"""Native Discord read client — the Discord counterpart to subscribestar_client.

Mirrors gallery-dl 1.32.13's `extractor/discord.py` (rule 130: gallery-dl is the
known-working base), adapted to the native core's client contract
(`ingest_core` module docstring): `iter_posts` / `extract_media`, plus the
post-first `post_record_key` and the `post_meta` date the revisit window reads.

What is mirrored exactly, because drift in any of it changes what we fetch or
where it lands on disk:

  - API v10, `Authorization: <user token>` (a USER token, not a bot token).
  - gallery-dl's request profile: its date-derived Firefox User-Agent,
    `Accept: */*`, `Accept-Language`, `Referer: https://discord.com/`.
  - `GET /channels/{id}/messages?limit=100&before=<last id>`, newest first,
    stopping on a short page. Message types {0, 19, 21} only.
  - The walk: a text/news channel's own messages then its threads, a forum's
    threads, a category's children, a server's text/news/forum channels.
  - Files: attachments, then embeds of type image/gifv/video (FC configures
    `embeds: all`, which for files is the same three plus rich/link embeds that
    carry an image), then forwarded `message_snapshots`, numbered from 1 across
    the lot — the `num` in `{date}_{message_id}_{num}_{filename}`.
  - Text: `content`, rich-embed author/title/description/fields/footer, poll.

Two deliberate departures, both about the walk order, neither about content:

  - Threads are walked newest-CREATED first (by id), not by last-message time.
    A backfill resumes from a checkpointed channel; last-message order shifts
    between chunks whenever someone posts, which can move an unwalked thread
    above the resume point and skip it. Creation order only ever grows at the
    front, where the next tick finds it.
  - A 403 on a thread or a nested channel skips that feed instead of failing
    the walk. gallery-dl skips only nested channels; one private thread the
    token cannot read would otherwise stop every channel after it.

FC runs on a plain-HTTP homelab; nothing here uses a secure-context Web API.
"""

from __future__ import annotations

import hashlib
import logging
import re
import time
from collections.abc import Iterator
from dataclasses import dataclass
from datetime import date
from urllib.parse import unquote

import requests

from .native_ingest_common import (
    NativeAuthError,
    NativeDriftError,
    NativeIngestError,
    retry_after_seconds,
)

log = logging.getLogger(__name__)

API_ROOT = "https://discord.com/api/v10"
_ROOT = "https://discord.com"

_TIMEOUT_SECONDS = 60.0
_MESSAGES_BATCH = 100
_THREADS_BATCH = 25
# gallery-dl retries a 429 up to its default 4 retries, waiting
# `request_interval_429` (60s) between them. Discord's Retry-After is exact, so
# it is honoured when present; 60s is the fallback and the cap.
_MAX_429_RETRIES = 4
_429_WAIT_SECONDS = 60.0

# https://discord.com/developers/docs/resources/message#message-object-message-types
# DEFAULT, REPLY, CHAT_INPUT_COMMAND — the ones that carry user content.
MESSAGE_TYPES = frozenset({0, 19, 21})
# https://discord.com/developers/docs/resources/channel#channel-object-channel-types
_TEXT = frozenset({0, 5})               # text, announcement: messages + threads
_DIRECT = frozenset({1, 3, 10, 11, 12})  # DMs and threads: messages only
_FORUM = frozenset({15, 16})            # forum, media: threads only
_CATEGORY = 4
_SERVER_WALK = _TEXT | _FORUM
_EMBED_TYPES = frozenset({"image", "gifv", "video"})

_URL_RE = re.compile(
    r"^(?:https?://)?(?:www\.|ptb\.|canary\.)?discord(?:app)?\.com/channels/"
    r"(?P<server>@me|\d+)(?:/(?:\d+/threads/)?(?P<channel>\d+))?(?P<rest>/.*)?/?$"
)


class DiscordAPIError(NativeIngestError):
    """Base for native Discord client failures."""


class DiscordAuthError(DiscordAPIError, NativeAuthError):
    """401 (the token is invalid or expired) or a 403 on the channel the
    source names. The fix is a new token, not a new client."""


class DiscordDriftError(DiscordAPIError, NativeDriftError):
    """A response did not have the shape the walk depends on."""


def firefox_user_agent(today: date | None = None) -> str:
    """gallery-dl's default User-Agent: a Firefox whose version advances every
    four weeks (`util._ff_ver`, "147 on 2026-01-13"). Computed the same way so
    the profile keeps matching the gallery-dl this replaced."""
    ver = ((today or date.today()).toordinal() - 735_513) // 28
    return (
        f"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:{ver}.0) "
        f"Gecko/20100101 Firefox/{ver}.0"
    )


def nameext_from_url(url: str) -> tuple[str, str]:
    """gallery-dl's `text.nameext_from_url`: the URL's last path segment,
    unquoted, split at the last dot when the extension is at most 16 chars
    (lowercased); otherwise the whole name and no extension."""
    filename = unquote(url.partition("?")[0].rpartition("/")[2])
    name, _, ext = filename.rpartition(".")
    if name and len(ext) <= 16:
        return name, ext.lower()
    return filename, ""


def parse_source_url(url: str) -> tuple[str | None, str | None]:
    """`(server_id, channel_id)` from a Discord channel/server URL. `server_id`
    is None for a DM (`@me`); `channel_id` is None for a whole server. Raises
    DiscordAPIError for anything else, including a link to a single message —
    a message is not something a source can subscribe to."""
    m = _URL_RE.match((url or "").strip())
    if not m or (m.group("rest") or "").strip("/"):
        raise DiscordAPIError(
            f"Not a Discord channel or server link: {url!r} "
            "(expected https://discord.com/channels/<server>[/<channel>])"
        )
    server = m.group("server")
    channel = m.group("channel")
    if server == "@me":
        if not channel:
            raise DiscordAPIError(f"A DM link needs a channel id: {url!r}")
        return None, channel
    return server, channel


def message_text(message: dict) -> str:
    """gallery-dl's `extract_message_text`: the body plus the text of rich
    embeds and polls, newline-joined, empties dropped."""
    parts = [message.get("content") or ""]
    for embed in message.get("embeds") or []:
        if embed.get("type") != "rich":
            continue
        parts.append((embed.get("author") or {}).get("name") or "")
        parts.append(embed.get("title") or "")
        parts.append(embed.get("description") or "")
        for fld in embed.get("fields") or []:
            parts.append(fld.get("name") or "")
            parts.append(fld.get("value") or "")
        parts.append((embed.get("footer") or {}).get("text") or "")
    poll = message.get("poll")
    if poll:
        parts.append(((poll.get("question") or {}).get("text")) or "")
        for answer in poll.get("answers") or []:
            parts.append(((answer.get("poll_media") or {}).get("text")) or "")
    return "\n".join(p for p in parts if p)


@dataclass
class MediaItem:
    """One file of a Discord message. `filename`/`extension` are gallery-dl's
    split of the URL; `num` is its 1-based position across the message's files,
    which is what names it on disk.

    `media_id` is what the seen-ledger keys on, and it is deliberately NOT
    `num`: an edit that removes a file renumbers the ones after it, and a
    positional key would then call a different file seen. It is the
    attachment's id, or for an embed (which has none) a hash of its URL path —
    the query string is a signature that changes on every fetch. `filehash` is
    always None; nothing in a signed CDN URL is a content hash."""

    url: str
    filename: str
    extension: str
    kind: str
    post_id: str
    num: int
    media_id: str
    filehash: str | None = None


class DiscordClient:
    """Synchronous Discord API v10 read client for one user token."""

    def __init__(
        self,
        token: str | None,
        *,
        request_sleep: float = 0.0,
        max_retries: int = _MAX_429_RETRIES,
        session: requests.Session | None = None,
    ):
        self._session = session or requests.Session()
        self._session.headers.update({
            "User-Agent": firefox_user_agent(),
            "Accept": "*/*",
            "Accept-Language": "en-US,en;q=0.5",
            "Referer": _ROOT + "/",
        })
        if token:
            self._session.headers["Authorization"] = token
        self._token = token
        self._request_sleep = request_sleep or 0.0
        self._max_retries = max_retries
        self._server: dict = {}
        self._channels: dict[str, dict] = {}
        self._skip_feed = False

    # -- request -----------------------------------------------------------

    def _get(self, endpoint: str, params: dict | None = None):
        if not self._token:
            raise DiscordAuthError("No Discord token is configured for this source")
        if self._request_sleep > 0:
            time.sleep(self._request_sleep)
        url = API_ROOT + endpoint
        attempt = 0
        while True:
            try:
                resp = self._session.get(url, params=params, timeout=_TIMEOUT_SECONDS)
            except requests.RequestException as exc:
                raise DiscordAPIError(f"Discord request failed ({endpoint}): {exc}") from exc
            if resp.status_code == 429 and attempt < self._max_retries:
                attempt += 1
                delay = retry_after_seconds(
                    resp, attempt, base=_429_WAIT_SECONDS, cap=_429_WAIT_SECONDS,
                )
                log.warning(
                    "Discord 429 (%s) — waiting %.1fs (retry %d/%d)",
                    endpoint, delay, attempt, self._max_retries,
                )
                time.sleep(delay)
                continue
            break
        if resp.status_code == 401:
            raise DiscordAuthError(
                "Discord rejected the token (HTTP 401) — it is invalid or has "
                "expired; copy a fresh one from the browser",
                status_code=401,
            )
        if resp.status_code != 200:
            raise DiscordAPIError(
                f"Discord returned HTTP {resp.status_code} ({endpoint})",
                status_code=resp.status_code,
                retry_after=_retry_after(resp),
            )
        try:
            return resp.json()
        except ValueError as exc:
            raise DiscordDriftError(
                f"Discord returned non-JSON for {endpoint} ({len(resp.content)} bytes)"
            ) from exc

    # -- metadata (gallery-dl parse_server / parse_channel) -----------------

    def _load_server(self, server_id: str) -> None:
        server = self._get(f"/guilds/{server_id}")
        if not isinstance(server, dict) or "id" not in server:
            raise DiscordDriftError(f"Discord server {server_id} came back without an id")
        self._server = {
            "server": server.get("name") or "",
            "server_id": str(server["id"]),
            "owner_id": server.get("owner_id"),
        }
        channels = self._get(f"/guilds/{server_id}/channels")
        if not isinstance(channels, list):
            raise DiscordDriftError(f"Discord server {server_id} channel list is not a list")
        # Categories first, so every child can name its parent.
        for channel in sorted(channels, key=lambda ch: ch.get("type") != _CATEGORY):
            self._parse_channel(channel)

    def _parse_channel(self, channel: dict) -> dict:
        parent_id = channel.get("parent_id")
        meta = {
            "channel": channel.get("name") or "",
            "channel_id": str(channel.get("id")),
            "channel_type": channel.get("type"),
            "channel_topic": channel.get("topic") or "",
            "parent_id": parent_id,
            "is_thread": "thread_metadata" in channel,
        }
        parent = self._channels.get(parent_id) if parent_id else None
        if parent:
            meta["parent"] = parent["channel"]
            meta["parent_type"] = parent["channel_type"]
        if meta["channel_type"] in {1, 3}:
            recipients = channel.get("recipients") or []
            meta["channel"] = "DMs"
            meta["recipients"] = [u.get("username") for u in recipients]
            meta["recipients_id"] = [u.get("id") for u in recipients]
        self._channels[meta["channel_id"]] = meta
        return meta

    def _channel_meta(self, channel_id: str) -> dict:
        if channel_id not in self._channels:
            self._parse_channel(self._get(f"/channels/{channel_id}"))
        return self._channels[channel_id]

    def _threads(self, channel_id: str) -> list[dict]:
        """Every thread of a channel or forum, newest-created first (see the
        module docstring for why not last-message order)."""
        threads: list[dict] = []
        offset = 0
        while True:
            data = self._get(f"/channels/{channel_id}/threads/search", {
                "sort_by": "last_message_time",
                "sort_order": "desc",
                "limit": _THREADS_BATCH,
                "offset": offset,
            })
            batch = (data.get("threads") or []) if isinstance(data, dict) else []
            threads.extend(batch)
            if len(batch) < _THREADS_BATCH:
                break
            offset += len(batch)
        threads.sort(key=lambda t: int(t.get("id") or 0), reverse=True)
        return threads

    # -- the walk ------------------------------------------------------------

    def _feeds(self, channel_id: str, *, safe: bool) -> Iterator[tuple[str, bool]]:
        """`(channel_id, safe)` for every message feed under `channel_id`, in
        gallery-dl's order. `safe` feeds are skipped on a 403."""
        try:
            ctype = self._channel_meta(channel_id)["channel_type"]
        except DiscordAPIError as exc:
            if exc.status_code != 403:
                raise
            if not safe:
                raise DiscordAuthError(
                    f"The Discord token cannot see channel {channel_id} (HTTP 403)",
                    status_code=403,
                ) from exc
            log.info("Discord: no access to channel %s — skipped", channel_id)
            return
        if ctype in _TEXT or ctype in _DIRECT:
            yield channel_id, safe
        if ctype in _TEXT or ctype in _FORUM:
            try:
                threads = self._threads(channel_id)
            except DiscordAPIError as exc:
                if exc.status_code != 403:
                    raise
                log.info("Discord: cannot list threads of %s — skipped", channel_id)
                threads = []
            for thread in threads:
                yield self._parse_channel(thread)["channel_id"], True
        elif ctype == _CATEGORY:
            for child in list(self._channels.values()):
                if child.get("parent_id") == channel_id:
                    yield from self._feeds(child["channel_id"], safe=True)
        elif ctype not in _DIRECT and not safe:
            raise DiscordAPIError(
                f"Discord channel {channel_id} is of type {ctype}, which has no messages"
            )

    def _source_feeds(self, url: str) -> Iterator[tuple[str, bool]]:
        server_id, channel_id = parse_source_url(url)
        self._server, self._channels = {}, {}
        if server_id is not None:
            self._load_server(server_id)
        if channel_id is not None:
            yield from self._feeds(channel_id, safe=False)
            return
        for meta in list(self._channels.values()):
            if meta["channel_type"] in _SERVER_WALK:
                yield from self._feeds(meta["channel_id"], safe=True)

    def skip_feed(self) -> None:
        """Optional core seam (#4413): end the current channel and go on to the
        next one. A tick's early-out means THIS channel has nothing new, not
        that the server has nothing new."""
        self._skip_feed = True

    def iter_posts(
        self, campaign_id: str, cursor: str | None = None
    ) -> Iterator[tuple[dict, dict, str | None]]:
        """Yield `(message, channel_meta, page_cursor)` for every content
        message the source reaches, channel by channel, each newest first.

        `campaign_id` is the source URL. The cursor is `<channel_id>:<before>`
        — the channel and the `before` id that fetched the page (empty for a
        channel's first page) — so a backfill resumes inside the right channel
        and re-fetches the page it was cut in. A cursor naming a channel the
        walk no longer reaches (a deleted thread) restarts from the top rather
        than walking nothing.
        """
        resume_channel, _, resume_before = (cursor or "").partition(":")
        resuming = bool(resume_channel)
        feeds = list(self._source_feeds(campaign_id)) if resuming else None
        if feeds is not None and resume_channel not in {cid for cid, _ in feeds}:
            log.warning(
                "Discord: resume channel %s is no longer in %s — restarting",
                resume_channel, campaign_id,
            )
            resuming = False
        for channel_id, safe in feeds if feeds is not None else self._source_feeds(campaign_id):
            before = None
            if resuming:
                if channel_id != resume_channel:
                    continue
                resuming = False
                before = resume_before or None
            yield from self._iter_channel(channel_id, before, safe=safe)

    def _iter_channel(
        self, channel_id: str, before: str | None, *, safe: bool
    ) -> Iterator[tuple[dict, dict, str | None]]:
        self._skip_feed = False
        meta = {**self._server, **self._channels.get(channel_id, {})}
        while True:
            page_cursor = f"{channel_id}:{before or ''}"
            try:
                messages = self._get(
                    f"/channels/{channel_id}/messages",
                    {"limit": _MESSAGES_BATCH, "before": before},
                )
            except DiscordAPIError as exc:
                if exc.status_code != 403:
                    raise
                if not safe:
                    raise DiscordAuthError(
                        f"The Discord token cannot read channel {channel_id} (HTTP 403)",
                        status_code=403,
                    ) from exc
                log.info("Discord: no access to messages of %s — skipped", channel_id)
                return
            if not isinstance(messages, list):
                raise DiscordDriftError(
                    f"Discord messages of {channel_id} came back as "
                    f"{type(messages).__name__}, not a list"
                )
            for message in messages:
                if message.get("type") not in MESSAGE_TYPES:
                    continue
                message["_meta"] = meta
                yield message, meta, page_cursor
                if self._skip_feed:
                    return
            if len(messages) < _MESSAGES_BATCH:
                return
            before = str(messages[-1]["id"])

    # -- per-message -------------------------------------------------------

    @staticmethod
    def extract_media(post: dict, included: dict | None = None) -> list[MediaItem]:
        """gallery-dl's file list for one message: attachments, then the first
        of video/image/thumbnail `proxy_url` of each file-bearing embed, then
        the same for every forwarded snapshot; numbered from 1 across them."""
        mid = str(post.get("id") or "")
        snapshots = [post] + [
            (s or {}).get("message") or {}
            for s in post.get("message_snapshots") or []
            if ((s or {}).get("message") or {}).get("type", 0) in MESSAGE_TYPES
        ]
        found: list[tuple[str, str, str | None]] = []
        for snap in snapshots:
            for att in snap.get("attachments") or []:
                if att.get("url"):
                    aid = att.get("id")
                    found.append((att["url"], "attachment", str(aid) if aid else None))
            for embed in snap.get("embeds") or []:
                if embed.get("type") not in _EMBED_TYPES:
                    continue
                for fld in ("video", "image", "thumbnail"):
                    url = (embed.get(fld) or {}).get("proxy_url")
                    if url:
                        found.append((url, "embed", None))
                        break
        items = []
        for num, (url, kind, fid) in enumerate(found, start=1):
            name, ext = nameext_from_url(url)
            if fid is None:
                path = url.partition("?")[0].encode()
                fid = "u" + hashlib.sha1(path, usedforsecurity=False).hexdigest()[:32]
            items.append(MediaItem(
                url=url, filename=name, extension=ext, kind=kind, post_id=mid,
                num=num, media_id=fid,
            ))
        return items

    @staticmethod
    def post_meta(post: dict) -> dict:
        """No title (Discord has none); `date` is the message timestamp, ISO
        with an offset — what the core's revisit window reads."""
        return {"title": None, "date": post.get("timestamp")}

    @classmethod
    def post_record_key(cls, post: dict) -> tuple[str, str] | None:
        """`(message:<id>, <id>)` — gates the message record through the seen
        ledger, like `post:<id>` on the other platforms.

        None for a message with no files. gallery-dl wrote a sidecar only
        beside a file, so a text-only chat line never became a post, and the
        drop grouping (discord_grouping) is built on that: a channel's chatter
        recorded as posts would bury the drops it exists to surface."""
        mid = post.get("id")
        mid = str(mid) if mid is not None else ""
        if not mid or not cls.extract_media(post):
            return None
        return (f"message:{mid}", mid)

    # -- verify ------------------------------------------------------------

    def describe(self, server_id: str | None, channel_id: str | None) -> dict:
        """The display names behind a server/channel pair, for the browser
        extension's Add panel. Best-effort per name: one that can't be read
        comes back None, and the other is still returned."""
        out: dict = {"server": None, "channel": None, "parent": None}
        if server_id:
            try:
                out["server"] = (self._get(f"/guilds/{server_id}") or {}).get("name") or None
            except DiscordAPIError:
                pass
        if channel_id:
            try:
                meta = self._parse_channel(self._get(f"/channels/{channel_id}"))
                out["channel"] = meta.get("channel") or None
            except (DiscordAPIError, AttributeError):
                pass
        return out

    def verify_auth(self, url: str) -> tuple[bool | None, str]:
        """Is the token valid, and can it see what the source names?"""
        try:
            server_id, channel_id = parse_source_url(url)
        except DiscordAPIError as exc:
            return None, str(exc)
        try:
            me = self._get("/users/@me")
            if channel_id is not None:
                self._get(f"/channels/{channel_id}")
            elif server_id is not None:
                self._get(f"/guilds/{server_id}")
        except DiscordAuthError as exc:
            return False, f"Discord rejected the token — {exc}"
        except DiscordAPIError as exc:
            if exc.status_code in (403, 404):
                return False, (
                    "The token is valid, but its account cannot see "
                    f"{'this channel' if channel_id else 'this server'} "
                    f"(HTTP {exc.status_code})"
                )
            return None, f"Couldn't verify (network/HTTP issue): {exc}"
        who = (me or {}).get("username") if isinstance(me, dict) else None
        return True, f"Token valid{f' ({who})' if who else ''} — the source is readable."


def _retry_after(resp: requests.Response) -> float | None:
    hdr = resp.headers.get("Retry-After")
    try:
        return float(hdr) if hdr else None
    except (TypeError, ValueError):
        return None