import { NextRequest, NextResponse } from "next/server";
import { prisma } from "@/lib/db";
import { requireApiAuthWithOrg, handleApiError } from "@/lib/api-auth";

type Ctx = { params: Promise<{ id: string }> };

export async function POST(request: NextRequest, ctx: Ctx) {
  try {
    const session = await requireApiAuthWithOrg();
    const orgId = session.user.orgId!;
    const { id: sourceId } = await ctx.params;

    const body = await request.json().catch(() => ({}));
    const { targetPersonId } = body;

    if (!targetPersonId) {
      return NextResponse.json({ error: "targetPersonId is required" }, { status: 400 });
    }
    if (sourceId === targetPersonId) {
      return NextResponse.json({ error: "Cannot merge a person into themselves" }, { status: 400 });
    }

    const [source, target] = await Promise.all([
      prisma.person.findUnique({ where: { id: sourceId } }),
      prisma.person.findUnique({ where: { id: targetPersonId } }),
    ]);

    if (!source || source.organizationId !== orgId) {
      return NextResponse.json({ error: "Source person not found" }, { status: 404 });
    }
    if (!target || target.organizationId !== orgId) {
      return NextResponse.json({ error: "Target person not found" }, { status: 404 });
    }

    // 1. Move all cards from source to target
    await prisma.responseCard.updateMany({
      where: { personId: sourceId },
      data: { personId: targetPersonId },
    });

    // 2. Merge fieldData: target values take priority, fill gaps from source
    const mergedFieldData = {
      ...((source.fieldData as object) ?? {}),
      ...((target.fieldData as object) ?? {}),
    };

    // 3. Update target's core fields if target's are null but source's are not
    const updates: Record<string, unknown> = {
      fieldData: Object.keys(mergedFieldData).length > 0 ? mergedFieldData : null,
    };
    if (!target.email && source.email) updates.email = source.email;
    if (!target.cellPhone && source.cellPhone) updates.cellPhone = source.cellPhone;

    const targetPerson = await prisma.person.update({
      where: { id: targetPersonId },
      data: updates,
      include: { _count: { select: { cards: true } } },
    });

    // 4. Mark source as merged
    await prisma.person.update({
      where: { id: sourceId },
      data: { mergedIntoId: targetPersonId },
    });

    return NextResponse.json({ success: true, targetPerson });
  } catch (error) {
    return handleApiError(error);
  }
}