import { NextResponse } from "next/server"
import { and, eq } from "drizzle-orm"
import { db } from "@/lib/db"
import { leases, rent_payments } from "@/lib/db/schema"
import { getSessionUser } from "@/lib/session"

export async function POST(request: Request) {
  const user = await getSessionUser()
  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 401 })

  const { year, month } = await request.json() as { year: number; month: number }
  if (!year || month === undefined) return NextResponse.json({ error: "year and month required" }, { status: 400 })

  // Get all active leases with rent amount
  const activeLeases = await db
    .select({
      id: leases.id,
      tenant_id: leases.tenant_id,
      property_id: leases.property_id,
      unit_id: leases.unit_id,
      rent_amount: leases.rent_amount,
    })
    .from(leases)
    .where(and(eq(leases.user_id, user.id), eq(leases.status, "active")))

  if (!activeLeases.length) return NextResponse.json({ created: 0, skipped: 0 })

  // Build due date: first of selected month
  const pad = (n: number) => String(n).padStart(2, "0")
  const due_date = `${year}-${pad(month + 1)}-01`

  // Check which already exist for this month
  const existing = await db
    .select({ tenant_id: rent_payments.tenant_id })
    .from(rent_payments)
    .where(and(eq(rent_payments.user_id, user.id), eq(rent_payments.due_date, due_date)))

  const existingTenantIds = new Set(existing.map((p) => p.tenant_id))

  const toInsert = activeLeases
    .filter((l) => !existingTenantIds.has(l.tenant_id))
    .map((l) => ({
      user_id:     user.id,
      tenant_id:   l.tenant_id,
      property_id: l.property_id,
      unit_id:     l.unit_id ?? null,
      amount:      l.rent_amount,
      due_date,
      status:      "pending" as const,
    }))

  if (toInsert.length === 0) {
    return NextResponse.json({ created: 0, skipped: activeLeases.length, message: "All payments already exist for this month." })
  }

  await db.insert(rent_payments).values(toInsert)

  return NextResponse.json({
    created: toInsert.length,
    skipped: existingTenantIds.size,
    message: `Created ${toInsert.length} payment${toInsert.length !== 1 ? "s" : ""} for ${due_date.slice(0, 7)}.`,
  })
}