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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2021-2022 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
//
//===----------------------------------------------------------------------===//
struct DefaultSearcherState<Searched: Collection> {
enum Position {
case index(Searched.Index)
case done
}
var position: Position
let end: Searched.Index
}
protocol CollectionSearcher {
associatedtype Searched: Collection
associatedtype State
func state(for searched: Searched, in range: Range<Searched.Index>) -> State
func search(
_ searched: Searched,
_ state: inout State
) -> Range<Searched.Index>?
}
protocol StatelessCollectionSearcher: CollectionSearcher
where State == DefaultSearcherState<Searched>
{
func search(
_ searched: Searched,
in range: Range<Searched.Index>) -> Range<Searched.Index>?
}
extension StatelessCollectionSearcher {
func state(
for searched: Searched,
in range: Range<Searched.Index>
) -> State {
State(position: .index(range.lowerBound), end: range.upperBound)
}
func search(
_ searched: Searched,
_ state: inout State
) -> Range<Searched.Index>? {
guard
case .index(let index) = state.position,
let range = search(searched, in: index..<state.end)
else { return nil }
if range.isEmpty {
if range.upperBound == searched.endIndex {
state.position = .done
} else {
state.position = .index(searched.index(after: range.upperBound))
}
} else {
state.position = .index(range.upperBound)
}
return range
}
}
// MARK: Searching from the back
protocol BackwardCollectionSearcher {
associatedtype BackwardSearched: BidirectionalCollection
associatedtype BackwardState
func backwardState(
for searched: BackwardSearched,
in range: Range<BackwardSearched.Index>) -> BackwardState
func searchBack(
_ searched: BackwardSearched,
_ state: inout BackwardState
) -> Range<BackwardSearched.Index>?
}
protocol BackwardStatelessCollectionSearcher: BackwardCollectionSearcher
where BackwardState == DefaultSearcherState<BackwardSearched>
{
func searchBack(
_ searched: BackwardSearched,
in range: Range<BackwardSearched.Index>
) -> Range<BackwardSearched.Index>?
}
extension BackwardStatelessCollectionSearcher {
func backwardState(
for searched: BackwardSearched,
in range: Range<BackwardSearched.Index>
) -> BackwardState {
BackwardState(position: .index(range.upperBound), end: range.lowerBound)
}
func searchBack(
_ searched: BackwardSearched,
_ state: inout BackwardState) -> Range<BackwardSearched.Index>? {
guard
case .index(let index) = state.position,
let range = searchBack(searched, in: state.end..<index)
else { return nil }
if range.isEmpty {
if range.lowerBound == searched.startIndex {
state.position = .done
} else {
state.position = .index(searched.index(before: range.lowerBound))
}
} else {
state.position = .index(range.lowerBound)
}
return range
}
}
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