//===--- Concatenate.swift.gyb - Concatenate sequence elements-*- swift -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//

// Unfortunately it is required to make some types in this file public
// (@testable) just because _lazyConcatenate is called from the
// stdlib unit tests.

/// The `GeneratorType` used by `_ConcatenateSequenceView`,
/// `_ForwardConcatenateView`, and `_BidirectionalConcatenateView`.
/// Generates a sequence of the elements of the elements of its
/// argument.
public // @testable
struct _ConcatenateSequenceGenerator<
  Outer: GeneratorType where Outer.Element : SequenceType
>: GeneratorType, SequenceType {

  /// Construct around a generator for the outer sequence
  init(_ outer: Outer) {
    self._outer = outer
  }

  /// Advance to the next element and return it, or `nil` if no next
  /// element exists.
  ///
  /// Requires: `next()` has not been applied to a copy of `self`
  /// since the copy was made, and no preceding call to `self.next()`
  /// has returned `nil`.
  public // @testable
  mutating func next() -> Outer.Element.Generator.Element? {
    do {
      if _fastPath(_inner != nil) {
        let ret = _inner!.next()
        if _fastPath(ret != nil) {
          return ret
        }
      }
      let s = _outer.next()
      if _slowPath(s == nil) {
        return nil
      }
      _inner = s!.generate()
    }
    while true
  }

  /// `_ConcatenateSequenceGenerator` is also a `SequenceType`, so it
  /// `generate`\ 's a copy of itself
  public // @testable
  func generate() -> _ConcatenateSequenceGenerator {
    return self
  }

  var _outer: Outer
  var _inner: Outer.Element.Generator? = nil
}

//===--- Sequences --------------------------------------------------------===//

/// A `SequenceType` whose elements consist of those *contained in* in
/// the elements of its `Base` sequence.
struct _ConcatenateSequenceView<
  Base: SequenceType where Base.Generator.Element: SequenceType
> : SequenceType {


  /// Present the elmeents of the elements of `base`
  init(_ base: Base) {
    self._base = base
  }

  /// Return a *generator* over the elements of this *sequence*.
  ///
  /// Complexity: O(1)
  func generate() -> _ConcatenateSequenceGenerator<Base.Generator> {
    return _ConcatenateSequenceGenerator(_base.generate())
  }

  var _base: Base
}

/// Return a sequence that is a concatenation of the elements of
/// `source`\ 's elements
func _lazyConcatenate<
  S:SequenceType
  where S.Generator.Element: SequenceType
>(source: S) -> LazySequence<_ConcatenateSequenceView<S>> {
  return LazySequence(_ConcatenateSequenceView(source))
}

/// Return an `Array` containing the results of mapping `transform`
/// over `source`.
func _concatenate<
  S:SequenceType
  where S.Generator.Element: SequenceType
>(
  source: S
) -> [S.Generator.Element.Generator.Element] {
  return _lazyConcatenate(source).array
}

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

% for traversal in ('Forward', 'Bidirectional'):
%   View = '_%sConcatenateView' % traversal
%   Self = '_Lazy%sCollection' % traversal
%   Index = '_Concatenate%sIndex' % traversal
%   IndexProtocol = '%sIndexType' % traversal

/// A wrapper for a `${IndexProtocol}` for a collection of
/// collections, that can be used to index the inner elements.
public // @testable
struct ${Index}<
  C: CollectionType
    where C.Index : ${IndexProtocol},
          C.Generator.Element: CollectionType,
          C.Generator.Element.Index : ${IndexProtocol}
> : ${IndexProtocol} {
  typealias Outer = C.Index
  typealias Inner = C.Generator.Element.Index
  var _data: C
  var _outer: Outer
  var _inner: Inner?

  init(_ data: C, _ outer: Outer, _ inner: Inner?) {
    self._data = data
    self._outer = outer
    self._inner = inner
  }

  static func adjustForward(
    data: C, var _ outer: Outer, _ inner: Inner?
  ) -> ${Index} {
    if _fastPath(inner != nil) {
      if _fastPath(inner! != data[outer].endIndex) {
        return ${Index}(data, outer, inner)
      }
      ++outer
    }
    for ; outer != data.endIndex ; ++outer {
      if !isEmpty(data[outer]) {
        return ${Index}(data, outer, data[outer].startIndex)
      }
    }
    return ${Index}(data, outer, nil)
  }

  /// Returns the next consecutive value after `self`.
  ///
  /// Requires: the next value is representable.
  public // @testable
  func successor() -> ${Index} {
    return ${Index}.adjustForward(_data, _outer, _inner!.successor())
  }

  % if traversal == 'Bidirectional':
  /// Returns the previous consecutive value before `self`.
  ///
  /// Requires: the previous value is representable.
  public // @testable
  func predecessor() -> ${Index} {

    var outer = _outer
    var inner = _inner

    while inner == nil || inner! == _data[outer].startIndex {
      inner = _data[--outer].endIndex
    }
    return ${Index}(_data, outer, inner!.predecessor())
  }
% end
}

public // @testable
func == <I> (lhs: ${Index}<I>, rhs: ${Index}<I>) -> Bool {
  return lhs._outer == rhs._outer && lhs._inner == rhs._inner
}

/// The lazy `CollectionType` returned by `lazyConcatenate(c)` where `c` is a
/// `CollectionType` having an `Index` conforming to `${IndexProtocol}`
public // @testable
struct ${View}<
  C: CollectionType
    where C.Index: ${IndexProtocol},
          C.Generator.Element: CollectionType,
          C.Generator.Element.Index : ${IndexProtocol}
> : CollectionType {
  /// A type that represents a valid position in the collection.
  ///
  /// Valid indices consist of the position of every element and a
  /// "past the end" position that's not valid for use as a subscript.
  typealias Index = ${Index}<C>

  init(_ _base: C) {
    self._base = _base
  }

  /// Return a *generator* over the elements of this *sequence*.
  ///
  /// Complexity: O(1)
  public // @testable
  func generate() -> _ConcatenateSequenceGenerator<C.Generator> {
    return _ConcatenateSequenceGenerator(_base.generate())
  }

  /// The position of the first element in a non-empty collection.
  ///
  /// Identical to `endIndex` in an empty collection.
  public // @testable
  var startIndex: Index {
    return ${Index}.adjustForward(_base, _base.startIndex, nil)
  }

  /// 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 // @testable
  var endIndex: Index {
    return ${Index}(_base, _base.endIndex, nil)
  }

  /// Access the element at `position`.
  ///
  /// Requires: `position` is a valid position in `self` and
  /// `position != endIndex`.
  public // @testable
  subscript(position: Index) -> C.Generator.Element.Generator.Element {
    return _base[position._outer][position._inner!]
  }

  var _base: C
}

/// Return a collection that is a concatenation of the elements of
/// `source`\ 's elements
public // @testable
func _lazyConcatenate<
  C: CollectionType
    where C.Index: ${IndexProtocol},
          C.Generator.Element: CollectionType,
          C.Generator.Element.Index : ${IndexProtocol}
>(source: C) -> Lazy${traversal}Collection<${View}<C>> {
  return Lazy${traversal}Collection(${View}(source))
}

% end

/// Return an `Array` containing the results of mapping `transform`
/// over `source`.
func _concatenate<
  C : CollectionType
  where C.Generator.Element : CollectionType
>(
  source: C
) -> [C.Generator.Element.Generator.Element] {
  return _lazyConcatenate(source).array
}

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