nadekobot/src/NadekoBot/Modules/Music/Common/Impl/RedisTrackCacher.cs

using System.Runtime.CompilerServices;
using System.Text.Json;
using StackExchange.Redis;

namespace NadekoBot.Modules.Music;

public sealed class RedisTrackCacher : ITrackCacher
{
    private readonly ConnectionMultiplexer _multiplexer;

    public RedisTrackCacher(ConnectionMultiplexer multiplexer)
        => _multiplexer = multiplexer;

    public async Task<string?> GetOrCreateStreamLink(
        string id,
        MusicPlatform platform,
        Func<Task<(string StreamUrl, TimeSpan Expiry)>> streamUrlFactory
    )
    {
        var trackStreamKey = CreateStreamKey(id, platform);
            
        var value = await GetStreamFromCacheInternalAsync(trackStreamKey);
            
        // if there is no cached value
        if (value == default)
        {
            // otherwise retrieve and cache a new value, and run this method again
            var success = await CreateAndCacheStreamUrlAsync(trackStreamKey, streamUrlFactory);
            if (!success)
                return null;
                
            return await GetOrCreateStreamLink(id, platform, streamUrlFactory);
        }

        // cache new one for future use
        _ = Task.Run(() => CreateAndCacheStreamUrlAsync(trackStreamKey, streamUrlFactory));
            
        return value;
    }
        
        

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string CreateStreamKey(string id, MusicPlatform platform)
        => $"track:stream:{platform}:{id}";

    private async Task<bool> CreateAndCacheStreamUrlAsync(
        string trackStreamKey,
        Func<Task<(string StreamUrl, TimeSpan Expiry)>> factory)
    {
        try
        {
            var data = await factory();
            if (data == default)
                return false;

            await CacheStreamUrlInternalAsync(trackStreamKey, data.StreamUrl, data.Expiry);
            return true;
        }
        catch (Exception ex)
        {
            Log.Error(ex, "Error resolving stream link for {TrackCacheKey}", trackStreamKey);
            return false;
        }
    }

    public Task CacheStreamUrlAsync(string id, MusicPlatform platform, string url, TimeSpan expiry)
        => CacheStreamUrlInternalAsync(CreateStreamKey(id, platform), url, expiry);

    private async Task CacheStreamUrlInternalAsync(string trackStreamKey, string url, TimeSpan expiry)
    {
        // keys need to be expired after an hour
        // to make sure client doesn't get an expired stream url
        // to achieve this, track keys will be just pointers to real data
        // but that data will expire
            
        var db = _multiplexer.GetDatabase();
        var dataKey = $"entry:{Guid.NewGuid()}:{trackStreamKey}";
        await db.StringSetAsync(dataKey, url, expiry: expiry);
        await db.ListRightPushAsync(trackStreamKey, dataKey);
    }

    private async Task<string?> GetStreamFromCacheInternalAsync(string trackStreamKey)
    {
        // Job of the method which retrieves keys is to pop the elements
        // from the list of cached trackurls until it finds a non-expired key

        var db = _multiplexer.GetDatabase();
        while(true)
        {
            string? dataKey = await db.ListLeftPopAsync(trackStreamKey);
            if (dataKey == default)
                return null;

            var streamUrl = await db.StringGetAsync(dataKey);
            if (streamUrl == default)
                continue;

            return streamUrl;
        }
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string CreateCachedDataKey(string id, MusicPlatform platform)
        => $"track:data:{platform}:{id}";
        
    public Task CacheTrackDataAsync(ICachableTrackData data)
    {
        var db = _multiplexer.GetDatabase();

        var trackDataKey = CreateCachedDataKey(data.Id, data.Platform);
        var dataString = JsonSerializer.Serialize((object)data);
        // cache for 1 day
        return db.StringSetAsync(trackDataKey, dataString, expiry: TimeSpan.FromDays(1));
    }

    public async Task<ICachableTrackData?> GetCachedDataByIdAsync(string id, MusicPlatform platform)
    {
        var db = _multiplexer.GetDatabase();
            
        var trackDataKey = CreateCachedDataKey(id, platform);
        var data = await db.StringGetAsync(trackDataKey);
        if (data == default)
            return null;

        return JsonSerializer.Deserialize<CachableTrackData>(data);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string CreateCachedQueryDataKey(string query, MusicPlatform platform)
        => $"track:query_to_id:{platform}:{query}";
    public async Task<ICachableTrackData?> GetCachedDataByQueryAsync(string query, MusicPlatform platform)
    {
        query = Uri.EscapeDataString(query.Trim());
            
        var db = _multiplexer.GetDatabase();
        var queryDataKey = CreateCachedQueryDataKey(query, platform);

        var trackId = await db.StringGetAsync(queryDataKey);
        if (trackId == default)
            return null;

        return await GetCachedDataByIdAsync(trackId, platform);
    }

    public async Task CacheTrackDataByQueryAsync(string query, ICachableTrackData data)
    {
        query = Uri.EscapeDataString(query.Trim());

        // first cache the data
        await CacheTrackDataAsync(data);
            
        // then map the query to cached data's id
        var db = _multiplexer.GetDatabase();

        var queryDataKey = CreateCachedQueryDataKey(query, data.Platform);
        await db.StringSetAsync(queryDataKey, data.Id, TimeSpan.FromDays(7));
    }
        
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string CreateCachedPlaylistKey(string playlistId, MusicPlatform platform)
        => $"playlist:{platform}:{playlistId}";
    public async Task<IReadOnlyCollection<string>> GetPlaylistTrackIdsAsync(string playlistId, MusicPlatform platform)
    {
        var db = _multiplexer.GetDatabase();
        var key = CreateCachedPlaylistKey(playlistId, platform);
        var vals = await db.ListRangeAsync(key);
        if (vals == default || vals.Length == 0)
            return Array.Empty<string>();

        return vals.Select(x => x.ToString()).ToList();
    }

    public async Task CachePlaylistTrackIdsAsync(string playlistId, MusicPlatform platform, IEnumerable<string> ids)
    {
        var db = _multiplexer.GetDatabase();
        var key = CreateCachedPlaylistKey(playlistId, platform);
        await db.ListRightPushAsync(key, ids.Select(x => (RedisValue) x).ToArray());
        await db.KeyExpireAsync(key, TimeSpan.FromDays(7));
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string CreateCachedPlaylistQueryKey(string query, MusicPlatform platform)
        => $"playlist:query:{platform}:{query}";
    public Task CachePlaylistIdByQueryAsync(string query, MusicPlatform platform, string playlistId)
    {
        query = Uri.EscapeDataString(query.Trim());
        var key = CreateCachedPlaylistQueryKey(query, platform);
        var db = _multiplexer.GetDatabase();
        return db.StringSetAsync(key, playlistId, TimeSpan.FromDays(7));
    }

    public async Task<string?> GetPlaylistIdByQueryAsync(string query, MusicPlatform platform)
    {
        query = Uri.EscapeDataString(query.Trim());
        var key = CreateCachedPlaylistQueryKey(query, platform);

        var val = await _multiplexer.GetDatabase().StringGetAsync(key);
        if (val == default)
            return null;

        return val;
    }
}