import SwiftUI

public struct AIButtonStyle: ButtonStyle {
  public static let pressedScale: CGFloat = 0.97

  public enum Kind: Hashable {
    case primary
    case secondary
    case danger

    var foregroundColor: Color { foregroundColor(isEnabled: true) }

    var backgroundColor: Color { backgroundColor(isEnabled: true) }

    func foregroundColor(isEnabled: Bool) -> Color {
      switch self {
      case .primary: return isEnabled ? AITheme.onPrimary : AITheme.muted
      case .danger: return isEnabled ? AITheme.onDanger : AITheme.muted
      case .secondary: return isEnabled ? AITheme.ink : AITheme.muted
      }
    }

    func backgroundColor(isEnabled: Bool) -> Color {
      if isEnabled { return kindBackground }
      // 禁用态：实心主色按钮保留主色淡版，其余退回中性灰。
      return self == .primary
        ? AITheme.primary.opacity(AITheme.disabledFillOpacity)
        : AITheme.control
    }

    private var kindBackground: Color {
      switch self {
      case .primary: return AITheme.primary
      case .secondary: return AITheme.control
      case .danger: return AITheme.danger
      }
    }

    /// 禁用态下主按钮必须还能看出"这是主行动"。
    /// 之前三种 kind 禁用后都塌成同一块 control 灰，表单里"取消"和"保存"长得一模一样，
    /// 用户只能靠文字猜哪个是提交。这里让实心主色按钮改用同色相淡填充 + 描边，灰底次按钮不套。
    var usesTintedDisabledTreatment: Bool {
      self == .primary
    }
  }

  public enum Size: Hashable {
    case compact
    case regular
    case large
    case icon
    case toolbar
    case toolbarInline
  }

  private let kind: Kind
  private let size: Size
  private let fixedWidthRequest: CGFloat?
  let fillsWidth: Bool
  @Environment(\.isEnabled) private var isEnabled

  public init(
    kind: Kind = .secondary,
    size: Size = .regular,
    fixedWidth: CGFloat? = nil,
    fillsWidth: Bool = false
  ) {
    self.kind = kind
    self.size = size
    self.fixedWidthRequest = fixedWidth
    self.fillsWidth = fillsWidth
  }

  public func makeBody(configuration: Configuration) -> some View {
    let height: CGFloat =
      switch size {
      case .compact: AITheme.compactButtonHeight
      case .large: AITheme.largeButtonHeight
      case .icon: AITheme.iconButtonSize
    case .regular: AITheme.buttonHeight
    case .toolbar: AITheme.toolbarButtonHeight
    case .toolbarInline: AITheme.toolbarButtonHeight
      }

    let isTintedDisabled = kind.usesTintedDisabledTreatment && !isEnabled

    configuration.label
      .labelStyle(.titleAndIcon)
      .font(
        .system(size: size == .compact || size == .toolbarInline ? 15 : 16, weight: .semibold)
      )
      .lineLimit(1)
      .foregroundStyle(kind.foregroundColor(isEnabled: isEnabled))
      .padding(.horizontal, fixedWidth == nil ? (kind == .secondary ? 12 : 14) : 0)
      .frame(
        minWidth: (!fillsWidth && fixedWidth == nil) ? minimumWidth : 0,
        minHeight: height
      )
      .frame(maxWidth: fillsWidth ? .infinity : nil)
      .frame(width: fixedWidth)
      .background(
        // 主色面用纯色。之前的 primaryTop/primaryBottom 竖向渐变在系统里会被合成成灰紫，
        // 实测 #3B82F6 掉到 #6B81CA，整片按钮发脏。
        AnyShapeStyle(kind.backgroundColor(isEnabled: isEnabled))
      )
      .shadow(
        color: (kind == .secondary || isTintedDisabled) ? .clear : .black.opacity(0.10),
        radius: 12,
        x: 0,
        y: 5
      )
      .clipShape(
        RoundedRectangle(
          cornerRadius: cornerRadius,
          style: .continuous
        )
      )
      .overlay {
        RoundedRectangle(
          cornerRadius: cornerRadius,
          style: .continuous
        )
        .strokeBorder(
          isTintedDisabled
            ? AITheme.primary.opacity(AITheme.disabledStrokeOpacity)
            : size == .toolbarInline && kind == .primary
              ? AITheme.primary.opacity(0.28)
              : (kind == .secondary || !isEnabled ? AITheme.line : .clear)
        )
      }
      .scaleEffect(configuration.isPressed ? Self.pressedScale : 1)
      .opacity(configuration.isPressed ? 0.82 : 1)
  }

  /// 工具栏里的图标按钮需要更小的圆角，否则 34pt 方块看起来像被切过。
  private var cornerRadius: CGFloat {
    switch size {
    case .toolbarInline: return AITheme.toolbarButtonHeight / 2
    case .icon: return AITheme.iconButtonRadius
    default: return AITheme.buttonRadius
    }
  }

  private var minimumWidth: CGFloat {
    switch size {
    case .compact: return AITheme.compactButtonMinWidth
    case .regular: return AITheme.regularButtonMinWidth
    case .large: return 92
    case .icon: return AITheme.iconButtonSize
    case .toolbar, .toolbarInline: return AITheme.toolbarButtonMinWidth
    }
  }

  private var fixedWidth: CGFloat? {
    fixedWidthRequest ?? (size == .icon ? AITheme.iconButtonSize : (size == .toolbar ? AITheme.toolbarButtonWidth : nil))
  }
}