//  Appearance.swift
//  GreenshotMac
//
//  Appearance handling and the shared material/shape vocabulary for the UI.
//  Everything here follows the system appearance by default; the user can override it.

import AppKit

enum AppearanceMode: String, CaseIterable {
    case system
    case light
    case dark

    var title: String {
        switch self {
        case .system: return "Match system"
        case .light: return "Light"
        case .dark: return "Dark"
        }
    }

    var nsAppearance: NSAppearance? {
        switch self {
        case .system: return nil                      // nil = inherit from macOS
        case .light: return NSAppearance(named: .aqua)
        case .dark: return NSAppearance(named: .darkAqua)
        }
    }
}

@MainActor
enum Theme {

    /// Applies the user's appearance choice to the whole app.
    static func apply() {
        NSApp.appearance = Configuration.shared.appearanceMode.nsAppearance
    }

    // MARK: - Shapes

    /// Corner radius used for panels and preview wells.
    /// macOS 27 moved back towards squarer, more consistent radii than Tahoe used.
    ///
    /// These are `nonisolated` because default argument expressions are evaluated
    /// outside the main actor, and `panelRadius` is used as one below.
    nonisolated static let panelRadius: CGFloat = 10
    /// Corner radius used for buttons and small chips.
    nonisolated static let controlRadius: CGFloat = 6

    // MARK: - Materials

    /// A translucent backdrop that picks up whatever is behind the window and adapts
    /// to light/dark automatically. Used for toolbars, style bars and dialog chrome.
    ///
    /// On macOS 26 the system materials render with the Liquid Glass treatment; on earlier
    /// systems they fall back to the classic vibrancy blur. Either way the colours come from
    /// the system rather than being hard coded, so an appearance override is respected.
    static func backdrop(material: NSVisualEffectView.Material = .headerView,
                         blending: NSVisualEffectView.BlendingMode = .withinWindow,
                         radius: CGFloat = 0) -> NSVisualEffectView {
        let view = NSVisualEffectView()
        view.material = material
        view.blendingMode = blending
        view.state = .followsWindowActiveState
        view.translatesAutoresizingMaskIntoConstraints = false
        if radius > 0 {
            view.wantsLayer = true
            view.layer?.cornerRadius = radius
            view.layer?.cornerCurve = .continuous
            view.layer?.masksToBounds = true
        }
        return view
    }

    /// Fills a container with a child view, inset by `inset` on every edge.
    static func fill(_ child: NSView, in container: NSView, inset: CGFloat = 0) {
        child.translatesAutoresizingMaskIntoConstraints = false
        container.addSubview(child)
        NSLayoutConstraint.activate([
            child.leadingAnchor.constraint(equalTo: container.leadingAnchor, constant: inset),
            child.trailingAnchor.constraint(equalTo: container.trailingAnchor, constant: -inset),
            child.topAnchor.constraint(equalTo: container.topAnchor, constant: inset),
            child.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: -inset)
        ])
    }

    /// A hairline divider that reads correctly in both appearances.
    ///
    /// `axis` is the direction the line runs. A separator NSBox has no intrinsic size
    /// across its thin edge, so that dimension must be pinned or Auto Layout is free to
    /// stretch the divider over the content next to it.
    static func divider(axis: NSUserInterfaceLayoutOrientation = .horizontal) -> NSBox {
        let box = NSBox()
        box.boxType = .separator
        box.translatesAutoresizingMaskIntoConstraints = false
        switch axis {
        case .horizontal:
            box.heightAnchor.constraint(equalToConstant: 1).isActive = true
        case .vertical:
            box.widthAnchor.constraint(equalToConstant: 1).isActive = true
        @unknown default:
            break
        }
        return box
    }

    /// True when the person has dialled transparency down, either with the macOS 27
    /// transparency slider or the Reduce Transparency accessibility setting.
    static var prefersOpaqueSurfaces: Bool {
        NSWorkspace.shared.accessibilityDisplayShouldReduceTransparency
    }

    /// Wraps `content` in a Liquid Glass panel on macOS 26 and later, falling back to a
    /// vibrancy backdrop on older systems. Used for floating surfaces such as the
    /// destination picker's preview well — not for toolbars, which macOS 27 wants to read
    /// as solid bars rather than floating glass.
    static func panel(_ content: NSView,
                      radius: CGFloat = panelRadius,
                      material: NSVisualEffectView.Material = .underPageBackground,
                      inset: CGFloat = 0) -> NSView {
        if #available(macOS 26.0, *), !prefersOpaqueSurfaces {
            let glass = NSGlassEffectView()
            glass.translatesAutoresizingMaskIntoConstraints = false
            glass.cornerRadius = radius
            content.translatesAutoresizingMaskIntoConstraints = false
            glass.contentView = content
            return glass
        }
        let view = backdrop(material: material, radius: radius)
        fill(content, in: view, inset: inset)
        return view
    }

    /// The bezel style for a chrome button: Liquid Glass where the system has it.
    static func styleButton(_ button: NSButton) {
        if #available(macOS 26.0, *) {
            button.bezelStyle = .glass
        } else {
            button.bezelStyle = .texturedRounded
        }
    }

    /// Groups nearby glass elements so the system can merge them into one shape
    /// instead of rendering each separately.
    static func glassGroup(_ views: [NSView]) -> NSView? {
        guard #available(macOS 26.0, *), !prefersOpaqueSurfaces else { return nil }
        let container = NSGlassEffectContainerView()
        container.translatesAutoresizingMaskIntoConstraints = false
        let stack = NSStackView(views: views)
        stack.orientation = .horizontal
        stack.spacing = 4
        container.contentView = stack
        return container
    }

    // MARK: - Window chrome

    /// Gives a window the unified, translucent titlebar used throughout the app.
    static func styleWindowChrome(_ window: NSWindow, fullSizeContent: Bool = false) {
        window.titlebarAppearsTransparent = true
        window.isMovableByWindowBackground = true
        if fullSizeContent {
            window.styleMask.insert(.fullSizeContentView)
        }
    }
}

extension Notification.Name {
    /// Posted when the appearance override changes, so open windows can re-apply it.
    static let appearanceChanged = Notification.Name("GreenshotMacAppearanceChanged")
}