import SwiftUI

public protocol TextLabelStyle {

  associatedtype Body: View
  typealias Configuration = TextLabelConfiguration

  func makeBody(configuration: Self.Configuration) -> Self.Body
}

extension TextLabelStyle {
  public func combining<Other: TextLabelStyle>(_ style: Other) -> AnyTextLabelStyle {
    AnyTextLabelStyle(style: self).combining(style)
  }
}

public struct TextLabelConfiguration {

  /// A type erased label for a text label.
  public struct Label: View {
    public var body: AnyView

    public init<Content: View>(content: Content) {
      body = AnyView(content)
    }
  }

  public let label: TextLabelConfiguration.Label
}

public struct AnyTextLabelStyle: TextLabelStyle {
  private var _makeBody: (Configuration) -> AnyView

  internal init(makeBody: @escaping (Configuration) -> AnyView) {
    self._makeBody = makeBody
  }

  public init<S: TextLabelStyle>(style: S) {
    self._makeBody = { configuration in
      AnyView(style.makeBody(configuration: configuration))
    }
  }

  public func makeBody(configuration: Configuration) -> some View {
    _makeBody(configuration)
  }

  public func combining<S: TextLabelStyle>(_ style: S) -> Self {
    Self.init { configuration in
      AnyView(
        self.makeBody(
          configuration: TextLabelConfiguration(
            label: .init(content: style.makeBody(configuration: configuration))
          )
        ))
    }
  }
}

public struct AutomaticTextLabelStyle: TextLabelStyle {
  public func makeBody(configuration: Configuration) -> some View {
    configuration.label
  }
}

private struct TextLabelStyleKey: EnvironmentKey {
  static let defaultValue = AnyTextLabelStyle(style: AutomaticTextLabelStyle())
}

private struct SectionHeaderLabelStyleKey: EnvironmentKey {
  static let defaultValue = AnyTextLabelStyle(style: AutomaticTextLabelStyle())
}

extension EnvironmentValues {
  public var textLabelStyle: AnyTextLabelStyle {
    get { self[TextLabelStyleKey.self] }
    set { self[TextLabelStyleKey.self] = newValue }
  }

  public var sectionHeaderLabelStyle: AnyTextLabelStyle {
    get { self[SectionHeaderLabelStyleKey.self] }
    set { self[SectionHeaderLabelStyleKey.self] = newValue }
  }
}

public struct FontTextLabelStyle: TextLabelStyle {
  let font: Font?
  let fontWeight: Font.Weight?

  public func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .font(font)
      .fontWeight(fontWeight)
  }
}

public struct ColoredTextLabelStyle: TextLabelStyle {

  let primary: Color
  let secondary: Color?
  let tertiary: Color?

  @ViewBuilder
  public func makeBody(configuration: Configuration) -> some View {
    switch (secondary, tertiary) {
    case let (.some(secondary), .some(tertiary)):
      configuration.label.foregroundStyle(primary, secondary, tertiary)
    case let (.some(secondary), .none):
      configuration.label.foregroundStyle(primary, secondary)
    case let (.none, .some(tertiary)):
      configuration.label.foregroundStyle(primary, tertiary)
    case (.none, .none):
      configuration.label.foregroundStyle(primary)
    }
  }

  public func font(_ font: Font? = nil, fontWeight: Font.Weight? = nil) -> AnyTextLabelStyle {
    self.combining(.font(font, fontWeight: fontWeight))
  }
}

extension TextLabelStyle where Self == AutomaticTextLabelStyle {
  public static var automatic: Self {
    .init()
  }
}

extension TextLabelStyle where Self == FontTextLabelStyle {
  public static func font(_ font: Font? = nil, fontWeight: Font.Weight? = nil) -> Self {
    .init(font: font, fontWeight: fontWeight)
  }

  public static var heavyTitle2: Self {
    .font(.title2, fontWeight: .heavy)
  }
}

extension TextLabelStyle where Self == ColoredTextLabelStyle {

  public static func colored(_ color: Color) -> Self {
    .init(primary: color, secondary: nil, tertiary: nil)
  }

  public static func colored(_ primary: Color, _ secondary: Color, _ tertiary: Color? = nil) -> Self {
    .init(primary: primary, secondary: secondary, tertiary: tertiary)
  }

  public static var secondary: Self {
    self.colored(.secondary)
  }
}

extension AnyTextLabelStyle {

  public static var boldSecondary: AnyTextLabelStyle {
    ColoredTextLabelStyle(primary: .secondary, secondary: nil, tertiary: nil)
      .combining(.font(fontWeight: .bold))
  }

}

public struct PillViewTextLabelStyle: TextLabelStyle {
  
  let labelColor: Color?
  let pillColor: Color
  
  public func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .foregroundStyle(labelColor ?? .primary)
      .background {
        Capsule()
          .foregroundStyle(pillColor)
      }
  }
}

extension TextLabelStyle where Self == PillViewTextLabelStyle {
  public static func pill(
    pillColor: Color,
    labelColor: Color? = nil
  ) -> Self {
    .init(labelColor: labelColor, pillColor: pillColor)
  }
}

extension View {

  public func textLabelStyle(_ style: AnyTextLabelStyle) -> some View {
    environment(\.textLabelStyle, style)
  }

  public func textLabelStyle<S: TextLabelStyle>(_ style: S) -> some View {
    textLabelStyle(AnyTextLabelStyle(style: style))
  }

  public func sectionHeaderLabelStyle<S: TextLabelStyle>(_ style: S) -> some View {
    environment(\.sectionHeaderLabelStyle, AnyTextLabelStyle(style: style))
  }
}