import { NextRequest, NextResponse } from 'next/server'
import prisma from '@/lib/prisma'
import { getMobileUserId } from '@/lib/mobile-auth'
import { computeSm2Update } from '@/lib/flashcards/sm2'

export async function POST(req: NextRequest) {
  const userId = getMobileUserId(req)
  if (!userId) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })

  const body = await req.json()
  const cardId = typeof body.cardId === 'string' ? body.cardId : null
  const grade = typeof body.grade === 'number' ? body.grade : null

  if (!cardId || grade === null || grade < 1 || grade > 4) {
    return NextResponse.json({ error: 'cardId and grade (1–4) required' }, { status: 400 })
  }

  const card = await prisma.flashcard.findFirst({
    where: { id: cardId, deck: { userId } },
    select: { id: true, interval: true, easinessFactor: true },
  })
  if (!card) return NextResponse.json({ error: 'Card not found' }, { status: 404 })

  const { easinessFactor, interval, nextReviewAt } = computeSm2Update(grade, {
    easinessFactor: card.easinessFactor,
    interval: card.interval,
  })

  await prisma.$transaction([
    prisma.flashcard.update({
      where: { id: cardId },
      data: { easinessFactor, interval, nextReviewAt },
    }),
    prisma.flashcardReview.create({
      data: { cardId, grade, reviewedAt: new Date() },
    }),
  ])

  return NextResponse.json({ ok: true, nextReviewAt, interval })
}