Pulse/Sources/PulseUI/Views/TimingView.swift

// The MIT License (MIT)
//
// Copyright (c) 2020–2022 Alexander Grebenyuk (github.com/kean).

import SwiftUI

#if os(iOS) || os(macOS) || os(tvOS)

struct TimingView: View {
    let viewModel: TimingViewModel

    var body: some View {
#if os(tvOS)
        List(viewModel.sections) {
            TimingSectionView(viewModel: $0, parent: viewModel)
        }.frame(maxWidth: 1000)
#else
        VStack(spacing: 16) {
            ForEach(viewModel.sections) {
                TimingSectionView(viewModel: $0, parent: viewModel)
            }
        }
#endif
    }
}

private struct TimingSectionView: View {
    let viewModel: TimingRowSectionViewModel
    let parent: TimingViewModel

    var body: some View {
        VStack(spacing: 6) {
            HStack {
                Text(viewModel.title)
                    .font(.subheadline)
                    .lineLimit(1)
                    .foregroundColor(viewModel.isHeader ? .secondary : .primary)
                Spacer()
            }.padding(.top, viewModel.isHeader ? 16 : 0)
            if viewModel.isHeader {
                Divider()
            }
            if !viewModel.items.isEmpty {
                ForEach(viewModel.items) {
                    TimingRowView(viewModel: $0, parent: parent)
                }
            }
        }
    }
}

private struct TimingRowView: View {
    let viewModel: TimingRowViewModel
    let parent: TimingViewModel

#if os(tvOS)
    let barHeight: CGFloat = 20
#else
    let barHeight: CGFloat = 14
#endif

    @Environment(\.sizeCategory) var sizeCategory

    var body: some View {
        HStack(alignment: .center, spacing: 12) {
            ZStack(alignment: .leading) {
                makeTitle(viewModel.title)
                makeTitle(parent.longestTitle).invisible() // Calculates width
            }.layoutPriority(1)

            bar
            
            ZStack(alignment: .leading) {
                makeValue(viewModel.value)
                makeValue(parent.longestValue).invisible() // Calculates width
            }.layoutPriority(1)
        }
    }

    private var bar: some View {
        GeometryReader { proxy in
            let start = max(0, min(1, viewModel.start))
            let length = min(1 - start, viewModel.length)
            RoundedRectangle(cornerRadius: 2 * sizeCategory.scale)
                .fill(Color(viewModel.color))
                .frame(width: max(2, proxy.size.width * length))
                .padding(.leading, proxy.size.width * start)
        }
        .frame(height: barHeight * sizeCategory.scale)

    }

    private func makeTitle(_ text: String) -> some View {
        Text(text)
            .font(.footnote)
            .lineLimit(1)
            .foregroundColor(.secondary)
    }

    private func makeValue(_ text: String) -> some View {
        Text(text)
            .font(.system(.caption, design: .monospaced))
            .lineLimit(1)
            .foregroundColor(.secondary)
    }
}

final class TimingViewModel {
    let sections: [TimingRowSectionViewModel]

    init(sections: [TimingRowSectionViewModel]) {
        self.sections = sections
    }

    private(set) lazy var longestTitle: String = {
        allRows.map(\.title).max { $0.count < $1.count } ?? ""
    }()

    private(set) lazy var longestValue: String = {
        allRows.map(\.value).max { $0.count < $1.count } ?? ""
    }()

    private var allRows: [TimingRowViewModel] {
        sections.flatMap(\.items)
    }
}

final class TimingRowSectionViewModel: Identifiable {
    let title: String
    let items: [TimingRowViewModel]
    var isHeader = false

    var id: ObjectIdentifier { ObjectIdentifier(self) }

    init(title: String, items: [TimingRowViewModel], isHeader: Bool = false) {
        self.title = title
        self.items = items
        self.isHeader = isHeader
    }
}

final class TimingRowViewModel: Identifiable {
    let title: String
    let value: String
    let color: UXColor
    // [0, 1]
    let start: CGFloat
    // [0, 1]
    let length: CGFloat

    var id: ObjectIdentifier { ObjectIdentifier(self) }

    init(title: String, value: String, color: UXColor, start: CGFloat, length: CGFloat) {
        self.title = title
        self.value = value
        self.color = color
        self.start = start
        self.length = length
    }
}

#if DEBUG
struct TimingView_Previews: PreviewProvider {
    static var previews: some View {
        TimingView(viewModel: .init(sections: mockSections))
            .padding()
#if !os(tvOS)
            .previewLayout(.sizeThatFits)
#endif
    }
}

private let mockSections = [
    TimingRowSectionViewModel(title: "Response", items: [
        TimingRowViewModel(title: "Scheduling", value: "0.01ms", color: .systemBlue, start: 0.0, length: 0.001),
        TimingRowViewModel(title: "Waiting", value: "41.2ms", color: .systemBlue, start: 0.0, length: 0.4),
        TimingRowViewModel(title: "Download", value: "0.2ms", color: .systemRed, start: 0.4, length: 0.05)
    ]),
    TimingRowSectionViewModel(title: "Cache Lookup", items: [
        TimingRowViewModel(title: "Waiting", value: "50.2ms", color: .systemYellow, start: 0.45, length: 0.3),
        TimingRowViewModel(title: "Download", value: "30.0ms", color: .systemGreen, start: 0.75, length: 100.0)
    ])
]
#endif

#endif