LargestSymbolView.swift

//
//  LargestSymbolView.swift
//
//  Created by Alex Rosenberg on 1/24/24.
//

import SwiftUI

// This view modifier takes a list of SF Symbols systemImage names
// and lays out as the largest frame needed to hold any of those
// images.

extension View {
    func frameForLargestSymbol(symbols: [String],
                               alignment: Alignment = .center,
                               font: Font? = nil,
                               scale: Image.Scale? = nil) -> some View {
        modifier(LargestSymbolModifier(symbols: symbols, alignment: alignment, font: font, scale: scale))
    }
}

private struct LargestSymbolModifier: ViewModifier {
    let symbols: [String]
    let alignment: Alignment
    var font: Font?
    var scale: Image.Scale?

    func body(content: Content) -> some View {
        ZStack(alignment: alignment) {
            content
            LargestSymbolView(symbols: symbols, alignment: alignment, font: font, scale: scale)
        }
    }
}

extension View {
    @ViewBuilder
    func ifCondition<TrueContent: View>(_ condition: Bool, then trueContent: (Self) -> TrueContent) -> some View {
        if condition {
            trueContent(self)
        } else {
            self
        }
    }
}

private struct LargestSymbolView: View {
    var symbols : [String]
    var alignment: Alignment = .center
    var font: Font?
    var scale: Image.Scale?
    
    @State private var itemSize = CGSize.zero
    
    var body: some View {
        ZStack(alignment: alignment) {
            ForEach(Array(symbols), id: \.self) { item in
                Image(systemName: item)
                    .ifCondition(font != nil) { image in
                        image.font(font)
                    }
                    .ifCondition(scale != nil) { image in
                        image.imageScale(scale.unsafelyUnwrapped)
                    }
                .background(GeometryReader {
                    Color.clear.preference(key: ItemSize.self,
                                           value: $0.frame(in: .local).size)
                })
                .hidden()
            }
        }.onPreferenceChange(ItemSize.self) {
            itemSize = $0
            //print("size is now \(itemSize.width),\(itemSize.height)")
        }
    }
}

private struct ItemSize: PreferenceKey {
    typealias Value = CGSize

    static var defaultValue: CGSize { .zero }
    static func reduce(value: inout Value, nextValue: () -> Value) {
        let next = nextValue()
        value = CGSize(width: max(value.width,next.width),
                       height: max(value.height,next.height))
    }
}

#Preview {
    LargestSymbolView(symbols: ["speaker.slash.fill",
                                "speaker.wave.1.fill",
                                "speaker.wave.2.fill",
                                "speaker.wave.3.fill"],
                      alignment: .leading)
}