TreapMergeSplit.swift

//
//  TreapMergeSplit.swift
//  TreapExample
//
//  Created by Robert Thompson on 7/27/15.
//  Copyright © 2016 Robert Thompson
/* Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.*/

import Foundation
public extension Treap {
  internal func split(_ key: Key) -> (left: Treap, right: Treap) {
    var current = self
    let val: Element
    if let newVal = self.get(key) {
      // swiftlint:disable force_try
      current = try! current.delete(key: key)
      // swiftlint:enable force_try
      val = newVal
    } else if case let .node(_, newVal, _, _, _) = self {
      val = newVal
    } else {
      fatalError("No values in treap")
    }
    
    switch self {
    case .node:
      if case let .node(_, _, _, left, right) = current.set(key: key, val: val, p: -1) {
        return (left: left, right: right)
      } else {
        return (left: .empty, right: .empty)
      }
    default:
      return (left: .empty, right: .empty)
    }
  }
  
  internal var leastKey: Key? {
    switch self {
    case .empty:
      return nil
    case let .node(key, _, _, .empty, _):
      return key
    case let .node(_, _, _, left, _):
      return left.leastKey
    }
  }
  
  internal var mostKey: Key? {
    switch self {
    case .empty:
      return nil
    case let .node(key, _, _, _, .empty):
      return key
    case let .node(_, _, _, _, right):
      return right.mostKey
    }
  }
}

internal func merge<Key: Comparable, Element>(_ left: Treap<Key, Element>, right: Treap<Key, Element>) -> Treap<Key, Element> {
  switch (left, right) {
  case (.empty, _):
    return right
  case (_, .empty):
    return left
    
  case let (.node(leftKey, leftVal, leftP, leftLeft, leftRight), .node(rightKey, rightVal, rightP, rightLeft, rightRight)):
    if leftP < rightP {
      return .node(key: leftKey, val: leftVal, p: leftP, left: leftLeft, right: merge(leftRight, right: right))
    } else {
      return .node(key: rightKey, val: rightVal, p: rightP, left: merge(rightLeft, right: left), right: rightRight)
    }
  default:
    break
  }
  return .empty
}

extension Treap: CustomStringConvertible {
  public var description: String {
    get {
      return Treap.descHelper(self, indent: 0)
    }
  }
  
  fileprivate static func descHelper(_ treap: Treap<Key, Element>, indent: Int) -> String {
    if case let .node(key, value, priority, left, right) = treap {
      var result = ""
      let tabs = String(repeating: "\t", count: indent)
      
      result += descHelper(left, indent: indent + 1)
      result += "\n" + tabs + "\(key), \(value), \(priority)\n"
      result += descHelper(right, indent: indent + 1)
      
      return result
    } else {
      return ""
    }
  }
}