CombineLatestMany.swift

//
//  CombineLatestMany.swift
//  CombineExt
//
//  Created by Jasdev Singh on 22/03/2020.
//  Copyright © 2020 Combine Community. All rights reserved.
//

#if canImport(Combine)
import Combine

@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
public extension Publisher {
    /// Projects `self` and a `Collection` of `Publisher`s onto a type-erased publisher that chains `combineLatest` calls on
    /// the inner publishers. This is a variadic overload on Combine’s variants that top out at arity three.
	///
    /// - parameter others: A `Collection`-worth of other publishers with matching output and failure types to combine with.
    ///
    /// - returns: A type-erased publisher with value events from `self` and each of the inner publishers `combineLatest`’d
    /// together in an array.
    func combineLatest<Others: Collection>(with others: Others)
        -> AnyPublisher<[Output], Failure>
        where Others.Element: Publisher, Others.Element.Output == Output, Others.Element.Failure == Failure {
        let seed = map { [$0] }.eraseToAnyPublisher()

        return others.reduce(seed) { combined, next in
            combined
                .combineLatest(next)
                .map { $0 + [$1] }
                .eraseToAnyPublisher()
        }
    }

    /// Projects `self` and a `Collection` of `Publisher`s onto a type-erased publisher that chains `combineLatest` calls on
    /// the inner publishers. This is a variadic overload on Combine’s variants that top out at arity three.
	///
    /// - parameter others: A `Collection`-worth of other publishers with matching output and failure types to combine with.
    ///
    /// - returns: A type-erased publisher with value events from `self` and each of the inner publishers `combineLatest`’d
    /// together in an array.
    func combineLatest<Other: Publisher>(with others: Other...)
        -> AnyPublisher<[Output], Failure>
        where Other.Output == Output, Other.Failure == Failure {
        combineLatest(with: others)
    }
}

@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
public extension Collection where Element: Publisher {
    /// Projects a `Collection` of `Publisher`s onto a type-erased publisher that chains `combineLatest` calls on
    /// the inner publishers. This is a variadic overload on Combine’s variants that top out at arity three.
    ///
    /// - returns: A type-erased publisher with value events from each of the inner publishers `combineLatest`’d
    /// together in an array.
    func combineLatest() -> AnyPublisher<[Element.Output], Element.Failure> {
        switch count {
        case 0:
            return Empty().eraseToAnyPublisher()
        case 1:
            return self[startIndex]
                .combineLatest(with: [Element]())
        default:
            let first = self[startIndex]
            let others = self[index(after: startIndex)...]

            return first
                .combineLatest(with: others)
        }
    }
}
#endif