//===--- ArrayBuffer.swift - Dynamic storage for Swift Array --------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
//  This is the class that implements the storage and object management for
//  Swift Array.
//
//===----------------------------------------------------------------------===//

#if _runtime(_ObjC)
import SwiftShims

internal typealias _ArrayBridgeStorage
  = _BridgeStorage<_ContiguousArrayStorageBase, _NSArrayCoreType>

public struct _ArrayBuffer<T> : _ArrayBufferType {

  public typealias Element = T

  /// create an empty buffer
  public init() {
    _storage = _ArrayBridgeStorage(native: _emptyArrayStorage)
  }

  public init(nsArray: _NSArrayCoreType) {
    _sanityCheck(_isClassOrObjCExistential(T.self))
    _storage = _ArrayBridgeStorage(objC: nsArray)
  }

  /// Returns an `_ArrayBuffer<U>` containing the same elements.
  /// Requires: the elements actually have dynamic type `U`, and `U`
  /// is a class or `@objc` existential.
  func castToBufferOf<U>(_: U.Type) -> _ArrayBuffer<U> {
    _sanityCheck(_isClassOrObjCExistential(T.self))
    _sanityCheck(_isClassOrObjCExistential(U.self))
    return _ArrayBuffer<U>(storage: _storage)
  }

  var needsElementTypeCheck: Bool {
    // NSArray's need an element typecheck when the element type isn't AnyObject
    return _isClassOrObjCExistential(T.self)
      && _storage.isObjC
      && !(AnyObject.self is T.Type)
  }
  
  //===--- private --------------------------------------------------------===//
  internal init(storage: _ArrayBridgeStorage) {
    _storage = storage
  }

  internal var _storage: _ArrayBridgeStorage
}

extension _ArrayBuffer {
  /// Adopt the storage of source
  public
  init(_ source: NativeBuffer) {
    _storage = _ArrayBridgeStorage(native: source._storage)
  }
  
  /// Return true iff this buffer's storage is uniquely-referenced.
  mutating func isUniquelyReferenced() -> Bool {
    if !_isClassOrObjCExistential(T.self) {
      return _storage.isUniquelyReferenced_native_noSpareBits()
    }
    return _storage.isUniquelyReferencedNative()
  }

  /// Convert to an NSArray.
  /// Precondition: _isBridgedToObjectiveC(Element.self)
  /// O(1) if the element type is bridged verbatim, O(N) otherwise
  public func _asCocoaArray() -> _NSArrayCoreType {
    _sanityCheck(
      _isBridgedToObjectiveC(T.self),
      "Array element type is not bridged to ObjectiveC")

    return _fastPath(_isNative) ? _native._asCocoaArray() : _nonNative
  }

  /// If this buffer is backed by a uniquely-referenced mutable
  /// _ContiguousArrayBuffer that can be grown in-place to allow the self
  /// buffer store minimumCapacity elements, returns that buffer.
  /// Otherwise, returns nil
  public
  mutating func requestUniqueMutableBackingBuffer(minimumCapacity: Int)
    -> NativeBuffer?
  {
    if _fastPath(isUniquelyReferenced()) {
      let b = _native
      if _fastPath(b.capacity >= minimumCapacity) {
        return b
      }
    }
    return nil
  }

  public
  mutating func isMutableAndUniquelyReferenced() -> Bool {
    return isUniquelyReferenced()
  }
  
  /// If this buffer is backed by a `_ContiguousArrayBuffer`
  /// containing the same number of elements as `self`, return it.
  /// Otherwise, return `nil`.
  public func requestNativeBuffer() -> NativeBuffer? {
    if !_isClassOrObjCExistential(T.self) {
      return _native
    }
    return _fastPath(_storage.isNative) ? _native : nil
  }

  /// Replace the given subRange with the first newCount elements of
  /// the given collection.
  ///
  /// Requires: this buffer is backed by a uniquely-referenced
  /// _ContiguousArrayBuffer
  public
  mutating func replace<C: CollectionType where C.Generator.Element == Element>(
    #subRange: Range<Int>, with newCount: Int, elementsOf newValues: C
  ) {
    _arrayNonSliceInPlaceReplace(&self, subRange, newCount, newValues)
  }

  // We have two versions of type check: one that takes a range and the other
  // checks one element. The reason for this is that the ARC optimizer does not
  // handle loops atm. and so can get blocked by the presence of a loop (over
  // the range). This loop is not necessary for a single element access.
  func _typeCheck(index: Int) {
    if !_isClassOrObjCExistential(T.self) {
      return
    }
    
    if _slowPath(needsElementTypeCheck) {
      _sanityCheck(
        !_isNative, "A native array that needs a type check?")

      let ns = _nonNative
      // Could be sped up, e.g. by using
      // enumerateObjectsAtIndexes:options:usingBlock:
      _precondition(ns.objectAtIndex(index) is T,
                    "NSArray element failed to match the Swift Array Element type")
    }
  }

  func _typeCheck(subRange: Range<Int>) {
    if !_isClassOrObjCExistential(T.self) {
      return
    }

    if _slowPath(needsElementTypeCheck) {
      for i in subRange {
        _typeCheck(i)
      }
    }
  }
  
  /// Copy the given subRange of this buffer into uninitialized memory
  /// starting at target.  Return a pointer past-the-end of the
  /// just-initialized memory.
  @inline(never) // The copy loop blocks retain release matching.
  public
  func _uninitializedCopy(subRange: Range<Int>, target: UnsafeMutablePointer<T>)
         -> UnsafeMutablePointer<T> {
    _typeCheck(subRange)
    if _fastPath(_isNative) {
      return _native._uninitializedCopy(subRange, target: target)
    }

    let nonNative = _nonNative

    let nsSubRange = SwiftShims._SwiftNSRange(
      location:subRange.startIndex,
      length: subRange.endIndex - subRange.startIndex)

    let buffer = UnsafeMutablePointer<AnyObject>(target)
    
    // Copies the references out of the NSArray without retaining them
    nonNative.getObjects(buffer, range: nsSubRange)
    
    // Make another pass to retain the copied objects
    var result = target
    for i in subRange {
      result.initialize(result.memory)
      ++result
    }
    return result
  }
  
  /// Return a _SliceBuffer containing the given subRange of values
  /// from this buffer.
  public
  subscript(subRange: Range<Int>) -> _SliceBuffer<T> {
    _typeCheck(subRange)
    
    if _fastPath(_isNative) {
      return _native[subRange]
    }

    let nonNative = self._nonNative

    let subRangeCount = Swift.count(subRange)
    
    // Look for contiguous storage in the NSArray
    let cocoa = _CocoaArrayWrapper(nonNative)
    let start = cocoa.contiguousStorage(subRange)
    if start != nil {
      return _SliceBuffer(owner: nonNative, start: UnsafeMutablePointer(start),
          count: subRangeCount, hasNativeBuffer: false)
    }
    
    // No contiguous storage found; we must allocate
    var result = _ContiguousArrayBuffer<T>(
        count: subRangeCount, minimumCapacity: 0)

    // Tell Cocoa to copy the objects into our storage
    cocoa.buffer.getObjects(
      UnsafeMutablePointer(result.baseAddress),
      range: _SwiftNSRange(location: subRange.startIndex, length: subRangeCount)
    )

    return _SliceBuffer(result)
  }

  /// If the elements are stored contiguously, a pointer to the first
  /// element. Otherwise, nil.
  public
  var baseAddress: UnsafeMutablePointer<T> {
    if (_fastPath(_isNative)) {
      return _native.baseAddress
    }
    return nil
  }
  
  /// How many elements the buffer stores
  public
  var count: Int {
    get {
      return _fastPath(_isNative) ? _native.count : _nonNative.count
    }
    set {
      _sanityCheck(_isNative, "attempting to update count of Cocoa array")
      _native.count = newValue
    }
  }
  
  /// Return whether the given `index` is valid for subscripting, i.e. `0
  /// ≤ index < count`
  internal func _isValidSubscript(index : Int) -> Bool {
    if _fastPath(_isNative) {
      /// Note we call through to the native buffer here as it has a more
      /// optimal implementation than just doing 'index < count'
      return _native._isValidSubscript(index)
    }
    return index >= 0 && index < count
  }

  /// How many elements the buffer can store without reallocation
  public
  var capacity: Int {
    return _fastPath(_isNative) ? _native.capacity : _nonNative.count
  }

  /// Get/set the value of the ith element
  public
  subscript(i: Int) -> T {
    get {
      if _isClassOrObjCExistential(T.self) {
        _typeCheck(i)
      }
      if _fastPath(_isNative) {
        return _native[i]
      }
      return unsafeBitCast(_nonNative.objectAtIndex(i), T.self)
    }
    
    nonmutating set {
      if _fastPath(_isNative) {
        _native[i] = newValue
      }
      else {
        var refCopy = self
        refCopy.replace(
          subRange: i...i, with: 1, elementsOf: CollectionOfOne(newValue))
      }
    }
  }

  /// Call `body(p)`, where `p` is an `UnsafeBufferPointer` over the
  /// underlying contiguous storage.  If no such storage exists, it is
  /// created on-demand.
  public
  func withUnsafeBufferPointer<R>(
    body: (UnsafeBufferPointer<Element>)->R
  ) -> R {
    if _fastPath(_isNative) {
      let ret = body(UnsafeBufferPointer(start: self.baseAddress, count: count))
      _fixLifetime(self)
      return ret
    }
    return ContiguousArray(self).withUnsafeBufferPointer(body)
  }
  
  /// Call `body(p)`, where `p` is an `UnsafeMutableBufferPointer`
  /// over the underlying contiguous storage.  Requires: such
  /// contiguous storage exists or the buffer is empty
  public
  mutating func withUnsafeMutableBufferPointer<R>(
    body: (UnsafeMutableBufferPointer<T>)->R
  ) -> R {
    _sanityCheck(
      baseAddress != nil || count == 0,
      "Array is bridging an opaque NSArray; can't get a pointer to the elements"
    )
    let ret = body(
      UnsafeMutableBufferPointer(start: baseAddress, count: count))
    _fixLifetime(self)
    return ret
  }
  
  /// An object that keeps the elements stored in this buffer alive
  public
  var owner: AnyObject {
    return _fastPath(_isNative) ? _native._storage : _nonNative
  }
  
  /// 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: UnsafePointer<Void> {
    if _isNative {
      return _native.identity
    }
    else {
      return unsafeAddressOf(_nonNative)
    }
  }
  
  //===--- CollectionType conformance -------------------------------------===//
  /// The position of the first element in a non-empty collection.
  ///
  /// Identical to `endIndex` in an empty collection.
  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
  /// `successor()`.
  public var endIndex: Int {
    return count
  }

  /// Return a *generator* over the elements of this *sequence*.
  ///
  /// Complexity: O(1)
  public func generate() -> IndexingGenerator<_ArrayBuffer> {
    return IndexingGenerator(self)
  }
  
  //===--- private --------------------------------------------------------===//
  typealias Storage = _ContiguousArrayStorage<T>
  typealias NativeBuffer = _ContiguousArrayBuffer<T>

  func _invariantCheck() -> Bool {
    return true
  }

  var _isNative: Bool {
    if !_isClassOrObjCExistential(T.self) {
      return true
    }
    else {
      return _storage.isNative
    }
  }

  /// Our native representation.
  ///
  /// Requires: `_isNative`
  var _native: NativeBuffer {
    return NativeBuffer(
      _isClassOrObjCExistential(T.self)
      ? _storage.nativeInstance : _storage.nativeInstance_noSpareBits)
  }

  var _nonNative: _NSArrayCoreType {
    _sanityCheck(_isClassOrObjCExistential(T.self))
    return _storage.objCInstance
  }
}
#endif