import { NextResponse } from "next/server";
import { z } from "zod";

import { snapshotUser } from "@/lib/audit-snapshots";
import { createAuditLog } from "@/lib/audit-log";
import {
  APPROVAL_FLOW,
  canManageUsers,
  getLegacyApprovalPreference,
  normalizeApprovalPermissions
} from "@/lib/domain";
import prisma from "@/lib/prisma";
import { getCurrentViewer } from "@/lib/session";

const userRoleSchema = z.enum(["ADMIN", "FINANCE", "MEMBER"]);
const approvalPermissionSchema = z.enum(APPROVAL_FLOW);

const updateUserSchema = z.object({
  role: userRoleSchema,
  workingGroupId: z.union([z.string().trim().min(1), z.literal(""), z.null(), z.undefined()]),
  approvalPermissions: z.array(approvalPermissionSchema).default([])
});

function serializeManagedUser(user: {
  id: string;
  name: string;
  username: string;
  role: "ADMIN" | "FINANCE" | "MEMBER";
  workingGroupId: string | null;
  workingGroup: { name: string } | null;
  approvalPreference: "CHAIR_A" | "CHAIR_B" | "FINANCE" | null;
  approvalPermissions: ("CHAIR_A" | "CHAIR_B" | "FINANCE")[];
  _count: {
    createdExpenses: number;
    approvals: number;
  };
}) {
  return {
    id: user.id,
    name: user.username,
    username: user.username,
    role: user.role,
    workingGroupId: user.workingGroupId,
    workingGroupName: user.workingGroup?.name ?? null,
    approvalPermissions: normalizeApprovalPermissions(user.role, user.approvalPermissions, user.approvalPreference),
    createdExpensesCount: user._count.createdExpenses,
    approvalsCount: user._count.approvals
  };
}

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

export async function PATCH(request: Request, { params }: Context) {
  const { id } = await params;
  const viewer = await getCurrentViewer();

  if (!viewer) {
    return NextResponse.json({ error: "Nicht angemeldet." }, { status: 401 });
  }

  if (!canManageUsers(viewer.role)) {
    return NextResponse.json({ error: "Nur Vorstand oder Finanz-AG duerfen Nutzer bearbeiten." }, { status: 403 });
  }

  const body = await request.json().catch(() => null);
  const parsed = updateUserSchema.safeParse(body);

  if (!parsed.success) {
    return NextResponse.json({ error: "Bitte Rolle, AG und Freigaberollen korrekt angeben." }, { status: 400 });
  }

  const user = await prisma.user.findUnique({
    where: { id }
  });

  if (!user) {
    return NextResponse.json({ error: "Nutzer nicht gefunden." }, { status: 404 });
  }

  const workingGroupId = typeof parsed.data.workingGroupId === "string" && parsed.data.workingGroupId.length > 0
    ? parsed.data.workingGroupId
    : null;

  if (parsed.data.role === "MEMBER" && !workingGroupId) {
    return NextResponse.json({ error: "AG-Mitglieder brauchen eine AG-Zuordnung." }, { status: 400 });
  }

  if (workingGroupId) {
    const workingGroup = await prisma.workingGroup.findUnique({
      where: { id: workingGroupId }
    });

    if (!workingGroup) {
      return NextResponse.json({ error: "Die ausgewaehlte AG wurde nicht gefunden." }, { status: 404 });
    }
  }

  if (user.role === "ADMIN" && parsed.data.role !== "ADMIN") {
    const adminCount = await prisma.user.count({
      where: { role: "ADMIN" }
    });

    if (adminCount <= 1) {
      return NextResponse.json({ error: "Mindestens ein Vorstandskonto muss erhalten bleiben." }, { status: 400 });
    }
  }

  const approvalPermissions = normalizeApprovalPermissions(parsed.data.role, parsed.data.approvalPermissions, null);
  const approvalPreference = getLegacyApprovalPreference(approvalPermissions);
  const previousSnapshot = snapshotUser(user);

  const updatedUser = await prisma.user.update({
    where: { id },
    data: {
      role: parsed.data.role,
      workingGroupId,
      approvalPreference,
      approvalPermissions: {
        set: approvalPermissions
      }
    }
  });

  const refreshedUser = await prisma.user.findUniqueOrThrow({
    where: { id: updatedUser.id },
    include: {
      workingGroup: {
        select: {
          name: true
        }
      },
      _count: {
        select: {
          approvals: true,
          createdExpenses: true
        }
      }
    }
  });

  await createAuditLog(prisma, {
    actorId: viewer.id,
    action: "user.update",
    entityType: "user",
    entityId: updatedUser.id,
    entityLabel: updatedUser.username,
    summary: `Nutzer ${updatedUser.username} wurde aktualisiert.`,
    metadata: {
      workingGroupId: updatedUser.workingGroupId,
      role: updatedUser.role,
      approvalPermissions: updatedUser.approvalPermissions,
      rollback: {
        kind: "user.update",
        previous: previousSnapshot
      }
    }
  });

  return NextResponse.json({ user: serializeManagedUser(refreshedUser) });
}

export async function DELETE(_: Request, { params }: Context) {
  const { id } = await params;
  const viewer = await getCurrentViewer();

  if (!viewer) {
    return NextResponse.json({ error: "Nicht angemeldet." }, { status: 401 });
  }

  if (!canManageUsers(viewer.role)) {
    return NextResponse.json({ error: "Nur Vorstand oder Finanz-AG dürfen Nutzer löschen." }, { status: 403 });
  }

  if (viewer.id === id) {
    return NextResponse.json({ error: "Du kannst dein eigenes Konto hier nicht löschen." }, { status: 400 });
  }

  const user = await prisma.user.findUnique({
    where: { id },
    include: {
      _count: {
        select: {
          approvals: true,
          createdExpenses: true
        }
      }
    }
  });

  if (!user) {
    return NextResponse.json({ error: "Nutzer nicht gefunden." }, { status: 404 });
  }

  if (user._count.approvals > 0 || user._count.createdExpenses > 0) {
    return NextResponse.json(
      { error: "Nutzer mit Freigaben oder Ausgaben können nicht gelöscht werden." },
      { status: 400 }
    );
  }

  if (user.role === "ADMIN") {
    const adminCount = await prisma.user.count({
      where: { role: "ADMIN" }
    });

    if (adminCount <= 1) {
      return NextResponse.json({ error: "Mindestens ein Admin muss erhalten bleiben." }, { status: 400 });
    }
  }

  await prisma.user.delete({
    where: { id }
  });

  await createAuditLog(prisma, {
    actorId: viewer.id,
    action: "user.delete",
    entityType: "user",
    entityId: user.id,
    entityLabel: user.username,
    summary: `Nutzer ${user.username} wurde geloescht.`,
    metadata: {
      rollback: {
        kind: "user.delete",
        deleted: snapshotUser(user)
      }
    }
  });

  return NextResponse.json({ ok: true });
}