Swiftgram/submodules/ComponentFlow/Source/Components/HStack.swift

import Foundation
import UIKit

public enum HStackAlignment {
    case left
    case alternatingLeftRight
}

public final class HStack<ChildEnvironment: Equatable>: CombinedComponent {
    public typealias EnvironmentType = ChildEnvironment

    private let items: [AnyComponentWithIdentity<ChildEnvironment>]
    private let spacing: CGFloat
    private let alignment: HStackAlignment

    public init(_ items: [AnyComponentWithIdentity<ChildEnvironment>], spacing: CGFloat, alignment: HStackAlignment = .left) {
        self.items = items
        self.spacing = spacing
        self.alignment = alignment
    }

    public static func ==(lhs: HStack<ChildEnvironment>, rhs: HStack<ChildEnvironment>) -> Bool {
        if lhs.items != rhs.items {
            return false
        }
        if lhs.spacing != rhs.spacing {
            return false
        }
        if lhs.alignment != rhs.alignment {
            return false
        }
        return true
    }

    public static var body: Body {
        let children = ChildMap(environment: ChildEnvironment.self, keyedBy: AnyHashable.self)

        return { context in
            var remainingWidth: CGFloat = context.availableSize.width
            var updatedChildren: [_UpdatedChildComponent] = []
            
            for item in context.component.items {
                let child = children[item.id].update(
                    component: item.component, environment: {
                        context.environment[ChildEnvironment.self]
                    },
                    availableSize: CGSize(width: remainingWidth, height: context.availableSize.height),
                    transition: context.transition
                )
                updatedChildren.append(child)
                remainingWidth -= context.component.spacing + child.size.width
            }
            
            var size = CGSize(width: 0.0, height: 0.0)
            switch context.component.alignment {
            case .left:
                for child in updatedChildren {
                    size.width += child.size.width
                    size.height = max(size.height, child.size.height)
                }
                size.width += context.component.spacing * CGFloat(updatedChildren.count - 1)
                
                var nextX = 0.0
                for child in updatedChildren {
                    context.add(child
                        .position(child.size.centered(in: CGRect(origin: CGPoint(x: nextX, y: floor((size.height - child.size.height) * 0.5)), size: child.size)).center)
                        .appear(.default(scale: true, alpha: true))
                        .disappear(.default(scale: true, alpha: true))
                    )
                    nextX += child.size.width
                    nextX += context.component.spacing
                }
            case .alternatingLeftRight:
                size.width = context.availableSize.width
                for child in updatedChildren {
                    size.height = max(size.height, child.size.height)
                }
                
                var nextLeftX = 0.0
                var nextRightX = size.width
                for i in 0 ..< updatedChildren.count {
                    let child = updatedChildren[i]
                    let childFrame: CGRect
                    if i % 2 == 0 {
                        childFrame = CGRect(origin: CGPoint(x: nextLeftX, y: floor((size.height - child.size.height) * 0.5)), size: child.size)
                        nextLeftX += child.size.width
                        nextLeftX += context.component.spacing
                    } else {
                        childFrame = CGRect(origin: CGPoint(x: nextRightX - child.size.width, y: floor((size.height - child.size.height) * 0.5)), size: child.size)
                        nextRightX -= child.size.width
                        nextRightX -= context.component.spacing
                    }
                    
                    context.add(child
                        .position(child.size.centered(in: childFrame).center)
                        .appear(.default(scale: true, alpha: true))
                        .disappear(.default(scale: true, alpha: true))
                    )
                }
            }

            return size
        }
    }
}