//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 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

/// Class used whose sole instance is used as storage for empty
/// arrays.  The instance is defined in the runtime and statically
/// initialized.  See stdlib/runtime/GlobalObjects.cpp for details.
/// Because it's statically referenced, it requires non-lazy realization
/// by the Objective-C runtime.
@objc_non_lazy_realization
internal final class _EmptyArrayStorage
  : _ContiguousArrayStorageBase {

  init(_doNotCallMe: ()) {
    _sanityCheckFailure("creating instance of _EmptyArrayStorage")
  }
  
  var countAndCapacity: _ArrayBody

#if _runtime(_ObjC)
  override func _withVerbatimBridgedUnsafeBuffer<R>(
    _ body: (UnsafeBufferPointer<AnyObject>) throws -> R
  ) rethrows -> R? {
    return try body(UnsafeBufferPointer(start: nil, count: 0))
  }

  // FIXME(ABI): remove 'Void' arguments here and elsewhere in this file, they
  // are a workaround for an old compiler limitation.
  override func _getNonVerbatimBridgedCount(_ dummy: Void) -> Int {
    return 0
  }

  override func _getNonVerbatimBridgedHeapBuffer(
    _ dummy: Void
  ) -> _HeapBuffer<Int, AnyObject> {
    return _HeapBuffer<Int, AnyObject>(
      _HeapBufferStorage<Int, AnyObject>.self, 0, 0)
  }
#endif

  override func canStoreElements(ofDynamicType _: Any.Type) -> Bool {
    return false
  }

  /// A type that every element in the array is.
  override var staticElementType: Any.Type {
    return Void.self
  }
}

/// The empty array prototype.  We use the same object for all empty
/// `[Native]Array<Element>`s.
internal var _emptyArrayStorage : _EmptyArrayStorage {
  return Builtin.bridgeFromRawPointer(
    Builtin.addressof(&_swiftEmptyArrayStorage))
}

// FIXME: This whole class is a workaround for
// <rdar://problem/18560464> Can't override generic method in generic
// subclass.  If it weren't for that bug, we'd override
// _withVerbatimBridgedUnsafeBuffer directly in
// _ContiguousArrayStorage<Element>.
class _ContiguousArrayStorage1 : _ContiguousArrayStorageBase {
#if _runtime(_ObjC)
  /// If the `Element` is bridged verbatim, invoke `body` on an
  /// `UnsafeBufferPointer` to the elements and return the result.
  /// Otherwise, return `nil`.
  final override func _withVerbatimBridgedUnsafeBuffer<R>(
    _ body: (UnsafeBufferPointer<AnyObject>) throws -> R
  ) rethrows -> R? {
    var result: R? = nil
    try self._withVerbatimBridgedUnsafeBufferImpl {
      result = try body($0)
    }
    return result
  }

  /// If `Element` is bridged verbatim, invoke `body` on an
  /// `UnsafeBufferPointer` to the elements.
  internal func _withVerbatimBridgedUnsafeBufferImpl(
    _ body: (UnsafeBufferPointer<AnyObject>) throws -> Void
  ) rethrows {
    _sanityCheckFailure(
      "Must override _withVerbatimBridgedUnsafeBufferImpl in derived classes")
  }
#endif
}

// The class that implements the storage for a ContiguousArray<Element>
@_versioned
final class _ContiguousArrayStorage<Element> : _ContiguousArrayStorage1 {

  deinit {
    __manager._elementPointer.deinitialize(
      count: __manager._headerPointer.pointee.count)
    __manager._headerPointer.deinitialize()
    _fixLifetime(__manager)
  }

#if _runtime(_ObjC)
  /// If `Element` is bridged verbatim, invoke `body` on an
  /// `UnsafeBufferPointer` to the elements.
  internal final override func _withVerbatimBridgedUnsafeBufferImpl(
    _ body: (UnsafeBufferPointer<AnyObject>) throws -> Void
  ) rethrows {
    if _isBridgedVerbatimToObjectiveC(Element.self) {
      let count = __manager.header.count
      let elements = UnsafeRawPointer(__manager._elementPointer)
        .assumingMemoryBound(to: AnyObject.self)
      defer { _fixLifetime(__manager) }
      try body(UnsafeBufferPointer(start: elements, count: count))
    }
  }

  /// Returns the number of elements in the array.
  ///
  /// - Precondition: `Element` is bridged non-verbatim.
  override internal func _getNonVerbatimBridgedCount(_ dummy: Void) -> Int {
    _sanityCheck(
      !_isBridgedVerbatimToObjectiveC(Element.self),
      "Verbatim bridging should be handled separately")
    return __manager.header.count
  }

  /// Bridge array elements and return a new buffer that owns them.
  ///
  /// - Precondition: `Element` is bridged non-verbatim.
  override internal func _getNonVerbatimBridgedHeapBuffer(_ dummy: Void) ->
    _HeapBuffer<Int, AnyObject> {
    _sanityCheck(
      !_isBridgedVerbatimToObjectiveC(Element.self),
      "Verbatim bridging should be handled separately")
    let count = __manager.header.count
    let result = _HeapBuffer<Int, AnyObject>(
      _HeapBufferStorage<Int, AnyObject>.self, count, count)
    let resultPtr = result.baseAddress
    let p = __manager._elementPointer
    for i in 0..<count {
      (resultPtr + i).initialize(to: _bridgeAnythingToObjectiveC(p[i]))
    }
    _fixLifetime(__manager)
    return result
  }
#endif

  /// Returns `true` if the `proposedElementType` is `Element` or a subclass of
  /// `Element`.  We can't store anything else without violating type
  /// safety; for example, the destructor has static knowledge that
  /// all of the elements can be destroyed as `Element`.
  override func canStoreElements(
    ofDynamicType proposedElementType: Any.Type
  ) -> Bool {
#if _runtime(_ObjC)
    return proposedElementType is Element.Type
#else
    // FIXME: Dynamic casts don't currently work without objc. 
    // rdar://problem/18801510
    return false
#endif
  }

  /// A type that every element in the array is.
  override var staticElementType: Any.Type {
    return Element.self
  }

  internal // private
  typealias Manager = ManagedBufferPointer<_ArrayBody, Element>

  internal // private
  var __manager: Manager {
    return Manager(_uncheckedUnsafeBufferObject: self)
  }
}

@_fixed_layout
public // @testable
struct _ContiguousArrayBuffer<Element> : _ArrayBufferProtocol {

  /// Make a buffer with uninitialized elements.  After using this
  /// method, you must either initialize the `count` elements at the
  /// result's `.firstElementAddress` or set the result's `.count`
  /// to zero.
  public init(uninitializedCount: Int, minimumCapacity: Int) {
    let realMinimumCapacity = Swift.max(uninitializedCount, minimumCapacity)
    if realMinimumCapacity == 0 {
      self = _ContiguousArrayBuffer<Element>()
    }
    else {
      __bufferPointer = ManagedBufferPointer(
        _uncheckedBufferClass: _ContiguousArrayStorage<Element>.self,
        minimumCapacity: realMinimumCapacity)

      _initStorageHeader(
        count: uninitializedCount, capacity: __bufferPointer.capacity)

      _fixLifetime(__bufferPointer)
    }
  }

  /// Initialize using the given uninitialized `storage`.
  /// The storage is assumed to be uninitialized. The returned buffer has the
  /// body part of the storage initialized, but not the elements.
  ///
  /// - Warning: The result has uninitialized elements.
  /// 
  /// - Warning: storage may have been stack-allocated, so it's
  ///   crucial not to call, e.g., `malloc_size` on it.
  internal init(count: Int, storage: _ContiguousArrayStorage<Element>) {
    __bufferPointer = ManagedBufferPointer(
      _uncheckedUnsafeBufferObject: storage)

    _initStorageHeader(count: count, capacity: count)

    _fixLifetime(__bufferPointer)
  }

  internal init(_ storage: _ContiguousArrayStorageBase) {
    __bufferPointer = ManagedBufferPointer(
      _uncheckedUnsafeBufferObject: storage)
  }

  /// Initialize the body part of our storage.
  ///
  /// - Warning: does not initialize elements
  internal func _initStorageHeader(count: Int, capacity: Int) {
#if _runtime(_ObjC)
    let verbatim = _isBridgedVerbatimToObjectiveC(Element.self)
#else
    let verbatim = false
#endif

    __bufferPointer._headerPointer.initialize(to: 
      _ArrayBody(
        count: count,
        capacity: capacity,
        elementTypeIsBridgedVerbatim: verbatim))
  }

  /// True, if the array is native and does not need a deferred type check.
  var arrayPropertyIsNativeTypeChecked: Bool {
    return true
  }

  /// A pointer to the first element.
  public var firstElementAddress: UnsafeMutablePointer<Element> {
    return __bufferPointer._elementPointer
  }

  public var firstElementAddressIfContiguous: UnsafeMutablePointer<Element>? {
    return firstElementAddress
  }

  /// Call `body(p)`, where `p` is an `UnsafeBufferPointer` over the
  /// underlying contiguous storage.
  public func withUnsafeBufferPointer<R>(
    _ body: (UnsafeBufferPointer<Element>) throws -> R
  ) rethrows -> R {
    defer { _fixLifetime(self) }
    return try body(UnsafeBufferPointer(start: firstElementAddress,
      count: count))
  }

  /// Call `body(p)`, where `p` is an `UnsafeMutableBufferPointer`
  /// over the underlying contiguous storage.
  public mutating func withUnsafeMutableBufferPointer<R>(
    _ body: (UnsafeMutableBufferPointer<Element>) throws -> R
  ) rethrows -> R {
    defer { _fixLifetime(self) }
    return try body(
      UnsafeMutableBufferPointer(start: firstElementAddress, count: count))
  }

  //===--- _ArrayBufferProtocol conformance -----------------------------------===//
  /// Create an empty buffer.
  public init() {
    __bufferPointer = ManagedBufferPointer(
      _uncheckedUnsafeBufferObject: _emptyArrayStorage)
  }

  public init(_ buffer: _ContiguousArrayBuffer, shiftedToStartIndex: Int) {
    _sanityCheck(shiftedToStartIndex == 0, "shiftedToStartIndex must be 0")
    self = buffer
  }

  public mutating func requestUniqueMutableBackingBuffer(
    minimumCapacity: Int
  ) -> _ContiguousArrayBuffer<Element>? {
    if _fastPath(isUniquelyReferenced() && capacity >= minimumCapacity) {
      return self
    }
    return nil
  }

  public mutating func isMutableAndUniquelyReferenced() -> Bool {
    return isUniquelyReferenced()
  }

  public mutating func isMutableAndUniquelyReferencedOrPinned() -> Bool {
    return isUniquelyReferencedOrPinned()
  }

  /// If this buffer is backed by a `_ContiguousArrayBuffer`
  /// containing the same number of elements as `self`, return it.
  /// Otherwise, return `nil`.
  public func requestNativeBuffer() -> _ContiguousArrayBuffer<Element>? {
    return self
  }

  @_versioned
  func getElement(_ i: Int) -> Element {
    _sanityCheck(i >= 0 && i < count, "Array index out of range")
    return firstElementAddress[i]
  }

  /// Get or set the value of the ith element.
  public subscript(i: Int) -> Element {
    get {
      return getElement(i)
    }
    nonmutating set {
      _sanityCheck(i >= 0 && i < count, "Array index out of range")

      // FIXME: Manually swap because it makes the ARC optimizer happy.  See
      // <rdar://problem/16831852> check retain/release order
      // firstElementAddress[i] = newValue
      var nv = newValue
      let tmp = nv
      nv = firstElementAddress[i]
      firstElementAddress[i] = tmp
    }
  }

  /// The number of elements the buffer stores.
  public var count: Int {
    get {
      return __bufferPointer.header.count
    }
    nonmutating set {
      _sanityCheck(newValue >= 0)

      _sanityCheck(
        newValue <= capacity,
        "Can't grow an array buffer past its capacity")

      __bufferPointer._headerPointer.pointee.count = newValue
    }
  }

  /// Traps unless the given `index` is valid for subscripting, i.e.
  /// `0 ≤ index < count`.
  @inline(__always)
  func _checkValidSubscript(_ index : Int) {
    _precondition(
      (index >= 0) && (index < __bufferPointer.header.count),
      "Index out of range"
    )
  }

  /// The number of elements the buffer can store without reallocation.
  public var capacity: Int {
    return __bufferPointer.header.capacity
  }

  /// Copy the elements in `bounds` from this buffer into uninitialized
  /// memory starting at `target`.  Return a pointer "past the end" of the
  /// just-initialized memory.
  @discardableResult
  public func _copyContents(
    subRange bounds: Range<Int>,
    initializing target: UnsafeMutablePointer<Element>
  ) -> UnsafeMutablePointer<Element> {
    _sanityCheck(bounds.lowerBound >= 0)
    _sanityCheck(bounds.upperBound >= bounds.lowerBound)
    _sanityCheck(bounds.upperBound <= count)

    let initializedCount = bounds.upperBound - bounds.lowerBound
    target.initialize(
      from: firstElementAddress + bounds.lowerBound, count: initializedCount)
    _fixLifetime(owner)
    return target + initializedCount
  }

  /// Returns a `_SliceBuffer` containing the given `bounds` of values
  /// from this buffer.
  public subscript(bounds: Range<Int>) -> _SliceBuffer<Element> {
    get {
      return _SliceBuffer(
        owner: __bufferPointer.buffer,
        subscriptBaseAddress: subscriptBaseAddress,
        indices: bounds,
        hasNativeBuffer: true)
    }
    set {
      fatalError("not implemented")
    }
  }

  /// Returns `true` iff this buffer's storage is uniquely-referenced.
  ///
  /// - Note: This does not mean the buffer is mutable.  Other factors
  ///   may need to be considered, such as whether the buffer could be
  ///   some immutable Cocoa container.
  public mutating func isUniquelyReferenced() -> Bool {
    return __bufferPointer.isUniqueReference()
  }

  /// Returns `true` iff this buffer's storage is either
  /// uniquely-referenced or pinned.  NOTE: this does not mean
  /// the buffer is mutable; see the comment on isUniquelyReferenced.
  public mutating func isUniquelyReferencedOrPinned() -> Bool {
    return __bufferPointer._isUniqueOrPinnedReference()
  }

#if _runtime(_ObjC)
  /// Convert to an NSArray.
  ///
  /// - Precondition: `Element` is bridged to Objective-C.
  ///
  /// - Complexity: O(1).
  public func _asCocoaArray() -> _NSArrayCore {
    if count == 0 {
      return _emptyArrayStorage
    }
    if _isBridgedVerbatimToObjectiveC(Element.self) {
      return _storage
    }
    return _SwiftDeferredNSArray(_nativeStorage: _storage)
  }
#endif

  /// An object that keeps the elements stored in this buffer alive.
  public var owner: AnyObject {
    return _storage
  }

  /// An object that keeps the elements stored in this buffer alive.
  public var nativeOwner: AnyObject {
    return _storage
  }

  /// A value that identifies the storage used by the buffer.
  ///
  /// Two buffers address the same elements when they have the same
  /// identity and count.
  public var identity: UnsafeRawPointer {
    return UnsafeRawPointer(firstElementAddress)
  }
  
  /// Returns `true` iff we have storage for elements of the given
  /// `proposedElementType`.  If not, we'll be treated as immutable.
  func canStoreElements(ofDynamicType proposedElementType: Any.Type) -> Bool {
    return _storage.canStoreElements(ofDynamicType: proposedElementType)
  }

  /// Returns `true` if the buffer stores only elements of type `U`.
  ///
  /// - Precondition: `U` is a class or `@objc` existential.
  ///
  /// - Complexity: O(N).
  func storesOnlyElementsOfType<U>(
    _: U.Type
  ) -> Bool {
    _sanityCheck(_isClassOrObjCExistential(U.self))

    if _fastPath(_storage.staticElementType is U.Type) {
      // Done in O(1)
      return true
    }

    // Check the elements
    for x in self {
      if !(x is U) {
        return false
      }
    }
    return true
  }

  internal var _storage: _ContiguousArrayStorageBase {
    return Builtin.castFromNativeObject(__bufferPointer._nativeBuffer)
  }

  var __bufferPointer: ManagedBufferPointer<_ArrayBody, Element>
}

/// Append the elements of `rhs` to `lhs`.
public func += <Element, C : Collection>(
  lhs: inout _ContiguousArrayBuffer<Element>, rhs: C
) where C.Iterator.Element == Element {

  let oldCount = lhs.count
  let newCount = oldCount + numericCast(rhs.count)

  if _fastPath(newCount <= lhs.capacity) {
    lhs.count = newCount
    (lhs.firstElementAddress + oldCount).initialize(from: rhs)
  }
  else {
    var newLHS = _ContiguousArrayBuffer<Element>(
      uninitializedCount: newCount,
      minimumCapacity: _growArrayCapacity(lhs.capacity))

    newLHS.firstElementAddress.moveInitialize(
      from: lhs.firstElementAddress, count: oldCount)
    lhs.count = 0
    swap(&lhs, &newLHS)
    (lhs.firstElementAddress + oldCount).initialize(from: rhs)
  }
}

extension _ContiguousArrayBuffer : RandomAccessCollection {
  /// The position of the first element in a non-empty collection.
  ///
  /// In an empty collection, `startIndex == endIndex`.
  public var startIndex: Int {
    return 0
  }
  /// 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
  /// `index(after:)`.
  public var endIndex: Int {
    return count
  }

  public typealias Indices = CountableRange<Int>
}

extension Sequence {
  public func _copyToContiguousArray() -> ContiguousArray<Iterator.Element> {
    return _copySequenceToContiguousArray(self)
  }
}

internal func _copySequenceToContiguousArray<
  S : Sequence
>(_ source: S) -> ContiguousArray<S.Iterator.Element> {
  let initialCapacity = source.underestimatedCount
  var builder =
    _UnsafePartiallyInitializedContiguousArrayBuffer<S.Iterator.Element>(
      initialCapacity: initialCapacity)

  var iterator = source.makeIterator()

  // FIXME(performance): use _copyContents(initializing:).

  // Add elements up to the initial capacity without checking for regrowth.
  for _ in 0..<initialCapacity {
    builder.addWithExistingCapacity(iterator.next()!)
  }

  // Add remaining elements, if any.
  while let element = iterator.next() {
    builder.add(element)
  }

  return builder.finish()
}

extension Collection {
  public func _copyToContiguousArray() -> ContiguousArray<Iterator.Element> {
    return _copyCollectionToContiguousArray(self)
  }
}

extension _ContiguousArrayBuffer {
  public func _copyToContiguousArray() -> ContiguousArray<Element> {
    return ContiguousArray(_buffer: self)
  }
}

/// This is a fast implementation of _copyToContiguousArray() for collections.
///
/// It avoids the extra retain, release overhead from storing the
/// ContiguousArrayBuffer into
/// _UnsafePartiallyInitializedContiguousArrayBuffer. Since we do not support
/// ARC loops, the extra retain, release overhead cannot be eliminated which
/// makes assigning ranges very slow. Once this has been implemented, this code
/// should be changed to use _UnsafePartiallyInitializedContiguousArrayBuffer.
internal func _copyCollectionToContiguousArray<
  C : Collection
>(_ source: C) -> ContiguousArray<C.Iterator.Element>
{
  let count: Int = numericCast(source.count)
  if count == 0 {
    return ContiguousArray()
  }

  let result = _ContiguousArrayBuffer<C.Iterator.Element>(
    uninitializedCount: count,
    minimumCapacity: 0)

  var p = result.firstElementAddress
  var i = source.startIndex
  for _ in 0..<count {
    // FIXME(performance): use _copyContents(initializing:).
    p.initialize(to: source[i])
    source.formIndex(after: &i)
    p += 1
  }
  _expectEnd(i, source)
  return ContiguousArray(_buffer: result)
}

/// A "builder" interface for initializing array buffers.
///
/// This presents a "builder" interface for initializing an array buffer
/// element-by-element. The type is unsafe because it cannot be deinitialized
/// until the buffer has been finalized by a call to `finish`.
internal struct _UnsafePartiallyInitializedContiguousArrayBuffer<Element> {
  internal var result: _ContiguousArrayBuffer<Element>
  internal var p: UnsafeMutablePointer<Element>
  internal var remainingCapacity: Int

  /// Initialize the buffer with an initial size of `initialCapacity`
  /// elements.
  @inline(__always) // For performance reasons.
  init(initialCapacity: Int) {
    if initialCapacity == 0 {
      result = _ContiguousArrayBuffer()
    } else {
      result = _ContiguousArrayBuffer(
        uninitializedCount: initialCapacity,
        minimumCapacity: 0)
    }

    p = result.firstElementAddress
    remainingCapacity = result.capacity
  }

  /// Add an element to the buffer, reallocating if necessary.
  @inline(__always) // For performance reasons.
  mutating func add(_ element: Element) {
    if remainingCapacity == 0 {
      // Reallocate.
      let newCapacity = max(_growArrayCapacity(result.capacity), 1)
      var newResult = _ContiguousArrayBuffer<Element>(
        uninitializedCount: newCapacity, minimumCapacity: 0)
      p = newResult.firstElementAddress + result.capacity
      remainingCapacity = newResult.capacity - result.capacity
      newResult.firstElementAddress.moveInitialize(
        from: result.firstElementAddress, count: result.capacity)
      result.count = 0
      swap(&result, &newResult)
    }
    addWithExistingCapacity(element)
  }

  /// Add an element to the buffer, which must have remaining capacity.
  @inline(__always) // For performance reasons.
  mutating func addWithExistingCapacity(_ element: Element) {
    _sanityCheck(remainingCapacity > 0,
      "_UnsafePartiallyInitializedContiguousArrayBuffer has no more capacity")
    remainingCapacity -= 1

    p.initialize(to: element)
    p += 1
  }

  /// Finish initializing the buffer, adjusting its count to the final
  /// number of elements.
  ///
  /// Returns the fully-initialized buffer. `self` is reset to contain an
  /// empty buffer and cannot be used afterward.
  @inline(__always) // For performance reasons.
  mutating func finish() -> ContiguousArray<Element> {
    // Adjust the initialized count of the buffer.
    result.count = result.capacity - remainingCapacity

    return finishWithOriginalCount()
  }

  /// Finish initializing the buffer, assuming that the number of elements
  /// exactly matches the `initialCount` for which the initialization was
  /// started.
  ///
  /// Returns the fully-initialized buffer. `self` is reset to contain an
  /// empty buffer and cannot be used afterward.
  @inline(__always) // For performance reasons.
  mutating func finishWithOriginalCount() -> ContiguousArray<Element> {
    _sanityCheck(remainingCapacity == result.capacity - result.count,
      "_UnsafePartiallyInitializedContiguousArrayBuffer has incorrect count")
    var finalResult = _ContiguousArrayBuffer<Element>()
    swap(&finalResult, &result)
    remainingCapacity = 0
    return ContiguousArray(_buffer: finalResult)
  }
}