result/src/Result/Extensions/Extensions.Enumerable.cs

// Copyright (c) The Geekeey Authors
// SPDX-License-Identifier: EUPL-1.2

namespace Geekeey.Extensions.Result;

/// <summary>
/// Extensions for or relating to <see cref="Result{T}"/>.
/// </summary>
public static partial class Extensions
{
	/// <summary>
	/// Turns a sequence of results into a single result containing the success values in the results only if all the
	/// results have success values.
	/// </summary>
	/// <param name="results">The results to turn into a single sequence.</param>
	/// <typeparam name="T">The type of the success values in the results.</typeparam>
	/// <returns>A single result containing a sequence of all the success values from the original sequence of results,
	/// or the first failure value encountered within the sequence.</returns>
	/// <remarks>
	/// This method completely enumerates the input sequence before returning and is not lazy. As a consequence of this,
	/// the sequence within the returned result is an <see cref="IReadOnlyList{T}"/>.
	/// </remarks>
	public static Result<IReadOnlyList<T>> Join<T>(this IEnumerable<Result<T>> results)
	{
		_ = results.TryGetNonEnumeratedCount(out var count);
		var list = new List<T>(count);

		foreach (var result in results)
		{
			if (!result.TryGetValue(out var value, out var error))
			{
				return new Result<IReadOnlyList<T>>(error);
			}

			list.Add(value);
		}

		return list;
	}

	/// <inheritdoc cref="Join{T}(System.Collections.Generic.IEnumerable{Geekeey.Extensions.Result.Result{T}})"/>
	/// <remarks>
	/// For parallel execution of the async tasks, one should await the <c>Task.WhenAll()</c> of the provided list
	/// before calling this function
	/// </remarks>
	/// <seealso cref="Join{T}(System.Collections.Generic.IEnumerable{Geekeey.Extensions.Result.Result{T}})"/>
	// ReSharper disable once InconsistentNaming
	public static async Task<Result<IReadOnlyList<T>>> Join<T>(this IEnumerable<Task<Result<T>>> results)
	{
		_ = results.TryGetNonEnumeratedCount(out var count);
		var list = new List<T>(count);

		foreach (var result in results)
		{
			if (!(await result).TryGetValue(out var value, out var error))
			{
				return new Result<IReadOnlyList<T>>(error);
			}

			list.Add(value);
		}

		return list;
	}

	/// <inheritdoc cref="Join{T}(System.Collections.Generic.IEnumerable{Geekeey.Extensions.Result.Result{T}})"/>
	/// <remarks>
	/// For parallel execution of the async tasks, one should await the <c>Task.WhenAll()</c> of the provided list
	/// before calling this function
	/// </remarks>
	/// <seealso cref="Join{T}(System.Collections.Generic.IEnumerable{Geekeey.Extensions.Result.Result{T}})"/>
	// ReSharper disable once InconsistentNaming
	public static async ValueTask<Result<IReadOnlyList<T>>> Join<T>(this IEnumerable<ValueTask<Result<T>>> results)
	{
		_ = results.TryGetNonEnumeratedCount(out var count);
		var list = new List<T>(count);

		foreach (var result in results)
		{
			if (!(await result).TryGetValue(out var value, out var error))
			{
				return new Result<IReadOnlyList<T>>(error);
			}

			list.Add(value);
		}

		return list;
	}
}