internal import jsi

/// A Swift representation of a JavaScript BigInt. BigInt is a built-in JavaScript object that provides
/// a way to represent whole numbers larger than 2^53 - 1, which is the largest number JavaScript can
/// reliably represent with the Number primitive.
///
/// BigInts can be created from 64-bit integers (signed or unsigned) and can be converted back to
/// 64-bit integers with optional validation to ensure no data loss.
///
/// ## Example Usage
/// ```swift
/// let runtime = JavaScriptRuntime()
///
/// // Create from Int64
/// let bigInt = JavaScriptBigInt(runtime, fromInt64: 9007199254740991)
///
/// // Create from UInt64
/// let largeBigInt = JavaScriptBigInt(runtime, fromUint64: UInt64.max)
///
/// // Convert to string with different radixes
/// let decimal = bigInt.toString(radix: 10)  // "9007199254740991"
/// let hex = bigInt.toString(radix: 16)      // "1fffffffffffff"
/// let binary = bigInt.toString(radix: 2)    // "11111111111111111111111111111111111111111111111111111"
///
/// // Safe conversion back to integers
/// if bigInt.isInt64() {
///   let value = try bigInt.asInt64()  // Safe conversion
/// }
///
/// // Equality testing
/// let another = JavaScriptBigInt(runtime, fromInt64: 9007199254740991)
/// if bigInt == another {
///   print("BigInts are equal")
/// }
/// ```
///
/// - Note: BigInt values cannot be mixed with Number values in arithmetic operations in JavaScript.
/// You must explicitly convert between them.
public struct JavaScriptBigInt: JavaScriptType, Sendable, ~Copyable {
  internal weak let runtime: JavaScriptRuntime?
  internal var pointee: facebook.jsi.BigInt

  /// Creates a BigInt from an existing JSI BigInt.
  internal init(_ runtime: JavaScriptRuntime, _ bigInt: consuming facebook.jsi.BigInt) {
    self.runtime = runtime
    self.pointee = bigInt
  }

  /// Creates a BigInt from a signed 64-bit integer.
  ///
  /// - Parameters:
  ///   - runtime: The JavaScript runtime
  ///   - value: The Int64 value to convert to BigInt
  public init(_ runtime: JavaScriptRuntime, fromInt64 value: Int64) {
    self.runtime = runtime
    self.pointee = facebook.jsi.BigInt.fromInt64(runtime.pointee, value)
  }

  /// Creates a BigInt from an unsigned 64-bit integer.
  ///
  /// - Parameters:
  ///   - runtime: The JavaScript runtime
  ///   - value: The UInt64 value to convert to BigInt
  public init(_ runtime: JavaScriptRuntime, fromUint64 value: UInt64) {
    self.runtime = runtime
    self.pointee = facebook.jsi.BigInt.fromUint64(runtime.pointee, value)
  }

  /// Creates a BigInt from a string representation.
  ///
  /// This initializer parses a string to create a BigInt value. The string can be in decimal format
  /// or use prefixes for other bases (e.g., "0x" for hexadecimal, "0o" for octal, "0b" for binary).
  /// Unlike the numeric initializers which are limited to 64-bit ranges, this initializer can create
  /// BigInt values of arbitrary size.
  ///
  /// - Parameters:
  ///   - runtime: The JavaScript runtime
  ///   - string: A string representation of the number to parse. Can include:
  ///     - Decimal: "12345" or "-12345"
  ///     - Hexadecimal: "0xFF" or "0xff"
  ///     - Octal: "0o77"
  ///     - Binary: "0b1111"
  ///
  /// - Throws: An error if the string cannot be parsed as a valid BigInt. This can occur if:
  ///   - The string is empty
  ///   - The string contains invalid characters
  ///   - The string format is not recognized by JavaScript's `BigInt()` constructor
  ///
  /// - Note: This method calls JavaScript's `BigInt()` constructor internally, so it follows
  ///   the same parsing rules as JavaScript. Whitespace is trimmed automatically.
  ///
  /// ## Examples
  /// ```swift
  /// // Create from decimal string
  /// let bigInt1 = try JavaScriptBigInt(runtime, string: "123456789012345678901234567890")
  ///
  /// // Create from hexadecimal string
  /// let bigInt2 = try JavaScriptBigInt(runtime, string: "0xFFFFFFFFFFFFFFFF")
  ///
  /// // Create from binary string
  /// let bigInt3 = try JavaScriptBigInt(runtime, string: "0b11111111")
  ///
  /// // Create from octal string
  /// let bigInt4 = try JavaScriptBigInt(runtime, string: "0o777")
  ///
  /// // Negative values
  /// let bigInt5 = try JavaScriptBigInt(runtime, string: "-999999999999999999")
  ///
  /// // Handle errors
  /// do {
  ///   let bigInt = try JavaScriptBigInt(runtime, string: "invalid")
  /// } catch {
  ///   print("Failed to parse BigInt: \(error)")
  /// }
  /// ```
  public init(_ runtime: JavaScriptRuntime, string: String) throws {
    self.runtime = runtime
    self.pointee =
      try runtime
      .global()
      .getPropertyAsFunction("BigInt")
      .call(arguments: string)
      .pointee
      .getBigInt(runtime.pointee)
  }

  // MARK: - Conversions to Integer Types

  /// Returns whether this BigInt can be losslessly converted to a signed 64-bit integer.
  ///
  /// If this returns `true`, calling `asInt64()` will succeed without throwing.
  ///
  /// - Returns: `true` if the BigInt fits in an Int64 range, `false` otherwise
  public func isInt64() -> Bool {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return pointee.isInt64(runtime.pointee)
  }

  /// Returns whether this BigInt can be losslessly converted to an unsigned 64-bit integer.
  ///
  /// If this returns `true`, calling `asUint64()` will succeed without throwing.
  ///
  /// - Returns: `true` if the BigInt fits in a UInt64 range, `false` otherwise
  public func isUint64() -> Bool {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return pointee.isUint64(runtime.pointee)
  }

  /// Returns this BigInt truncated to a signed 64-bit integer.
  ///
  /// This method always succeeds but may lose data if the BigInt is outside the Int64 range.
  /// Use `isInt64()` first to check if conversion is lossless, or use `asInt64()` for safe conversion.
  ///
  /// - Returns: The truncated Int64 value
  public func getInt64() -> Int64 {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return pointee.getInt64(runtime.pointee)
  }

  /// Returns this BigInt truncated to an unsigned 64-bit integer.
  ///
  /// This method always succeeds but may lose data if the BigInt is outside the UInt64 range.
  /// Use `isUint64()` first to check if conversion is lossless, or use `asUint64()` for safe conversion.
  ///
  /// - Returns: The truncated UInt64 value
  public func getUint64() -> UInt64 {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return pointee.getUint64(runtime.pointee)
  }

  /// Returns this BigInt as a signed 64-bit integer, throwing an error if the conversion is lossy.
  ///
  /// Use this method when you need to ensure no data is lost during conversion.
  ///
  /// - Returns: The Int64 value
  /// - Throws: `BigIntConversionError` if the BigInt is outside the Int64 range
  public func asInt64() throws -> Int64 {
    guard isInt64() else {
      throw BigIntConversionError.outOfInt64Range
    }
    return getInt64()
  }

  /// Returns this BigInt as an unsigned 64-bit integer, throwing an error if the conversion is lossy.
  ///
  /// Use this method when you need to ensure no data is lost during conversion.
  ///
  /// - Returns: The UInt64 value
  /// - Throws: `BigIntConversionError` if the BigInt is outside the UInt64 range
  public func asUint64() throws -> UInt64 {
    guard isUint64() else {
      throw BigIntConversionError.outOfUint64Range
    }
    return getUint64()
  }

  // MARK: - String Conversion

  /// Converts this BigInt to a string representation in the specified radix (base).
  ///
  /// The radix can be any value from 2 to 36. Common bases include:
  /// - 2: Binary
  /// - 8: Octal
  /// - 10: Decimal (default)
  /// - 16: Hexadecimal
  ///
  /// - Parameter radix: The base to use for string conversion (2-36). Defaults to 10.
  /// - Returns: A string representation of the BigInt
  /// - Throws: `BigIntConversionError.invalidRadix` if radix is not in the valid range
  ///
  /// ## Examples
  /// ```swift
  /// let bigInt = JavaScriptBigInt(runtime, fromInt64: 255)
  /// bigInt.toString(radix: 2)   // "11111111"
  /// bigInt.toString(radix: 8)   // "377"
  /// bigInt.toString(radix: 10)  // "255"
  /// bigInt.toString(radix: 16)  // "ff"
  /// ```
  public func toString(radix: Int = 10) throws -> String {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    guard radix >= 2 && radix <= 36 else {
      throw BigIntConversionError.invalidRadix(radix)
    }
    let jsiString = pointee.toString(runtime.pointee, Int32(radix))
    return String(jsiString.utf16(runtime.pointee))
  }

  // MARK: - JavaScriptType

  public func asValue() -> JavaScriptValue {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return JavaScriptValue(runtime, facebook.jsi.Value(runtime.pointee, pointee))
  }

  /// Returns the BigInt as a `facebook.jsi.Value` instance.
  internal func asJSIValue() -> facebook.jsi.Value {
    guard let runtime else {
      FatalError.runtimeLost()
    }
    return facebook.jsi.Value(runtime.pointee, pointee)
  }

  // MARK: - Equality

  /// Tests whether two BigInts are strictly equal (represent the same numeric value).
  ///
  /// This performs a strict equality check as defined by JavaScript's `===` operator for BigInts.
  ///
  /// - Parameters:
  ///   - lhs: The first BigInt to compare
  ///   - rhs: The second BigInt to compare
  /// - Returns: `true` if the BigInts represent the same value, `false` otherwise
  public static func == (lhs: borrowing JavaScriptBigInt, rhs: borrowing JavaScriptBigInt) -> Bool {
    guard let runtime = lhs.runtime else {
      FatalError.runtimeLost()
    }
    return facebook.jsi.BigInt.strictEquals(runtime.pointee, lhs.pointee, rhs.pointee)
  }
}

extension JavaScriptBigInt: JavaScriptRepresentable {
  public static func fromJavaScriptValue(_ value: JavaScriptValue) -> JavaScriptBigInt {
    return value.getBigInt()
  }

  public func toJavaScriptValue(in runtime: JavaScriptRuntime) -> JavaScriptValue {
    return asValue()
  }
}

extension JavaScriptBigInt: JSIRepresentable {
  static func fromJSIValue(_ value: borrowing facebook.jsi.Value, in runtime: facebook.jsi.IRuntime) -> JavaScriptBigInt
  {
    fatalError("Not implemented: Use JavaScriptValue.getBigInt() instead")
  }

  func toJSIValue(in runtime: facebook.jsi.IRuntime) -> facebook.jsi.Value {
    return asJSIValue()
  }
}

// MARK: - Errors

/// Errors that can occur when working with BigInt conversions.
public enum BigIntConversionError: Error, CustomStringConvertible {
  /// The BigInt value is outside the valid Int64 range (-2^63 to 2^63-1)
  case outOfInt64Range

  /// The BigInt value is outside the valid UInt64 range (0 to 2^64-1)
  case outOfUint64Range

  /// The radix parameter is not in the valid range (2-36)
  case invalidRadix(Int)

  public var description: String {
    switch self {
    case .outOfInt64Range:
      return "BigInt value is outside the Int64 range (-9223372036854775808 to 9223372036854775807)"
    case .outOfUint64Range:
      return "BigInt value is outside the UInt64 range (0 to 18446744073709551615)"
    case .invalidRadix(let radix):
      return "Invalid radix \(radix). Radix must be between 2 and 36."
    }
  }
}