Think.swift

import SwiftUI
import MarkdownUI
import Splash

@available(iOS 18.0, *)
struct Think: View {
    @Environment(\.colorScheme) private var colorScheme

    @Namespace private var ns
    @State private var position = ScrollPosition(edge: .top)
    @Binding var isScrolling: Bool
    @State private var scrollTask: Task<Void, Never>? = nil
    let text: String

    var theme: Splash.Theme {
        switch colorScheme {
        case .dark:
            return .midnight(withFont: .init(size: 16))
        default:
            return .sunset(withFont: .init(size: 16))
        }
    }

    var backgroundColor: SwiftUI.Color {
        colorScheme == .dark ? .black : .white
    }

    var body: some View {
        ScrollView {
            HStack {
                Text(text)
                Spacer()
            }
        }
        .contentMargins(.top, 12)
        .contentMargins(.bottom, 8)
        .scrollPosition($position)
        .frame(height: 100)
        .overlay(alignment: .top) {
            LinearGradient(
                gradient: Gradient(colors: [
                    backgroundColor,
                    backgroundColor.opacity(0),
                ]),
                startPoint: .top,
                endPoint: .bottom
            )
            .opacity(1)
            .frame(height: 20)
            .allowsHitTesting(false)
        }
        .overlay(alignment: .bottom) {
            LinearGradient(
                gradient: Gradient(colors: [
                    backgroundColor,
                    backgroundColor.opacity(0),
                ]),
                startPoint: .bottom,
                endPoint: .top
            )
            .opacity(1)
            .frame(height: 20)
            .allowsHitTesting(false)
        }
        .onChange(of: text) { _, new in
            scrollTask?.cancel()
            scrollTask = Task { @MainActor in
                try? await Task.sleep(for: .milliseconds(300))
                if !isScrolling {
                    isScrolling = true
                    withAnimation(.easeOut(duration: 0.25)) {
                        position.scrollTo(edge: .bottom)
                    } completion: {
                        isScrolling = false
                    }
                }
            }
        }
    }
}

#Preview {
    if #available(iOS 18.0, *) {
        Think(isScrolling: .constant(false), text: "")
    } else {
        // Fallback on earlier versions
    }
}