dramaling-vocab-learning/backend/DramaLing.Api/Services/Infrastructure/Caching/HybridCacheService.cs

using DramaLing.Api.Services.Infrastructure.Caching;

namespace DramaLing.Api.Services.Caching;

/// <summary>
/// 混合快取服務，使用組合模式結合記憶體和分散式快取
/// </summary>
public class HybridCacheService : ICacheService
{
    private readonly ICacheProvider _memoryProvider;
    private readonly ICacheProvider? _distributedProvider;
    private readonly IDatabaseCacheManager _databaseCacheManager;
    private readonly ICacheStrategyManager _strategyManager;
    private readonly ILogger<HybridCacheService> _logger;
    private readonly CacheStats _stats;

    public HybridCacheService(
        ICacheProvider memoryProvider,
        ICacheProvider? distributedProvider,
        IDatabaseCacheManager databaseCacheManager,
        ICacheStrategyManager strategyManager,
        ILogger<HybridCacheService> logger)
    {
        _memoryProvider = memoryProvider ?? throw new ArgumentNullException(nameof(memoryProvider));
        _distributedProvider = distributedProvider;
        _databaseCacheManager = databaseCacheManager ?? throw new ArgumentNullException(nameof(databaseCacheManager));
        _strategyManager = strategyManager ?? throw new ArgumentNullException(nameof(strategyManager));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _stats = new CacheStats { LastUpdated = DateTime.UtcNow };

        _logger.LogInformation("HybridCacheService initialized with {MemoryProvider} and {DistributedProvider}",
            _memoryProvider.ProviderName, _distributedProvider?.ProviderName ?? "No Distributed Cache");
    }

    public async Task<T?> GetAsync<T>(string key) where T : class
    {
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException(nameof(key));

        try
        {
            // L1: 記憶體快取
            var memoryResult = await _memoryProvider.GetAsync<T>(key);
            if (memoryResult != null)
            {
                _stats.HitCount++;
                return memoryResult;
            }

            // L2: 分散式快取
            if (_distributedProvider != null)
            {
                var distributedResult = await _distributedProvider.GetAsync<T>(key);
                if (distributedResult != null)
                {
                    // 回填到記憶體快取
                    var memoryExpiry = _strategyManager.CalculateMemoryExpiry(key);
                    await _memoryProvider.SetAsync(key, distributedResult, memoryExpiry);

                    _stats.HitCount++;
                    return distributedResult;
                }
            }

            // L3: 資料庫快取 (僅適用於分析結果)
            if (key.StartsWith("analysis:"))
            {
                var dbResult = await _databaseCacheManager.GetFromDatabaseCacheAsync<T>(key);
                if (dbResult != null)
                {
                    // 回填到上層快取
                    await SetMultiLevelCacheAsync(key, dbResult);
                    _stats.HitCount++;
                    return dbResult;
                }
            }

            _stats.MissCount++;
            return null;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error getting cache for key: {Key}", key);
            _stats.MissCount++;
            return null;
        }
    }

    public async Task<bool> SetAsync<T>(string key, T value, TimeSpan? expiry = null) where T : class
    {
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException(nameof(key));

        if (value == null)
            throw new ArgumentNullException(nameof(value));

        try
        {
            var smartExpiry = expiry ?? _strategyManager.CalculateSmartExpiry(key, value);
            var tasks = new List<Task<bool>>();

            // L1: 記憶體快取
            var memoryExpiry = TimeSpan.FromMinutes(Math.Min(smartExpiry.TotalMinutes, 30));
            tasks.Add(_memoryProvider.SetAsync(key, value, memoryExpiry));

            // L2: 分散式快取
            if (_distributedProvider != null)
            {
                tasks.Add(_distributedProvider.SetAsync(key, value, smartExpiry));
            }

            var results = await Task.WhenAll(tasks);
            var success = results.Any(r => r);

            if (success)
            {
                _stats.TotalKeys++;
                _logger.LogDebug("Cache set for key: {Key}, expiry: {Expiry}", key, smartExpiry);
            }

            return success;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error setting cache for key: {Key}", key);
            return false;
        }
    }

    public async Task<bool> RemoveAsync(string key)
    {
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException(nameof(key));

        try
        {
            var tasks = new List<Task<bool>>
            {
                _memoryProvider.RemoveAsync(key)
            };

            if (_distributedProvider != null)
            {
                tasks.Add(_distributedProvider.RemoveAsync(key));
            }

            var results = await Task.WhenAll(tasks);
            return results.Any(r => r);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error removing cache for key: {Key}", key);
            return false;
        }
    }

    public async Task<bool> ExistsAsync(string key)
    {
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException(nameof(key));

        try
        {
            if (await _memoryProvider.ExistsAsync(key))
                return true;

            if (_distributedProvider != null)
                return await _distributedProvider.ExistsAsync(key);

            return false;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error checking cache existence for key: {Key}", key);
            return false;
        }
    }

    public async Task<bool> ExpireAsync(string key, TimeSpan expiry)
    {
        if (string.IsNullOrEmpty(key))
            throw new ArgumentNullException(nameof(key));

        try
        {
            var value = await GetAsync<object>(key);
            if (value != null)
            {
                return await SetAsync(key, value, expiry);
            }
            return false;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error setting expiry for key: {Key}", key);
            return false;
        }
    }

    public async Task<bool> ClearAsync()
    {
        try
        {
            var tasks = new List<Task<bool>>
            {
                _memoryProvider.ClearAsync()
            };

            if (_distributedProvider != null)
            {
                tasks.Add(_distributedProvider.ClearAsync());
            }

            await Task.WhenAll(tasks);
            return true;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error clearing cache");
            return false;
        }
    }

    public async Task<Dictionary<string, T?>> GetManyAsync<T>(IEnumerable<string> keys) where T : class
    {
        var keyList = keys.ToList();
        var result = new Dictionary<string, T?>();

        if (!keyList.Any())
            return result;

        try
        {
            var tasks = keyList.Select(async key =>
            {
                var value = await GetAsync<T>(key);
                return new KeyValuePair<string, T?>(key, value);
            });

            var results = await Task.WhenAll(tasks);
            return results.ToDictionary(r => r.Key, r => r.Value);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error getting multiple cache values");
            return result;
        }
    }

    public async Task<bool> SetManyAsync<T>(Dictionary<string, T> keyValuePairs, TimeSpan? expiry = null) where T : class
    {
        if (!keyValuePairs.Any())
            return true;

        try
        {
            var tasks = keyValuePairs.Select(async kvp =>
                await SetAsync(kvp.Key, kvp.Value, expiry));

            var results = await Task.WhenAll(tasks);
            return results.All(r => r);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error setting multiple cache values");
            return false;
        }
    }

    public Task<CacheStats> GetStatsAsync()
    {
        _stats.LastUpdated = DateTime.UtcNow;
        return Task.FromResult(_stats);
    }

    private async Task SetMultiLevelCacheAsync<T>(string key, T value) where T : class
    {
        var expiry = _strategyManager.CalculateSmartExpiry(key, value);
        var memoryExpiry = _strategyManager.CalculateMemoryExpiry(key);

        await _memoryProvider.SetAsync(key, value, memoryExpiry);

        if (_distributedProvider != null)
        {
            await _distributedProvider.SetAsync(key, value, expiry);
        }
    }
}