import SwiftUI

/// An equatable description of SwiftUI `Text`. Useful for storing rich text in state for the
/// purpose of rendering in a view hierarchy.
///
/// Although `SwiftUI.Text` and `SwiftUI.LocalizedStringKey` are value types that conform to
/// `Equatable`, their `==` do not return `true` when used with seemingly equal values. If we were
/// to naively store these values in state, our tests may begin to fail.
///
/// `TextState` solves this problem by providing an interface similar to `SwiftUI.Text` that can be
/// held in state and asserted against.
///
/// Let's say you wanted to hold some dynamic, styled text content in your app state. You could use
/// `TextState`:
///
///     struct AppState: Equatable {
///       var label: TextState
///     }
///
/// Your reducer can then assign a value to this state using an API similar to that of
/// `SwiftUI.Text`.
///
///     state.label = TextState("Hello, ") + TextState(name).bold() + TextState("!")
///
/// And your view store can render it directly:
///
///     var body: some View {
///       WithViewStore(self.store) { viewStore in
///         viewStore.label
///       }
///     }
///
/// Certain SwiftUI APIs, like alerts and action sheets, take `Text` values and, not views. To
/// convert `TextState` to `SwiftUI.Text` for this purpose, you can use the `Text` initializer:
///
///     Alert(title: Text(viewStore.label))
///
/// The Composable Architecture comes with a few convenience APIs for alerts and action sheets that
/// wrap `TextState` under the hood. See `AlertState` and `ActionState` accordingly.
///
/// In the future, should `SwiftUI.Text` and `SwiftUI.LocalizedStringKey` reliably conform to
/// `Equatable`, `TextState` may be deprecated.
///
/// - Note: `TextState` does not support _all_ `LocalizedStringKey` permutations at this time
///   (interpolated `SwiftUI.Image`s, for example. `TextState` also uses reflection to determine
///   `LocalizedStringKey` equatability, so be mindful of edge cases.
public struct TextState: Equatable, Hashable {
  fileprivate var modifiers: [Modifier] = []
  fileprivate let storage: Storage

  fileprivate enum Modifier: Equatable, Hashable {
    case baselineOffset(CGFloat)
    case bold
    case font(Font?)
    case fontWeight(Font.Weight?)
    case foregroundColor(Color?)
    case italic
    case kerning(CGFloat)
    case strikethrough(active: Bool, color: Color?)
    case tracking(CGFloat)
    case underline(active: Bool, color: Color?)
  }

  fileprivate enum Storage: Equatable, Hashable {
    indirect case concatenated(TextState, TextState)
    case localized(LocalizedStringKey, tableName: String?, bundle: Bundle?, comment: StaticString?)
    case verbatim(String)

    static func == (lhs: Self, rhs: Self) -> Bool {
      switch (lhs, rhs) {
      case let (.concatenated(l1, l2), .concatenated(r1, r2)):
        return l1 == r1 && l2 == r2

      case let (.localized(lk, lt, lb, lc), .localized(rk, rt, rb, rc)):
        return lk.formatted(tableName: lt, bundle: lb, comment: lc)
          == rk.formatted(tableName: rt, bundle: rb, comment: rc)

      case let (.verbatim(lhs), .verbatim(rhs)):
        return lhs == rhs

      case let (.localized(key, tableName, bundle, comment), .verbatim(string)),
        let (.verbatim(string), .localized(key, tableName, bundle, comment)):
        return key.formatted(tableName: tableName, bundle: bundle, comment: comment) == string

      // NB: We do not attempt to equate concatenated cases.
      default:
        return false
      }
    }

    func hash(into hasher: inout Hasher) {
      enum Key {
        case concatenated
        case localized
        case verbatim
      }

      switch self {
      case let (.concatenated(first, second)):
        hasher.combine(Key.concatenated)
        hasher.combine(first)
        hasher.combine(second)

      case let .localized(key, tableName, bundle, comment):
        hasher.combine(Key.localized)
        hasher.combine(key.formatted(tableName: tableName, bundle: bundle, comment: comment))

      case let .verbatim(string):
        hasher.combine(Key.verbatim)
        hasher.combine(string)
      }
    }
  }
}

extension TextState {
  public init(verbatim content: String) {
    self.storage = .verbatim(content)
  }

  @_disfavoredOverload
  public init<S>(_ content: S) where S: StringProtocol {
    self.init(verbatim: String(content))
  }

  public init(
    _ key: LocalizedStringKey,
    tableName: String? = nil,
    bundle: Bundle? = nil,
    comment: StaticString? = nil
  ) {
    self.storage = .localized(key, tableName: tableName, bundle: bundle, comment: comment)
  }

  public static func + (lhs: Self, rhs: Self) -> Self {
    .init(storage: .concatenated(lhs, rhs))
  }

  public func baselineOffset(_ baselineOffset: CGFloat) -> Self {
    var `self` = self
    `self`.modifiers.append(.baselineOffset(baselineOffset))
    return `self`
  }

  public func bold() -> Self {
    var `self` = self
    `self`.modifiers.append(.bold)
    return `self`
  }

  public func font(_ font: Font?) -> Self {
    var `self` = self
    `self`.modifiers.append(.font(font))
    return `self`
  }

  public func fontWeight(_ weight: Font.Weight?) -> Self {
    var `self` = self
    `self`.modifiers.append(.fontWeight(weight))
    return `self`
  }

  public func foregroundColor(_ color: Color?) -> Self {
    var `self` = self
    `self`.modifiers.append(.foregroundColor(color))
    return `self`
  }

  public func italic() -> Self {
    var `self` = self
    `self`.modifiers.append(.italic)
    return `self`
  }

  public func kerning(_ kerning: CGFloat) -> Self {
    var `self` = self
    `self`.modifiers.append(.kerning(kerning))
    return `self`
  }

  public func strikethrough(_ active: Bool = true, color: Color? = nil) -> Self {
    var `self` = self
    `self`.modifiers.append(.strikethrough(active: active, color: color))
    return `self`
  }

  public func tracking(_ tracking: CGFloat) -> Self {
    var `self` = self
    `self`.modifiers.append(.tracking(tracking))
    return `self`
  }

  public func underline(_ active: Bool = true, color: Color? = nil) -> Self {
    var `self` = self
    `self`.modifiers.append(.underline(active: active, color: color))
    return `self`
  }
}

extension Text {
  public init(_ state: TextState) {
    let text: Text
    switch state.storage {
    case let .concatenated(first, second):
      text = Text(first) + Text(second)
    case let .localized(content, tableName, bundle, comment):
      text = .init(content, tableName: tableName, bundle: bundle, comment: comment)
    case let .verbatim(content):
      text = .init(verbatim: content)
    }
    self = state.modifiers.reduce(text) { text, modifier in
      switch modifier {
      case let .baselineOffset(baselineOffset):
        return text.baselineOffset(baselineOffset)
      case .bold:
        return text.bold()
      case let .font(font):
        return text.font(font)
      case let .fontWeight(weight):
        return text.fontWeight(weight)
      case let .foregroundColor(color):
        return text.foregroundColor(color)
      case .italic:
        return text.italic()
      case let .kerning(kerning):
        return text.kerning(kerning)
      case let .strikethrough(active, color):
        return text.strikethrough(active, color: color)
      case let .tracking(tracking):
        return text.tracking(tracking)
      case let .underline(active, color):
        return text.underline(active, color: color)
      }
    }
  }
}

extension TextState: View {
  public var body: some View {
    Text(self)
  }
}

extension String {
  public init(state: TextState, locale: Locale? = nil) {
    switch state.storage {
    case let .concatenated(lhs, rhs):
      self = String(state: lhs, locale: locale) + String(state: rhs, locale: locale)

    case let .localized(key, tableName, bundle, comment):
      self = key.formatted(
        locale: locale,
        tableName: tableName,
        bundle: bundle,
        comment: comment
      )

    case let .verbatim(string):
      self = string
    }
  }
}

extension LocalizedStringKey: CustomDebugOutputConvertible {
  // NB: `LocalizedStringKey` conforms to `Equatable` but returns false for equivalent format
  //     strings. To account for this we reflect on it to extract and string-format its storage.
  func formatted(
    locale: Locale? = nil,
    tableName: String? = nil,
    bundle: Bundle? = nil,
    comment: StaticString? = nil
  ) -> String {
    let children = Array(Mirror(reflecting: self).children)
    let key = children[0].value as! String
    let arguments: [CVarArg] = Array(Mirror(reflecting: children[2].value).children)
      .compactMap {
        let children = Array(Mirror(reflecting: $0.value).children)
        let value: Any
        let formatter: Formatter?
        // `LocalizedStringKey.FormatArgument` differs depending on OS/platform.
        if children[0].label == "storage" {
          (value, formatter) =
            Array(Mirror(reflecting: children[0].value).children)[0].value as! (Any, Formatter?)
        } else {
          value = children[0].value
          formatter = children[1].value as? Formatter
        }
        return formatter?.string(for: value) ?? value as! CVarArg
      }

    let format = NSLocalizedString(
      key,
      tableName: tableName,
      bundle: bundle ?? .main,
      value: "",
      comment: comment.map(String.init) ?? ""
    )
    return String(format: format, locale: locale, arguments: arguments)
  }

  public var debugOutput: String {
    self.formatted().debugDescription
  }
}

extension TextState: CustomDebugOutputConvertible {
  public var debugOutput: String {
    func debugOutputHelp(_ textState: Self) -> String {
      var output: String
      switch textState.storage {
      case let .concatenated(lhs, rhs):
        output = debugOutputHelp(lhs) + debugOutputHelp(rhs)
      case let .localized(key, tableName, bundle, comment):
        output = key.formatted(tableName: tableName, bundle: bundle, comment: comment)
      case let .verbatim(string):
        output = string
      }
      for modifier in textState.modifiers {
        switch modifier {
        case let .baselineOffset(baselineOffset):
          output = "<baseline-offset=\(baselineOffset)>\(output)</baseline-offset>"
        case .bold, .fontWeight(.some(.bold)):
          output = "**\(output)**"
        case .font(.some):
          break  // TODO: capture Font description using DSL similar to TextState and print here
        case let .fontWeight(.some(weight)):
          func describe(weight: Font.Weight) -> String {
            switch weight {
            case .black: return "black"
            case .bold: return "bold"
            case .heavy: return "heavy"
            case .light: return "light"
            case .medium: return "medium"
            case .regular: return "regular"
            case .semibold: return "semibold"
            case .thin: return "thin"
            default: return "\(weight)"
            }
          }
          output = "<font-weight=\(describe(weight: weight))>\(output)</font-weight>"
        case let .foregroundColor(.some(color)):
          output = "<foreground-color=\(color)>\(output)</foreground-color>"
        case .italic:
          output = "_\(output)_"
        case let .kerning(kerning):
          output = "<kerning=\(kerning)>\(output)</kerning>"
        case let .strikethrough(active: true, color: .some(color)):
          output = "<s color=\(color)>\(output)</s>"
        case .strikethrough(active: true, color: .none):
          output = "~~\(output)~~"
        case let .tracking(tracking):
          output = "<tracking=\(tracking)>\(output)</tracking>"
        case let .underline(active: true, color):
          output = "<u\(color.map { " color=\($0)" } ?? "")>\(output)</u>"
        case .font(.none),
          .fontWeight(.none),
          .foregroundColor(.none),
          .strikethrough(active: false, color: _),
          .underline(active: false, color: _):
          break
        }
      }
      return output
    }

    return #"""
      \#(Self.self)(
      \#(debugOutputHelp(self).indent(by: 2))
      )
      """#
  }
}