ServerManagementUtils/robin/Services/Monitoring/MonitoringService.cs

using System.Extensions;
using System.Extensions.Core;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Robin.Options;
using Robin.Services.Persistence;

namespace Robin.Services.Monitoring;

public sealed class MonitoringService(
    PositionPersistenceService persistenceService,
    IOptions<MonitorOptions> options,
    ILogger<MonitoringService> logger
) : IHostedLifecycleService
{
    private readonly PositionPersistenceService persistenceService = persistenceService;
    private readonly MonitorOptions options = options.Value;
    private readonly CancellationTokenSource cancellationTokenSource = new();
    private readonly ILogger<MonitoringService> logger = logger;
    private readonly List<Task> watchers = [];

    public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    public Task StartedAsync(CancellationToken cancellationToken) =>
        this.MonitorFiles(cancellationToken);

    public Task StartingAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    public Task StopAsync(CancellationToken cancellationToken) => this.CancelMonitors();

    public Task StoppedAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    public Task StoppingAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    public Task CancelMonitors()
    {
        this.cancellationTokenSource.Cancel();
        return Task.WhenAll(this.watchers);
    }

    public async Task MonitorFiles(CancellationToken cancellationToken)
    {
        var scopedLogger = this.logger.CreateScopedLogger();
        scopedLogger.LogDebug(
            "Starting file monitoring service. Parsing provided paths {paths}",
            string.Join(", ", this.options.Paths)
        );
        var expandedPaths = ExpandPaths(this.options.Paths);
        scopedLogger.LogInformation(
            "Monitoring the following files: {files}",
            string.Join(", ", expandedPaths)
        );

        var cts = CancellationTokenSource.CreateLinkedTokenSource(
            cancellationToken,
            this.cancellationTokenSource.Token
        );
        foreach (var filePath in expandedPaths)
        {
            this.watchers.Add(Task.Run(() => this.MonitorFile(filePath, cts.Token), cts.Token));
        }
    }

    private async Task MonitorFile(string filePath, CancellationToken cancellationToken)
    {
        var scopedLogger = this.logger.CreateScopedLogger();
        if (!File.Exists(filePath))
        {
            scopedLogger.LogWarning("File does not exist: {filePath}", filePath);
            return;
        }

        scopedLogger.LogInformation("Starting to monitor file: {filePath}", filePath);
        var previousPosition = this.persistenceService.GetPosition(filePath);
        using var fs = new FileStream(
            filePath,
            FileMode.Open,
            FileAccess.Read,
            FileShare.ReadWrite | FileShare.Delete
        );

        if (fs.Length < previousPosition)
        {
            previousPosition = 0;
        }

        if (previousPosition > 0)
        {
            fs.Seek(previousPosition, SeekOrigin.Begin);
        }

        using var reader = new StreamReader(fs);
        while (
            (await reader.ReadLineAsync(cancellationToken)) is string line
            && !line.IsNullOrEmpty()
        )
        {
            scopedLogger.LogDebug("Read line: {line}", line);
            //TODO: Publish to IPublishingService
            await this.persistenceService.SavePositionAsync(
                filePath,
                fs.Position,
                cancellationToken
            );
        }
    }

    private static List<string> ExpandPaths(List<string>? patterns)
    {
        if (patterns is null || patterns.Count == 0)
        {
            return [];
        }

        var results = new List<string>();
        foreach (var pattern in patterns)
        {
            var directory = Path.GetDirectoryName(pattern);
            var filePattern = Path.GetFileName(pattern);
            if (string.IsNullOrEmpty(directory) || !Directory.Exists(directory))
            {
                continue;
            }

            results.AddRange(Directory.GetFiles(directory, filePattern));
        }

        return results;
    }
}