├── .gitignore
├── .swiftpm
    └── xcode
    │   └── package.xcworkspace
    │       ├── contents.xcworkspacedata
    │       └── xcshareddata
    │           └── IDEWorkspaceChecks.plist
├── Tests
    ├── LinuxMain.swift
    └── SpacedRepetitionSchedulerTests
    │   ├── XCTestManifests.swift
    │   └── SpacedRepetitionSchedulerTests.swift
├── .swiftformat
├── Package.swift
├── Sources
    └── SpacedRepetitionScheduler
    │   ├── Array+RecallEaseLinearSearch.swift
    │   ├── PromptSchedulingMode.swift
    │   ├── RecallEase.swift
    │   ├── TimeInterval+Fuzzing.swift
    │   ├── Documentation.docc
    │       └── Documentation.md
    │   ├── SchedulingParameters.swift
    │   └── PromptSchedulingMetadata.swift
├── CHANGELOG.md
├── README.md
└── LICENSE


/.gitignore:
--------------------------------------------------------------------------------
1 | .DS_Store
2 | /.build
3 | /Packages
4 | /*.xcodeproj
5 | xcuserdata/
6 | 


--------------------------------------------------------------------------------
/.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata:
--------------------------------------------------------------------------------
1 | <?xml version="1.0" encoding="UTF-8"?>
2 | <Workspace
3 |    version = "1.0">
4 |    <FileRef
5 |       location = "container:../..">
6 |    </FileRef>
7 | </Workspace>
8 | 


--------------------------------------------------------------------------------
/Tests/LinuxMain.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import XCTest
 4 | 
 5 | import SpacedRepetitionSchedulerTests
 6 | 
 7 | var tests = [XCTestCaseEntry]()
 8 | tests += SpacedRepetitionSchedulerTests.allTests()
 9 | XCTMain(tests)
10 | 


--------------------------------------------------------------------------------
/.swiftpm/xcode/package.xcworkspace/xcshareddata/IDEWorkspaceChecks.plist:
--------------------------------------------------------------------------------
1 | <?xml version="1.0" encoding="UTF-8"?>
2 | <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
3 | <plist version="1.0">
4 | <dict>
5 | 	<key>IDEDidComputeMac32BitWarning</key>
6 | 	<true/>
7 | </dict>
8 | </plist>
9 | 


--------------------------------------------------------------------------------
/Tests/SpacedRepetitionSchedulerTests/XCTestManifests.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import XCTest
 4 | 
 5 | #if !canImport(ObjectiveC)
 6 |   public func allTests() -> [XCTestCaseEntry] {
 7 |     return [
 8 |       testCase(SpacedRepetitionSchedulerTests.allTests),
 9 |     ]
10 |   }
11 | #endif
12 | 


--------------------------------------------------------------------------------
/.swiftformat:
--------------------------------------------------------------------------------
 1 | --binarygrouping none
 2 | --decimalgrouping none
 3 | --exclude Package.swift
 4 | --header "Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license."
 5 | --hexgrouping none
 6 | --indent 2
 7 | --octalgrouping none
 8 | --patternlet inline
 9 | --stripunusedargs closure-only
10 | --wraparguments beforefirst
11 | --wrapcollections beforefirst
12 | --self init-only
13 | 


--------------------------------------------------------------------------------
/Package.swift:
--------------------------------------------------------------------------------
 1 | // swift-tools-version:5.5
 2 | 
 3 | import PackageDescription
 4 | 
 5 | let package = Package(
 6 |   name: "SpacedRepetitionScheduler",
 7 |   products: [
 8 |     .library(
 9 |       name: "SpacedRepetitionScheduler",
10 |       targets: ["SpacedRepetitionScheduler"]
11 |     ),
12 |   ],
13 |   dependencies: [],
14 |   targets: [
15 |     .target(
16 |       name: "SpacedRepetitionScheduler",
17 |       dependencies: []
18 |     ),
19 |     .testTarget(
20 |       name: "SpacedRepetitionSchedulerTests",
21 |       dependencies: ["SpacedRepetitionScheduler"]
22 |     ),
23 |   ]
24 | )
25 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/Array+RecallEaseLinearSearch.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import Foundation
 4 | 
 5 | public extension Array where Element == (key: RecallEase, value: PromptSchedulingMetadata) {
 6 |   /// Performs a linear search through the receiver for a given ``RecallEase`` and returns the associated ``PromptSchedulingMetadata``.
 7 |   subscript(_ answer: RecallEase) -> PromptSchedulingMetadata? {
 8 |     for (candidateAnswer, item) in self where candidateAnswer == answer {
 9 |       return item
10 |     }
11 |     return nil
12 |   }
13 | }
14 | 


--------------------------------------------------------------------------------
/CHANGELOG.md:
--------------------------------------------------------------------------------
 1 | # Changelog
 2 | 
 3 | ## Version 0.5.0 -- 2024-03-23
 4 | 
 5 | - Add `Sendable` conformances
 6 | 
 7 | ## Version 0.4.0 -- 2024-01-18
 8 | 
 9 | - Added many synthesized protocol conformances (thanks @DandyLyons)
10 | 
11 | ## Version 0.3.0 -- 2021-09-18
12 | 
13 | - Uses swift-tools 5.5 now that Xcode 13 is at a Release Candidate. This adds DocC support for this package.
14 | 
15 | ## Version 0.2.1 -- 2021-06-27
16 | 
17 | ### Changed
18 | 
19 | - Switched back to swift-tools 5.4. This loses DocC. Otherwise, this is compatible with release 0.2.0
20 | 
21 | ## Version 0.2.0 -- 2021-06-27
22 | 
23 | ### Changed
24 | 
25 | - A pretty big refactor of the APIs to strive for more fluent usage at callsites. This version is not compatable with Version 0.1.
26 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/PromptSchedulingMode.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import Foundation
 4 | 
 5 | /// Determines which time interval recommendation algorithm to use with prompts.
 6 | public enum PromptSchedulingMode: Hashable, Codable, Sendable {
 7 |   /// Represents a prompt in the *learning* mode.
 8 |   ///
 9 |   /// An item stays in the learning state until it has been recalled a specific number of times, determined by the number of items in the ``SchedulingParameters/learningIntervals`` array.
10 |   /// - parameter step: How many learning steps have been completed. `step == 0` implies a new card.
11 |   case learning(step: Int)
12 | 
13 |   /// Represents a prompt in the *review* mode.
14 |   ///
15 |   /// Items in the review state are scheduled at increasingly longer intervals with each successful recall.
16 |   case review
17 | }
18 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/RecallEase.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import Foundation
 4 | 
 5 | /// Rating for how easy it is to recall the information associated with a prompt.
 6 | public enum RecallEase: Int, CaseIterable, Codable, Hashable, Sendable {
 7 |   /// The learner was not able to recall the information associated with a prompt.
 8 |   case again
 9 | 
10 |   /// The learner had difficulty recalling the information associated with a prompt and would like to review the corresponding prompt more frequently.
11 |   case hard
12 | 
13 |   /// The learner could recall the information associated with a prompt with the expected amount of difficulty, and would like to normally space out future reviews of this prompt.
14 |   case good
15 | 
16 |   /// The learner effortlessly recalled the information associated with a prompt, and would like to greatly space out future reviews of the prompt.
17 |   case easy
18 | }
19 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/TimeInterval+Fuzzing.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import Foundation
 4 | 
 5 | public extension TimeInterval {
 6 |   /// A TimeInterval that is close to, but not necessarily identical to, the receiver.
 7 |   /// - note: The value will fall within the bounds defined by `self.fuzzRange`
 8 |   func fuzzed() -> TimeInterval {
 9 |     return Double.random(in: fuzzRange)
10 |   }
11 | 
12 |   /// To keep cards added at the same time from always being scheduled together, we apply "fuzz" to the time interval.
13 |   /// - note: This logic is transcribed from anki schedv2.py _fuzzIvlRange
14 |   var fuzzRange: ClosedRange<Double> {
15 |     if self < 2 * .day {
16 |       return self ... self
17 |     }
18 |     if self < 3 * .day {
19 |       return 2 * .day ... 3 * .day
20 |     }
21 |     var fuzz: TimeInterval
22 |     if self < 7 * .day {
23 |       fuzz = self / 4
24 |     } else if self < 30 * .day {
25 |       fuzz = max(2 * .day, self * 0.15)
26 |     } else {
27 |       fuzz = max(4 * .day, self * 0.05)
28 |     }
29 |     fuzz = max(1, fuzz)
30 |     return (self - fuzz) ... (self + fuzz)
31 |   }
32 | }
33 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/Documentation.docc/Documentation.md:
--------------------------------------------------------------------------------
 1 | # ``SpacedRepetitionScheduler``
 2 | 
 3 | Implements an Anki-style spaced repetition scheduler for active recall prompts.
 4 | 
 5 | ## Overview
 6 | 
 7 | In a learning system that uses [active recall](https://en.wikipedia.org/wiki/Active_recall), 
 8 | learners are presented with a *prompt* and rate their ability to recall the corresponding information. 
 9 | `SpacedRepetitionScheduler` recommends a time interval to wait before showing a learner the same *prompt* again, given 
10 | his/her history of recalling the information associated with this prompt and how well he/she did 
11 | recalling the associated information this time. The recommended time intervals for a given prompt will increase the more frequently
12 | the learner recalls the information associated with a prompt.
13 | 
14 | `SpacedRepetitionScheduler` considers a prompt to be in one of two modes when making time interval recommendations: *learning* or *review*.
15 | 
16 | - In the *learning* mode, the learner must successfully recall the corresponding information a specific number of times with specific time intervals between recall attempts. After successfully recalling the associated information the specified number of times, the prompt graduates to the *review* state.
17 | - In the *review* mode, the amount of time between successive reviews of a prompt increases by a geometric progression with each successful recall.
18 | 
19 | 
20 | ## Topics
21 | 
22 | ### Representing prompts
23 | 
24 | - ``PromptSchedulingMetadata``
25 | - ``PromptSchedulingMode``
26 | 
27 | ### Scheduling parameters
28 | 
29 | - ``RecallEase``
30 | - ``SchedulingParameters``
31 | 


--------------------------------------------------------------------------------
/README.md:
--------------------------------------------------------------------------------
 1 | # SpacedRepetitionScheduler
 2 | 
 3 | Implements an Anki-style spaced repetition scheduler for active recall prompts.
 4 | 
 5 | ## Overview
 6 | 
 7 | In a learning system that uses [active recall](https://en.wikipedia.org/wiki/Active_recall), 
 8 | learners are presented with a *prompt* and rate their ability to recall the corresponding information. 
 9 | `SpacedRepetitionScheduler` recommends a time interval to wait before showing a learner the same *prompt* again, given 
10 | his/her history of recalling the information associated with this prompt and how well he/she did 
11 | recalling the associated information this time. The recommended time intervals for a given prompt will increase the more frequently
12 | the learner recalls the information associated with a prompt.
13 | 
14 | `SpacedRepetitionScheduler` considers a prompt to be in one of two modes when making time interval recommendations: *learning* or *review*.
15 | 
16 | - In the *learning* mode, the learner must successfully recall the corresponding information a specific number of times with specific time intervals between recall attempts. After successfully recalling the associated information the specified number of times, the prompt graduates to the *review* state.
17 | - In the *review* mode, the amount of time between successive reviews of a prompt increases by a geometric progression with each successful recall.
18 | 
19 | 
20 | ## Where to start in the code
21 | 
22 | ### Representing prompts
23 | 
24 | - `PromptSchedulingMetadata` -- Information needed to determine the recommended time to review a prompt again.
25 | - `PromptSchedulingMode` -- Whether the prompt is in *learning* or *review* mode.
26 | 
27 | ### Scheduling parameters
28 | 
29 | - `RecallEase` -- Rating for how easy it is to recall the information associated with a prompt.
30 | - `SchedulingParameters` -- Holds parameters used to determine the recommended time to schedule the next review of a prompt.
31 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/SchedulingParameters.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import Foundation
 4 | 
 5 | public extension TimeInterval {
 6 |   static let minute: TimeInterval = 60
 7 |   static let day: TimeInterval = 60 * 60 * 24
 8 | }
 9 | 
10 | /// Holds parameters used to determine the recommended time to schedule the next review of a prompt.
11 | public struct SchedulingParameters: Codable, Equatable, Sendable {
12 |   /// Creates a `SpacedReptitionScheduler` with the specified scheduling parameters.
13 |   ///
14 |   /// - parameter learningIntervals: The time intervals between successive successful recalls of a prompt in *learning* mode. The number of items in this array determines how many times a learner must successfully recall a prompt for it to graduate to the *review* mode.
15 |   /// - parameter easyGraduatingInterval: The ideal interval for reviewing a prompt again after it graduates from *learning* to *review* with a recall ease of *easy*.
16 |   /// - parameter goodGraduatingInterval: The ideal interval for reviewing a prompt again after it graduates from *learning* to *review* with a recall ease of *good*.
17 |   /// - parameter easyBoost: An additional mutiplicative factor for the scheduling interval when a prompt is in *review* mode and its recall ease is *easy*.
18 |   public init(
19 |     learningIntervals: [TimeInterval],
20 |     easyGraduatingInterval: TimeInterval = 4 * .day,
21 |     goodGraduatingInterval: TimeInterval = 1 * .day,
22 |     easyBoost: Double = 1.3
23 |   ) {
24 |     self.learningIntervals = learningIntervals
25 |     self.easyGraduatingInterval = easyGraduatingInterval
26 |     self.goodGraduatingInterval = goodGraduatingInterval
27 |     self.easyBoost = easyBoost
28 |   }
29 | 
30 |   /// The intervals between successive steps when "learning" an item.
31 |   public let learningIntervals: [TimeInterval]
32 | 
33 |   /// The ideal interval for reviewing a prompt again after it graduates from *learning* to *review* with a recall ease of *easy*.
34 |   public let easyGraduatingInterval: TimeInterval
35 | 
36 |   /// The ideal interval for reviewing a prompt again after it graduates from *learning* to *review* with a recall ease of *good*.
37 |   public let goodGraduatingInterval: TimeInterval
38 | 
39 |   /// An additional mutiplicative factor for the scheduling interval when a prompt is in *review* mode and its recall ease is *easy*.
40 |   public let easyBoost: Double
41 | }
42 | 


--------------------------------------------------------------------------------
/Tests/SpacedRepetitionSchedulerTests/SpacedRepetitionSchedulerTests.swift:
--------------------------------------------------------------------------------
 1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
 2 | 
 3 | import SpacedRepetitionScheduler
 4 | import XCTest
 5 | 
 6 | final class SpacedRepetitionSchedulerTests: XCTestCase {
 7 |   let schedulingParameters = SchedulingParameters(
 8 |     learningIntervals: [1 * .minute, 10 * .minute]
 9 |   )
10 | 
11 |   func testScheduleNewCard() {
12 |     let newItem = PromptSchedulingMetadata(mode: .learning(step: 0))
13 |     let results = newItem.allPossibleUpdates(with: schedulingParameters)
14 | 
15 |     // shouldn't be a "hard" answer
16 |     XCTAssertEqual(results.count, RecallEase.allCases.count - 1)
17 |     // Check that the repetition count increased for all items.
18 |     for result in results {
19 |       XCTAssertEqual(result.value.reviewCount, 1)
20 |     }
21 | 
22 |     XCTAssertEqual(results[.again]?.mode, .learning(step: 0))
23 |     XCTAssertEqual(results[.again]?.interval, schedulingParameters.learningIntervals[0])
24 | 
25 |     // Cards that were "easy" immediately leave the learning state.
26 |     XCTAssertEqual(results[.easy]?.mode, .review)
27 |     XCTAssertEqual(results[.easy]?.interval, schedulingParameters.easyGraduatingInterval)
28 | 
29 |     // Cards that were "good" move to the next state.
30 |     XCTAssertEqual(results[.good]?.mode, .learning(step: 1))
31 |     XCTAssertEqual(results[.good]?.interval, schedulingParameters.learningIntervals[1])
32 |   }
33 | 
34 |   func testScheduleReadyToGraduateCard() {
35 |     let readyToGraduateItem = PromptSchedulingMetadata(
36 |       mode: .learning(step: schedulingParameters.learningIntervals.count - 1)
37 |     )
38 |     let results = readyToGraduateItem.allPossibleUpdates(with: schedulingParameters)
39 | 
40 |     // shouldn't be a "hard" answer
41 |     XCTAssertEqual(results.count, RecallEase.allCases.count - 1)
42 |     // Check that the repetition count increased for all items.
43 |     for result in results {
44 |       XCTAssertEqual(result.value.reviewCount, 1)
45 |     }
46 | 
47 |     XCTAssertEqual(results[.again]?.mode, .learning(step: 0))
48 |     XCTAssertEqual(results[.again]?.interval, schedulingParameters.learningIntervals[0])
49 | 
50 |     // Cards that were "easy" immediately leave the learning state.
51 |     XCTAssertEqual(results[.easy]?.mode, .review)
52 |     XCTAssertEqual(results[.easy]?.interval, schedulingParameters.easyGraduatingInterval)
53 | 
54 |     // Cards that were "good" graduate.
55 |     XCTAssertEqual(results[.good]?.mode, .review)
56 |     XCTAssertEqual(results[.good]?.interval, schedulingParameters.goodGraduatingInterval)
57 |   }
58 | 
59 |   func testProgressFromNewToReview() throws {
60 |     var item = PromptSchedulingMetadata()
61 | 
62 |     for _ in 0 ..< schedulingParameters.learningIntervals.count {
63 |       // Answer the item as "good"
64 |       try item.update(with: schedulingParameters, recallEase: .good, timeIntervalSincePriorReview: 0)
65 |     }
66 |     XCTAssertEqual(item.mode, .review)
67 |     XCTAssertEqual(item.interval, schedulingParameters.goodGraduatingInterval)
68 |   }
69 | 
70 |   func testScheduleReviewCard() {
71 |     let reviewItem = PromptSchedulingMetadata(
72 |       mode: .review,
73 |       reviewCount: 5,
74 |       interval: 4 * .day
75 |     )
76 |     let delay: TimeInterval = .day
77 |     let results = reviewItem.allPossibleUpdates(with: schedulingParameters, timeIntervalSincePriorReview: delay)
78 |     XCTAssertEqual(results[.again]?.lapseCount, 1)
79 |     XCTAssertEqual(results[.again]?.interval, schedulingParameters.learningIntervals.first)
80 |     XCTAssertEqual(results[.again]?.mode, .learning(step: 0))
81 |     XCTAssertEqual(results[.again]!.reviewSpacingFactor, 2.3, accuracy: 0.01)
82 | 
83 |     XCTAssertEqual(results[.hard]?.lapseCount, 0)
84 |     XCTAssertEqual(results[.hard]?.mode, .review)
85 |     XCTAssertEqual(results[.hard]!.reviewSpacingFactor, 2.5 - 0.15, accuracy: 0.01)
86 |     XCTAssertEqual(results[.hard]!.interval, reviewItem.interval * 1.2, accuracy: 0.01)
87 | 
88 |     XCTAssertEqual(results[.good]?.lapseCount, 0)
89 |     XCTAssertEqual(results[.good]?.mode, .review)
90 |     XCTAssertEqual(results[.good]!.reviewSpacingFactor, 2.5, accuracy: 0.01)
91 |     XCTAssertEqual(results[.good]!.interval, (reviewItem.interval + delay / 2) * reviewItem.reviewSpacingFactor, accuracy: 0.01)
92 | 
93 |     XCTAssertEqual(results[.easy]?.lapseCount, 0)
94 |     XCTAssertEqual(results[.easy]?.mode, .review)
95 |     XCTAssertEqual(results[.easy]!.reviewSpacingFactor, 2.5 + 0.15, accuracy: 0.01)
96 |     XCTAssertEqual(results[.easy]!.interval, (reviewItem.interval + delay) * reviewItem.reviewSpacingFactor * schedulingParameters.easyBoost, accuracy: 0.01)
97 |   }
98 | }
99 | 


--------------------------------------------------------------------------------
/Sources/SpacedRepetitionScheduler/PromptSchedulingMetadata.swift:
--------------------------------------------------------------------------------
  1 | // Copyright © 2020  Brian Dewey. Covered by the Apache 2.0 license.
  2 | 
  3 | import Foundation
  4 | 
  5 | /// Information needed to determine the recommended time to review a prompt again.
  6 | public struct PromptSchedulingMetadata: Hashable, Codable, Sendable {
  7 |   /// The learning state of this prompt.
  8 |   public var mode: PromptSchedulingMode
  9 | 
 10 |   /// How many times this prompt has been reviewed.
 11 |   public var reviewCount: Int
 12 | 
 13 |   /// How many times this prompt regressed from "review" back to "learning"
 14 |   public var lapseCount: Int
 15 | 
 16 |   /// The ideal amount of time until seeing this prompt again.
 17 |   public var interval: TimeInterval
 18 | 
 19 |   /// The multiplicative factor for increasing the delay for seeing this prompt again, if ``mode`` is `.review`.
 20 |   public var reviewSpacingFactor: Double
 21 | 
 22 |   /// Creates prompt metadata with specific values.
 23 |   public init(
 24 |     mode: PromptSchedulingMode = .learning(step: 0),
 25 |     reviewCount: Int = 0,
 26 |     lapseCount: Int = 0,
 27 |     interval: TimeInterval = 0,
 28 |     reviewSpacingFactor: Double = 2.5
 29 |   ) {
 30 |     self.mode = mode
 31 |     self.reviewCount = reviewCount
 32 |     self.lapseCount = lapseCount
 33 |     self.reviewSpacingFactor = reviewSpacingFactor
 34 |     self.interval = interval
 35 |   }
 36 | 
 37 |   enum SchedulingError: Error {
 38 |     /// Error when we try to say that recall was "hard" for an item in the `learning` state.  This is not a valid scheduling option and should not be shown to a learner.
 39 |     case noHardRecallForLearningItems
 40 |   }
 41 | 
 42 |   /// Updates the receiver given the prompt was recalled with specified `recallEase` after `timeIntervalSincePastReview`.
 43 |   /// - Parameters:
 44 |   ///   - schedulingParameters: Parameters used to compute the ideal time to review a prompt again.
 45 |   ///   - recallEase: A value representing how easy the learner recalled the information associated with the prompt.
 46 |   ///   - timeIntervalSincePriorReview: The duration of time since the prompt was last reviewed.
 47 |   /// - Returns: An updated value for ``PromptSchedulingMetadata``
 48 |   public mutating func update(
 49 |     with schedulingParameters: SchedulingParameters,
 50 |     recallEase: RecallEase,
 51 |     timeIntervalSincePriorReview: TimeInterval
 52 |   ) throws {
 53 |     reviewCount += 1
 54 |     switch (mode, recallEase) {
 55 |     case (.learning, .again):
 56 |       moveToFirstStep(schedulingParameters: schedulingParameters)
 57 |     case (.learning, .easy):
 58 |       // Immediate graduation!
 59 |       mode = .review
 60 |       interval = schedulingParameters.easyGraduatingInterval
 61 |     case (.learning, .hard):
 62 |       // Not a valid answer -- no "hard" for something we're learning
 63 |       throw SchedulingError.noHardRecallForLearningItems
 64 |     case (.learning(let step), .good):
 65 |       // Move to the next step.
 66 |       if step < (schedulingParameters.learningIntervals.count - 1) {
 67 |         interval = schedulingParameters.learningIntervals[step + 1]
 68 |         mode = .learning(step: step + 1)
 69 |       } else {
 70 |         // Graduate to "review"
 71 |         mode = .review
 72 |         interval = schedulingParameters.goodGraduatingInterval
 73 |       }
 74 |     case (.review, .again):
 75 |       lapseCount += 1
 76 |       reviewSpacingFactor = max(1.3, reviewSpacingFactor - 0.2)
 77 |       moveToFirstStep(schedulingParameters: schedulingParameters)
 78 |     case (.review, .hard):
 79 |       interval *= 1.2
 80 |       reviewSpacingFactor = max(1.3, reviewSpacingFactor - 0.15)
 81 |     case (.review, .good):
 82 |       // Expand interval by factor, fuzzing the result, and ensuring that it at least moves forward
 83 |       // by the "hard" amount.
 84 |       interval = (interval + timeIntervalSincePriorReview / 2) * reviewSpacingFactor
 85 |     case (.review, .easy):
 86 |       interval = (interval + timeIntervalSincePriorReview) * reviewSpacingFactor * schedulingParameters.easyBoost
 87 |       reviewSpacingFactor += 0.15
 88 |     }
 89 |   }
 90 | 
 91 |   /// Updates the receiver given the prompt was recalled with specified `recallEase` after `timeIntervalSincePastReview`.
 92 |   /// - Parameters:
 93 |   ///   - schedulingParameters: Parameters used to compute the ideal time to review a prompt again.
 94 |   ///   - recallEase: A value representing how easy the learner recalled the information associated with the prompt.
 95 |   ///   - timeIntervalSincePastReview: The duration of time since the prompt was last reviewed.
 96 |   /// - Returns: An updated value for ``PromptSchedulingMetadata``
 97 |   public func updating(
 98 |     with schedulingParameters: SchedulingParameters,
 99 |     recallEase: RecallEase,
100 |     timeIntervalSincePriorReview: TimeInterval
101 |   ) throws -> PromptSchedulingMetadata {
102 |     var copy = self
103 |     try copy.update(
104 |       with: schedulingParameters,
105 |       recallEase: recallEase,
106 |       timeIntervalSincePriorReview: timeIntervalSincePriorReview
107 |     )
108 |     return copy
109 |   }
110 | 
111 |   /// Returns a mapping of possible ``RecallEase`` values to updated ``PromptSchedulingMetadata`` values.
112 |   /// - Parameters:
113 |   ///   - promptSchedulingMetadata: The current ``PromptSchedulingMetadata`` for a prompt.
114 |   ///   - timeIntervalSincePastReview: The duration of time since the prompt was last reviewed.
115 |   /// - Returns: An array of key/value pairs associating a valid ``RecallEase`` to an updated ``PromptSchedulingMetadata`` if the prompt was recalled with that ease value.
116 |   public func allPossibleUpdates(
117 |     with schedulingParameters: SchedulingParameters,
118 |     timeIntervalSincePriorReview: TimeInterval = 0
119 |   ) -> [(key: RecallEase, value: PromptSchedulingMetadata)] {
120 |     let result = RecallEase.allCases.compactMap { recallEase -> (RecallEase, PromptSchedulingMetadata)? in
121 |       guard let updatedMetadata = try? self.updating(with: schedulingParameters, recallEase: recallEase, timeIntervalSincePriorReview: timeIntervalSincePriorReview) else {
122 |         return nil
123 |       }
124 |       return (recallEase, updatedMetadata)
125 |     }
126 |     return result
127 |   }
128 | 
129 |   private mutating func moveToFirstStep(schedulingParameters: SchedulingParameters) {
130 |     // Go back to the initial learning step, schedule out a tiny bit.
131 |     mode = .learning(step: 0)
132 |     interval = schedulingParameters.learningIntervals.first ?? .minute
133 |   }
134 | }
135 | 


--------------------------------------------------------------------------------
/LICENSE:
--------------------------------------------------------------------------------
  1 |                                  Apache License
  2 |                            Version 2.0, January 2004
  3 |                         http://www.apache.org/licenses/
  4 | 
  5 |    TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
  6 | 
  7 |    1. Definitions.
  8 | 
  9 |       "License" shall mean the terms and conditions for use, reproduction,
 10 |       and distribution as defined by Sections 1 through 9 of this document.
 11 | 
 12 |       "Licensor" shall mean the copyright owner or entity authorized by
 13 |       the copyright owner that is granting the License.
 14 | 
 15 |       "Legal Entity" shall mean the union of the acting entity and all
 16 |       other entities that control, are controlled by, or are under common
 17 |       control with that entity. For the purposes of this definition,
 18 |       "control" means (i) the power, direct or indirect, to cause the
 19 |       direction or management of such entity, whether by contract or
 20 |       otherwise, or (ii) ownership of fifty percent (50%) or more of the
 21 |       outstanding shares, or (iii) beneficial ownership of such entity.
 22 | 
 23 |       "You" (or "Your") shall mean an individual or Legal Entity
 24 |       exercising permissions granted by this License.
 25 | 
 26 |       "Source" form shall mean the preferred form for making modifications,
 27 |       including but not limited to software source code, documentation
 28 |       source, and configuration files.
 29 | 
 30 |       "Object" form shall mean any form resulting from mechanical
 31 |       transformation or translation of a Source form, including but
 32 |       not limited to compiled object code, generated documentation,
 33 |       and conversions to other media types.
 34 | 
 35 |       "Work" shall mean the work of authorship, whether in Source or
 36 |       Object form, made available under the License, as indicated by a
 37 |       copyright notice that is included in or attached to the work
 38 |       (an example is provided in the Appendix below).
 39 | 
 40 |       "Derivative Works" shall mean any work, whether in Source or Object
 41 |       form, that is based on (or derived from) the Work and for which the
 42 |       editorial revisions, annotations, elaborations, or other modifications
 43 |       represent, as a whole, an original work of authorship. For the purposes
 44 |       of this License, Derivative Works shall not include works that remain
 45 |       separable from, or merely link (or bind by name) to the interfaces of,
 46 |       the Work and Derivative Works thereof.
 47 | 
 48 |       "Contribution" shall mean any work of authorship, including
 49 |       the original version of the Work and any modifications or additions
 50 |       to that Work or Derivative Works thereof, that is intentionally
 51 |       submitted to Licensor for inclusion in the Work by the copyright owner
 52 |       or by an individual or Legal Entity authorized to submit on behalf of
 53 |       the copyright owner. For the purposes of this definition, "submitted"
 54 |       means any form of electronic, verbal, or written communication sent
 55 |       to the Licensor or its representatives, including but not limited to
 56 |       communication on electronic mailing lists, source code control systems,
 57 |       and issue tracking systems that are managed by, or on behalf of, the
 58 |       Licensor for the purpose of discussing and improving the Work, but
 59 |       excluding communication that is conspicuously marked or otherwise
 60 |       designated in writing by the copyright owner as "Not a Contribution."
 61 | 
 62 |       "Contributor" shall mean Licensor and any individual or Legal Entity
 63 |       on behalf of whom a Contribution has been received by Licensor and
 64 |       subsequently incorporated within the Work.
 65 | 
 66 |    2. Grant of Copyright License. Subject to the terms and conditions of
 67 |       this License, each Contributor hereby grants to You a perpetual,
 68 |       worldwide, non-exclusive, no-charge, royalty-free, irrevocable
 69 |       copyright license to reproduce, prepare Derivative Works of,
 70 |       publicly display, publicly perform, sublicense, and distribute the
 71 |       Work and such Derivative Works in Source or Object form.
 72 | 
 73 |    3. Grant of Patent License. Subject to the terms and conditions of
 74 |       this License, each Contributor hereby grants to You a perpetual,
 75 |       worldwide, non-exclusive, no-charge, royalty-free, irrevocable
 76 |       (except as stated in this section) patent license to make, have made,
 77 |       use, offer to sell, sell, import, and otherwise transfer the Work,
 78 |       where such license applies only to those patent claims licensable
 79 |       by such Contributor that are necessarily infringed by their
 80 |       Contribution(s) alone or by combination of their Contribution(s)
 81 |       with the Work to which such Contribution(s) was submitted. If You
 82 |       institute patent litigation against any entity (including a
 83 |       cross-claim or counterclaim in a lawsuit) alleging that the Work
 84 |       or a Contribution incorporated within the Work constitutes direct
 85 |       or contributory patent infringement, then any patent licenses
 86 |       granted to You under this License for that Work shall terminate
 87 |       as of the date such litigation is filed.
 88 | 
 89 |    4. Redistribution. You may reproduce and distribute copies of the
 90 |       Work or Derivative Works thereof in any medium, with or without
 91 |       modifications, and in Source or Object form, provided that You
 92 |       meet the following conditions:
 93 | 
 94 |       (a) You must give any other recipients of the Work or
 95 |           Derivative Works a copy of this License; and
 96 | 
 97 |       (b) You must cause any modified files to carry prominent notices
 98 |           stating that You changed the files; and
 99 | 
100 |       (c) You must retain, in the Source form of any Derivative Works
101 |           that You distribute, all copyright, patent, trademark, and
102 |           attribution notices from the Source form of the Work,
103 |           excluding those notices that do not pertain to any part of
104 |           the Derivative Works; and
105 | 
106 |       (d) If the Work includes a "NOTICE" text file as part of its
107 |           distribution, then any Derivative Works that You distribute must
108 |           include a readable copy of the attribution notices contained
109 |           within such NOTICE file, excluding those notices that do not
110 |           pertain to any part of the Derivative Works, in at least one
111 |           of the following places: within a NOTICE text file distributed
112 |           as part of the Derivative Works; within the Source form or
113 |           documentation, if provided along with the Derivative Works; or,
114 |           within a display generated by the Derivative Works, if and
115 |           wherever such third-party notices normally appear. The contents
116 |           of the NOTICE file are for informational purposes only and
117 |           do not modify the License. You may add Your own attribution
118 |           notices within Derivative Works that You distribute, alongside
119 |           or as an addendum to the NOTICE text from the Work, provided
120 |           that such additional attribution notices cannot be construed
121 |           as modifying the License.
122 | 
123 |       You may add Your own copyright statement to Your modifications and
124 |       may provide additional or different license terms and conditions
125 |       for use, reproduction, or distribution of Your modifications, or
126 |       for any such Derivative Works as a whole, provided Your use,
127 |       reproduction, and distribution of the Work otherwise complies with
128 |       the conditions stated in this License.
129 | 
130 |    5. Submission of Contributions. Unless You explicitly state otherwise,
131 |       any Contribution intentionally submitted for inclusion in the Work
132 |       by You to the Licensor shall be under the terms and conditions of
133 |       this License, without any additional terms or conditions.
134 |       Notwithstanding the above, nothing herein shall supersede or modify
135 |       the terms of any separate license agreement you may have executed
136 |       with Licensor regarding such Contributions.
137 | 
138 |    6. Trademarks. This License does not grant permission to use the trade
139 |       names, trademarks, service marks, or product names of the Licensor,
140 |       except as required for reasonable and customary use in describing the
141 |       origin of the Work and reproducing the content of the NOTICE file.
142 | 
143 |    7. Disclaimer of Warranty. Unless required by applicable law or
144 |       agreed to in writing, Licensor provides the Work (and each
145 |       Contributor provides its Contributions) on an "AS IS" BASIS,
146 |       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
147 |       implied, including, without limitation, any warranties or conditions
148 |       of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
149 |       PARTICULAR PURPOSE. You are solely responsible for determining the
150 |       appropriateness of using or redistributing the Work and assume any
151 |       risks associated with Your exercise of permissions under this License.
152 | 
153 |    8. Limitation of Liability. In no event and under no legal theory,
154 |       whether in tort (including negligence), contract, or otherwise,
155 |       unless required by applicable law (such as deliberate and grossly
156 |       negligent acts) or agreed to in writing, shall any Contributor be
157 |       liable to You for damages, including any direct, indirect, special,
158 |       incidental, or consequential damages of any character arising as a
159 |       result of this License or out of the use or inability to use the
160 |       Work (including but not limited to damages for loss of goodwill,
161 |       work stoppage, computer failure or malfunction, or any and all
162 |       other commercial damages or losses), even if such Contributor
163 |       has been advised of the possibility of such damages.
164 | 
165 |    9. Accepting Warranty or Additional Liability. While redistributing
166 |       the Work or Derivative Works thereof, You may choose to offer,
167 |       and charge a fee for, acceptance of support, warranty, indemnity,
168 |       or other liability obligations and/or rights consistent with this
169 |       License. However, in accepting such obligations, You may act only
170 |       on Your own behalf and on Your sole responsibility, not on behalf
171 |       of any other Contributor, and only if You agree to indemnify,
172 |       defend, and hold each Contributor harmless for any liability
173 |       incurred by, or claims asserted against, such Contributor by reason
174 |       of your accepting any such warranty or additional liability.
175 | 
176 |    END OF TERMS AND CONDITIONS
177 | 
178 |    APPENDIX: How to apply the Apache License to your work.
179 | 
180 |       To apply the Apache License to your work, attach the following
181 |       boilerplate notice, with the fields enclosed by brackets "[]"
182 |       replaced with your own identifying information. (Don't include
183 |       the brackets!)  The text should be enclosed in the appropriate
184 |       comment syntax for the file format. We also recommend that a
185 |       file or class name and description of purpose be included on the
186 |       same "printed page" as the copyright notice for easier
187 |       identification within third-party archives.
188 | 
189 |    Copyright [yyyy] [name of copyright owner]
190 | 
191 |    Licensed under the Apache License, Version 2.0 (the "License");
192 |    you may not use this file except in compliance with the License.
193 |    You may obtain a copy of the License at
194 | 
195 |        http://www.apache.org/licenses/LICENSE-2.0
196 | 
197 |    Unless required by applicable law or agreed to in writing, software
198 |    distributed under the License is distributed on an "AS IS" BASIS,
199 |    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
200 |    See the License for the specific language governing permissions and
201 |    limitations under the License.
202 | 


--------------------------------------------------------------------------------