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Leveraging Interactive Custom View Controller Transitions

At Ibotta, we're constantly striving to provide our savers with the best possible user experience. As an iOS engineer, there are a number of super powerful APIs at my disposal to provide a top noch mobile UX.

One such API is the custom view controller transitioning capabilities contained within UIKit. These protocols provide an interface to control how one view controller is presented over another, and level of customization available to the programmer is significant.

Let's consider the basic use case of a card modal presentation. When a user selects an item on one view, another detail view is presented over the top. The presented detail view can then be dismissed by swiping down. This downward swipe is generally interactive, meaning the view follows the movement of your thumb as you swipe to dismiss.

This pattern is quite common across iOS applications, especially apps which have payment capabilities. With Ibotta's entrance into the payments

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import SwiftUI
import PlaygroundSupport

let ipsum = "Lorem Ipsum is simply dummy text of the printing and typesetting industry."

extension CGFloat {
    static var random: CGFloat {
        return CGFloat(arc4random()) / CGFloat(UInt32.max)
    }
}

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import SwiftUI
import PlaygroundSupport

final class Item: Identifiable {
    let color: Color
    let id = UUID()
    var displayDetail: Bool
    init(color: Color, displayDetail: Bool = false) {
        self.color = color
        self.displayDetail = displayDetail

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    private func executeShellCommand(_ command: String) {
        let task = Process()
        let pipe = Pipe()

        task.standardOutput = pipe
        task.arguments = ["-c", command]
        task.launchPath = "/bin/bash"
//        task.launch()

        let outputHandle = pipe.fileHandleForReading

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protocol ResourcesContaining {
    var beans: Double { get set }
    var milk: Double { get set }
    var water: Double { get set }
    func hasRequiredResources(for resourceSet: [Resource]) -> Bool
}

extension ResourcesContaining {
    func hasRequiredResources(for resourceSet: [Resource]) -> Bool {
        var currentBeans = self.beans

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enum Node<T> where T: Equatable & Comparable {
    case empty
    indirect case value(left: Node<T>, value: T, right: Node<T>)
}

extension Node {
    func isValid(within range: ClosedRange<T>) -> Bool {
        switch self {
        case .empty:
            return true

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final class CardPresentationCoordinator: UIPercentDrivenInteractiveTransition {
    var hasStartedInteraction = false
    var shouldFinishTransition = false
}

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final class RansomNoteBuilder {
    func isValidRansomNote(note: String, in magazine: String) -> Bool {
        
        var lookup = magazine.reduce(into: [Character:Int]()) { dictionary, letter in
            dictionary[letter] = (dictionary[letter] ?? 0) + 1
        }
        
        for character in note {
            guard let count = lookup[character], count > 0 else { return false }
            lookup[character] = count - 1

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final class Node {
    let left: Node?
    let right: Node?
    let value: Int
    
    init(left: Node? = nil, right: Node? = nil, value: Int) {
        self.left = left
        self.right = right
        self.value = value
    }

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let test = "abba"

class Solution {
    func expandPalindrome(input: String, startIndex: Int, endIndex: Int) -> (Int, Int) {
        var start = startIndex
        var end = endIndex
        let inputArray = Array(input)
        var result = (start, end)