TestUtilities.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Algorithms open source project
//
// Copyright (c) 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//

import XCTest

extension Sequence {
  func isSorted(by f: (Element, Element) -> Bool) -> Bool {
    zip(self, self.dropFirst()).allSatisfy { !f($1, $0) }
  }
}

extension Sequence where Element: Comparable {
  func isSorted() -> Bool {
    isSorted(by: <)
  }
}

extension Numeric {
  func factorial() -> Self {
    guard self != 0 else { return 1 }
    return self * (self - 1).factorial()
  }
}

struct SplitMix64: RandomNumberGenerator {
  private var state: UInt64

  init(seed: UInt64) {
    self.state = seed
  }

  mutating func next() -> UInt64 {
    self.state &+= 0x9e37_79b9_7f4a_7c15
    var z: UInt64 = self.state
    z = (z ^ (z &>> 30)) &* 0xbf58_476d_1ce4_e5b9
    z = (z ^ (z &>> 27)) &* 0x94d0_49bb_1331_11eb
    return z ^ (z &>> 31)
  }
}

// An eraser helper to any mutable collection
struct AnyMutableCollection<Base> where Base: MutableCollection {
  var base: Base
}

extension AnyMutableCollection: MutableCollection {
  typealias Index = Base.Index
  typealias Element = Base.Element

  var startIndex: Base.Index { base.startIndex }
  var endIndex: Base.Index { base.endIndex }

  func index(after i: Index) -> Index {
    base.index(after: i)
  }

  subscript(position: Base.Index) -> Base.Element {
    _read { yield base[position] }
    set { base[position] = newValue }
  }
}

extension MutableCollection {
  func eraseToAnyMutableCollection() -> AnyMutableCollection<Self> {
    AnyMutableCollection(base: self)
  }
}

func expectEqualSequences<S1: Sequence, S2: Sequence>(
  _ expression1: @autoclosure () throws -> S1,
  _ expression2: @autoclosure () throws -> S2,
  _ message: @autoclosure () -> String = "",
  file: StaticString = (#file), line: UInt = #line
) rethrows where S1.Element: Equatable, S1.Element == S2.Element {
  try expectEqualSequences(
    expression1(), expression2(), by: ==,
    message(), file: file, line: line)
}

// Two sequences contains exactly the same element but not necessarily in the same order.
func expectUnorderedEqualSequences<S1: Sequence, S2: Sequence>(
  _ expression1: @autoclosure () throws -> S1,
  _ expression2: @autoclosure () throws -> S2,
  file: StaticString = (#file), line: UInt = #line
) rethrows where S1.Element: Equatable, S1.Element == S2.Element {
  var s1 = Array(try expression1())
  var missing: [S1.Element] = []
  for elt in try expression2() {
    guard let idx = s1.firstIndex(of: elt) else {
      missing.append(elt)
      continue
    }
    s1.remove(at: idx)
  }

  XCTAssertTrue(
    missing.isEmpty,
    "first sequence missing '\(missing)' elements from second sequence",
    file: file, line: line
  )

  XCTAssertTrue(
    s1.isEmpty, "first sequence contains \(s1) missing from second sequence",
    file: file, line: line
  )
}

func expectEqualSequences<S1: Sequence, S2: Sequence>(
  _ expression1: @autoclosure () throws -> S1,
  _ expression2: @autoclosure () throws -> S2,
  by areEquivalent: (S1.Element, S1.Element) -> Bool,
  _ message: @autoclosure () -> String = "",
  file: StaticString = (#file), line: UInt = #line
) rethrows where S1.Element == S2.Element {

  func fail(_ reason: String) {
    let message = message()
    XCTFail(
      message.isEmpty ? reason : "\(message) - \(reason)",
      file: file, line: line)
  }

  var iter1 = try expression1().makeIterator()
  var iter2 = try expression2().makeIterator()
  var idx = 0
  while true {
    switch (iter1.next(), iter2.next()) {
    case (let e1?, let e2?) where areEquivalent(e1, e2):
      idx += 1
      continue
    case (let e1?, let e2?):
      fail(
        "element \(e1) on first sequence does not match element \(e2) on second sequence at position \(idx)"
      )
    case (_?, nil):
      fail("second sequence shorter than first")
    case (nil, _?):
      fail("first sequence shorter than second")
    case (nil, nil): break
    }
    return
  }
}

func requireLazySequence<S: LazySequenceProtocol>(_: S) {}
func requireLazyCollection<S: LazyCollectionProtocol>(_: S) {}

/// Asserts two collections are equal by using their indices to access elements.
func expectEqualCollections<C1: Collection, C2: Collection>(
  _ expression1: @autoclosure () throws -> C1,
  _ expression2: @autoclosure () throws -> C2,
  _ message: @autoclosure () -> String = "",
  file: StaticString = (#file), line: UInt = #line
) rethrows where C1.Element: Equatable, C1.Element == C2.Element {
  let c1 = try expression1()
  let c2 = try expression2()
  XCTAssertEqual(
    c1.indices.count, c2.indices.count, message(), file: file, line: line)
  for index in zip(c1.indices, c2.indices) {
    XCTAssertEqual(c1[index.0], c2[index.1], message(), file: file, line: line)
  }
}

struct IndexValidator<C: Collection> {
  let testRandomAccess = true
  let indicesIncludingEnd: (C) -> [C.Index]

  /// Creates a new instance of an index validator that can verify that indices
  /// of a collection behave correctly and consistently.
  ///
  /// Usage:
  ///
  ///     let validator = IndexValidator<ReversedCollection<String>>()
  ///     validator.validate("abc".reversed())
  ///     validator.validate("xyz".reversed(), expectedCount: 3)
  ///
  /// - Parameters:
  ///   - testRandomAccess: If `true`, also tests the correctness of the methods
  ///     `index(_:offsetBy:)`, `index(_:offsetBy:limitedBy:)`, and
  ///     `distance(from:to:)`. Only useful if the collection overrides these
  ///     methods. Defaults to `true`.
  ///   - indicesIncludingEnd: A closure that returns the expected indices of
  ///     the given collection, including its `endIndex`, in ascending order.
  ///     Only use this parameter if you are able to compute the indices of the
  ///     collection independently of the `Collection` conformance, e.g. by
  ///     using the contents of the collection directly.
  init(
    testRandomAccess: Bool = true,
    indicesIncludingEnd: @escaping (C) -> [C.Index] = {
      $0.indices + [$0.endIndex]
    }
  ) {
    self.indicesIncludingEnd = indicesIncludingEnd
  }
}

extension IndexValidator {
  fileprivate struct Validator {
    let collection: C
    let count: Int
    let indicesIncludingEnd: [C.Index]
    let file: StaticString
    let line: UInt
  }

  /// Verifies that all index traversal methods behave as expected.
  ///
  /// Verifies the correctness of the implementations of `startIndex`,
  /// `endIndex`, `indices`, `count`, `isEmpty`, `index(before:)`,
  /// `index(after:)`, `index(_:offsetBy:)`, `index(_:offsetBy:limitedBy:)`, and
  /// `distance(from:to:)` by calling them with just about all possible input
  /// combinations.
  ///
  /// - Complexity: O(*n*^3) where *n* is the length of the collection if the
  ///   collection conforms to `RandomAccessCollection`, otherwise O(*n*^4).
  func validate(
    _ collection: C,
    expectedCount: Int? = nil,
    file: StaticString = #file, line: UInt = #line
  ) {
    let indicesIncludingEnd = self.indicesIncludingEnd(collection)
    let count = indicesIncludingEnd.count - 1

    let validator = Validator(
      collection: collection,
      count: count,
      indicesIncludingEnd: indicesIncludingEnd,
      file: file, line: line)

    validator.validateForward(
      testRandomAccess: testRandomAccess,
      expectedCount: expectedCount)
  }
}

extension IndexValidator where C: BidirectionalCollection {
  func validate(
    _ collection: C, expectedCount: Int? = nil,
    file: StaticString = #file, line: UInt = #line
  ) {
    let indicesIncludingEnd = self.indicesIncludingEnd(collection)
    let count = indicesIncludingEnd.count - 1

    let validator = Validator(
      collection: collection,
      count: count,
      indicesIncludingEnd: indicesIncludingEnd,
      file: file, line: line)

    validator.validateForward(
      testRandomAccess: testRandomAccess,
      expectedCount: expectedCount)
    validator.validateBackward(testRandomAccess: testRandomAccess)
  }
}

extension IndexValidator.Validator {
  func validateForward(testRandomAccess: Bool, expectedCount: Int?) {
    if let expectedCount = expectedCount {
      XCTAssertEqual(
        expectedCount, count, "Count mismatch", file: file, line: line)
    }

    XCTAssertEqual(
      collection.count, count,
      "Count mismatch",
      file: file, line: line)
    XCTAssertEqual(
      collection.isEmpty, count == 0,
      "Emptiness mismatch",
      file: file, line: line)
    XCTAssertEqual(
      collection.startIndex, indicesIncludingEnd.first,
      "`startIndex` does not equal the first index",
      file: file, line: line)
    XCTAssertEqual(
      collection.endIndex, indicesIncludingEnd.last,
      "`endIndex` does not equal the last index",
      file: file, line: line)

    validateIndexAfter()
    validateIndices()
    validateIndexComparisons()

    if testRandomAccess {
      validateDistanceFromTo()
      validateIndexOffsetBy()
      validateIndexOffsetByLimitedBy()
    }
  }

  func validateIndexAfter() {
    var index = collection.startIndex

    for (offset, expected) in indicesIncludingEnd.enumerated().dropFirst() {
      collection.formIndex(after: &index)
      XCTAssertEqual(
        index, expected,
        """
        `startIndex` incremented \(offset) times does not equal index at \
        offset \(offset)
        """,
        file: file, line: line)
    }
  }

  func validateIndices() {
    XCTAssertEqual(collection.indices.count, count)
    for (offset, index) in collection.indices.enumerated() {
      XCTAssertEqual(
        index, indicesIncludingEnd[offset],
        "Index mismatch at offset \(offset) in `indices`",
        file: file, line: line)
    }
  }

  func validateIndexComparisons() {
    for (offsetA, a) in indicesIncludingEnd.enumerated() {
      XCTAssertEqual(
        a, a,
        "Index at offset \(offsetA) does not equal itself",
        file: file, line: line)
      XCTAssertFalse(
        a < a,
        "Index at offset \(offsetA) is less than itself",
        file: file, line: line)

      for (offsetB, b) in indicesIncludingEnd[..<offsetA].enumerated() {
        XCTAssertNotEqual(
          a, b,
          "Index at offset \(offsetA) equals index at offset \(offsetB)",
          file: file, line: line)
        XCTAssertLessThan(
          b, a,
          """
          Index at offset \(offsetB) is not less than index at offset \(offsetA)
          """,
          file: file, line: line)
      }
    }
  }

  func validateDistanceFromTo() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (endOffset, end) in indicesIncludingEnd.enumerated().dropFirst(
        startOffset)
      {
        let distance = endOffset - startOffset
        XCTAssertEqual(
          collection.distance(from: start, to: end), distance,
          """
          Distance from index at offset \(startOffset) to index at offset \
          \(endOffset) does not equal \(distance)
          """,
          file: file, line: line)
      }
    }
  }

  func validateIndexOffsetBy() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (endOffset, end) in indicesIncludingEnd.enumerated().dropFirst(
        startOffset)
      {
        let distance = endOffset - startOffset
        XCTAssertEqual(
          collection.index(start, offsetBy: distance), end,
          """
          Index at offset \(startOffset) offset by \(distance) does not \
          equal index at offset \(endOffset)
          """,
          file: file, line: line)
      }
    }
  }

  func validateIndexOffsetByLimitedBy() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (limitOffset, limit) in indicesIncludingEnd.enumerated() {
        // verifies that the target index corresponding to each offset in
        // `range` can or cannot be reached from `start` using
        // `chain.index(start, offsetBy: _, limitedBy: limit)`, depending on
        // the value of `pastLimit`
        func checkTargetRange(_ range: ClosedRange<Int>, pastLimit: Bool) {
          for targetOffset in range {
            let distance = targetOffset - startOffset
            let end = collection.index(
              start, offsetBy: distance, limitedBy: limit)

            if pastLimit {
              XCTAssertNil(
                end,
                """
                Index at offset \(startOffset) offset by \(distance) limited \
                by index at offset \(limitOffset) does not equal `nil`
                """,
                file: file, line: line)
            } else {
              XCTAssertEqual(
                end, indicesIncludingEnd[targetOffset],
                """
                Index at offset \(startOffset) offset by \(distance) limited \
                by index at offset \(limitOffset) does not equal index at \
                offset \(targetOffset)
                """,
                file: file, line: line)
            }
          }
        }

        if limit >= start {
          // the limit has an effect
          checkTargetRange(startOffset...limitOffset, pastLimit: false)
          checkTargetRange((limitOffset + 1)...(count + 1), pastLimit: true)
        } else {
          // the limit has no effect
          checkTargetRange(startOffset...count, pastLimit: false)
        }
      }
    }
  }
}

extension IndexValidator.Validator where C: BidirectionalCollection {
  func validateBackward(testRandomAccess: Bool) {
    validateIndexBefore()

    if testRandomAccess {
      validateDistanceFromTo()
      validateIndexOffsetBy()
      validateIndexOffsetByLimitedBy()
    }
  }

  func validateIndexBefore() {
    var index = collection.endIndex

    for (offset, expected) in indicesIncludingEnd.enumerated().dropLast()
      .reversed()
    {
      collection.formIndex(before: &index)
      XCTAssertEqual(
        index, expected,
        """
        `endIndex` decremented \(count - offset) times does not equal index \
        at offset \(offset)
        """,
        file: file, line: line)
    }
  }

  func validateDistanceFromTo() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (endOffset, end) in indicesIncludingEnd.enumerated().prefix(
        startOffset)
      {
        let distance = endOffset - startOffset
        XCTAssertEqual(
          collection.distance(from: start, to: end), distance,
          """
          Distance from index at offset \(startOffset) to index at offset \
          \(endOffset) does not equal \(distance)
          """,
          file: file, line: line)
      }
    }
  }

  func validateIndexOffsetBy() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (endOffset, end) in indicesIncludingEnd.enumerated().prefix(
        startOffset)
      {
        let distance = endOffset - startOffset
        XCTAssertEqual(
          collection.index(start, offsetBy: distance), end,
          """
          Index at offset \(startOffset) offset by \(distance) does not \
          equal index at offset \(endOffset)
          """,
          file: file, line: line)
      }
    }
  }

  func validateIndexOffsetByLimitedBy() {
    for (startOffset, start) in indicesIncludingEnd.enumerated() {
      for (limitOffset, limit) in indicesIncludingEnd.enumerated() {
        // verifies that the target index corresponding to each offset in
        // `range` can or cannot be reached from `start` using
        // `chain.index(start, offsetBy: _, limitedBy: limit)`, depending on
        // the value of `pastLimit`
        func checkTargetRange(_ range: ClosedRange<Int>, pastLimit: Bool) {
          for targetOffset in range {
            let distance = targetOffset - startOffset
            let end = collection.index(
              start, offsetBy: distance, limitedBy: limit)

            if pastLimit {
              XCTAssertNil(
                end,
                """
                Index at offset \(startOffset) offset by \(distance) limited \
                by index at offset \(limitOffset) does not equal `nil`
                """,
                file: file, line: line)
            } else {
              XCTAssertEqual(
                end, indicesIncludingEnd[targetOffset],
                """
                Index at offset \(startOffset) offset by \(distance) limited \
                by index at offset \(limitOffset) does not equal index at \
                offset \(targetOffset)
                """,
                file: file, line: line)
            }
          }
        }

        if limit <= start {
          // the limit has an effect
          checkTargetRange(limitOffset...startOffset, pastLimit: false)
          checkTargetRange(-1...(limitOffset - 1), pastLimit: true)
        } else {
          // the limit has no effect
          checkTargetRange(0...startOffset, pastLimit: false)
        }
      }
    }
  }
}