using System.Collections.Concurrent;
using JdeScoping.DataSync.Dev.Contracts;
using JdeScoping.DataSync.Etl.Results;
using Microsoft.Extensions.Logging;

namespace JdeScoping.DataSync.Dev;

/// <summary>
/// Registry for development ETL pipelines that load from cached protobuf files.
/// Uses JSON configuration via IDevEtlPipelineFactory.
/// </summary>
public class DevEtlRegistry
{
    private readonly IDevEtlPipelineFactory _pipelineFactory;
    private readonly string _cacheDirectory;
    private readonly ILogger<DevEtlRegistry>? _logger;

    public DevEtlRegistry(
        IDevEtlPipelineFactory pipelineFactory,
        string cacheDirectory,
        ILogger<DevEtlRegistry>? logger = null)
    {
        _pipelineFactory = pipelineFactory ?? throw new ArgumentNullException(nameof(pipelineFactory));

        if (string.IsNullOrWhiteSpace(cacheDirectory))
            throw new ArgumentException("Cache directory is required.", nameof(cacheDirectory));

        if (!Directory.Exists(cacheDirectory))
            throw new DirectoryNotFoundException($"Cache directory not found: {cacheDirectory}");

        _cacheDirectory = cacheDirectory;
        _logger = logger;
    }

    public IEnumerable<string> GetAvailableTables() => _pipelineFactory.GetAvailableTables();

    public async Task<PipelineResult> RunAsync(string tableName, CancellationToken cancellationToken = default)
    {
        _logger?.LogInformation("Running dev ETL for {TableName}", tableName);

        var pipeline = _pipelineFactory.GetPipeline(tableName, _cacheDirectory);
        var result = await pipeline.ExecuteAsync(cancellationToken);

        if (result.Success)
            _logger?.LogInformation("Completed {TableName}: {Rows} rows in {Elapsed:g}",
                tableName, result.TotalRows, result.Elapsed);
        else
            _logger?.LogError(result.Error, "Failed {TableName}: {Error}",
                tableName, result.Error?.Message);

        return result;
    }

    public async Task<IReadOnlyList<PipelineResult>> RunAllAsync(CancellationToken cancellationToken = default)
    {
        var results = new List<PipelineResult>();

        foreach (var tableName in GetAvailableTables())
        {
            cancellationToken.ThrowIfCancellationRequested();
            var result = await RunAsync(tableName, cancellationToken);
            results.Add(result);
        }

        return results;
    }

    /// <summary>
    /// Runs all dev ETL pipelines with parallelization.
    /// Small/medium tables run concurrently, very large tables run sequentially at the end.
    /// </summary>
    /// <param name="maxDegreeOfParallelism">Maximum concurrent table loads (default 4).</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    public async Task<IReadOnlyList<PipelineResult>> RunAllParallelAsync(
        int maxDegreeOfParallelism = 4,
        CancellationToken cancellationToken = default)
    {
        var results = new ConcurrentBag<PipelineResult>();
        using var semaphore = new SemaphoreSlim(maxDegreeOfParallelism);

        // Separate tables by size - run very large ones sequentially at the end
        var smallMediumTables = GetAvailableTables()
            .Where(t => !_pipelineFactory.IsVeryLargeTable(t))
            .ToList();
        var veryLargeTables = GetAvailableTables()
            .Where(t => _pipelineFactory.IsVeryLargeTable(t))
            .ToList();

        _logger?.LogInformation(
            "Running {ParallelCount} tables in parallel (max {MaxParallel}), then {SequentialCount} large tables sequentially",
            smallMediumTables.Count, maxDegreeOfParallelism, veryLargeTables.Count);

        // Run small/medium tables in parallel
        var tasks = smallMediumTables.Select(async tableName =>
        {
            await semaphore.WaitAsync(cancellationToken);
            try
            {
                var result = await RunAsync(tableName, cancellationToken);
                results.Add(result);
            }
            finally
            {
                semaphore.Release();
            }
        });

        await Task.WhenAll(tasks);

        // Run very large tables sequentially (IO-bound, would contend)
        foreach (var tableName in veryLargeTables)
        {
            cancellationToken.ThrowIfCancellationRequested();
            var result = await RunAsync(tableName, cancellationToken);
            results.Add(result);
        }

        return results.ToList();
    }
}