//===--- ExistentialCollection.swift.gyb ----------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import SwiftShims

% traversals = ['Forward', 'Bidirectional', 'RandomAccess']

@noreturn @inline(never)
internal func _abstract(file: StaticString = __FILE__, line: UWord = __LINE__) {
  fatalError("Method must be overridden", file: file, line: line)
}

//===--- Generator --------------------------------------------------------===//
//===----------------------------------------------------------------------===//

public class _AnyGeneratorBase {}

/// An abstract `GeneratorType` base class over `Element` elements.
///
/// Use this as a `Sequence`'s associated `Generator` type when you
/// don't want to expose details of the concrete generator, a subclass.
///
/// It is an error to create instances of `AnyGenerator` that are not
/// also instances of an `AnyGenerator` subclass.
///
/// - seealso:
///   - `struct AnySequence<S : SequenceType>`
///   - `func anyGenerator<G : GeneratorType>(base: G) -> AnyGenerator<G.Element>`
///   - `func anyGenerator<Element>(body: ()->Element?) -> AnyGenerator<Element>`
public class AnyGenerator<Element> : _AnyGeneratorBase, GeneratorType {
  @available(*, unavailable, renamed="Element")
  public typealias T = Element

  /// Initialize the instance.  May only be called from a subclass
  /// initializer.
  override public init() {
    super.init()
    _debugPrecondition(
      _typeID(self) != unsafeBitCast(AnyGenerator.self, ObjectIdentifier.self),
      "AnyGenerator<Element> instances can not be created; create a subclass instance instead.")
  }

  /// Advance to the next element and return it, or `nil` if no next
  /// element exists.
  ///
  /// - Note: Subclasses must override this method.
  public func next() -> Element? {_abstract()}
}

/// Every `GeneratorType` can also be a `SequenceType`.  Note that
/// traversing the sequence consumes the generator.
extension AnyGenerator : SequenceType {
  /// Returns `self`.
  public func generate() -> AnyGenerator { return self }
}

//===--- Generic Factories ------------------------------------------------===//
// The following two functions should be initializers, but we can't
// yet express that in the language.

/// Return a `GeneratorType` instance that wraps `base` but whose type
/// depends only on the type of `G.Element`.
///
/// Example:
///
///     func countStrings() -> AnyGenerator<String> {
///       let lazyStrings = lazy(0..<10).map { String($0) }
///
///       // This is a really complicated type of no interest to our
///       // clients.
///       let g: MapSequenceGenerator<RangeGenerator<Int>, String>
///         = lazyStrings.generate()
///       return anyGenerator(g)
///     }
public func anyGenerator<G: GeneratorType>(base: G) -> AnyGenerator<G.Element> {
  return _GeneratorBox(base)
}

internal class _FunctionGenerator<Element> : AnyGenerator<Element> {
  init(_ body: ()->Element?) {
    self.body = body
  }
  override func next() -> Element? { return body() }
  let body: ()->Element?
}

/// Return a `GeneratorType` instance whose `next` method invokes
/// `body` and returns the result.
///
/// Example:
///
///     var x = 7
///     let g = anyGenerator { x < 15 ? x++ : nil }
///     let a = Array(g) // [ 7, 8, 9, 10, 11, 12, 13, 14 ]
public func anyGenerator<Element>(body: ()->Element?) -> AnyGenerator<Element> {
  return _FunctionGenerator(body)
}

internal final class _GeneratorBox<
  Base: GeneratorType
> : AnyGenerator<Base.Element> {
  init(_ base: Base) { self.base = base }
  override func next() -> Base.Element? { return base.next() }
  var base: Base
}

internal func _typeID(instance: AnyObject) -> ObjectIdentifier {
  return ObjectIdentifier(instance.dynamicType)
}

//===--- Sequence ---------------------------------------------------------===//
//===----------------------------------------------------------------------===//

internal class _AnySequenceBox {
  // FIXME: can't make _AnySequenceBox generic and return
  // _AnyGenerator<Element> here due to <rdar://20211022>
  func generate() -> _AnyGeneratorBase {_abstract()}

  func _underestimateCount() -> Int  {_abstract()}
  // FIXME: can't traffic in UnsafeMutablePointer<Element> and
  // _ContiguousArrayBuffer<Element> here due to <rdar://20164041>
  func _initializeTo(ptr: UnsafeMutablePointer<Void>) {_abstract()}
  func _copyToNativeArrayBuffer() -> _ContiguousArrayStorageBase {_abstract()}
}

internal class _AnyCollectionBoxBase : _AnySequenceBox {
  init(startIndex: _ForwardIndexBoxType, endIndex: _ForwardIndexBoxType) {
    self.startIndex = startIndex
    self.endIndex = endIndex
  }
  let startIndex: _ForwardIndexBoxType
  let endIndex: _ForwardIndexBoxType
}

% for Kind in ['Sequence', 'Collection']:
// FIXME: can't make this a protocol due to <rdar://20209031>
internal class _${Kind}Box<S : ${Kind}Type>
  : _Any${Kind}Box${'<S.Generator.Element>'if Kind == 'Collection' else ''} {
  typealias Element = S.Generator.Element

  override func generate() -> _AnyGeneratorBase {
    // FIXME: an intermediate variable is a workaround for:
    // <rdar://problem/20582672> _GeneratorBox(_base.generate()) does
    // not compile when put into one expression
    let x = _base.generate()
    return _GeneratorBox(x)
  }
  override func _underestimateCount() -> Int {
    return _base.underestimateCount()
  }
  override func _initializeTo(ptr: UnsafeMutablePointer<Void>) {
    _base._initializeTo(UnsafeMutablePointer(ptr))
  }
  override func _copyToNativeArrayBuffer() -> _ContiguousArrayStorageBase {
    return _base._copyToNativeArrayBuffer()._storage
  }
%   if Kind == 'Collection':
  override func _count() -> IntMax {
    return numericCast(_base.count)
  }
  override subscript(position: _ForwardIndexBoxType) -> Element {
    if let i = position._unbox() as S.Index? {
      return _base[i]
    }
    fatalError("Index type mismatch!")
  }
  init(
    _ base: S,
    startIndex: _ForwardIndexBoxType,
    endIndex: _ForwardIndexBoxType
  ) {
    self._base = base
    super.init(startIndex: startIndex, endIndex: endIndex)
  }
%   else:
  init(_ base: S) {
    self._base = base
  }
%   end
  internal var _base: S
}
% end

internal struct _ClosureBasedSequence<Generator : GeneratorType>
  : SequenceType {

  internal init(_ makeUnderlyingGenerator: () -> Generator) {
    self._makeUnderlyingGenerator = makeUnderlyingGenerator
  }

  internal func generate() -> Generator {
    return _makeUnderlyingGenerator()
  }

  internal var _makeUnderlyingGenerator: () -> Generator
}

/// A type-erased sequence.
///
/// Forwards operations to an arbitrary underlying sequence having the
/// same `Element` type, hiding the specifics of the underlying
/// `SequenceType`.
///
/// - SeeAlso: `AnyGenerator<Element>`.
public struct AnySequence<Element> : SequenceType {
  @available(*, unavailable, renamed="Element")
  public typealias T = Element

  /// Wrap and forward operations to to `base`.
  public init<S: SequenceType where S.Generator.Element == Element>(_ base: S) {
    _box = _SequenceBox(base)
  }

  /// Create a sequence whose `generate()` method forwards to
  /// `makeUnderlyingGenerator`.
  public init<G : GeneratorType where G.Element == Element>(
    _ makeUnderlyingGenerator: () -> G
  ) {
    self.init(_ClosureBasedSequence(makeUnderlyingGenerator))
  }

  /// Return a *generator* over the elements of this *sequence*.
  ///
  /// - Complexity: O(1).
  public func generate() -> AnyGenerator<Element> {
    return unsafeDowncast(_box.generate())
  }

  internal let _box: _AnySequenceBox
}

% for Kind in ['Sequence'] + [t + 'Collection' for t in traversals]:
extension Any${Kind} {
  public func underestimateCount() -> Int {
    return _box._underestimateCount()
  }
  
  public func _initializeTo(ptr: UnsafeMutablePointer<Element>) {
    _box._initializeTo(UnsafeMutablePointer(ptr))
  }
  
  public func _copyToNativeArrayBuffer() -> _ContiguousArrayBuffer<Element> {
    return _ContiguousArrayBuffer(self._box._copyToNativeArrayBuffer())
  }
}

% end

//===--- ForwardIndex -----------------------------------------------------===//
//===----------------------------------------------------------------------===//

internal protocol _ForwardIndexBoxType : class {
  var typeID: ObjectIdentifier {get}
  func successor() -> _ForwardIndexBoxType
  func _successorInPlace()
  func equals(other: _ForwardIndexBoxType) -> Bool
  func _unbox<T : ForwardIndexType>() -> T?
  func _distanceTo(other: _ForwardIndexBoxType) -> AnyForwardIndex.Distance
  // FIXME: Can't return Self from _advancedBy pending <rdar://20181253>
  func _advancedBy(distance: AnyForwardIndex.Distance) -> _ForwardIndexBoxType
  func _advancedBy(
    distance: AnyForwardIndex.Distance,
    _ limit: _ForwardIndexBoxType
  ) -> _ForwardIndexBoxType
}

internal class _ForwardIndexBox<
  BaseIndex: ForwardIndexType
> : _ForwardIndexBoxType {
  required init(_ base: BaseIndex) {
    self.base = base
  }

  func successor() -> _ForwardIndexBoxType {
    return self.dynamicType.init(self.base.successor())
  }

  func _successorInPlace() {
    self.base._successorInPlace()
  }

  func unsafeUnbox(other: _ForwardIndexBoxType) -> BaseIndex {
    return (unsafeDowncast(other) as _ForwardIndexBox).base
  }

  func equals(other: _ForwardIndexBoxType) -> Bool {
    return base == unsafeUnbox(other)
  }

  func _distanceTo(other: _ForwardIndexBoxType) -> AnyForwardIndex.Distance {
    return numericCast(distance(base, unsafeUnbox(other)))
  }

  func _advancedBy(n: AnyForwardIndex.Distance) -> _ForwardIndexBoxType {
    return self.dynamicType.init(advance(base, numericCast(n)))
  }

  func _advancedBy(
    n: AnyForwardIndex.Distance,
    _ limit: _ForwardIndexBoxType
  ) -> _ForwardIndexBoxType {
    return self.dynamicType.init(advance(base, numericCast(n), unsafeUnbox(limit)))
  }

  func _unbox<T : ForwardIndexType>() -> T? {
    if T.self is BaseIndex.Type {
      _sanityCheck(BaseIndex.self is T.Type)
      // This bit cast is really nothing as we have proven they are
      // the same type.
      return unsafeBitCast(base, T.self)
    }
    return nil
  }

  var typeID: ObjectIdentifier { return _typeID(self) }

  internal // private
  var base: BaseIndex
}

//===--- BidirectionalIndex -----------------------------------------------===//
//===----------------------------------------------------------------------===//

internal protocol _BidirectionalIndexBoxType : _ForwardIndexBoxType {
  func predecessor() -> _BidirectionalIndexBoxType
  func _predecessorInPlace()
}

internal class _BidirectionalIndexBox<
  BaseIndex: BidirectionalIndexType
> : _ForwardIndexBox<BaseIndex>, _BidirectionalIndexBoxType {
  required init(_ base: BaseIndex) {
    super.init(base)
  }

  override func successor() -> _ForwardIndexBoxType {
    return self.dynamicType.init(self.base.successor())
  }

  func predecessor() -> _BidirectionalIndexBoxType {
    return self.dynamicType.init(self.base.predecessor())
  }

  func _predecessorInPlace() {
    self.base._predecessorInPlace()
  }
}

//===--- RandomAccessIndex -----------------------------------------------===//
//===----------------------------------------------------------------------===//

internal protocol _RandomAccessIndexBoxType : _BidirectionalIndexBoxType {}

internal final class _RandomAccessIndexBox<
  BaseIndex: RandomAccessIndexType
> : _BidirectionalIndexBox<BaseIndex>, _RandomAccessIndexBoxType {
  required init(_ base: BaseIndex) {
    super.init(base)
  }
}

//===--- All Index Protocols ----------------------------------------------===//
//===----------------------------------------------------------------------===//

% for Traversal in traversals:

%   Self = 'Any%sIndex' % Traversal
/// A wrapper over an underlying `${Traversal}IndexType` that hides
/// the specific underlying type.
///
/// - SeeAlso: `Any${Traversal}Collection`
public struct ${Self} : ${Traversal}IndexType {
  public typealias Distance = IntMax

  /// Wrap and forward operations to `base`.
  public init<BaseIndex: ${Traversal}IndexType>(_ base: BaseIndex) {
    _box = _${Traversal}IndexBox(base)
  }

  /// Return the next consecutive value in a discrete sequence of
  /// `${Self}` values.
  ///
  /// - Requires: `self` has a well-defined successor.
  public func successor() -> ${Self} {
    return ${Self}(_box.successor())
  }

  public mutating func _successorInPlace() {
    if _fastPath(_isUnique_native(&_box)) {
      _box._successorInPlace()
    }
    else {
      self = successor()
    }
  }

  % if Traversal != 'Forward':
  /// Return the previous consecutive value in a discrete sequence of
  /// `${Self}` values.
  ///
  /// - Requires: `self` has a well-defined predecessor.
  public func predecessor() -> ${Self} {
    return ${Self}(_box.predecessor())
  }

  public mutating func _predecessorInPlace() {
    if _fastPath(_isUnique_native(&_box)) {
      _box._predecessorInPlace()
    }
    else {
      self = predecessor()
    }
  }
  % end

  % if Traversal == 'RandomAccess':
  /// Return the minimum number of applications of `successor` or
  /// `predecessor` required to reach `other` from `self`.
  ///
  /// - Requires: `self` and `other` wrap instances of the same type.
  public func distanceTo(other: ${Self}) -> Distance {
    return _box._distanceTo(other._box)
  }

  /// Return `self` offset by `n` steps.
  ///
  /// - Returns: If `n > 0`, the result of applying `successor` to
  ///   `self` `n` times.  If `n < 0`, the result of applying
  ///   `predecessor` to `self` `n` times. Otherwise, `self`.
  public func advancedBy(amount: Distance) -> ${Self} {
    return ${Self}(_box._advancedBy(amount))
  }
  % end

  //===--- private --------------------------------------------------------===//

  internal var _typeID: ObjectIdentifier {
    return _box.typeID
  }

  internal init(_ box: _ForwardIndexBoxType) {
    self._box = box${
      '' if Traversal == 'Forward' else ' as! _%sIndexBoxType' % Traversal}
  }

  // _box is passed inout to _isUnique.  Although its value
  // is unchanged, it must appear mutable to the optimizer.
  internal var _box: _${Traversal}IndexBoxType

  public func _distanceTo(other: ${Self}) -> ${Self}.Distance {
    precondition(
      self._typeID == other._typeID,
      "distance: base index types differ.")
    return self._box._distanceTo(other._box)
  }
}

public func ~> (
  start: ${Self}, distance : (_Advance, ${Self}.Distance)
) -> ${Self} {
  return ${Self}(start._box._advancedBy(distance.1))
}

public func ~> (
  start: ${Self},
  args: (_Advance, (${Self}.Distance, ${Self}))
) -> ${Self} {
  precondition(
    start._typeID == args.1.1._typeID, "advance: base index types differ.")
  return ${Self}(start._box._advancedBy(args.1.0, args.1.1._box))
}

/// Return true iff `lhs` and `rhs` wrap equal underlying
/// `${Self}`s.
///
/// - Requires: The types of indices wrapped by `lhs` and `rhs` are
///   identical.
public func == (lhs: ${Self}, rhs: ${Self}) -> Bool {
  precondition(lhs._typeID == rhs._typeID, "base index types differ.")
  return lhs._box.equals(rhs._box)
}
% end

//===--- Collections ------------------------------------------------------===//
//===----------------------------------------------------------------------===//

internal class _AnyCollectionBox<Element> : _AnyCollectionBoxBase {
  subscript(_: _ForwardIndexBoxType) -> Element {_abstract()}
  func _count() -> IntMax {_abstract()}

  // FIXME: should be inherited, but a known bug prevents it since
  // this class is generic.
  override init(
    startIndex: _ForwardIndexBoxType,
    endIndex: _ForwardIndexBoxType
  ) {
    super.init(startIndex: startIndex, endIndex: endIndex)
  }
}

/// A protocol for `AnyForwardCollection<Element>`,
/// `AnyBidirectionalCollection<Element>`, and
/// `AnyRandomAccessCollection<Element>`.
///
/// This protocol can be considered an implementation detail of the
/// `===` and `!==` implementations for these types.
public protocol AnyCollectionType : CollectionType {
  /// Identifies the underlying collection stored by `self`. Instances
  /// copied from one another have the same `_underlyingCollectionID`.
  var _underlyingCollectionID: ObjectIdentifier {get}
}

/// Return true iff `lhs` and `rhs` store the same underlying collection.
public func === <
  L: AnyCollectionType, R: AnyCollectionType
>(lhs: L, rhs: R) -> Bool {
  return lhs._underlyingCollectionID == rhs._underlyingCollectionID
}

/// Returns false iff `lhs` and `rhs` store the same underlying collection.
public func !== <
  L: AnyCollectionType, R: AnyCollectionType
>(lhs: L, rhs: R) -> Bool {
  return lhs._underlyingCollectionID != rhs._underlyingCollectionID
}

% for (ti, Traversal) in enumerate(traversals):
/// A type-erased wrapper over any collection with indices that
/// support ${Traversal.lower().replace('omacc', 'om acc')} traversal.
///
/// Forwards operations to an arbitrary underlying collection having the
/// same `Element` type, hiding the specifics of the underlying
/// `CollectionType`.
///
/// - SeeAlso: ${', '.join('`Any%sType`' % t for t in (2 * traversals)[ti + 1 : ti + 3]) }
public struct Any${Traversal}Collection<Element> : AnyCollectionType {
  @available(*, unavailable, renamed="Element")
  public typealias T = Element

  typealias Box = _AnyCollectionBox<Element>

%   for SubTraversal in traversals[ti:]:
  /// Create an `Any${Traversal}Collection` that stores `base` as its
  /// underlying collection.
  ///
  /// - Complexity: O(1).
  public init<
    C: CollectionType
      where C.Index: ${SubTraversal}IndexType, C.Generator.Element == Element
  >(_ base: C) {
    self._box = _CollectionBox<C>(
      base,
      startIndex: _${SubTraversal}IndexBox(base.startIndex),
      endIndex: _${SubTraversal}IndexBox(base.endIndex))
  }

  /// Create an `Any${Traversal}Collection` having the same underlying
  /// collection as `other`.
  ///
  /// - Postcondition: The result is `===` to `other`.
  ///
  /// - Complexity: O(1).
  public init(_ other: Any${SubTraversal}Collection<Element>) {
    self._box = other._box
  }
%   end

%   for SuperTraversal in traversals[:ti]:
  /// If the indices of the underlying collection stored by `other`
  /// satisfy `${Traversal}IndexType`, create an
  /// `Any${Traversal}Collection` having the same underlying
  /// collection as `other`.  Otherwise, the result is `nil`.
  ///
  /// - Complexity: O(1).
  public init?(_ other: Any${SuperTraversal}Collection<Element>) {
    if !(other._box.startIndex is _${Traversal}IndexBoxType) {
      return nil
    }
    _sanityCheck(other._box.endIndex is _${Traversal}IndexBoxType)
    self._box = other._box
  }
%   end

  /// Returns a *generator* over the elements of this *collection*.
  ///
  /// - Complexity: O(1).
  public func generate() -> AnyGenerator<Element> {
    return unsafeDowncast(_box.generate())
  }

  /// The position of the first element in a non-empty collection.
  ///
  /// In an empty collection, `startIndex == endIndex`.
  public var startIndex: Any${Traversal}Index {
    return Any${Traversal}Index(_box.startIndex)
  }

  /// The collection's "past the end" position.
  ///
  /// `endIndex` is not a valid argument to `subscript`, and is always
  /// reachable from `startIndex` by zero or more applications of
  /// `successor()`.
  public var endIndex: Any${Traversal}Index {
    return Any${Traversal}Index(_box.endIndex)
  }

  /// Access the element indicated by `position`.
  ///
  /// - Requires: `position` indicates a valid position in `self` and
  ///   `position != endIndex`.
  public subscript(position: Any${Traversal}Index) -> Element {
    return _box[position._box]
  }

  /// Return the number of elements.
  ///
  /// - Complexity: ${'O(1)' if Traversal == 'RandomAccess' else 'O(N)'}.
  public var count: IntMax {
    return _box._count()
  }

  /// Uniquely identifies the stored underlying collection.
  public // due to language limitations only
  var _underlyingCollectionID: ObjectIdentifier {
    return ObjectIdentifier(_box)
  }

  internal let _box: Box
}
% end