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

export async function GET(req: NextRequest) {
  try {
    const session = await auth()
    if (!session?.user?.id) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })

    const canvasId = req.nextUrl.searchParams.get('id')
    if (!canvasId) return NextResponse.json({ error: 'Missing id' }, { status: 400 })

    const canvas = await prisma.canvas.findUnique({
      where: { id: canvasId, userId: session.user.id },
    })
    if (!canvas) return NextResponse.json({ error: 'Not found' }, { status: 404 })

    let parsed: any
    try { parsed = JSON.parse(canvas.data) } catch {
      return NextResponse.json({ error: 'Invalid data' }, { status: 500 })
    }

    if (parsed.type !== 'pptx' || !parsed.base64) {
      return NextResponse.json({ error: 'Not a PPTX canvas' }, { status: 400 })
    }

    const byteChars = atob(parsed.base64)
    const bytes = new Uint8Array(byteChars.length)
    for (let i = 0; i < byteChars.length; i++) bytes[i] = byteChars.charCodeAt(i)

    const filename = parsed.filename || `${canvas.name.replace(/[^a-zA-Z0-9]/g, '_')}.pptx`

    // Auto-delete after serving
    await prisma.canvas.delete({ where: { id: canvasId } })

    return new NextResponse(bytes, {
      headers: {
        'Content-Type': 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
        'Content-Disposition': `attachment; filename="${filename}"`,
        'Content-Length': String(bytes.length),
      },
    })
  } catch (error) {
    console.error('[Canvas Download]', error)
    return NextResponse.json({ error: 'Internal Server Error' }, { status: 500 })
  }
}