using Microsoft.Extensions.Hosting;
using OwnerNumberMigration.ValueParsing;

namespace OwnerNumberMigration.Migrations;

public abstract class AttributeMigrationTask<T> : IHostedService
{
    private readonly IAttributeMigration _migration;
    private readonly CancellationTokenSource _cancellation = new();
    private readonly IMigrationManager _manager;

    private Task? _runningMigration;

    protected AttributeMigrationTask
    (
        string sourceAttribute,
        string destinationAttribute,
        AttributeMigrationFactory<T> factory,
        IParsingStrategyFactory strategyFactory,
        IMigrationManager manager
    )
    {
        _manager = manager;
        _migration = factory
        (
            sourceAttribute,
            strategyFactory.CreateParsingStrategy<T>(sourceAttribute),
            destinationAttribute
        );
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        if (cancellationToken.IsCancellationRequested) return Task.CompletedTask;

        _manager.Start(_runningMigration = _migration.Migrate(_cancellation.Token));

        return Task.CompletedTask;
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        if (_runningMigration is not null)
        {
            if (!_runningMigration.IsCompleted)
            {
                _cancellation.Cancel();
                try
                {
                    await _runningMigration;
                }
                catch (TaskCanceledException)
                {
                }
            }

            _runningMigration.Dispose();
        }

        _cancellation.Dispose();
    }
}