import AppKit
import SwiftUI

/// A shape with a fill, layered drop shadows, layered inset shadows and a hairline edge: a physical part.
public struct PhysicalSurface: View {
    private let fill: AnyShapeStyle
    private let cornerRadius: CGFloat
    private let shadows: [ShadowLayer]
    private let edge: Color?
    @Environment(\.colorScheme) private var scheme

    public init(fill: AnyShapeStyle, cornerRadius: CGFloat, shadows: [ShadowLayer], edge: Color? = Palette.lineSeamDark) {
        self.fill = fill
        self.cornerRadius = cornerRadius
        self.shadows = shadows
        self.edge = edge
    }

    public var body: some View {
        let shape = RoundedRectangle(cornerRadius: cornerRadius, style: .circular)
        ZStack {
            shadows.filter { !$0.inset }.reduce(AnyView(shape.fill(fill))) { view, layer in
                AnyView(view.shadow(color: layer.color(scheme), radius: layer.blur / 2, x: layer.x, y: layer.y))
            }
            ForEach(Array(shadows.filter(\.inset).enumerated()), id: \.offset) { _, layer in
                InsetShadow(layer: layer, cornerRadius: cornerRadius)
            }
            if let edge {
                shape.strokeBorder(edge, lineWidth: Border.hairline)
            }
        }
    }
}

/// A shadow cast inwards from the edge of a rounded rectangle.
struct InsetShadow: View {
    let layer: ShadowLayer
    let cornerRadius: CGFloat
    @Environment(\.colorScheme) private var scheme

    var body: some View {
        Canvas { context, size in
            let rect = CGRect(origin: .zero, size: size)
            context.clip(to: Path(roundedRect: rect, cornerRadius: cornerRadius))
            context.drawLayer { inner in
                inner.addFilter(.blur(radius: layer.blur / 2))
                let hole = rect.insetBy(dx: layer.spread, dy: layer.spread).offsetBy(dx: layer.x, dy: layer.y)
                var frame = Path(rect.insetBy(dx: -size.width, dy: -size.height))
                frame.addPath(Path(roundedRect: hole, cornerRadius: max(0, cornerRadius - layer.spread)))
                inner.fill(frame, with: .color(layer.color(scheme)), style: FillStyle(eoFill: true))
            }
        }
        .allowsHitTesting(false)
    }
}

/// Faceplate of matt plastic, sitting above the chassis.
public struct PanelBackground: View {
    public init() {}
    public var body: some View {
        PhysicalSurface(fill: AnyShapeStyle(Palette.surfacePanel), cornerRadius: Radius.none, shadows: Shadows.panel)
    }
}

/// A recessed area (input fields, display windows).
public struct WellBackground: View {
    public init() {}
    public var body: some View {
        PhysicalSurface(fill: AnyShapeStyle(Palette.surfaceWell), cornerRadius: Radius.none, shadows: Shadows.well)
    }
}

/// Dark display glass for the counter.
public struct DisplayBackground: View {
    public init() {}
    public var body: some View {
        PhysicalSurface(fill: AnyShapeStyle(Palette.surfaceDisplay), cornerRadius: Radius.none, shadows: Shadows.well)
    }
}

/// Cassette-label cream, for lists of transcripts and dictionary entries.
public struct PaperBackground: View {
    public init() {}
    public var body: some View {
        PhysicalSurface(fill: AnyShapeStyle(Palette.surfacePaper), cornerRadius: Radius.none, shadows: Shadows.well)
    }
}

/// An engraved groove: a dark line with a light line below it.
public struct SeamDivider: View {
    public init() {}
    public var body: some View {
        VStack(spacing: 0) {
            Rectangle().fill(Palette.lineSeamDark).frame(height: Border.hairline)
            Rectangle().fill(Palette.lineSeamLight).frame(height: Border.hairline)
        }
        .accessibilityHidden(true)
    }
}

/// Small capitals silkscreen label.
public struct SilkLabel: View {
    private let text: String
    private let style: TextStyle

    public init(_ text: String, style: TextStyle = Typography.label) {
        self.text = text
        self.style = style
    }

    public var body: some View {
        Text(text).textStyle(style).foregroundStyle(Palette.inkTertiary)
    }
}

/// Brushed aluminium: a vertical gradient with a horizontal grain.
public struct BrushedBackground: View {
    @Environment(\.colorScheme) private var scheme
    public init() {}

    public var body: some View {
        ZStack {
            LinearGradient(colors: [Palette.surfaceMetalHigh, Palette.surfaceMetalLow], startPoint: .top, endPoint: .bottom)
            Image(nsImage: scheme == .dark ? BrushedTexture.dark : BrushedTexture.light)
                .resizable(resizingMode: .tile)
        }
    }
}

enum BrushedTexture {
    private static let side = 256
    private static let gain = 2.2   // makes the token grain value visible as streak opacity

    static let light = make(grain: Texture.brushedGrainLight)
    static let dark = make(grain: Texture.brushedGrainDark)

    private struct SplitMix64: RandomNumberGenerator {
        var state: UInt64
        mutating func next() -> UInt64 {
            state &+= 0x9E37_79B9_7F4A_7C15
            var z = state
            z = (z ^ (z >> 30)) &* 0xBF58_476D_1CE4_E5B9
            z = (z ^ (z >> 27)) &* 0x94D0_49BB_1331_11EB
            return z ^ (z >> 31)
        }
    }

    /// A seeded grain: every row has its own brightness and pixels vary only slightly, which gives fine horizontal streaks.
    private static func make(grain: Double) -> NSImage {
        var rng = SplitMix64(state: 7)
        let rows = (0..<side).map { _ in Double.random(in: 0...1, using: &rng) }
        var pixels = [UInt8](repeating: 0, count: side * side * 4)
        for y in 0..<side {
            let row = rows[y]
            for x in 0..<side {
                let value = row * 0.9 + Double.random(in: 0...1, using: &rng) * 0.1
                let alpha = min(1, abs(value - 0.5) * 2 * grain * gain)
                let shade = value > 0.5 ? 1.0 : 0.0
                let index = (y * side + x) * 4
                let premultiplied = UInt8(shade * alpha * 255)
                pixels[index] = premultiplied
                pixels[index + 1] = premultiplied
                pixels[index + 2] = premultiplied
                pixels[index + 3] = UInt8(alpha * 255)
            }
        }
        let provider = CGDataProvider(data: Data(pixels) as CFData)!
        let image = CGImage(
            width: side, height: side, bitsPerComponent: 8, bitsPerPixel: 32, bytesPerRow: side * 4,
            space: CGColorSpaceCreateDeviceRGB(),
            bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue),
            provider: provider, decode: nil, shouldInterpolate: false, intent: .defaultIntent)!
        return NSImage(cgImage: image, size: NSSize(width: side, height: side))
    }
}