import { fsrs as createFSRS, createEmptyCard, Rating, type Card, type Grade } from "ts-fsrs"

const scheduler = createFSRS({ maximum_interval: 365, request_retention: 0.9 })

export type FsrsGrade = "again" | "hard" | "good" | "easy"

const gradeMap: Record<FsrsGrade, Grade> = {
  again: Rating.Again,
  hard: Rating.Hard,
  good: Rating.Good,
  easy: Rating.Easy,
}

export function buildFsrsCard(params: {
  stability?: number
  difficulty?: number
  reps?: number
  lapses?: number
  due?: Date
}): Card {
  const card = createEmptyCard(params.due ?? new Date())
  return {
    ...card,
    stability: params.stability ?? card.stability,
    difficulty: params.difficulty ?? card.difficulty,
    reps: params.reps ?? 0,
    lapses: params.lapses ?? 0,
    due: params.due ?? card.due,
  }
}

export function gradeCard(card: Card, grade: FsrsGrade, now: Date = new Date()) {
  const result = scheduler.next(card, now, gradeMap[grade])
  return {
    card: result.card,
    log: result.log,
  }
}

export function getRetrievability(card: Card, now: Date = new Date()): number {
  const r = scheduler.get_retrievability(card, now, false)
  return typeof r === "number" ? r : parseFloat(r)
}

export function skillCodeFromGrade(correct: boolean, responseMs: number): FsrsGrade {
  if (!correct) return "again"
  if (responseMs > 8000) return "hard"
  if (responseMs > 4000) return "good"
  return "easy"
}