YouTube-Manager/Manager.App/Services/System/CacheService.cs

using System.Security.Cryptography;
using System.Text;
using DotBased.Logging;
using DotBased.Monads;
using Manager.Data.Contexts;
using Manager.Data.Entities.Cache;
using Manager.YouTube;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;

namespace Manager.App.Services.System;

public class CacheService(ILogger<CacheService> logger, IHostEnvironment environment) : ExtendedBackgroundService(nameof(CacheService), "Manages caching.", logger, TimeSpan.FromHours(5))
{
    private DirectoryInfo? _cacheDirectory;
    private PooledDbContextFactory<CacheDbContext>? _dbContextFactory;
    private const string DataSubDir = "data";
    
    protected override Task InitializeAsync(CancellationToken stoppingToken)
    {
        _cacheDirectory = new DirectoryInfo(Path.Combine(Directory.GetCurrentDirectory(), "cache"));
        _cacheDirectory.Create();
        Directory.CreateDirectory(Path.Combine(_cacheDirectory.FullName, DataSubDir));
        LogEvent($"Cache directory: {_cacheDirectory.FullName}");
        
        var dbContextOptionsBuilder = new DbContextOptionsBuilder<CacheDbContext>();
        dbContextOptionsBuilder.UseSqlite($"Data Source={Path.Combine(_cacheDirectory.FullName, "cache_index.db")}");
        _dbContextFactory = new PooledDbContextFactory<CacheDbContext>(dbContextOptionsBuilder.Options);
        
        return Task.CompletedTask;
    }

    protected override async Task ExecuteServiceAsync(CancellationToken stoppingToken)
    {
        if (environment.IsDevelopment())
        {
            LogEvent("Development mode detected, skipping cache cleaning...");
            return;
        }

        try
        {
            await ClearCacheAsync(stoppingToken);
        }
        catch (Exception e)
        {
            logger.LogError(e, "Error in execution of service.");
            LogEvent($"Service execution failed. {e.Message}", LogSeverity.Error);
            throw;
        }
    }

    public string CreateCacheUrl(string originalUrl) => $"/api/v1/cache?url={originalUrl}";

    public async Task<Result<CacheFile>> CacheFromUrl(string url, CancellationToken cancellationToken = default)
    {
        try
        {
            if (string.IsNullOrWhiteSpace(url))
            {
                return ResultError.Fail("Url is empty.");
            }

            if (_cacheDirectory == null)
            {
                return ResultError.Fail("Cache directory is not initialized.");
            }

            if (_dbContextFactory == null)
            {
                return ResultError.Fail("Context factory is not initialized.");
            }

            await using var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
            
            var urlKeyBytes = SHA1.HashData(Encoding.UTF8.GetBytes(url));
            var urlKey = Convert.ToHexString(urlKeyBytes);
            var cacheEntity = await context.Cache.FirstOrDefaultAsync(c => c.Id == urlKey, cancellationToken: cancellationToken);
            if (cacheEntity == null)
            {
                var downloadResult = await NetworkService.DownloadBytesAsync(new HttpRequestMessage(HttpMethod.Get, url));
                if (!downloadResult.IsSuccess)
                {
                    LogEvent($"Failed to download from url: {url}");
                    return ResultError.Fail("Download failed.");
                }
                var download = downloadResult.Value;
                await using var downloadFile = File.Create(Path.Combine(_cacheDirectory.FullName, DataSubDir, $"{urlKey}.cache"));
                await downloadFile.WriteAsync(download.Data.AsMemory(0, download.Data.Length), cancellationToken);

                cacheEntity = new CacheEntity
                {
                    Id = urlKey,
                    CachedAtUtc = DateTime.UtcNow,
                    ContentLength = download.ContentLength,
                    ContentType = download.ContentType,
                    OriginalFileName = download.FileName,
                };
                
                context.Cache.Add(cacheEntity);
                var saved = await context.SaveChangesAsync(cancellationToken);
                if (saved <= 0)
                {
                    LogEvent($"Cache entity {cacheEntity.Id} could not be saved.", LogSeverity.Error);
                    return ResultError.Fail("Failed to save to cache db.");
                }

                return new CacheFile(download.Data, download.ContentType, download.FileName);
            }

            var filePath = Path.Combine(_cacheDirectory.FullName, DataSubDir, $"{urlKey}.cache");
            var buffer = await File.ReadAllBytesAsync(filePath, cancellationToken);
            if (buffer.Length == 0)
            {
                LogEvent($"Failed to read data from disk. File: {filePath}", LogSeverity.Error);
                return ResultError.Fail($"Error reading data from disk. File: {filePath}");
            }

            return new CacheFile(buffer.ToArray(), cacheEntity.ContentType, cacheEntity.OriginalFileName);
        }
        catch (Exception e)
        {
            return ResultError.Error(e, "Cache error.");
        }
    }

    private async Task ClearCacheAsync(CancellationToken cancellationToken)
    {
        if (_dbContextFactory == null)
        {
            throw new InvalidOperationException("No DbContext factory configured.");
        }

        if (_cacheDirectory == null)
        {
            throw new InvalidOperationException("No cache directory configured.");
        }

        await using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
        
        var toRemove = dbContext.Cache.Where(c => c.CachedAtUtc < DateTime.UtcNow.AddDays(-1));
        if (!toRemove.Any())
        {
            LogEvent("No items found to purge from cache.");
            return;
        }

        var totalToRemove = toRemove.Count();
        LogEvent($"Found {totalToRemove} cache items that are older than 1 day(s)");
        
        var deleted = new List<CacheEntity>();
        foreach (var entity in toRemove)
        {
            var pathToFile = Path.Combine(_cacheDirectory.FullName, DataSubDir, $"{entity.Id}.cache");
            if (!File.Exists(pathToFile))
            {
                deleted.Add(entity);
                continue;
            }

            try
            {
                File.Delete(pathToFile);
            }
            catch (Exception e)
            {
                logger.LogError(e, "Failed to delete cache entity with id: {EntityId}. Skipping cache entity...", entity.Id);
                continue;
            }
            deleted.Add(entity);
        }
        
        dbContext.RemoveRange(deleted);
        var dbDeleted = await dbContext.SaveChangesAsync(cancellationToken);
        if (dbDeleted < deleted.Count)
        {
            LogEvent("Could not delete all files from cache.", LogSeverity.Warning);
        }

        LogEvent($"Removed {dbDeleted}/{totalToRemove} items");
    }
}

public record CacheFile(byte[] Data, string? ContentType, string? OriginalFileName);