SwiftFSRS

An idiomatic and configurable Swift implementation of the FSRS spaced repetition algorithm.

Installation

Add the following to your Package.swift file:

dependencies: [
    .package(url: "https://github.com/4rays/swift-fsrs")
]

Usage

The Scheduler

The workhorse of the algorithm is the Scheduler protocol. It takes a card and a review and returns a new card and review log object.

Out of the box, the library ships with a short-term and a long-term scheduler. Use the short-term scheduler when you want to support multiple reviews of the same card in a single day. Use the long-term scheduler otherwise.

Here is how you can create your own scheduler:

import SwiftFSRS

struct CustomScheduler: Scheduler {
  func schedule(
    card: Card,
    algorithm: FSRSAlgorithm,
    reviewRating: ReviewRating,
    reviewTime: Date
  ) -> CardReview {
    // Implement your custom algorithm here
  }
}

The Algorithm

The library implements v5 of the FSRS algorithm out of the box. It can also support custom implementations.

import SwiftFSRS

let customAlgorithm = FSRSAlgorithm(
  decay: -0.5,
  factor: 19 / 81,
  requestRetention: 0.9,
  maximumInterval: 36500,
  parameters: [/* ... */]
)

scheduler.schedule(
  card: card,
  algorithm: customAlgorithm,
  reviewRating: .good,
  reviewTime: Date()
)

Scheduling a Review

To schedule a review for a given card:

import SwiftFSRS

let scheduler = LongTermScheduler()
let card = Card()

let review = scheduler.schedule(
  card: card,
  algorithm: .v5,
  reviewRating: .good, // or .easy, .hard, .again
  reviewTime: Date()
)

print(review.card)
print(review.log)

Cards don't have any content properties and are meant to be properties of your own type.

import SwiftFSRS

struct MyFlashCard {
  let question: String
  let answer: String
  let fsrsCard: Card
}

License

SwiftFSRS is available under the MIT license. See the LICENSE file for more info.