//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 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
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

extension String {
  // FIXME(strings): at least temporarily remove it to see where it was applied
  public init(_ substring: Substring) {
    self = String(substring._slice)
  }
}

public struct Substring : RangeReplaceableCollection, BidirectionalCollection {
  public typealias Index = String.Index
  public typealias IndexDistance = String.IndexDistance
  public typealias SubSequence = Substring

  internal var _slice: RangeReplaceableBidirectionalSlice<String>

  public init() {
    _slice = RangeReplaceableBidirectionalSlice()
  }

  public init(_base base: String, _ bounds: Range<Index>) {
    _slice = RangeReplaceableBidirectionalSlice(base: base, bounds: bounds)
  }

  internal init<R: RangeExpression>(_base base: String, _ bounds: R) where R.Bound == Index {
    self.init(_base: base, bounds.relative(to: base))
  }

  public var startIndex: Index { return _slice.startIndex }
  public var endIndex: Index { return _slice.endIndex }

  public func index(after i: Index) -> Index {
    _precondition(i < endIndex, "Cannot increment beyond endIndex")
    _precondition(i >= startIndex, "Cannot increment an invalid index")
    // FIXME(strings): slice types currently lack necessary bound checks
    return _slice.index(after: i)
  }

  public func index(before i: Index) -> Index {
    _precondition(i <= endIndex, "Cannot decrement an invalid index")
    _precondition(i > startIndex, "Cannot decrement beyond startIndex")
    // FIXME(strings): slice types currently lack necessary bound checks
    return _slice.index(before: i)
  }

  public func index(_ i: Index, offsetBy n: IndexDistance) -> Index {
    let result = _slice.index(i, offsetBy: n)
    // FIXME(strings): slice types currently lack necessary bound checks
    _precondition(
      (_slice._startIndex ... _slice.endIndex).contains(result),
      "Operation results in an invalid index")
    return result
  }

  public func index(
    _ i: Index, offsetBy n: IndexDistance, limitedBy limit: Index
  ) -> Index? {
    let result = _slice.index(i, offsetBy: n, limitedBy: limit)
    // FIXME(strings): slice types currently lack necessary bound checks
    _precondition(result.map {
        (_slice._startIndex ... _slice.endIndex).contains($0)
      } ?? true,
      "Operation results in an invalid index")
    return result
  }

  public func distance(from start: Index, to end: Index) -> IndexDistance {
    return _slice.distance(from: start, to: end)
  }

  public subscript(i: Index) -> Character {
    return _slice[i]
  }

  public mutating func replaceSubrange<C>(
    _ bounds: Range<Index>,
    with newElements: C
  ) where C : Collection, C.Iterator.Element == Iterator.Element {
    // FIXME(strings): slice types currently lack necessary bound checks
    _slice.replaceSubrange(bounds, with: newElements)
  }

% for Range in ['Range', 'ClosedRange']:

  public mutating func replaceSubrange(
    _ bounds: ${Range}<Index>, with newElements: Substring
  ) {
    replaceSubrange(bounds, with: newElements._slice)
  }

% end
}


extension Substring : CustomReflectable {
  public var customMirror: Mirror {
    return String(self).customMirror
  }
}

extension Substring : CustomPlaygroundQuickLookable {
  public var customPlaygroundQuickLook: PlaygroundQuickLook {
    return String(self).customPlaygroundQuickLook
  }
}

extension Substring : CustomStringConvertible {
  public var description: String {
    return String(self)
  }
}

extension Substring : CustomDebugStringConvertible {
  public var debugDescription: String {
    return String(self).debugDescription
  }
}

extension Substring : LosslessStringConvertible {
  public init?(_ description: String) {
    self.init(_base: description, description.startIndex ..< description.endIndex)
  }
}

extension Substring : Equatable {
  public static func ==(lhs: Substring, rhs: Substring) -> Bool {
    return String(lhs) == String(rhs)
  }

  // These are not Equatable requirements, but sufficiently similar to be in
  // this extension.
  // FIXME(strings): should be gone if/when an implicit conversion from/to
  // String is available.
  // FIXME(ABI):
  public static func ==(lhs: String, rhs: Substring) -> Bool {
    return lhs == String(rhs)
  }

  public static func ==(lhs: Substring, rhs: String) -> Bool {
    return String(lhs) == rhs
  }

  public static func !=(lhs: String, rhs: Substring) -> Bool {
    return lhs != String(rhs)
  }

  public static func !=(lhs: Substring, rhs: String) -> Bool {
    return String(lhs) != rhs
  }
}

extension Substring : Comparable {
  public static func <(lhs: Substring, rhs: Substring) -> Bool {
    return String(lhs) < String(rhs)
  }
}

extension Substring : Hashable {
  public var hashValue : Int {
    return String(self).hashValue
  }
}

extension Substring {
% for (property, ViewPrefix) in [
%   ('utf8', 'UTF8'),
%   ('utf16', 'UTF16'),
%   ('unicodeScalars', 'UnicodeScalar'),
%   ('characters', 'Character')]:
  public typealias ${ViewPrefix}Index = String.${ViewPrefix}View.Index

  public var ${property}: String.${ViewPrefix}View {
    get {
      return String(self).${property}
    }
    set {
      let base = String(describing: newValue)
      self = Substring(_base: base, base.startIndex ..< base.endIndex)
    }
  }
% end
}

#if _runtime(_ObjC)

extension Substring {
  public func hasPrefix(_ prefix: String) -> Bool {
    return String(self).hasPrefix(prefix)
  }

  public func hasSuffix(_ suffix: String) -> Bool {
    return String(self).hasSuffix(suffix)
  }
}

#endif

extension Substring {
  public func lowercased() -> String {
    return String(self).lowercased()
  }

  public func uppercased() -> String {
    return String(self).uppercased()
  }
}

extension Substring : TextOutputStream {
  public mutating func write(_ other: String) {
    append(contentsOf: other)
  }
}

extension Substring : TextOutputStreamable {
  public func write<Target : TextOutputStream>(to target: inout Target) {
    target.write(String(self))
  }
}

extension Substring : ExpressibleByUnicodeScalarLiteral {
  public init(unicodeScalarLiteral value: String) {
     self.init(_base: value, value.startIndex ..< value.endIndex)
  }
}
extension Substring : ExpressibleByExtendedGraphemeClusterLiteral {
  public init(extendedGraphemeClusterLiteral value: String) {
     self.init(_base: value, value.startIndex ..< value.endIndex)
  }
}

extension Substring : ExpressibleByStringLiteral {
  public init(stringLiteral value: String) {
     self.init(_base: value, value.startIndex ..< value.endIndex)
  }
}

// The purpose of this protocol is backward compatibility with Swift 3 code,
// where String subscripts returned String.
// Since the Substring returning subscripts are introduced by the protocol
// extension, they will be less specific than the String-returning ones
// declared on the String type itself, thus avoiding ambiguity.
public protocol _RangeSubscriptableString {
  associatedtype Index : Comparable
  func _subscript(_ bounds: Range<Index>) -> Substring
  func _subscript(_ bounds: ClosedRange<Index>) -> Substring
}

// Without the `where` subscripts will be ambiguous
extension _RangeSubscriptableString where Self : RangeReplaceableCollection {
% for Range in ['Range', 'ClosedRange']:
  public subscript(bounds: ${Range}<Index>) -> Substring {
    return _subscript(bounds)
  }
% end
}

extension String : _RangeSubscriptableString {
% for Range in ['Range', 'ClosedRange']:
  /// Accesses the text in the given range.
  ///
  /// - Complexity: O(*n*) if the underlying string is bridged from
  ///   Objective-C, where *n* is the length of the string; otherwise, O(1).
  public func _subscript(_ bounds: ${Range}<Index>) -> Substring {
    return Substring(_base: String(self._core), bounds)
  }
% end
}

extension Substring : _RangeSubscriptableString {
% for Range in ['Range', 'ClosedRange']:
  public func _subscript(_ bounds: ${Range}<Index>) -> Substring {
    let subSlice = _slice[bounds]
    let bounds = (lower: subSlice.startIndex, upper: subSlice.endIndex)
%   if Range == 'ClosedRange':
    // Creating Substring using the half-open range, since subSlice already
    // handled the ClosedRange case.
%   end
    return Substring(_base: _slice._base, Range(uncheckedBounds: bounds))
  }
% end
}

extension String {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String {
    return String(characters[bounds])
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String {
    return String(characters[bounds])
  }
}

extension Substring {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String {
    return String(self[bounds])
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String {
    return String(self[bounds] as Substring)
  }
}