name__ == "__main__":
    main()