import { database } from "~/database/context";
import { eq } from "drizzle-orm";
import * as schema from "~/database/schema";
import {
  findParticipantsBySportsSeasonId,
  updateParticipant,
  createParticipant,
  createManyParticipants,
} from "~/models/season-participant";
import { upsertSeasonMatchBulk, upsertMatchSubGame } from "~/models/season-match";
import {
  setMatchWinner,
  updatePlayoffMatch,
  advanceWinnerTemplate,
  findPlayoffMatchesByEventId,
  doesLoserAdvance,
  populateBracketFromDraw,
} from "~/models/playoff-match";
import {
  processMatchResult,
  autoCompleteRoundIfDone,
  processQualifyingBracketEvent,
  recalculateAffectedLeagues,
} from "~/models/scoring-calculator";
import { fanOutMajorIfPrimary } from "~/services/sync-tournament-results";
import { notifyQualifyingPointsUpdate } from "~/services/qualifying-points-discord.server";
import {
  recalculateParticipantQP,
  diffChangedQualifyingPoints,
} from "~/models/qualifying-points";
import { getScoringEventById, updateScoringEvent, isReadOnlySibling } from "~/models/scoring-event";
import { findMatchingTeamName, normalizeTeamName } from "~/lib/normalize-team-name";
import { buildUnmatchedTeamResolutionView } from "~/lib/unmatched-team-reconciliation";
import { getBracketTemplate } from "~/lib/bracket-templates";
import { PandaScoreMatchSyncAdapter } from "./pandascore";
import { EspnScheduleAdapter } from "./espn-schedule";
import { WikipediaTennisAdapter } from "./wikipedia-tennis";
import { playerKey, canonicalPlayerName, buildResolvedMatches } from "./tennis-draw-mapping";
import type {
  MatchSyncAdapter,
  MatchSyncResult,
  DrawSyncAdapter,
  DrawSyncResult,
  DrawSyncPreview,
  FetchedDraw,
  FetchedPlayer,
} from "./types";
import { logger } from "~/lib/logger";

function getMatchSyncAdapter(simulatorType: string): MatchSyncAdapter {
  switch (simulatorType) {
    case "cs2_major_qualifying_points":
      return new PandaScoreMatchSyncAdapter();
    case "mlb_bracket":
      return new EspnScheduleAdapter("baseball/mlb", 3);
    case "nba_bracket":
      return new EspnScheduleAdapter("basketball/nba", 3);
    case "mls_bracket":
      return new EspnScheduleAdapter("soccer/mls", 3);
    case "wnba_bracket":
      return new EspnScheduleAdapter("basketball/wnba", 3);
    case "nhl_bracket":
      return new EspnScheduleAdapter("hockey/nhl", 3);
    default:
      throw new Error(
        `No match sync adapter available for simulator type "${simulatorType}". ` +
          "CS2, MLB, NBA, MLS, WNBA, and NHL are currently supported."
      );
  }
}

export async function syncMatches(sportsSeasonId: string): Promise<MatchSyncResult> {
  const db = database();

  const sportsSeason = await db.query.sportsSeasons.findFirst({
    where: eq(schema.sportsSeasons.id, sportsSeasonId),
    with: { sport: true },
  });

  if (!sportsSeason) throw new Error(`Sports season ${sportsSeasonId} not found`);

  const externalSeasonId = sportsSeason.externalSeasonId;
  if (!externalSeasonId) {
    throw new Error(`Sports season "${sportsSeason.name}" has no externalSeasonId configured`);
  }

  const simulatorType = sportsSeason.sport?.simulatorType;
  if (!simulatorType) {
    throw new Error(`Sport "${sportsSeason.sport?.name ?? "(none)"}" has no simulator type configured`);
  }

  const adapter = getMatchSyncAdapter(simulatorType);
  const fetchedMatches = await adapter.fetchMatches(externalSeasonId);

  // Load participants, build lookup maps
  const participants = await findParticipantsBySportsSeasonId(sportsSeasonId);
  const participantNames = participants.map((p) => p.name);
  const participantByExternalId = new Map(
    participants.filter((p) => p.externalId).map((p) => [p.externalId as string, p])
  );
  const participantByName = new Map(participants.map((p) => [p.name, p]));

  async function resolveParticipant(externalId: string, name: string) {
    let participant = participantByExternalId.get(externalId) ?? null;
    if (!participant) {
      const matchedName = findMatchingTeamName(name, participantNames);
      if (matchedName) {
        participant = participantByName.get(matchedName) ?? null;
        if (participant && !participant.externalId) {
          await updateParticipant(participant.id, { externalId });
          participantByExternalId.set(externalId, participant);
        }
      }
    }
    return participant;
  }

  // Find the scoring event for this sports season (needed for CS2 stage lookup + playoff sync)
  const scoringEvents = await db.query.scoringEvents.findMany({
    where: eq(schema.scoringEvents.sportsSeasonId, sportsSeasonId),
  });

  // Split matches: Swiss (matchStage set) vs playoff bracket (matchStage null)
  const swissMatches = fetchedMatches.filter((m) => m.matchStage !== null && m.matchStage !== undefined);
  const bracketMatches = fetchedMatches.filter((m) => m.matchStage === null || m.matchStage === undefined);

  const unmatchedTeams: MatchSyncResult["unmatchedTeams"] = [];
  const errors: MatchSyncResult["errors"] = [];
  let swissCreated = 0;
  let swissUpdated = 0;
  let playoffUpdated = 0;

  // --- Swiss matches → season_matches ---
  if (swissMatches.length > 0) {
    // For CS2, use the scoring event that has cs2_major_stage_results
    const cs2Event = scoringEvents.find((e) => e.isQualifyingEvent) ?? scoringEvents[0] ?? null;

    const toUpsert = [];
    for (const m of swissMatches) {
      const p1 = await resolveParticipant(m.team1ExternalId, m.team1Name);
      const p2 = await resolveParticipant(m.team2ExternalId, m.team2Name);

      if (!p1) unmatchedTeams.push({ externalId: m.team1ExternalId, name: m.team1Name });
      if (!p2) unmatchedTeams.push({ externalId: m.team2ExternalId, name: m.team2Name });

      const winnerParticipant = m.winnerExternalId
        ? (await resolveParticipant(m.winnerExternalId, ""))
        : null;

      toUpsert.push({
        sportsSeasonId,
        scoringEventId: cs2Event?.id ?? null,
        participant1Id: p1?.id ?? null,
        participant2Id: p2?.id ?? null,
        winnerId: winnerParticipant?.id ?? null,
        participant1Score: m.team1Score,
        participant2Score: m.team2Score,
        matchStage: m.matchStage ?? null,
        matchRound: m.matchRound ?? null,
        matchday: m.matchday ?? null,
        isSeries: m.isSeries ?? false,
        status: m.status,
        scheduledAt: m.scheduledAt,
        startedAt: m.startedAt,
        completedAt: m.completedAt,
        externalMatchId: m.externalMatchId,
      });
    }

    const upserted = await upsertSeasonMatchBulk(toUpsert);

    // Track created vs updated (rough heuristic: if completedAt is within last 2 min, it's new)
    swissCreated = upserted.filter((r) => {
      const diff = r.createdAt ? Date.now() - r.createdAt.getTime() : Infinity;
      return diff < 120_000;
    }).length;
    swissUpdated = upserted.length - swissCreated;

    // Upsert sub-games (maps) for matches with subGames
    for (const m of swissMatches) {
      if (!m.subGames?.length) continue;
      const upsertedMatch = upserted.find((u) => u.externalMatchId === m.externalMatchId);
      if (!upsertedMatch) continue;
      for (const g of m.subGames) {
        const winnerParticipant = g.winnerExternalId
          ? (await resolveParticipant(g.winnerExternalId, ""))
          : null;
        try {
          await upsertMatchSubGame({
            seasonMatchId: upsertedMatch.id,
            gameNumber: g.gameNumber,
            gameLabel: g.gameLabel ?? null,
            participant1Score: g.team1Score,
            participant2Score: g.team2Score,
            winnerId: winnerParticipant?.id ?? null,
            status: g.status,
            externalGameId: g.externalGameId ?? null,
          });
        } catch (err) {
          logger.error(`[match-sync] Error upserting sub-game ${g.gameNumber} for match ${m.externalMatchId}:`, err);
        }
      }
    }
  }

  // --- Bracket matches → playoff_matches ---
  if (bracketMatches.length > 0 && scoringEvents.length === 0) {
    logger.warn(`[match-sync] ${bracketMatches.length} bracket match(es) found but no scoring events exist for season ${sportsSeasonId} — bracket sync skipped`);
  }

  if (bracketMatches.length > 0) {
    for (const event of scoringEvents) {
      const existingPlayoffMatches = await findPlayoffMatchesByEventId(event.id);
      if (existingPlayoffMatches.length === 0) continue;

      const bracketTemplate = event.bracketTemplateId
        ? getBracketTemplate(event.bracketTemplateId)
        : null;

      for (const m of bracketMatches) {
        if (m.status !== "complete") continue;

        const p1 = await resolveParticipant(m.team1ExternalId, m.team1Name);
        const p2 = await resolveParticipant(m.team2ExternalId, m.team2Name);
        if (!p1 || !p2) continue;

        const winnerParticipant = m.winnerExternalId
          ? await resolveParticipant(m.winnerExternalId, "")
          : null;
        if (!winnerParticipant) continue;

        const loserId = winnerParticipant.id === p1.id ? p2.id : p1.id;

        // Find the matching playoff_matches row: prefer external_match_id match, fall back to participant ID match
        let playoffMatch = existingPlayoffMatches.find(
          (pm) => pm.externalMatchId === m.externalMatchId
        );
        if (!playoffMatch) {
          playoffMatch = existingPlayoffMatches.find(
            (pm) =>
              !pm.isComplete &&
              ((pm.participant1Id === p1.id && pm.participant2Id === p2.id) ||
                (pm.participant1Id === p2.id && pm.participant2Id === p1.id))
          );
        }

        if (!playoffMatch) continue;
        if (playoffMatch.isComplete && playoffMatch.winnerId) continue; // idempotent

        try {
          await setMatchWinner(
            playoffMatch.id,
            winnerParticipant.id,
            loserId,
            winnerParticipant.id === p1.id ? (m.team1Score ?? undefined) : (m.team2Score ?? undefined),
            winnerParticipant.id === p1.id ? (m.team2Score ?? undefined) : (m.team1Score ?? undefined)
          );

          // Set external_match_id for future upserts
          if (!playoffMatch.externalMatchId) {
            await updatePlayoffMatch(playoffMatch.id, { externalMatchId: m.externalMatchId });
          }

          if (bracketTemplate) {
            try {
              await advanceWinnerTemplate(playoffMatch.id, winnerParticipant.id, bracketTemplate);
            } catch (err) {
              if (!(err instanceof Error && err.message.includes("already filled"))) throw err;
            }
          }

          const roundIsScoring = bracketTemplate?.rounds.find(
            (r) => r.name === playoffMatch.round
          )?.isScoring;

          await processMatchResult({
            round: playoffMatch.round,
            winnerId: winnerParticipant.id,
            loserId,
            isScoring: roundIsScoring !== undefined ? roundIsScoring : (playoffMatch.isScoring ?? true),
            sportsSeasonId,
            bracketTemplateId: event.bracketTemplateId ?? null,
            eventId: event.id,
            eventName: event.name ?? undefined,
            matchId: playoffMatch.id,
            loserAdvances: event.bracketTemplateId
              ? doesLoserAdvance(playoffMatch.round, playoffMatch.matchNumber, event.bracketTemplateId)
              : false,
          });

          await autoCompleteRoundIfDone(event.id, playoffMatch.round, sportsSeasonId, db);

          playoffUpdated++;
        } catch (err) {
          logger.error(`[match-sync] Error processing playoff match ${m.externalMatchId}:`, err);
          errors.push({
            externalMatchId: m.externalMatchId,
            error: err instanceof Error ? err.message : String(err),
          });
        }
      }
    }
  }

  return { swissCreated, swissUpdated, playoffUpdated, unmatchedTeams, errors };
}

// ===========================================================================
// Tennis Grand Slam draw sync
// ===========================================================================

function getDrawAdapter(simulatorType: string): DrawSyncAdapter {
  switch (simulatorType) {
    case "tennis_qualifying_points":
      return new WikipediaTennisAdapter();
    default:
      throw new Error(
        `No draw sync adapter available for simulator type "${simulatorType}". ` +
          "Tennis is currently supported.",
      );
  }
}

/** Validate the event, fetch + parse its draw. Read-only — used by sync & preview. */
async function loadTennisDraw(eventId: string) {
  const db = database();
  const event = await getScoringEventById(eventId);
  if (!event) throw new Error(`Scoring event ${eventId} not found`);
  if (isReadOnlySibling(event)) {
    throw new Error(
      "This event is a read-only window of a shared major. Sync the draw on the primary window; " +
        "results fan out here automatically.",
    );
  }
  if (!event.isQualifyingEvent) {
    throw new Error(`Event "${event.name}" is not a qualifying event; cannot sync a tennis draw.`);
  }
  const sourceKey = event.externalSourceKey;
  if (!sourceKey) {
    throw new Error(
      `Event "${event.name}" has no externalSourceKey (Wikipedia article title) configured.`,
    );
  }
  const sportsSeason = await db.query.sportsSeasons.findFirst({
    where: eq(schema.sportsSeasons.id, event.sportsSeasonId),
    with: { sport: true },
  });
  const simulatorType = sportsSeason?.sport?.simulatorType;
  if (!simulatorType) {
    throw new Error(`Sport for season ${event.sportsSeasonId} has no simulator type configured`);
  }
  const draw = await getDrawAdapter(simulatorType).fetchDraw(sourceKey);
  const template = getBracketTemplate(draw.templateId);
  if (!template) throw new Error(`Bracket template "${draw.templateId}" not found`);
  return { event, sportsSeasonId: event.sportsSeasonId, draw, template };
}

/** Distinct players across the whole draw, keyed by stable identity. */
function collectUniquePlayers(draw: FetchedDraw): Map<string, FetchedPlayer> {
  const players = new Map<string, FetchedPlayer>();
  for (const round of draw.rounds) {
    for (const match of round.matches) {
      for (const player of [match.player1, match.player2]) {
        if (player) players.set(playerKey(player), player);
      }
    }
  }
  return players;
}

type SeasonParticipant = Awaited<ReturnType<typeof findParticipantsBySportsSeasonId>>[number];

type PlayerLookups = {
  byExternalId: Map<string, SeasonParticipant>;
  byName: Map<string, SeasonParticipant>;
  names: string[];
  recon: { id: string; name: string; externalId: string | null }[];
};

function buildLookups(participants: SeasonParticipant[]): PlayerLookups {
  return {
    byExternalId: new Map(
      participants.filter((p) => p.externalId).map((p) => [p.externalId as string, p]),
    ),
    byName: new Map(participants.map((p) => [p.name, p])),
    names: participants.map((p) => p.name),
    recon: participants.map((p) => ({ id: p.id, name: p.name, externalId: p.externalId })),
  };
}

type Classification =
  | { kind: "matched"; participant: SeasonParticipant; backfill: boolean }
  | {
      kind: "create";
      name: string;
      suggestion: string | null;
      suggestionId: string | null;
    };

/** Read-only: decide how a drawn player resolves against existing participants. */
function classifyPlayer(player: FetchedPlayer, lk: PlayerLookups): Classification {
  const name = canonicalPlayerName(player);
  const byId = player.externalId ? lk.byExternalId.get(player.externalId) : undefined;
  if (byId) return { kind: "matched", participant: byId, backfill: false };

  const matchedName = findMatchingTeamName(name, lk.names);
  if (matchedName) {
    const p = lk.byName.get(matchedName);
    if (p) return { kind: "matched", participant: p, backfill: !p.externalId && !!player.externalId };
  }

  // No confident match. Surface the closest existing participant (if any) as a
  // possible duplicate to review.
  const view = buildUnmatchedTeamResolutionView(name, lk.recon);
  const top = view.confidence !== "none" ? view.topCandidates[0] ?? null : null;
  return {
    kind: "create",
    name,
    suggestion: top?.participantName ?? null,
    suggestionId: top?.participantId ?? null,
  };
}

/**
 * Dry run: report what a draw sync would do (matches, would-be participant
 * creations, likely duplicates, unfilled first-round slots) without any writes.
 */
export async function previewTennisDraw(eventId: string): Promise<DrawSyncPreview> {
  const { event, sportsSeasonId, draw } = await loadTennisDraw(eventId);
  const participants = await findParticipantsBySportsSeasonId(sportsSeasonId);
  const lk = buildLookups(participants);
  const uniquePlayers = collectUniquePlayers(draw);

  let matched = 0;
  const willCreate: DrawSyncPreview["willCreate"] = [];
  const possibleDuplicates: DrawSyncPreview["possibleDuplicates"] = [];

  for (const player of uniquePlayers.values()) {
    const c = classifyPlayer(player, lk);
    if (c.kind === "matched") {
      matched++;
    } else {
      willCreate.push({ name: c.name, externalId: player.externalId });
      if (c.suggestion && c.suggestionId) {
        possibleDuplicates.push({
          name: c.name,
          externalId: player.externalId,
          suggestion: c.suggestion,
          suggestionId: c.suggestionId,
        });
      }
    }
  }

  const firstRound = draw.rounds[0];
  const tbdFirstRound = firstRound
    ? firstRound.matches.reduce((n, m) => n + (m.player1 ? 0 : 1) + (m.player2 ? 0 : 1), 0)
    : 0;
  const allMatches = draw.rounds.flatMap((r) => r.matches);

  return {
    article: event.externalSourceKey ?? "",
    totalPlayers: uniquePlayers.size,
    matched,
    willCreate,
    possibleDuplicates,
    tbdFirstRound,
    totalMatches: allMatches.length,
    completedMatches: allMatches.filter((m) => m.winner !== null).length,
  };
}

/**
 * Populate and auto-score a tennis major's bracket from its external draw
 * (Wikipedia). Resolves every drawn player to a participant — matching by
 * external id, then name, else auto-creating — propagates new participants to
 * every sports season linked to the same tournament (so result fan-out lands),
 * writes the full bracket, and runs the qualifying-points scorer.
 *
 * Runs only on a major's primary window; read-only siblings receive results via
 * fan-out, not direct scoring.
 */
export async function syncTennisDraw(eventId: string): Promise<DrawSyncResult> {
  const db = database();

  const { event, sportsSeasonId, draw, template } = await loadTennisDraw(eventId);
  const roundIsScoring = new Map(template.rounds.map((r) => [r.name, r.isScoring]));

  // ---- Resolve players → participants (primary season) ----------------------
  const participants = await findParticipantsBySportsSeasonId(sportsSeasonId);
  const lk = buildLookups(participants);
  const uniquePlayers = collectUniquePlayers(draw);

  const keyToParticipantId = new Map<string, string>();
  const resolvedParticipants = new Map<
    string,
    { canonicalId: string | null; name: string; externalId: string | null }
  >();
  const unmatched: DrawSyncResult["unmatched"] = [];
  let participantsCreated = 0;

  for (const [key, player] of uniquePlayers) {
    const c = classifyPlayer(player, lk);
    let participant: SeasonParticipant;

    if (c.kind === "matched") {
      participant = c.participant;
      if (c.backfill && player.externalId) {
        await updateParticipant(participant.id, { externalId: player.externalId });
      }
    } else {
      // No confident match → auto-create so the bracket is complete; flag a
      // likely duplicate for admin review when it resembles an existing player.
      if (c.suggestion) unmatched.push({ name: c.name, externalId: player.externalId });
      participant = await createParticipant({
        sportsSeasonId,
        name: c.name,
        externalId: player.externalId ?? null,
      });
      lk.names.push(participant.name);
      lk.byName.set(participant.name, participant);
      lk.recon.push({ id: participant.id, name: participant.name, externalId: participant.externalId });
      if (participant.externalId) lk.byExternalId.set(participant.externalId, participant);
      participantsCreated++;
    }

    keyToParticipantId.set(key, participant.id);
    resolvedParticipants.set(key, {
      canonicalId: participant.participantId ?? null,
      name: participant.name,
      externalId: participant.externalId ?? null,
    });
  }

  // ---- Propagate participants to linked sibling seasons ---------------------
  if (event.tournamentId) {
    const linkedRows = await db
      .select({ sportsSeasonId: schema.scoringEvents.sportsSeasonId })
      .from(schema.scoringEvents)
      .where(eq(schema.scoringEvents.tournamentId, event.tournamentId));
    const linkedSeasonIds = [...new Set(linkedRows.map((r) => r.sportsSeasonId))].filter(
      (id) => id !== sportsSeasonId,
    );

    // Dedupe by canonical participant: two drawn players can fuzzy-match the same
    // existing participant, which would otherwise queue duplicate sibling inserts
    // and trip the (sportsSeasonId, name) unique index.
    const resolved = [
      ...new Map(
        [...resolvedParticipants.values()]
          .filter((r) => r.canonicalId)
          .map((r) => [r.canonicalId, r]),
      ).values(),
    ];

    for (const seasonId of linkedSeasonIds) {
      const sib = await findParticipantsBySportsSeasonId(seasonId);
      const sibCanon = new Set(sib.map((s) => s.participantId).filter(Boolean));
      const sibNames = new Set(sib.map((s) => normalizeTeamName(s.name)));

      const toCreate = resolved
        .filter(
          (r) =>
            r.canonicalId &&
            !sibCanon.has(r.canonicalId) &&
            !sibNames.has(normalizeTeamName(r.name)),
        )
        .map((r) => ({
          sportsSeasonId: seasonId,
          name: r.name,
          externalId: r.externalId,
          participantId: r.canonicalId,
        }));

      if (toCreate.length > 0) {
        await createManyParticipants(toCreate);
        participantsCreated += toCreate.length;
      }
    }
  }

  // ---- Write the bracket ----------------------------------------------------
  const resolvedMatches = buildResolvedMatches(draw, keyToParticipantId, roundIsScoring);

  // Ensure the event is configured for QP bracket scoring before populating.
  if (
    event.bracketTemplateId !== draw.templateId ||
    event.scoringStartsAtRound !== template.scoringStartsAtRound
  ) {
    await updateScoringEvent(eventId, {
      bracketTemplateId: draw.templateId,
      scoringStartsAtRound: template.scoringStartsAtRound,
    });
  }

  const { written, completed, newlyDecidedLoserIds } = await populateBracketFromDraw(
    eventId,
    resolvedMatches,
  );

  // ---- Score (qualifying points) + fan out to siblings ----------------------
  // Re-derive QP from the bracket and learn which participants' QP changed so the
  // Discord notification below only announces new/changed results on a re-sync.
  const changedParticipantIds = await rescoreTennisBracketAndDetectChanges(
    eventId,
    sportsSeasonId,
    db,
  );

  await recalculateAffectedLeagues(sportsSeasonId, db, {
    eventId,
    eventName: event.name ?? undefined,
  });
  await fanOutMajorIfPrimary(
    { id: event.id, isPrimary: event.isPrimary, tournamentId: event.tournamentId },
    { markComplete: false },
  );

  // Announce QP changes for the primary window. Sibling windows are announced by
  // the fan-out (via processQualifyingEvent); the primary is scored directly by
  // processQualifyingBracketEvent, which does NOT notify — so do it here. Run
  // outside the rescore transaction so the webhook HTTP call neither holds the
  // transaction open nor rolls back the score if Discord fails.
  //
  // Also announce players knocked out this sync in a non-scoring round (rounds
  // 1–3 of a Grand Slam), who earn no QP and so never appear via changedParticipantIds.
  // Fire even when no QP changed, so an early-round elimination is still surfaced.
  const newlyEliminatedIds = new Set(newlyDecidedLoserIds);
  if (changedParticipantIds.size > 0 || newlyEliminatedIds.size > 0) {
    try {
      await notifyQualifyingPointsUpdate(
        sportsSeasonId,
        eventId,
        db,
        changedParticipantIds,
        newlyEliminatedIds,
      );
    } catch (error) {
      logger.error(`[syncTennisDraw] QP Discord notification failed for event ${eventId}:`, error);
    }
  }

  return { matchesWritten: written, completed, participantsCreated, unmatched };
}

/**
 * Re-derive a tennis major's qualifying points from its bracket and report which
 * season participants' awarded QP changed since the previous scoring.
 *
 * The synced draw is authoritative for tennis, so this clears ALL event_results
 * for the event (including any manually-entered rows, e.g. a notParticipating
 * withdrawal) and rebuilds them from the bracket. Change detection therefore
 * snapshots each participant's awarded QP *before* the delete and diffs it against
 * the freshly written rows: a value that differs, or a participant scored for the
 * first time (null → value), counts as changed. Wrapped in a transaction so a
 * mid-rescore failure can't leave the event with results deleted-but-not-rebuilt.
 *
 * writeEventResultsQP (inside processQualifyingBracketEvent) upserts but never
 * deletes, so QP totals for participants who no longer earn points (e.g. an
 * early-round loser dropped from the rewritten results — only Round of 16+ losers
 * score) are recalculated by hand.
 *
 * Returns the set of season_participant ids whose QP changed, used to scope the
 * QP Discord notification so a re-sync that changes nothing announces nothing.
 */
export async function rescoreTennisBracketAndDetectChanges(
  eventId: string,
  sportsSeasonId: string,
  db: ReturnType<typeof database>,
): Promise<Set<string>> {
  let changed = new Set<string>();

  await db.transaction(async (tx) => {
    const beforeRows = await tx
      .select({
        id: schema.eventResults.seasonParticipantId,
        qp: schema.eventResults.qualifyingPointsAwarded,
      })
      .from(schema.eventResults)
      .where(eq(schema.eventResults.scoringEventId, eventId));
    await tx.delete(schema.eventResults).where(eq(schema.eventResults.scoringEventId, eventId));

    await processQualifyingBracketEvent(eventId, tx);

    const afterRows = await tx
      .select({
        id: schema.eventResults.seasonParticipantId,
        qp: schema.eventResults.qualifyingPointsAwarded,
      })
      .from(schema.eventResults)
      .where(eq(schema.eventResults.scoringEventId, eventId));
    const afterIds = new Set(afterRows.map((r) => r.id));

    for (const { id } of beforeRows) {
      if (!afterIds.has(id)) await recalculateParticipantQP(id, sportsSeasonId, tx);
    }

    changed = diffChangedQualifyingPoints(beforeRows, afterRows);
  });

  return changed;
}