FilterIf.swift

//
//  Filter.swift
//
//  Created by Daniel Tartaglia on 8/25/2018.
//  Copyright © 2019 Daniel Tartaglia. MIT License.
//
import RxSwift

extension ObservableType {

    /// Filters the source observable sequence using a trigger observable sequence producing Bool values.
    /// Elements only go through the filter when the trigger has not completed and
    ///   its last element was true. If either source or trigger error's, then the source errors.
    ///
    /// - Parameter trigger: Triggering event sequence.
    /// - Returns: Filtered observable sequence.
    func filter<O>(if trigger: O) -> Observable<Element> where O: ObservableType, O.Element == Bool {
        return self.withLatestFrom(trigger) { ($0, $1) }
            .filter { $0.1 }
            .map { $0.0 }
    }

    /// Filters the source observable sequence using a trigger observable sequence.
    /// Elements only go through the filter when the trigger has not completed and
    ///   its last element produces a true value from the pred. If either source or trigger error's, then the source errors.
    ///
    /// - Parameters:
    ///   - trigger: The sequence to compare with.
    ///   - pred: The predicate function to determine if the element should pass through.
    /// - Returns: An Observable of the same type that passed the filter test.
    func filter<O>(if trigger: O, _ pred: @escaping (Element, O.Element) -> Bool) -> Observable<Element> where O: ObservableType {
        return self.withLatestFrom(trigger) { ($0, $1) }
            .filter { pred($0.0, $0.1) }
            .map { $0.0 }
    }
}