import Library
import SwiftUI

/// Bodies, stars, nebulae and galaxies at true relative size. Zoom with the slider or a pinch;
/// objects between 1/100 of the shown width and the full width are drawn side by side.
struct ScaleScreen: View {
    var ink: Color
    var accent: Color
    /// log10 of the width shown, in metres.
    @State private var exponent = 7.4
    @State private var pinchStart: Double?
    @State private var selected: LibraryPage?

    private let range = 2.5...27.0

    private var width: Double { pow(10, exponent) }

    /// Zooms by a factor of ten per tap, snapping to the nearest whole power of ten first.
    private func zoomButton(_ symbol: String, _ label: String, by step: Double) -> some View {
        Button {
            withAnimation(.easeInOut(duration: 0.35)) {
                let snapped = step < 0 ? ceil(exponent) - 1 : floor(exponent) + 1
                exponent = min(max(snapped, range.lowerBound), range.upperBound)
            }
        } label: {
            Image(systemName: symbol).font(.title3).frame(width: 48, height: 48)
                .background(ink.opacity(0.1), in: Circle())
        }
        .buttonStyle(.plain)
        .accessibilityLabel(label)
        .disabled(step < 0 ? exponent <= range.lowerBound : exponent >= range.upperBound)
    }

    /// The width to two significant figures, for the label.
    private var roundedWidth: Double {
        let p = pow(10, floor(exponent) - 1)
        return (width / p).rounded() * p
    }

    private var shown: [ScaleObject] {
        Library.scaleObjects.filter { $0.meters <= width && $0.meters >= width / 100 }
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 16) {
            Text("Width shown: \(Library.formatSize(roundedWidth))").font(.subheadline.monospacedDigit()).dimmed(0.8)
            GeometryReader { geo in
                let side = geo.size.width
                ScrollView(.horizontal, showsIndicators: false) {
                    HStack(alignment: .bottom, spacing: 16) {
                        if shown.isEmpty {
                            Text("Nothing in the Library at this scale.").font(.footnote).dimmed(0.6)
                        }
                        ForEach(shown) { o in
                            let d = max(o.meters / width * side, 2)
                            Button {
                                selected = o.page.flatMap { Library.page(id: $0) }
                            } label: {
                                VStack(spacing: 6) {
                                    Circle().fill(o.page == nil ? ink.opacity(0.18) : (Color(hex: o.page.flatMap { Library.page(id: $0) }?.drawing?.color) ?? ink.opacity(0.55)))
                                        .overlay(Circle().stroke(ink.opacity(0.5), lineWidth: 0.5))
                                        .frame(width: d, height: d)
                                    Text(o.name).font(.caption2).lineLimit(1)
                                    Text(Library.formatSize(o.meters)).font(.caption2.monospacedDigit()).dimmed(0.6)
                                }
                                .frame(minWidth: 64)
                            }
                            .buttonStyle(.plain)
                            .disabled(o.page == nil)
                            .accessibilityLabel("\(o.name), \(Library.formatSize(o.meters))")
                        }
                    }
                    .frame(minHeight: geo.size.height, alignment: .bottom)
                    .padding(.horizontal, 4)
                }
                .defaultScrollAnchor(.trailing)
                .scrollClipDisabled()
            }
            .frame(maxHeight: .infinity)
            .gesture(MagnifyGesture()
                .onChanged { g in
                    if pinchStart == nil { pinchStart = exponent }
                    exponent = min(max(pinchStart! - log10(g.magnification), range.lowerBound), range.upperBound)
                }
                .onEnded { _ in pinchStart = nil })
            HStack(spacing: 12) {
                zoomButton("plus.magnifyingglass", "Zoom in", by: -1)
                Slider(value: $exponent, in: range) { Text("Width shown") }
                    .accessibilityValue(Library.formatSize(roundedWidth))
                zoomButton("minus.magnifyingglass", "Zoom out", by: 1)
            }
            Text("Each tap of + or − is a factor of ten. You can also drag the slider or pinch. Objects without a Library page are drawn faint.")
                .font(.caption2).dimmed(0.5)
        }
        .padding(20)
        .foregroundStyle(ink)
        .tint(accent)
        .background(Color.black.ignoresSafeArea())
        .navigationTitle("Scale of the universe")
        .navigationBarTitleDisplayMode(.inline)
        .sheet(item: $selected) { page in NavigationStack { LibraryPageView(page: page) } }
    }
}