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

export async function POST(
  request: NextRequest,
  { params }: { params: Promise<{ id: string }> },
) {
  try {
    const session = await auth()
    if (!session?.user?.id) {
      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
    }

    const { id: cardId } = await params
    const body = await request.json()
    const grade = typeof body.grade === 'number' ? body.grade : Number(body.grade)

    if (!Number.isFinite(grade) || grade < 1 || grade > 4) {
      return NextResponse.json({ error: 'Grade must be 1–4' }, { status: 400 })
    }

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

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

    const [savedCard] = await prisma.$transaction([
      prisma.flashcard.update({
        where: { id: cardId },
        data: {
          easinessFactor: updated.easinessFactor,
          interval: updated.interval,
          nextReviewAt: updated.nextReviewAt,
        },
      }),
      prisma.flashcardReview.create({
        data: { cardId, grade: Math.round(grade) },
      }),
    ])

    return NextResponse.json({
      card: {
        id: savedCard.id,
        interval: savedCard.interval,
        easinessFactor: savedCard.easinessFactor,
        nextReviewAt: savedCard.nextReviewAt.toISOString(),
      },
    })
  } catch (error) {
    console.error('[flashcards/[id]/review]', error)
    return NextResponse.json({ error: 'Review failed' }, { status: 500 })
  }
}