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

namespace Wabbajack.Common;

public static class AsyncParallelExtensions
{
    public static async Task PDoAll<TIn>(this IEnumerable<TIn> coll, Func<TIn, Task> mapFn)
    {
        var tasks = coll.Select(mapFn).ToList();
        await Task.WhenAll(tasks);
    }

    public static async Task PDoAll<TIn, TJob>(this IEnumerable<TIn> coll, IResource<TJob> limiter,
        Func<TIn, Task> mapFn)
    {
        var tasks = coll.Select(async x =>
        {
            using var job = await limiter.Begin("", 0, CancellationToken.None);
            await mapFn(x);
        }).ToList();
        await Task.WhenAll(tasks);
    }

    public static async IAsyncEnumerable<TOut> PMapAll<TIn, TOut>(this IEnumerable<TIn> coll,
        Func<TIn, Task<TOut>> mapFn)
    {
        var tasks = coll.Select(async x =>
        {
            return await Task.Run(() => mapFn(x));
        }).ToList();
        foreach (var itm in tasks) yield return await itm;
    }
    
    
    // Like PMapAll but don't keep defaults
    public static async IAsyncEnumerable<TOut> PKeepAll<TIn, TOut>(this IEnumerable<TIn> coll,
        Func<TIn, Task<TOut>> mapFn)
    where TOut : class
    {
        var tasks = coll.Select(mapFn).ToList();
        foreach (var itm in tasks)
        {
            var val = await itm;
            if (itm != default) 
                yield return await itm;
        }
    }

    public static async IAsyncEnumerable<TOut> PMapAll<TIn, TJob, TOut>(this IEnumerable<TIn> coll,
        IResource<TJob> limiter, Func<TIn, Task<TOut>> mapFn)
    {
        var tasks = coll.Select(mapFn).ToList();
        foreach (var itm in tasks)
        {
            using var job = await limiter.Begin("", 0, CancellationToken.None);
            yield return await itm;
        }
    }
    
    /// <summary>
    /// Faster version of PMapAll for when the function invocation will take a very small amount of time
    /// batches all the inputs into N groups and executes them all on one task, where N is the number of
    /// threads supported by the limiter
    /// </summary>
    /// <param name="coll"></param>
    /// <param name="limiter"></param>
    /// <param name="mapFn"></param>
    /// <typeparam name="TIn"></typeparam>
    /// <typeparam name="TJob"></typeparam>
    /// <typeparam name="TOut"></typeparam>
    /// <returns></returns>
    public static async IAsyncEnumerable<TOut> PMapAllBatched<TIn, TJob, TOut>(this IEnumerable<TIn> coll,
        IResource<TJob> limiter, Func<TIn, Task<TOut>> mapFn)
    {
        var asList = coll.ToList();
        
        var tasks = new List<Task<List<TOut>>>();

        tasks.AddRange(Enumerable.Range(0, limiter.MaxTasks).Select(i => Task.Run(async () =>
        {
            using var job = await limiter.Begin(limiter.Name, asList.Count / limiter.MaxTasks, CancellationToken.None);
            var list = new List<TOut>();
            for (var idx = i; idx < asList.Count; idx += limiter.MaxTasks)
            {
                job.ReportNoWait(1);
                list.Add(await mapFn(asList[idx]));
            }

            return list;
        })));

        foreach (var result in tasks)
        {
            foreach (var itm in (await result))
            {
                yield return itm;
            }
        }
    }
    
    public static async IAsyncEnumerable<TOut> PKeepAll<TIn, TJob, TOut>(this IEnumerable<TIn> coll,
        IResource<TJob> limiter, Func<TIn, Task<TOut>> mapFn)
    where TOut : class
    {
        var tasks = coll.Select(mapFn).ToList();
        foreach (var itm in tasks)
        {
            using var job = await limiter.Begin("", 0, CancellationToken.None);
            var itmA = await itm;
            if (itmA != default)
            {
                yield return await itm;
            }
        }
    }

    public static async Task<List<T>> ToList<T>(this IAsyncEnumerable<T> coll)
    {
        List<T> lst = new();
        await foreach (var itm in coll) lst.Add(itm);
        return lst;
    }

    public static async Task<T[]> ToArray<T>(this IAsyncEnumerable<T> coll)
    {
        List<T> lst = new();
        await foreach (var itm in coll) lst.Add(itm);
        return lst.ToArray();
    }

    public static async Task<IReadOnlyCollection<T>> ToReadOnlyCollection<T>(this IAsyncEnumerable<T> coll)
    {
        List<T> lst = new();
        await foreach (var itm in coll) lst.Add(itm);
        return lst;
    }

    public static async Task<HashSet<T>> ToHashSet<T>(this IAsyncEnumerable<T> coll, Predicate<T>? filter = default)
    {
        HashSet<T> lst = new();
        if (filter == default)
            await foreach (var itm in coll)
                lst.Add(itm);
        else
            await foreach (var itm in coll.Where(filter))
                lst.Add(itm);

        return lst;
    }

    public static async Task Do<T>(this IAsyncEnumerable<T> coll, Func<T, Task> fn)
    {
        await foreach (var itm in coll) await fn(itm);
    }

    public static async Task Do<T>(this IAsyncEnumerable<T> coll, Action<T> fn)
    {
        await foreach (var itm in coll) fn(itm);
    }

    public static async Task<IDictionary<TK, T>> ToDictionary<T, TK>(this IAsyncEnumerable<T> coll,
        Func<T, TK> kSelector)
        where TK : notnull
    {
        Dictionary<TK, T> dict = new();
        await foreach (var itm in coll) dict.Add(kSelector(itm), itm);
        return dict;
    }

    public static async Task<IDictionary<TK, TV>> ToDictionary<T, TK, TV>(this IAsyncEnumerable<T> coll,
        Func<T, TK> kSelector, Func<T, TV> vSelector)
        where TK : notnull
    {
        Dictionary<TK, TV> dict = new();
        await foreach (var itm in coll) dict.Add(kSelector(itm), vSelector(itm));
        return dict;
    }

    public static async IAsyncEnumerable<T> Where<T>(this IAsyncEnumerable<T> coll, Predicate<T> p)
    {
        await foreach (var itm in coll)
            if (p(itm))
                yield return itm;
    }

    public static async IAsyncEnumerable<TOut> SelectAsync<TIn, TOut>(this IEnumerable<TIn> coll,
        Func<TIn, ValueTask<TOut>> fn)
    {
        foreach (var itm in coll)
            yield return await fn(itm);
    }

    public static async IAsyncEnumerable<TOut> SelectMany<TIn, TOut>(this IEnumerable<TIn> coll,
        Func<TIn, ValueTask<IEnumerable<TOut>>> fn)
    {
        foreach (var itm in coll)
        foreach (var inner in await fn(itm))
            yield return inner;
    }

    public static async IAsyncEnumerable<TOut> Select<TIn, TOut>(this IAsyncEnumerable<TIn> coll,
        Func<TIn, ValueTask<TOut>> fn)
    {
        await foreach (var itm in coll)
            yield return await fn(itm);
    }

    public static async IAsyncEnumerable<TOut> SelectMany<TIn, TOut>(this IAsyncEnumerable<TIn> coll,
        Func<TIn, IEnumerable<TOut>> fn)
    {
        await foreach (var itm in coll)
        foreach (var inner in fn(itm))
            yield return inner;
    }
}