//===--- DifferentiationUnittest.swift.gyb --------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

@_exported import _Differentiation
import StdlibUnittest

public enum _GlobalLeakCount {
  public static var count = 0
}

/// Execute body and check expected leak count.
public func withLeakChecking(
  expectedLeakCount: Int = 0, file: String = #file, line: UInt = #line,
  _ body: () -> Void
) {
  // Note: compare expected leak count with relative leak count after
  // running `body`.
  // This approach is more robust than comparing leak count with zero
  // and resetting leak count to zero, which is stateful and causes issues.
  let beforeLeakCount = _GlobalLeakCount.count
  body()
  let leakCount = _GlobalLeakCount.count - beforeLeakCount
  expectEqual(
    expectedLeakCount, leakCount, "Leaks detected: \(leakCount)",
    file: file, line: line)
}

@inlinable
@_semantics("autodiff.nonvarying")
public func withoutDerivative<T, R>(at x: T, in body: (T) -> R) -> R
{
  body(x)
}

public extension Differentiable {
  /// Applies the given closure to the derivative of `self`.
  ///
  /// Returns `self` like an identity function. When the return value is used in
  /// a context where it is differentiated with respect to, applies the given
  /// closure to the derivative of the return value.
  @inlinable
  @differentiable(reverse, wrt: self)
  func withDerivative(_ body: @escaping (inout TangentVector) -> Void) -> Self {
    return self
  }

  @inlinable
  @derivative(of: withDerivative)
  internal func _vjpWithDerivative(
    _ body: @escaping (inout TangentVector) -> Void
  ) -> (value: Self, pullback: (TangentVector) -> TangentVector) {
    return (self, { grad in
      var grad = grad
      body(&grad)
      return grad
    })
  }
}

public extension TestSuite {
  /// Execute test function and check expected leak count.
  func testWithLeakChecking(
    _ name: String,
    expectedLeakCount: Int = 0,
    file: String = #file, line: UInt = #line,
    _ testFunction: @escaping () -> Void
  ) {
    test(name, file: file, line: line) {
      withLeakChecking(
        expectedLeakCount: expectedLeakCount, file: file,
        line: line, testFunction)
    }
  }
}

/// A resilient type that tracks the number of live instances of a wrapped
/// value type.
///
/// `Tracked<T>` is used to check for memory leaks in functions created via
/// automatic differentiation.
public struct Tracked<T> {
  internal class Box {
    fileprivate var value: T
    init(_ value: T) {
      self.value = value
      _GlobalLeakCount.count += 1
    }
    deinit {
      _GlobalLeakCount.count -= 1
    }
  }
  internal var handle: Box

  @differentiable(reverse where T: Differentiable, T == T.TangentVector)
  public init(_ value: T) {
    self.handle = Box(value)
  }

  @differentiable(reverse where T: Differentiable, T == T.TangentVector)
  public var value: T {
    get { handle.value }
    // FIXME: Disable setter until https://github.com/apple/swift/issues/55542 is fixed
    // set { handle.value = newValue }
  }
}

/// A non-resilient type that tracks the number of live instances of a wrapped
/// value type.
///
/// `NonresilientTracked<T>` is used to check for memory leaks in functions
/// created via automatic differentiation.
@frozen
public struct NonresilientTracked<T> {
  @usableFromInline
  internal class Box {
    fileprivate var value: T
    init(_ value: T) {
      self.value = value
      _GlobalLeakCount.count += 1
    }
    deinit {
      _GlobalLeakCount.count -= 1
    }
  }
  @usableFromInline
  internal var handle: Box

  @differentiable(reverse where T: Differentiable, T == T.TangentVector)
  public init(_ value: T) {
    self.handle = Box(value)
  }

  @differentiable(reverse where T: Differentiable, T == T.TangentVector)
  public var value: T {
    get { handle.value }
    // FIXME: Disable setter until https://github.com/apple/swift/issues/55542 is fixed
    // set { handle.value = newValue }
  }
}

% for Self in ['Tracked', 'NonresilientTracked']:

extension ${Self}: ExpressibleByFloatLiteral
where T: ExpressibleByFloatLiteral {
  public init(floatLiteral value: T.FloatLiteralType) {
    self.handle = Box(T(floatLiteral: value))
  }
}

extension ${Self}: CustomStringConvertible {
  public var description: String { return "${Self}(\(value))" }
}

extension ${Self}: ExpressibleByIntegerLiteral
where T: ExpressibleByIntegerLiteral {
  public init(integerLiteral value: T.IntegerLiteralType) {
    self.handle = Box(T(integerLiteral: value))
  }
}

extension ${Self}: Comparable where T: Comparable {
  public static func < (lhs: ${Self}, rhs: ${Self}) -> Bool {
    return lhs.value < rhs.value
  }
  public static func <= (lhs: ${Self}, rhs: ${Self}) -> Bool {
    return lhs.value <= rhs.value
  }
  public static func > (lhs: ${Self}, rhs: ${Self}) -> Bool {
    return lhs.value > rhs.value
  }
  public static func >= (lhs: ${Self}, rhs: ${Self}) -> Bool {
    return lhs.value >= rhs.value
  }
}

extension ${Self}: AdditiveArithmetic where T: AdditiveArithmetic {
  public static var zero: ${Self} { return ${Self}(T.zero) }
  public static func + (lhs: ${Self}, rhs: ${Self}) -> ${Self} {
    return ${Self}(lhs.value + rhs.value)
  }
  public static func - (lhs: ${Self}, rhs: ${Self}) -> ${Self} {
    return ${Self}(lhs.value - rhs.value)
  }
}

extension ${Self}: Equatable where T: Equatable {
  public static func == (lhs: ${Self}, rhs: ${Self}) -> Bool {
    return lhs.value == rhs.value
  }
}

extension ${Self}: Numeric where T: Numeric {
  public typealias Magnitude = ${Self}<T.Magnitude>

  public init?<U>(exactly source: U) where U: BinaryInteger {
    if let t = T(exactly: source) {
      self.init(t)
    }
    return nil
  }
  public var magnitude: Magnitude { return Magnitude(value.magnitude) }

  public static func * (lhs: ${Self}, rhs: ${Self}) -> ${Self} {
    return ${Self}(lhs.value * rhs.value)
  }

  public static func *= (lhs: inout ${Self}, rhs: ${Self}) {
    lhs = lhs * rhs
  }
}

extension ${Self}: SignedNumeric where T: SignedNumeric, T == T.Magnitude {
  public prefix static func - (operand: ${Self}) -> ${Self} {
    ${Self}(-operand.value)
  }
}

extension ${Self} where T: FloatingPoint {
  public static func / (lhs: ${Self}, rhs: ${Self}) -> ${Self} {
    return ${Self}(lhs.value / rhs.value)
  }

  public static func /= (lhs: inout ${Self}, rhs: ${Self}) {
    lhs = lhs / rhs
  }
}

extension ${Self}: Strideable
where T: Strideable, T.Stride == T.Stride.Magnitude {
  public typealias Stride = ${Self}<T.Stride>

  public func distance(to other: ${Self}) -> Stride {
    return Stride(value.distance(to: other.value))
  }
  public func advanced(by n: Stride) -> ${Self} {
    return ${Self}(value.advanced(by: n.value))
  }
}

// For now, `T` must be restricted to trivial types (like `Float` or `Tensor`).
extension ${Self}: Differentiable
where T: Differentiable, T == T.TangentVector {
  public typealias TangentVector = ${Self}<T.TangentVector>
}

extension ${Self} where T: Differentiable, T == T.TangentVector {
  @usableFromInline
  @derivative(of: init)
  internal static func _vjpInit(_ value: T)
    -> (value: Self, pullback: (Self.TangentVector) -> (T.TangentVector))
  {
    return (${Self}(value), { v in v.value })
  }

  @usableFromInline
  @derivative(of: init)
  internal static func _jvpInit(_ value: T)
    -> (value: Self, differential: (T.TangentVector) -> (Self.TangentVector))
  {
    return (${Self}(value), { v in ${Self}(v) })
  }

  @usableFromInline
  @derivative(of: value)
  internal func _vjpValue() -> (
    value: T, pullback: (T.TangentVector) -> Self.TangentVector
  ) {
    return (value, { v in ${Self}(v) })
  }

  @usableFromInline
  @derivative(of: value)
  internal func _jvpValue() -> (
    value: T, differential: (Self.TangentVector) -> T.TangentVector
  ) {
    return (value, { v in v.value })
  }
}

extension ${Self} where T: Differentiable, T == T.TangentVector {
  @usableFromInline
  @derivative(of: +)
  internal static func _vjpAdd(lhs: Self, rhs: Self)
    -> (value: Self, pullback: (Self) -> (Self, Self))
  {
    return (lhs + rhs, { v in (v, v) })
  }

  @usableFromInline
  @derivative(of: +)
  internal static func _jvpAdd(lhs: Self, rhs: Self)
    -> (value: Self, differential: (Self, Self) -> Self)
  {
    return (lhs + rhs, { $0 + $1 })
  }

  @usableFromInline
  @derivative(of: -)
  internal static func _vjpSubtract(lhs: Self, rhs: Self)
    -> (value: Self, pullback: (Self) -> (Self, Self))
  {
    return (lhs - rhs, { v in (v, .zero - v) })
  }

  @usableFromInline
  @derivative(of: -)
  internal static func _jvpSubtract(lhs: Self, rhs: Self)
    -> (value: Self, differential: (Self, Self) -> Self)
  {
    return (lhs - rhs, { $0 - $1 })
  }
}

extension ${Self}
where
  T: Differentiable & SignedNumeric, T == T.Magnitude,
  T == T.TangentVector
{
  @usableFromInline
  @derivative(of: *)
  internal static func _vjpMultiply(lhs: Self, rhs: Self)
    -> (value: Self, pullback: (Self) -> (Self, Self))
  {
    return (lhs * rhs, { v in (v * rhs, v * lhs) })
  }

  @usableFromInline
  @derivative(of: *)
  internal static func _jvpMultiply(lhs: Self, rhs: Self)
    -> (value: Self, differential: (Self, Self) -> (Self))
  {
    return (lhs * rhs, { (dx, dy) in dx * rhs + dy * lhs })
  }
}

extension ${Self}
where T: Differentiable & FloatingPoint, T == T.TangentVector {
  @usableFromInline
  @derivative(of: /)
  internal static func _vjpDivide(lhs: Self, rhs: Self)
    -> (value: Self, pullback: (Self) -> (Self, Self))
  {
    return (lhs / rhs, { v in (v / rhs, -lhs / (rhs * rhs) * v) })
  }

  @usableFromInline
  @derivative(of: /)
  internal static func _jvpDivide(lhs: Self, rhs: Self)
    -> (value: Self, differential: (Self, Self) -> (Self))
  {
    return (lhs / rhs, { (dx, dy) in dx / rhs - lhs / (rhs * rhs) * dy })
  }
}

// Differential operators for `${Self}<T>`.

public func gradient<T, R: FloatingPoint>(
  at x: T, of f: @differentiable(reverse) (T) -> ${Self}<R>
) -> T.TangentVector where R.TangentVector == R {
  return pullback(at: x, of: f)(1)
}

public func gradient<T, U, R: FloatingPoint>(
  at x: T, _ y: U, of f: @differentiable(reverse) (T, U) -> ${Self}<R>
) -> (T.TangentVector, U.TangentVector) where R.TangentVector == R {
  return pullback(at: x, y, of: f)(1)
}

public func derivative<T: FloatingPoint, R>(
  at x: ${Self}<T>, of f: @differentiable(reverse) (${Self}<T>) -> R
) -> R.TangentVector where T.TangentVector == T {
  return differential(at: x, of: f)(1)
}

public func derivative<T: FloatingPoint, U: FloatingPoint, R>(
  at x: ${Self}<T>, _ y: ${Self}<U>,
  of f: @differentiable(reverse) (${Self}<T>, ${Self}<U>) -> R
) -> R.TangentVector where T.TangentVector == T, U.TangentVector == U {
  return differential(at: x, y, of: f)(1, 1)
}

public func valueWithGradient<T, R: FloatingPoint>(
  at x: T, of f: @differentiable(reverse) (T) -> ${Self}<R>
) -> (value: ${Self}<R>, gradient: T.TangentVector) {
  let (y, pullback) = valueWithPullback(at: x, of: f)
  return (y, pullback(1))
}

public func valueWithDerivative<T: FloatingPoint, R>(
  at x: ${Self}<T>, of f: @differentiable(reverse) (${Self}<T>) -> R
) -> (value: R, derivative: R.TangentVector) {
  let (y, differential) = valueWithDifferential(at: x, of: f)
  return (y, differential(1))
}

% end