using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

using Humanizer;

using Serilog;

namespace MfGames.Nitride.Pipelines;

/// <summary>
/// A manager class for all of the pipelines. This class is responsible for
/// hooking everything up and handling the ordering of pipelines as they
/// are run.
/// </summary>
public class PipelineManager
{
    private readonly PipelineRunner.Factory createEntry;

    private readonly ILogger logger;

    private List<PipelineRunner> entries;

    private bool isSetup;

    private ICollection<IPipeline> pipelines;

    public PipelineManager(
        ILogger logger,
        IEnumerable<IPipeline> pipelines,
        PipelineRunner.Factory createEntry)
    {
        this.createEntry = createEntry;
        this.logger = logger.ForContext<PipelineManager>();
        this.pipelines = new HashSet<IPipeline>(pipelines);
        this.entries = null!;
    }

    public ICollection<IPipeline> Pipelines
    {
        get => this.pipelines;
        set => this.pipelines =
            value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Runs all of the pipelines in the appropriate order while running
    /// across multiple threads.
    /// </summary>
    /// <returns>A task with zero for success or otherwise an error code.</returns>
    public Task<int> RunAsync()
    {
        // Make sure everything is setup.
        DateTime started = DateTime.UtcNow;

        if (!this.Setup())
        {
            return Task.FromResult(1);
        }

        // Go through all  the entries and start each one. We gather the
        // resulting tasks and then wait for all of them to end.
        this.logger.Verbose(
            "Starting {Count:l}",
            "pipeline".ToQuantity(this.pipelines.Count));

        Task[] tasks = this.entries
            .Select(x => Task.Run(async () => await x.RunAsync()))
            .ToArray();

        var report = TimeSpan.FromSeconds(15);

        while (!Task.WaitAll(tasks, report))
        {
            var waiting = this.entries.Where(x => !x.IsFinished)
                .ToList();

            this.logger.Debug(
                "Waiting for {Count:l} to finish running",
                "pipeline".ToQuantity(waiting.Count));

            IOrderedEnumerable<IGrouping<PipelineRunnerState, PipelineRunner>>
                states =
                    waiting.GroupBy(x => x.State, x => x)
                        .OrderBy(x => (int)x.Key);

            foreach (IGrouping<PipelineRunnerState, PipelineRunner>? state in
                     states)
            {
                var statePipelines = state.OrderBy(x => x.Pipeline.ToString())
                    .ToList();

                this.logger.Verbose(
                    "Waiting for {Count:l} in {State}: {List:l}",
                    "pipeline".ToQuantity(statePipelines.Count),
                    state.Key,
                    string.Join(
                        ", ",
                        state.Key == PipelineRunnerState.Started
                            ? statePipelines.Select(
                                x => $"{x.Pipeline} ({x.ElapsedFromState})")
                            : statePipelines.Select(
                                x => x.Pipeline.ToString())));
            }
        }

        // Figure out our return code.
        bool hasErrors =
            this.entries.Any(x => x.State == PipelineRunnerState.Errored);

        this.logger.Information(
            "Completed in {Elapsed}",
            DateTime.UtcNow - started);

        return Task.FromResult(hasErrors ? 2 : 0);
    }

    /// <summary>
    /// Performs the final initialization and preparation for the pipelines
    /// and get them ready for deploying.
    /// </summary>
    private bool Setup()
    {
        // If we've already set up ourselves, then we do nothing.
        if (this.isSetup)
        {
            return true;
        }

        // If we don't have any pipelines, then we can't process.
        if (this.pipelines.Count == 0)
        {
            this.logger.Error(
                "There are no registered pipelines run, use"
                + " ConfigureContainer to include IPipeline instances");

            return false;
        }

        this.logger.Verbose(
            "Setting up {Count:l}",
            "pipeline".ToQuantity(this.pipelines.Count));

        // Wrap all the pipelines into entries. We do this before the next
        // step so we can have the entries depend on the entries.
        this.entries = this.pipelines.Select(x => this.createEntry(x))
            .ToList();

        // Go through and connect the pipelines together.
        foreach (PipelineRunner? entry in this.entries)
        {
            var dependencies = entry.Pipeline.GetDependencies()
                .ToList();

            foreach (IPipeline? dependency in dependencies)
            {
                // Get the entry for the dependency.
                PipelineRunner dependencyPipeline =
                    this.entries.Single(x => x.Pipeline == dependency);

                // Set up the bi-directional connection.
                entry.Incoming.Add(dependencyPipeline);
                dependencyPipeline.Outgoing.Add(entry);
            }
        }

        // Loop through all the entries and tell them we are done providing
        // and they can set up internal threads other structures.
        foreach (PipelineRunner? entry in this.entries)
        {
            entry.Initialize();
        }

        // We have run successfully.
        this.isSetup = true;

        return true;
    }
}