import SwiftUI

#if canImport(UIKit)
    import UIKit
#endif

/// Mask-Editor: Bild anzeigen, mit Drag-Gesten Rechtecke zeichnen, jede
/// Region mit Label versehen. Coordinaten 0..1 relativ zur Bild-Größe.
///
/// Output binding ist `regions`. Caller serialisiert via `MaskRegions.encode()`.
struct MaskEditorView: View {
    let image: PlatformImage
    @Binding var regions: [MaskRegion]

    @State private var dragStart: CGPoint?
    @State private var dragEnd: CGPoint?
    @State private var nextIdCounter: Int = 0

    var body: some View {
        VStack(alignment: .leading, spacing: 12) {
            Text("Tippe und ziehe auf das Bild, um eine Maske zu erstellen.")
                .font(.caption)
                .foregroundStyle(CardsTheme.mutedForeground)

            imageCanvas
                .aspectRatio(image.size.width / max(image.size.height, 1), contentMode: .fit)
                .frame(maxWidth: .infinity)
                .clipShape(RoundedRectangle(cornerRadius: 8))

            if regions.isEmpty {
                Text("Noch keine Maske")
                    .font(.caption)
                    .foregroundStyle(CardsTheme.mutedForeground)
            } else {
                ForEach(regions) { region in
                    maskRow(region: region)
                }
            }
        }
    }

    private var imageCanvas: some View {
        GeometryReader { geo in
            ZStack(alignment: .topLeading) {
                #if canImport(UIKit)
                    Image(uiImage: image).resizable().aspectRatio(contentMode: .fit)
                #else
                    Image(nsImage: image).resizable().aspectRatio(contentMode: .fit)
                #endif

                ForEach(regions) { region in
                    overlayRect(for: region, in: geo.size)
                }

                if let dragStart, let dragEnd {
                    let rect = normalizedRect(from: dragStart, to: dragEnd)
                    Rectangle()
                        .stroke(CardsTheme.warning, lineWidth: 2)
                        .background(Rectangle().fill(CardsTheme.warning.opacity(0.2)))
                        .frame(width: rect.width, height: rect.height)
                        .offset(x: rect.minX, y: rect.minY)
                }
            }
            .contentShape(Rectangle())
            .gesture(
                DragGesture(minimumDistance: 4)
                    .onChanged { value in
                        if dragStart == nil { dragStart = value.startLocation }
                        dragEnd = value.location
                    }
                    .onEnded { value in
                        commitDrag(start: value.startLocation, end: value.location, in: geo.size)
                    }
            )
        }
    }

    private func overlayRect(for region: MaskRegion, in size: CGSize) -> some View {
        Rectangle()
            .fill(CardsTheme.primary.opacity(0.6))
            .frame(width: region.w * size.width, height: region.h * size.height)
            .offset(x: region.x * size.width, y: region.y * size.height)
            .overlay(
                Text(region.label?.isEmpty == false ? region.label! : region.id)
                    .font(.caption2.weight(.bold))
                    .foregroundStyle(CardsTheme.primaryForeground)
                    .padding(2)
                    .offset(x: region.x * size.width + 2, y: region.y * size.height + 2),
                alignment: .topLeading
            )
    }

    private func maskRow(region: MaskRegion) -> some View {
        HStack(spacing: 8) {
            Image(systemName: "square.dashed")
                .foregroundStyle(CardsTheme.primary)
            TextField("Label (optional)", text: Binding(
                get: { region.label ?? "" },
                set: { newValue in updateLabel(for: region.id, to: newValue) }
            ))
            .textFieldStyle(.roundedBorder)
            Button(role: .destructive) {
                regions.removeAll { $0.id == region.id }
            } label: {
                Image(systemName: "trash")
                    .foregroundStyle(CardsTheme.error)
            }
            .buttonStyle(.plain)
        }
    }

    private func updateLabel(for id: String, to value: String) {
        guard let idx = regions.firstIndex(where: { $0.id == id }) else { return }
        let old = regions[idx]
        regions[idx] = MaskRegion(id: old.id, x: old.x, y: old.y, w: old.w, h: old.h, label: value)
    }

    private func normalizedRect(from start: CGPoint, to end: CGPoint) -> CGRect {
        let x = min(start.x, end.x)
        let y = min(start.y, end.y)
        let w = abs(end.x - start.x)
        let h = abs(end.y - start.y)
        return CGRect(x: x, y: y, width: w, height: h)
    }

    private func commitDrag(start: CGPoint, end: CGPoint, in size: CGSize) {
        defer {
            dragStart = nil
            dragEnd = nil
        }
        let rect = normalizedRect(from: start, to: end)
        // Mindestgröße 1% der Bildkante — Tap-Klicks ignorieren
        guard rect.width > size.width * 0.01, rect.height > size.height * 0.01 else { return }
        nextIdCounter += 1
        let id = String(format: "m%03d", nextIdCounter)
        let normalized = MaskRegion(
            id: id,
            x: rect.minX / size.width,
            y: rect.minY / size.height,
            w: rect.width / size.width,
            h: rect.height / size.height,
            label: nil
        )
        regions.append(normalized)
    }
}