"""Downloader for 0807.st direct links via curl.

0807.st serves the files directly but rejects requests that don't look like a
browser (requires a User-Agent and the Referer of the site page), and it
rejects multi-connection/range abuse patterns differently than curl - which is
why curl is used instead of aria2c here (see chat history: curl worked,
aria2c's default request got 403).

Downloads go to a .part file first and are renamed on success, so an
interrupted download is resumable (--continue-at -) and partial files are
never mistaken for finished ones.
"""

from __future__ import annotations

import logging
import os
import subprocess
from pathlib import Path
from urllib.parse import urlparse

log = logging.getLogger(__name__)

USER_AGENT = "Mozilla/5.0"
REFERER = "https://0807.st/"


class Zero807Error(Exception):
    """Base error for 0807 downloads."""


class Zero807NotFound(Zero807Error):
    """The file no longer exists (HTTP 404/410). Not retryable."""


def target_name(url: str) -> str:
    """Derive the filename from the URL path (e.g. /6saCNie.zip -> 6saCNie.zip)."""
    name = Path(urlparse(url).path).name
    if not name:
        raise Zero807Error(f"cannot derive a filename from URL: {url}")
    return name


def download(
    url: str,
    out_dir: Path,
    timeout_seconds: int = 7200,
    resume: bool = True,
) -> tuple[Path, int]:
    """Download one URL with curl; returns (final_path, size_bytes)."""
    name = target_name(url)
    out_dir.mkdir(parents=True, exist_ok=True)
    dest = out_dir / name
    tmp = dest.with_name(dest.name + ".part")

    if dest.exists() and dest.stat().st_size > 0:
        log.info("Skip existing: %s", dest)
        return dest, dest.stat().st_size

    cmd = [
        "curl", "-fSL",
        "--connect-timeout", "20",
        "--max-time", str(timeout_seconds),
        "--retry", "2", "--retry-delay", "5",
        "-A", USER_AGENT,
        "-e", REFERER,
        "-o", str(tmp),
    ]
    if resume:
        cmd.append("--continue-at")
        cmd.append("-")
    cmd.append(url)

    log.info("Downloading %s -> %s", url, dest.name)
    proc = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                          encoding="utf-8", errors="replace")
    if proc.returncode != 0:
        tail = [line for line in proc.stderr.strip().splitlines() if line][-3:]
        stderr = " | ".join(tail)
        # -f makes curl exit 22 on any HTTP error; dead links fail for good
        if "404" in stderr or "410" in stderr:
            raise Zero807NotFound(f"dead link (HTTP 404/410): {stderr}")
        raise Zero807Error(f"curl exit code {proc.returncode}: {stderr}")

    size = tmp.stat().st_size if tmp.exists() else 0
    if size == 0:
        tmp.unlink(missing_ok=True)
        raise Zero807Error(f"empty file for {name}")
    if dest.suffix.lower() == ".zip" and not tmp.read_bytes()[:2] == b"PK":
        log.warning("%s does not look like a ZIP file (first bytes are not PK)", name)
    os.replace(tmp, dest)
    return dest, size