//
//  CryptoSwift
//
//  Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
//  This software is provided 'as-is', without any express or implied warranty.
//
//  In no event will the authors be held liable for any damages arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
//
//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
//  - This notice may not be removed or altered from any source or binary distribution.
//

@usableFromInline
struct BatchedCollectionIndex<Base: Collection> {
  let range: Range<Base.Index>
}

extension BatchedCollectionIndex: Comparable {
  @usableFromInline
  static func == <Base>(lhs: BatchedCollectionIndex<Base>, rhs: BatchedCollectionIndex<Base>) -> Bool {
    lhs.range.lowerBound == rhs.range.lowerBound
  }

  @usableFromInline
  static func < <Base>(lhs: BatchedCollectionIndex<Base>, rhs: BatchedCollectionIndex<Base>) -> Bool {
    lhs.range.lowerBound < rhs.range.lowerBound
  }
}

protocol BatchedCollectionType: Collection {
  associatedtype Base: Collection
}

@usableFromInline
struct BatchedCollection<Base: Collection>: Collection {
  let base: Base
  let size: Int

  @usableFromInline
  init(base: Base, size: Int) {
    self.base = base
    self.size = size
  }

  @usableFromInline
  typealias Index = BatchedCollectionIndex<Base>

  private func nextBreak(after idx: Base.Index) -> Base.Index {
    self.base.index(idx, offsetBy: self.size, limitedBy: self.base.endIndex) ?? self.base.endIndex
  }

  @usableFromInline
  var startIndex: Index {
    Index(range: self.base.startIndex..<self.nextBreak(after: self.base.startIndex))
  }

  @usableFromInline
  var endIndex: Index {
    Index(range: self.base.endIndex..<self.base.endIndex)
  }

  @usableFromInline
  func index(after idx: Index) -> Index {
    Index(range: idx.range.upperBound..<self.nextBreak(after: idx.range.upperBound))
  }

  @usableFromInline
  subscript(idx: Index) -> Base.SubSequence {
    self.base[idx.range]
  }
}

extension Collection {
  @inlinable
  func batched(by size: Int) -> BatchedCollection<Self> {
    BatchedCollection(base: self, size: size)
  }
}
