FabledCurator/backend/app/services/post_association_service.py

"""The announcement matcher: which Patreon post announced which Discord drop.

Milestone 388, step E5.

Two of the operator's artists post a deliberately CROPPED fragment on Patreon
to signal that the real thing has landed in their Discord. This service
proposes those pairs, and proposes only — the operator accepts or dismisses,
following the FC-6.3 series matcher (task 737) rather than linking on its own.

## Why confirm-only is not caution for its own sake

A wrongly-asserted association tells the operator that two different pieces are
one. That is strictly worse than no link at all: no link leaves them exactly
where they already were, a wrong one actively misinforms and then propagates
into whatever reads the association. So the matcher's job is to make a SHORT
list worth reading, not a long list worth trusting.

## Two routes, because the evidence is of two different kinds

CIRCUMSTANTIAL evidence says two things happened near each other. It is
additive, weighted, and no single one of its signals may reach the threshold:

1. **Time proximity.** The Patreon post exists in order to announce the drop,
   so the two are minutes-to-hours apart. Nearly free, and strong.
2. **The post says so.** These announcements routinely name Discord or carry
   an invite link, which is close to a declaration.
3. **A shared marker.** The creator's own tie-back — `🍈🍈` in the Patreon
   title and `@everyone 🍈 🍈` in the Discord message — gated on how rare that
   marker is in THIS artist's posts, because a habitual emoji is punctuation.

IDENTITY evidence says two things are the same thing, and it gets its own
route (see `IDENTITY_FLOOR`):

4. **A shared working name.** The creator exports the teaser and the release
   from one file, and the internal name survives into both platforms
   untouched. Measured on the operator's artist: `ConnFront` ↔ `ConnFront`.
   This is the only signal that reaches a pair 23.8 hours apart, which
   proximity scores at 0.005.

## The one deliberately NOT built

**Crop-to-source matching is HELD, on the plan's own instruction** — it is
real work with real false-positive risk, and it is only worth building once
the cheap signals are shown to be insufficient against the operator's actual
artists. Half of this creator's recent teasers are screenshots carrying no
working name at all, and those pairs are out of reach here; that, measured, is
what would justify it.

Note also that a naive whole-image SigLIP similarity is NOT that signal. A
cropped teaser and its full version are exactly the pair a whole-image
comparison handles worst, so adding one as a "bonus" would mostly add noise
while looking like progress.

## Creator identity comes free, so E4 is not actually a prerequisite

The plan listed E4 (creator identity across the two channels) as a dependency.
It is not one for the pairs that matter today: a Patreon `Source` and a Discord
`Source` the operator has added under the same `Artist` already share
`Post.artist_id`, and the synthetic grouping inherits it (E2). E4 EXTENDS this
to creators whose association FC has to learn rather than being told; it is not
needed to represent an association FC already knows.

## A correction the plan carried, worth restating

`link_extract.py` does exist and does capture off-platform links — but only
file hosts (`SUPPORTED_HOSTS` is mega/gdrive/mediafire/dropbox/pixeldrain).
`host_for()` returns None for a Discord URL, so no `ExternalLink` row is ever
written for one. The declaration signal therefore reads the post body itself
rather than the extracted-links table the plan assumed it could use.
"""

from __future__ import annotations

import logging
import re
from collections import Counter
from dataclasses import dataclass
from datetime import UTC, datetime, timedelta

from sqlalchemy import func, or_, select
from sqlalchemy.ext.asyncio import AsyncSession

from ..models import ImageRecord, ImportSettings, Post, PostAssociation
from ..utils.text import html_to_plain
from .discord_grouping import DROP_GROUPER
from .post_naming import (
    IDENTITY_FLOOR,
    marker_frequencies,
    marker_overlap,
    shared_identity,
    token_frequencies,
    working_name_tokens,
)

log = logging.getLogger(__name__)

# Additive weights, summing to 1.0. Kept as constants rather than settings —
# the sensitivity knob that matters is the threshold, and per-signal weights
# are an over-tune (same call as series_match_service.WEIGHTS).
#
# THE RELATIONSHIP TO THE THRESHOLD IS THE DESIGN. No single weight may reach
# the default threshold, which is what makes "time proximity alone is never
# enough" arithmetic rather than aspirational: on a busy day an artist posts
# several times, and a matcher that could pair on proximity alone would turn
# every busy day into false pairs. A guard test pins this.
WEIGHTS = {"proximity": 0.45, "declared": 0.35, "marker": 0.20}

# A Discord INVITE in the body is close to a declaration; the bare word is
# weaker but still meaningful, because these posts are short and on-topic.
#
# "the server" and its possessives are here because the word `discord` is NOT
# how these creators actually write. Measured across 20,558 Patreon bodies:
# `discord` appears in 486 and `the server` in 37 — but the distribution is the
# point, not the totals. For the artist this step was built for, 21 of 42 posts
# say `discord` and 7 say `the server`, and it is the RECENT ones that say the
# latter: the phrasing drifted once the audience already knew where the server
# was. A vocabulary list written from old posts silently stops matching.
_INVITE = re.compile(r"discord\.(?:gg|com/invite)/", re.I)
_MENTION = re.compile(r"\b(?:discord|(?:the|our|my)\s+server)\b", re.I)

DECLARED_INVITE = 1.0
DECLARED_MENTION = 0.6

MAX_CANDIDATES = 25


@dataclass(frozen=True)
class _Corpus:
    """One artist's rare-token evidence, gathered once rather than per pair.

    Both rare-token signals are scoped to a single artist — a working name and
    a marker belong to the person who chose them — so the counts are useless
    across artists and expensive to rebuild per candidate. A sweep touches an
    artist's posts many times over; this is loaded on the first touch and kept
    for the life of the service.
    """

    tokens_by_post: dict[int, set[str]]
    token_posts: Counter[str]
    text_by_post: dict[int, str]
    marker_posts: Counter[str]


def proximity_signal(gap: timedelta, window: timedelta) -> float:
    """1.0 when the two posts are simultaneous, decaying linearly to 0 at the
    window's edge. Linear rather than a step, so a pair an hour outside a
    hand-tuned window degrades instead of vanishing."""
    if window <= timedelta(0):
        return 0.0
    seconds = abs(gap.total_seconds())
    if seconds >= window.total_seconds():
        return 0.0
    return round(1.0 - (seconds / window.total_seconds()), 4)


def declared_signal(description: str | None) -> float:
    """Does the announcement say, in its own body, that this is about Discord?

    The invite is matched against the RAW body and the bare mention against the
    stripped text, which is not fussiness — post bodies are HTML, and these
    creators put the invite in an anchor's `href`. `html_to_plain` discards
    attributes, so stripping first would have thrown away the strongest form of
    the signal and left only whatever the link text happened to say.

    The mention still reads stripped text, so `\bdiscord\b` is matched against
    prose rather than against markup and URLs, where it would fire on any link
    that merely passes through a discord domain.
    """
    if not description:
        return 0.0
    if _INVITE.search(description):
        return DECLARED_INVITE
    if _MENTION.search(html_to_plain(description) or ""):
        return DECLARED_MENTION
    return 0.0


def weighted_score(signals: dict) -> float:
    return round(sum(WEIGHTS[k] * signals.get(k, 0.0) for k in WEIGHTS), 4)


def _post_time(post: Post) -> datetime:
    return post.post_date or post.downloaded_at


class PostAssociationService:
    def __init__(self, session: AsyncSession):
        self.session = session
        self._corpora: dict[int, _Corpus] = {}

    async def _corpus(self, artist_id: int) -> _Corpus:
        if artist_id in self._corpora:
            return self._corpora[artist_id]

        paths_by_post: dict[int, list[str]] = {}
        rows = await self.session.execute(
            select(ImageRecord.primary_post_id, ImageRecord.path).where(
                ImageRecord.artist_id == artist_id,
                ImageRecord.primary_post_id.is_not(None),
            )
        )
        for post_id, path in rows:
            paths_by_post.setdefault(post_id, []).append(path)

        text_by_post: dict[int, str] = {}
        rows = await self.session.execute(
            select(Post.id, Post.post_title, Post.description).where(
                Post.artist_id == artist_id
            )
        )
        for post_id, title, description in rows:
            text_by_post[post_id] = "\n".join(
                part for part in (title, html_to_plain(description) or "") if part
            )

        corpus = _Corpus(
            tokens_by_post={
                pid: {t for path in paths for t in working_name_tokens(path)}
                for pid, paths in paths_by_post.items()
            },
            # Both counts take POSTS, which is why they are built from these
            # groupings rather than from flat lists — see post_naming.
            token_posts=token_frequencies(paths_by_post.values()),
            text_by_post=text_by_post,
            marker_posts=marker_frequencies(text_by_post.values()),
        )
        self._corpora[artist_id] = corpus
        return corpus

    async def _decided(self, announcement_id: int) -> set[int]:
        """Payload posts already proposed for this announcement, in ANY status.

        Dismissed pairs are included deliberately: re-proposing a pair the
        operator has already rejected on every subsequent scan is the single
        behaviour that makes a review queue get ignored.
        """
        rows = (await self.session.execute(
            select(PostAssociation.payload_post_id)
            .where(PostAssociation.announcement_post_id == announcement_id)
        )).scalars().all()
        return set(rows)

    async def _candidate_groups(
        self, announcement: Post, *, window: timedelta,
    ) -> list[Post]:
        """Synthetic Discord groupings by the SAME artist, inside the window.

        Same-artist is the identity signal and it is free (see the module
        docstring on E4). It is also a hard filter rather than a scored one:
        two different creators posting minutes apart is a coincidence, not
        evidence, and letting it score at all would mean a busy hour across the
        library could out-vote everything else.
        """
        at = _post_time(announcement)
        sort_key = func.coalesce(Post.post_date, Post.downloaded_at)
        return (await self.session.execute(
            select(Post)
            .where(
                Post.artist_id == announcement.artist_id,
                Post.synthesized_by == DROP_GROUPER,
                Post.id != announcement.id,
                sort_key >= at - window,
                sort_key <= at + window,
            )
            .order_by(sort_key)
            .limit(MAX_CANDIDATES)
        )).scalars().all()

    async def match_post(
        self, announcement_id: int, *, threshold: float, window_hours: float,
    ) -> int:
        """Score one announcement against nearby groupings. Returns proposals made."""
        announcement = await self.session.get(Post, announcement_id)
        if announcement is None or announcement.synthesized_by is not None:
            # A synthetic post cannot announce anything — FC wrote it.
            return 0

        window = timedelta(hours=window_hours)
        declared = declared_signal(announcement.description)
        already = await self._decided(announcement_id)
        corpus = await self._corpus(announcement.artist_id)
        here = corpus.tokens_by_post.get(announcement.id, set())
        here_text = corpus.text_by_post.get(announcement.id, "")

        made = 0
        for group in await self._candidate_groups(announcement, window=window):
            if group.id in already:
                continue
            identity, token = shared_identity(
                here,
                corpus.tokens_by_post.get(group.id, set()),
                corpus.token_posts,
            )
            circumstantial = {
                "proximity": proximity_signal(
                    _post_time(group) - _post_time(announcement), window,
                ),
                "declared": declared,
                "marker": marker_overlap(
                    here_text,
                    corpus.text_by_post.get(group.id, ""),
                    corpus.marker_posts,
                ),
            }
            score = weighted_score(circumstantial)
            # THE TWO ROUTES, and why identity is not simply a fourth weight.
            #
            # Circumstance and identity answer different questions. Proximity
            # and a declaration say two things happened near each other and
            # that one of them mentioned Discord; a working name the creator
            # uses on these two posts and nowhere else says they are the same
            # piece. Averaging those makes the threshold uninterpretable, and
            # it costs both: adding identity as a weight dilutes the others
            # enough that measured teaser/drop pairs an hour apart stop
            # proposing, while capping identity's contribution at its weight
            # means the strongest evidence available can never carry a pair on
            # its own.
            #
            # So identity may override, never dilute. Below the floor it is
            # recorded for the operator to read and moves nothing — which is
            # the conservative direction, since a wrong link asserts that two
            # different pieces are one.
            if identity >= IDENTITY_FLOOR:
                score = max(score, identity)
            if score < threshold:
                continue
            signals = {**circumstantial, "identity": identity}
            if token:
                # Carried so the queue can say WHY. A review queue that cannot
                # explain itself is one the operator learns to click through.
                signals["identity_token"] = token
            self.session.add(PostAssociation(
                announcement_post_id=announcement.id,
                payload_post_id=group.id,
                score=score,
                signals=signals,
                status="pending",
            ))
            made += 1
        return made

    async def list_pending(self) -> list[dict]:
        rows = (await self.session.execute(
            select(PostAssociation)
            .where(PostAssociation.status == "pending")
            .order_by(PostAssociation.score.desc(), PostAssociation.id.desc())
        )).scalars().all()
        return [
            {
                "id": a.id,
                "announcement_post_id": a.announcement_post_id,
                "payload_post_id": a.payload_post_id,
                "score": a.score,
                "signals": a.signals,
            }
            for a in rows
        ]

    async def accept(self, association_id: int) -> dict | None:
        a = await self.session.get(PostAssociation, association_id)
        if a is None:
            return None
        a.status = "linked"
        return {"id": a.id, "status": a.status}

    async def dismiss(self, association_id: int) -> dict | None:
        a = await self.session.get(PostAssociation, association_id)
        if a is None:
            return None
        # Kept, not deleted — the row is what remembers the rejection.
        a.status = "dismissed"
        return {"id": a.id, "status": a.status}

    async def linked_for(self, post_ids: list[int]) -> dict[int, list[dict]]:
        """Accepted links touching these posts, keyed by post id, BOTH ways.

        A post is either end of the relationship, and each end wants the other
        one: the teaser wants "the full set is over here", the grouping wants
        "this is what announced me". One query, both directions.
        """
        if not post_ids:
            return {}
        rows = (await self.session.execute(
            select(PostAssociation).where(
                PostAssociation.status == "linked",
                or_(
                    PostAssociation.announcement_post_id.in_(post_ids),
                    PostAssociation.payload_post_id.in_(post_ids),
                ),
            )
        )).scalars().all()
        out: dict[int, list[dict]] = {}
        for a in rows:
            if a.announcement_post_id in post_ids:
                out.setdefault(a.announcement_post_id, []).append(
                    {"role": "announces", "post_id": a.payload_post_id, "id": a.id}
                )
            if a.payload_post_id in post_ids:
                out.setdefault(a.payload_post_id, []).append(
                    {"role": "announced_by", "post_id": a.announcement_post_id, "id": a.id}
                )
        return out


async def rescan(session: AsyncSession, *, now: datetime | None = None) -> dict:
    """Score every recent non-synthetic post against nearby groupings."""
    settings = await ImportSettings.load(session)
    if not settings.discord_link_enabled:
        return {"enabled": False, "scanned": 0, "proposed": 0}

    now = now or datetime.now(UTC)
    window_hours = float(settings.discord_link_window_hours)
    # Only look at announcements that could still have a partner in range —
    # a full-library rescan is the manual button's job, not the sweep's.
    horizon = now - timedelta(hours=window_hours * 2)
    sort_key = func.coalesce(Post.post_date, Post.downloaded_at)
    ids = (await session.execute(
        select(Post.id).where(
            Post.synthesized_by.is_(None),
            Post.absorbed_by_post_id.is_(None),
            sort_key >= horizon,
        )
    )).scalars().all()

    svc = PostAssociationService(session)
    proposed = 0
    for pid in ids:
        proposed += await svc.match_post(
            pid,
            threshold=float(settings.discord_link_threshold),
            window_hours=window_hours,
        )
    log.info(
        "discord announcement matcher: scanned %d post(s), proposed %d pair(s)",
        len(ids), proposed,
    )
    return {"enabled": True, "scanned": len(ids), "proposed": proposed}