radio-explorer/server/stats.js

// Vote + play stats and the ranking algorithm.
//
// Score combines two signals:
//   - voteZ    = (up - down) / sqrt(up + down + 1)   z-like, penalizes small N
//   - playLog  = log10(plays + 1)                    gentle popularity boost
//   - score    = voteZ + 0.5 * playLog
//
// Net effect:
//   * A handful of downvotes on an obscure station sinks it hard.
//   * One stray upvote on a brand new station barely moves it.
//   * Popular stations float up only if they aren't being actively buried.
//   * Established + positively-voted stations dominate the top.

import { getDb } from './db/index.js';

export function computeScore({ up = 0, down = 0, plays = 0 } = {}) {
    const n = up + down;
    const voteZ = n === 0 ? 0 : (up - down) / Math.sqrt(n + 1);
    const playLog = Math.log10(plays + 1);
    return voteZ + 0.5 * playLog;
}

export function getStationStats(stationId, userId = null) {
    const db = getDb();
    const v = db.prepare(`
        SELECT
            COALESCE(SUM(CASE WHEN value =  1 THEN 1 ELSE 0 END), 0) AS up,
            COALESCE(SUM(CASE WHEN value = -1 THEN 1 ELSE 0 END), 0) AS down
        FROM station_votes WHERE station_id = ?
    `).get(stationId) || { up: 0, down: 0 };
    const p = db.prepare('SELECT plays FROM station_plays WHERE station_id = ?').get(stationId);
    const plays = p?.plays || 0;
    let myVote = 0;
    if (userId) {
        const r = db.prepare('SELECT value FROM station_votes WHERE user_id = ? AND station_id = ?').get(userId, stationId);
        myVote = r?.value || 0;
    }
    return { up: v.up, down: v.down, plays, myVote, score: computeScore({ up: v.up, down: v.down, plays }) };
}

// Bulk stats for many stations in one query. Returns a Map<station_id, stats>.
export function getStatsMap(userId = null) {
    const db = getDb();
    const rows = db.prepare(`
        SELECT
            s.id AS station_id,
            COALESCE(v.up,    0) AS up,
            COALESCE(v.down,  0) AS down,
            COALESCE(p.plays, 0) AS plays
        FROM stations s
        LEFT JOIN (
            SELECT station_id,
                   SUM(CASE WHEN value =  1 THEN 1 ELSE 0 END) AS up,
                   SUM(CASE WHEN value = -1 THEN 1 ELSE 0 END) AS down
            FROM station_votes GROUP BY station_id
        ) v ON v.station_id = s.id
        LEFT JOIN station_plays p ON p.station_id = s.id
    `).all();

    const my = new Map();
    if (userId) {
        for (const r of db.prepare('SELECT station_id, value FROM station_votes WHERE user_id = ?').all(userId)) {
            my.set(r.station_id, r.value);
        }
    }
    const out = new Map();
    for (const r of rows) {
        const myVote = my.get(r.station_id) || 0;
        out.set(r.station_id, {
            up: r.up, down: r.down, plays: r.plays, myVote,
            score: computeScore({ up: r.up, down: r.down, plays: r.plays })
        });
    }
    return out;
}

export function castVote(userId, stationId, value) {
    const db = getDb();
    if (value === 0 || value == null) {
        db.prepare('DELETE FROM station_votes WHERE user_id = ? AND station_id = ?').run(userId, stationId);
    } else if (value === 1 || value === -1) {
        db.prepare(`
            INSERT INTO station_votes (user_id, station_id, value) VALUES (?, ?, ?)
            ON CONFLICT(user_id, station_id) DO UPDATE SET value = excluded.value, created_at = CURRENT_TIMESTAMP
        `).run(userId, stationId, value);
    } else {
        throw new Error('vote value must be -1, 0 or 1');
    }
    return getStationStats(stationId, userId);
}

export function recordPlay(stationId) {
    getDb().prepare(`
        INSERT INTO station_plays (station_id, plays, last_played_at) VALUES (?, 1, datetime('now'))
        ON CONFLICT(station_id) DO UPDATE SET
            plays = station_plays.plays + 1,
            last_played_at = datetime('now')
    `).run(stationId);
}

// Sort helper used by routes. Mutates the array.
export function sortByMode(items, mode, statsMap) {
    const s = (id) => statsMap.get(id) || { up: 0, down: 0, plays: 0, score: 0 };
    switch (mode) {
        case 'hot':
            items.sort((a, b) => s(b.id).score - s(a.id).score || a.name.localeCompare(b.name));
            break;
        case 'top':
            items.sort((a, b) => (s(b.id).up - s(b.id).down) - (s(a.id).up - s(a.id).down) || a.name.localeCompare(b.name));
            break;
        case 'plays':
            items.sort((a, b) => s(b.id).plays - s(a.id).plays || a.name.localeCompare(b.name));
            break;
        case 'controversial':
            items.sort((a, b) => {
                const A = s(a.id), B = s(b.id);
                return Math.min(B.up, B.down) - Math.min(A.up, A.down) || a.name.localeCompare(b.name);
            });
            break;
        case 'name':
        default:
            items.sort((a, b) => a.name.localeCompare(b.name));
    }
    return items;
}