NSPredicate+Snippets.swift

// Snippets NSPredicate+Snippets.swift
//
// Copyright © 2016, Roy Ratcliffe, Pioneering Software, United Kingdom
//
// 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, EITHER
// EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. 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

extension NSPredicate {

  /// Returns all non-compound sub-predicates of this predicate. Includes this
  /// one if not a compound predicate.
  public var allSubpredicates: [NSPredicate] {
    var allSubpredicates = [NSPredicate]()
    var predicates = [self]
    while let predicate = predicates.popLast() {
      switch predicate {
      case let compoundPredicate as NSCompoundPredicate:
        predicates.append(contentsOf: compoundPredicate.subpredicates.flatMap { $0 as? NSPredicate })
      default:
        allSubpredicates.append(predicate)
      }
    }
    return allSubpredicates
  }

  /// Returns all comparison sub-predicates.
  public var allComparisonSubpredicates: [NSComparisonPredicate] {
    return allSubpredicates.flatMap { $0 as? NSComparisonPredicate }
  }

  /// Returns all sub-expressions found in all comparison sub-predicates.
  public var allSubexpressions: [NSExpression] {
    let comparisonPredicates = allComparisonSubpredicates
    let leftExpressions = comparisonPredicates.map { $0.leftExpression }
    let rightExpressions = comparisonPredicates.map { $0.rightExpression }
    return leftExpressions + rightExpressions
  }

  /// Returns all constant values found in all sub-expressions from all
  /// comparison sub-predicates.
  public var allConstantSubvalues: [Any] {
    return allSubexpressions.filter { $0.expressionType == .constantValue }.flatMap { $0.constantValue }
  }

}