add smart random

src/modules/decks/use-cases/get-random-card-in-deck-use-case.ts

@@ -0,0 +1,53 @@
+import { CommandHandler, ICommandHandler } from '@nestjs/cqrs'
+import { CardsRepository } from '../../cards/infrastructure/cards.repository'
+import { ForbiddenException, NotFoundException } from '@nestjs/common'
+import { DecksRepository } from '../infrastructure/decks.repository'
+import { Prisma } from '@prisma/client'
+import { pick } from 'remeda'
+
+export class GetRandomCardInDeckCommand {
+  constructor(public readonly userId: string, public readonly deckId: string) {}
+}
+type CardWithGrade = Prisma.cardGetPayload<{ include: { grades: true } }>
+@CommandHandler(GetRandomCardInDeckCommand)
+export class GetRandomCardInDeckHandler implements ICommandHandler<GetRandomCardInDeckCommand> {
+  constructor(
+    private readonly cardsRepository: CardsRepository,
+    private readonly decksRepository: DecksRepository
+  ) {}
+  private async getSmartRandomCard(cards: Array<CardWithGrade>) {
+    const selectionPool: Array<CardWithGrade> = []
+    cards.forEach(card => {
+      // Calculate the average grade for the card
+      const averageGrade =
+        card.grades.length === 0
+          ? 0
+          : card.grades.reduce((acc, grade) => acc + grade.grade, 0) / card.grades.length
+      // Calculate weight for the card, higher weight for lower grade card
+      const weight = 6 - averageGrade
+
+      // Add the card to the selection pool `weight` times
+      for (let i = 0; i < weight; i++) {
+        selectionPool.push(card)
+      }
+    })
+
+    return selectionPool[Math.floor(Math.random() * selectionPool.length)]
+  }
+
+  async execute(command: GetRandomCardInDeckCommand) {
+    const deck = await this.decksRepository.findDeckById(command.deckId)
+    if (!deck) throw new NotFoundException(`Deck with id ${command.deckId} not found`)
+
+    if (deck.userId !== command.userId && deck.isPrivate) {
+      throw new ForbiddenException(`You can't get a private deck that you don't own`)
+    }
+
+    const cards = await this.cardsRepository.findCardsByDeckIdWithGrade(
+      command.userId,
+      command.deckId
+    )
+    const smartRandomCard = await this.getSmartRandomCard(cards)
+    return pick(smartRandomCard, ['id', 'question', 'answer', 'deckId'])
+  }
+}