import { createHash } from 'node:crypto';
import type Database from 'better-sqlite3';
import { parseServerName, selectedZombieMap, zombieMaps } from '../../map-aliases.js';
import { parseGameEvent, type GameTelemetry } from '../../telemetry.js';

interface Match {
    id: number;
    map_key: string;
    game: string;
    status: 'active' | 'completed' | 'interrupted';
    highest_round: number;
    last_event: GameTelemetry['event'];
    last_fingerprint: string;
}

interface Participation {
    guid: string;
    last_round: number;
    present: number;
}

function mapIdentity(handle: Database.Database, report: GameTelemetry) {
    const server = handle
        .prepare('SELECT game, map, map_slug FROM servers WHERE name = ?')
        .get(report.server) as
        { game: string | null; map: string | null; map_slug: string | null } | undefined;
    const parsed = parseServerName(report.server);
    const game = (server?.game ?? parsed?.game ?? 'unknown').toLowerCase();
    const map = report.map.toLowerCase();
    // A shared engine map (notably zm_transit) is not enough to identify T6's
    // location/ruleset. Use the registered selection only when it matches.
    const parsedSlug = parsed?.mapCanonical === map ? parsed.mapSlug : undefined;
    const slug = server?.map === map ? (server.map_slug ?? parsedSlug) : parsedSlug;
    const candidates = zombieMaps(game).filter((entry) => entry.canonical === map);
    const selected =
        game === 't6' && candidates.length > 1 && !slug
            ? undefined
            : selectedZombieMap(game, map, slug);
    const variant = game === 't6' ? (selected?.slug ?? slug ?? 'unspecified') : '';
    return {
        game,
        map,
        key: [game, map, ...(variant ? [variant] : [])].join(':'),
        name:
            selected?.friendly ??
            (game === 't6' && candidates.length > 1
                ? `${map} (${slug ?? 'unspecified variant'})`
                : map)
    };
}

function fingerprint(report: GameTelemetry): string {
    // Receipt timestamps and roster ordering do not identify new gameplay.
    const { receivedAt: _receivedAt, timing: _timing, ...event } = report;
    const players = [...event.players].sort((a, b) => a.guid.localeCompare(b.guid));
    return createHash('sha256')
        .update(JSON.stringify({ ...event, players }))
        .digest('hex');
}

/** Called inside the same transaction as the latest scoreboard snapshot. */
export function recordLeaderboardTelemetry(handle: Database.Database, report: GameTelemetry): void {
    const identity = mapIdentity(handle, report);
    const signature = fingerprint(report);
    let match = handle
        .prepare(
            'SELECT * FROM leaderboard_matches WHERE server = ? AND server_deleted_at IS NULL ORDER BY id DESC LIMIT 1'
        )
        .get(report.server) as Match | undefined;
    if (match?.last_fingerprint === signature && match.map_key === identity.key) return;

    const isStart = report.event === 'game_start';
    const round = isStart ? 0 : report.round;
    const newMatch =
        !match ||
        match.map_key !== identity.key ||
        (isStart && (match.status !== 'active' || match.last_event !== 'game_start')) ||
        (!isStart && round < match.highest_round) ||
        ((report.event === 'round_change' || report.event === 'heartbeat') &&
            match.status !== 'active');

    if (newMatch) {
        if (match?.status === 'active') {
            handle
                .prepare(
                    "UPDATE leaderboard_matches SET status = 'interrupted', ended_at = ? WHERE id = ?"
                )
                .run(report.receivedAt, match.id);
        }
        const inserted = handle
            .prepare(
                `INSERT INTO leaderboard_matches
            (server, game, map, map_key, map_name, started_at, last_received_at, start_observed, last_event, last_fingerprint)
            VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
            )
            .run(
                report.server,
                identity.game,
                identity.map,
                identity.key,
                identity.name,
                report.receivedAt,
                report.receivedAt,
                Number(isStart),
                report.event,
                signature
            );
        match = {
            id: Number(inserted.lastInsertRowid),
            game: identity.game,
            map_key: identity.key,
            status: 'active',
            highest_round: 0,
            last_event: report.event,
            last_fingerprint: signature
        };
    }
    if (!match) return;

    if (isStart) {
        handle
            .prepare(
                'UPDATE leaderboard_matches SET start_players = COALESCE(start_players, ?) WHERE id = ?'
            )
            .run(report.players.length, match.id);
    }

    const previous = new Map(
        (
            handle
                .prepare(
                    'SELECT guid, last_round, present FROM leaderboard_match_players WHERE match_id = ?'
                )
                .all(match.id) as Participation[]
        ).map((player) => [player.guid, player])
    );
    handle
        .prepare('UPDATE leaderboard_match_players SET present = 0 WHERE match_id = ?')
        .run(match.id);
    const saveIdentity =
        handle.prepare(`INSERT INTO leaderboard_players (game, guid, name, first_seen_at, last_seen_at)
        VALUES (?, ?, ?, ?, ?) ON CONFLICT(game, guid) DO UPDATE SET
        name = CASE WHEN excluded.last_seen_at >= last_seen_at THEN excluded.name ELSE name END,
        last_seen_at = MAX(last_seen_at, excluded.last_seen_at)`);
    const savePlayer = handle.prepare(`INSERT INTO leaderboard_match_players
        (match_id, guid, highest_round, rounds_survived, kills, headshots, downs, revives, best_score,
            last_round, present, has_stats, completed, first_seen_at, last_seen_at, first_observed_round, present_at_start)
        VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 1, ?, ?, ?, ?, ?, ?)
        ON CONFLICT(match_id, guid) DO UPDATE SET
            highest_round = MAX(highest_round, excluded.highest_round),
            rounds_survived = rounds_survived + excluded.rounds_survived,
            kills = MAX(kills, excluded.kills), headshots = MAX(headshots, excluded.headshots),
            downs = MAX(downs, excluded.downs), revives = MAX(revives, excluded.revives),
            best_score = MAX(best_score, excluded.best_score), last_round = excluded.last_round,
            present = 1, has_stats = MAX(has_stats, excluded.has_stats),
            completed = MAX(completed, excluded.completed), last_seen_at = excluded.last_seen_at`);

    // Highest round includes late joins; total rounds only credits progression
    // while present at both ends of an observed interval. Entering round 8
    // completes round 7, but a player's first sighting at round 8 starts at zero.
    const completedRounds = Math.max(0, round - 1);
    for (const player of report.players) {
        const prior = previous.get(player.guid);
        const survived =
            !isStart && prior?.present ? Math.max(0, completedRounds - prior.last_round) : 0;
        saveIdentity.run(
            identity.game,
            player.guid,
            player.name,
            report.receivedAt,
            report.receivedAt
        );
        const stats = 'kills' in player ? player : null;
        savePlayer.run(
            match.id,
            player.guid,
            round,
            survived,
            stats?.kills ?? 0,
            stats?.headshots ?? 0,
            stats?.downs ?? 0,
            stats?.revives ?? 0,
            stats?.score ?? 0,
            completedRounds,
            Number(!isStart),
            Number(report.event === 'game_end'),
            report.receivedAt,
            report.receivedAt,
            round,
            Number(isStart)
        );
    }
    handle
        .prepare(
            `UPDATE leaderboard_matches SET highest_round = MAX(highest_round, ?),
        last_received_at = ?, last_event = ?, last_fingerprint = ?,
        status = CASE WHEN ? = 'game_end' THEN 'completed' ELSE status END,
        ended_at = CASE WHEN ? = 'game_end' THEN ? ELSE ended_at END WHERE id = ?`
        )
        .run(
            round,
            report.receivedAt,
            report.event,
            signature,
            report.event,
            report.event,
            report.receivedAt,
            match.id
        );
}

/** Seed the single surviving scoreboard per server once; older games are gone. */
export function backfillLeaderboard(handle: Database.Database): void {
    if (handle.prepare("SELECT 1 FROM settings WHERE key = 'leaderboard_v1'").get()) return;
    handle.transaction(() => {
        const reports = handle
            .prepare(
                `SELECT payload FROM server_telemetry WHERE payload IS NOT NULL ORDER BY received_at, server`
            )
            .all() as Array<{ payload: string }>;
        for (const row of reports) {
            let report: GameTelemetry;
            try {
                const stored = JSON.parse(row.payload);
                if (
                    typeof stored.receivedAt !== 'string' ||
                    !Number.isFinite(Date.parse(stored.receivedAt))
                )
                    continue;
                report = { ...parseGameEvent(stored), receivedAt: stored.receivedAt };
            } catch {
                continue;
            } // Legacy malformed snapshots cannot establish player records.
            recordLeaderboardTelemetry(handle, report);
        }
        handle.prepare("INSERT INTO settings (key, value) VALUES ('leaderboard_v1', '1')").run();
    })();
}