import { NextResponse } from "next/server";

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

type Context = {
  params: {
    id: string;
  };
};

function asRecord(value: unknown, label: string) {
  if (!value || typeof value !== "object" || Array.isArray(value)) {
    throw new Error(`${label} ist im Änderungsverlauf nicht vollständig hinterlegt.`);
  }

  return value as Record<string, unknown>;
}

function asString(value: unknown, label: string) {
  if (typeof value !== "string" || value.length === 0) {
    throw new Error(`${label} fehlt im Änderungsverlauf.`);
  }

  return value;
}

function asNullableString(value: unknown) {
  return typeof value === "string" && value.length > 0 ? value : null;
}

function asDate(value: unknown, label: string) {
  if (value === null || value === undefined || value === "") {
    return null;
  }

  const parsed = new Date(asString(value, label));

  if (Number.isNaN(parsed.getTime())) {
    throw new Error(`${label} ist ungültig.`);
  }

  return parsed;
}

function asNumber(value: unknown, label: string) {
  if (typeof value !== "number" || Number.isNaN(value)) {
    throw new Error(`${label} ist ungültig.`);
  }

  return value;
}

function asApprovalPermissions(value: unknown) {
  if (!Array.isArray(value)) {
    return [] as ("CHAIR_A" | "CHAIR_B" | "FINANCE")[];
  }

  return value.filter(
    (entry): entry is "CHAIR_A" | "CHAIR_B" | "FINANCE" =>
      entry === "CHAIR_A" || entry === "CHAIR_B" || entry === "FINANCE"
  );
}

export async function POST(_: Request, { params }: Context) {
  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 Zustände zurücksetzen." }, { status: 403 });
  }

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

  if (!auditLog) {
    return NextResponse.json({ error: "Log-Eintrag nicht gefunden." }, { status: 404 });
  }

  const rollback = getRollbackMetadata(auditLog.metadata);

  if (!rollback) {
    return NextResponse.json({ error: "Dieser Log-Eintrag enthält noch keinen wiederherstellbaren Zustand." }, { status: 400 });
  }

  try {
    await prisma.$transaction(async (tx) => {
      switch (rollback.kind) {
        case "budget.create": {
          const created = asRecord(rollback.created, "Budget");
          const budgetId = asString(created.id, "Budget-ID");
          const budget = await tx.budget.findUnique({
            where: { id: budgetId },
            include: {
              _count: {
                select: {
                  expenses: true
                }
              }
            }
          });

          if (!budget) {
            throw new Error("Das angelegte Budget existiert nicht mehr.");
          }

          if (budget._count.expenses > 0) {
            throw new Error("Das Budget hat bereits Ausgaben und kann nicht automatisch entfernt werden.");
          }

          await tx.budget.delete({
            where: { id: budgetId }
          });

          if (rollback.createdWorkingGroup) {
            const createdWorkingGroup = asRecord(rollback.createdWorkingGroup, "Arbeitsgruppe");
            const workingGroupId = asString(createdWorkingGroup.id, "AG-ID");
            const workingGroup = await tx.workingGroup.findUnique({
              where: { id: workingGroupId },
              include: {
                _count: {
                  select: {
                    members: true,
                    budgets: true,
                    expenses: true
                  }
                }
              }
            });

            if (
              workingGroup &&
              workingGroup._count.members === 0 &&
              workingGroup._count.budgets === 0 &&
              workingGroup._count.expenses === 0
            ) {
              await tx.workingGroup.delete({
                where: { id: workingGroup.id }
              });
            }
          }
          break;
        }

        case "budget.update": {
          const previous = asRecord(rollback.previous, "Budget");
          const budgetId = asString(previous.id, "Budget-ID");

          await tx.budget.update({
            where: { id: budgetId },
            data: {
              name: asString(previous.name, "Budgetname"),
              totalBudget: asNumber(previous.totalBudget, "Budgetbetrag"),
              releasedAmount: asNumber(previous.releasedAmount ?? 0, "Zus\u00e4tzliche Mittel\u00fcbergabe"),
              colorCode: asString(previous.colorCode, "Budgetfarbe")
            }
          });
          break;
        }

        case "budget.delete": {
          const deleted = asRecord(rollback.deleted, "Budget");

          await tx.budget.create({
            data: {
              id: asString(deleted.id, "Budget-ID"),
              name: asString(deleted.name, "Budgetname"),
              totalBudget: asNumber(deleted.totalBudget, "Budgetbetrag"),
              releasedAmount: asNumber(deleted.releasedAmount ?? 0, "Zus\u00e4tzliche Mittel\u00fcbergabe"),
              colorCode: asString(deleted.colorCode, "Budgetfarbe"),
              workingGroupId: asString(deleted.workingGroupId, "AG-ID"),
              periodId: asString(deleted.periodId, "Zeitraum-ID"),
              createdAt: asDate(deleted.createdAt, "Budget erstellt am") ?? new Date()
            }
          });
          break;
        }

        case "workingGroup.delete": {
          const deleted = asRecord(rollback.deleted, "Arbeitsgruppe");

          await tx.workingGroup.create({
            data: {
              id: asString(deleted.id, "AG-ID"),
              name: asString(deleted.name, "AG-Name"),
              createdAt: asDate(deleted.createdAt, "AG erstellt am") ?? new Date()
            }
          });
          break;
        }

        case "workingGroup.create": {
          const created = asRecord(rollback.created, "Arbeitsgruppe");
          const workingGroupId = asString(created.id, "AG-ID");
          const workingGroup = await tx.workingGroup.findUnique({
            where: { id: workingGroupId },
            include: {
              _count: {
                select: {
                  members: true,
                  budgets: true,
                  expenses: true
                }
              }
            }
          });

          if (!workingGroup) {
            throw new Error("Die angelegte AG existiert nicht mehr.");
          }

          if (workingGroup._count.members > 0 || workingGroup._count.budgets > 0 || workingGroup._count.expenses > 0) {
            throw new Error("Die AG wird bereits verwendet und kann nicht automatisch entfernt werden.");
          }

          await tx.workingGroup.delete({
            where: { id: workingGroupId }
          });
          break;
        }

        case "workingGroup.update": {
          const previous = asRecord(rollback.previous, "Arbeitsgruppe");
          const workingGroupId = asString(previous.id, "AG-ID");

          await tx.workingGroup.update({
            where: { id: workingGroupId },
            data: {
              name: asString(previous.name, "AG-Name")
            }
          });
          break;
        }

        case "period.create": {
          const created = asRecord(rollback.created, "Zeitraum");
          const periodId = asString(created.id, "Zeitraum-ID");
          const period = await tx.accountingPeriod.findUnique({
            where: { id: periodId },
            include: {
              _count: {
                select: {
                  budgets: true,
                  expenses: true
                }
              }
            }
          });

          if (!period) {
            throw new Error("Der angelegte Zeitraum existiert nicht mehr.");
          }

          if (period.isCurrent) {
            throw new Error("Der aktuell aktive Zeitraum kann nicht automatisch entfernt werden.");
          }

          if (period._count.expenses > 0) {
            throw new Error("Der Zeitraum enthält bereits Ausgaben und kann nicht automatisch entfernt werden.");
          }

          await tx.budget.deleteMany({
            where: {
              periodId
            }
          });

          await tx.accountingPeriod.delete({
            where: {
              id: periodId
            }
          });
          break;
        }

        case "period.delete": {
          const deleted = asRecord(rollback.deleted, "Zeitraum");

          await tx.accountingPeriod.create({
            data: {
              id: asString(deleted.id, "Zeitraum-ID"),
              name: asString(deleted.name, "Zeitraumname"),
              startsAt: asDate(deleted.startsAt, "Zeitraumstart") ?? new Date(),
              endsAt: asDate(deleted.endsAt, "Zeitraumende") ?? new Date(),
              isCurrent: Boolean(deleted.isCurrent),
              createdAt: asDate(deleted.createdAt, "Zeitraum erstellt am") ?? new Date()
            }
          });
          break;
        }

        case "period.setCurrent": {
          const previousCurrentPeriodId = asNullableString(rollback.previousCurrentPeriodId);

          await tx.accountingPeriod.updateMany({
            data: {
              isCurrent: false
            }
          });

          if (previousCurrentPeriodId) {
            await tx.accountingPeriod.update({
              where: {
                id: previousCurrentPeriodId
              },
              data: {
                isCurrent: true
              }
            });
          }
          break;
        }

        case "settings.update": {
          const previous = asRecord(rollback.previous, "App-Einstellungen");

          await tx.appSettings.upsert({
            where: {
              id: asString(previous.id, "Einstellungs-ID")
            },
            update: {
              approvalThreshold: asNumber(previous.approvalThreshold, "Freigabe-Schwelle")
            },
            create: {
              id: asString(previous.id, "Einstellungs-ID"),
              approvalThreshold: asNumber(previous.approvalThreshold, "Freigabe-Schwelle"),
              createdAt: asDate(previous.createdAt, "Einstellungen erstellt am") ?? new Date()
            }
          });
          break;
        }

        case "user.create": {
          const created = asRecord(rollback.created, "Nutzer");
          const userId = asString(created.id, "Nutzer-ID");

          if (viewer.id === userId) {
            throw new Error("Dein eigenes aktives Konto kann nicht über den Änderungsverlauf entfernt werden.");
          }

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

          if (!user) {
            throw new Error("Der angelegte Nutzer existiert nicht mehr.");
          }

          if (user._count.approvals > 0 || user._count.createdExpenses > 0) {
            throw new Error("Der Nutzer hat bereits Ausgaben oder Freigaben und kann nicht automatisch entfernt werden.");
          }

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

            if (adminCount <= 1) {
              throw new Error("Mindestens ein Vorstandskonto muss erhalten bleiben.");
            }
          }

          await tx.user.delete({
            where: { id: userId }
          });
          break;
        }

        case "user.delete": {
          const deleted = asRecord(rollback.deleted, "Nutzer");

          await tx.user.create({
            data: {
              id: asString(deleted.id, "Nutzer-ID"),
              name: asString(deleted.name, "Anzeigename"),
              username: asString(deleted.username, "Login-Name"),
              email: asNullableString(deleted.email),
              passwordHash: asString(deleted.passwordHash, "Passworthash"),
              role: asString(deleted.role, "Rolle") as "ADMIN" | "FINANCE" | "MEMBER",
              approvalPreference: asNullableString(deleted.approvalPreference) as "CHAIR_A" | "CHAIR_B" | "FINANCE" | null,
              approvalPermissions: asApprovalPermissions(deleted.approvalPermissions),
              workingGroupId: asNullableString(deleted.workingGroupId),
              createdAt: asDate(deleted.createdAt, "Nutzer erstellt am") ?? new Date()
            }
          });
          break;
        }

        case "user.update": {
          const previous = asRecord(rollback.previous, "Nutzer");
          const role = asString(previous.role, "Rolle") as "ADMIN" | "FINANCE" | "MEMBER";

          await tx.user.update({
            where: {
              id: asString(previous.id, "Nutzer-ID")
            },
            data: {
              name: asString(previous.name, "Anzeigename"),
              username: asString(previous.username, "Login-Name"),
              email: asNullableString(previous.email),
              role,
              approvalPreference: asNullableString(previous.approvalPreference) as "CHAIR_A" | "CHAIR_B" | "FINANCE" | null,
              approvalPermissions: asApprovalPermissions(previous.approvalPermissions),
              workingGroupId: asNullableString(previous.workingGroupId)
            }
          });
          break;
        }

        case "user.passwordReset": {
          await tx.user.update({
            where: {
              id: asString(rollback.userId, "Nutzer-ID")
            },
            data: {
              passwordHash: asString(rollback.previousPasswordHash, "Altes Passwort")
            }
          });
          break;
        }

        case "expense.create": {
          const created = asRecord(rollback.created, "Ausgabe");
          const expenseId = asString(created.id, "Ausgabe-ID");
          const expense = await tx.expense.findUnique({
            where: { id: expenseId },
            include: {
              _count: {
                select: {
                  approvals: true
                }
              }
            }
          });

          if (!expense) {
            throw new Error("Die angelegte Ausgabe existiert nicht mehr.");
          }

          if (expense._count.approvals > 0 || expense.paidAt || expense.documentedAt) {
            throw new Error("Die Ausgabe wurde bereits weiterverarbeitet und kann nicht automatisch entfernt werden.");
          }

          await tx.expense.delete({
            where: { id: expenseId }
          });
          break;
        }

        case "expense.delete": {
          const deleted = asRecord(rollback.deleted, "Ausgabe");

          await tx.expense.create({
            data: {
              id: asString(deleted.id, "Ausgabe-ID"),
              title: asString(deleted.title, "Titel"),
              description: asNullableString(deleted.description),
              amount: asNumber(deleted.amount, "Betrag"),
              creatorId: asString(deleted.creatorId, "Ersteller-ID"),
              agId: asString(deleted.agId, "AG-ID"),
              budgetId: asString(deleted.budgetId, "Budget-ID"),
              periodId: asString(deleted.periodId, "Zeitraum-ID"),
              approvalStatus: asString(deleted.approvalStatus, "Freigabestatus") as "PENDING" | "APPROVED",
              recurrence: asString(deleted.recurrence, "Wiederholung") as "NONE" | "MONTHLY",
              recurrenceStartAt: asDate(deleted.recurrenceStartAt, "Abo-Startdatum"),
              proofUrl: asNullableString(deleted.proofUrl),
              createdAt: asDate(deleted.createdAt, "Ausgabe erstellt am") ?? new Date(),
              paidAt: asDate(deleted.paidAt, "Bezahlt am"),
              documentedAt: asDate(deleted.documentedAt, "Dokumentiert am")
            }
          });
          break;
        }

        case "expense.approve": {
          const approval = asRecord(rollback.approval, "Freigabe");
          const expenseId = asString(approval.expenseId, "Ausgabe-ID");

          await tx.approval.delete({
            where: {
              id: asString(approval.id, "Freigabe-ID")
            }
          });

          const remainingApprovals = await tx.approval.findMany({
            where: {
              expenseId
            }
          });

          const approvalTypes = remainingApprovals.map((entry) => entry.approvalType);
          const approvalStatus = APPROVAL_FLOW.every((approvalType) => approvalTypes.includes(approvalType))
            ? "APPROVED"
            : "PENDING";

          await tx.expense.update({
            where: { id: expenseId },
            data: {
              approvalStatus
            }
          });
          break;
        }

        case "expense.markPaid": {
          await tx.expense.update({
            where: {
              id: asString(rollback.expenseId, "Ausgabe-ID")
            },
            data: {
              paidAt: asDate(rollback.previousPaidAt, "Vorheriger Bezahlt-Zeitpunkt")
            }
          });
          break;
        }

        case "expense.document": {
          await tx.expense.update({
            where: {
              id: asString(rollback.expenseId, "Ausgabe-ID")
            },
            data: {
              proofUrl: asNullableString(rollback.previousProofUrl),
              documentedAt: asDate(rollback.previousDocumentedAt, "Vorheriger Dokumentationszeitpunkt")
            }
          });
          break;
        }

        default:
          throw new Error("Dieser Änderungstyp kann aktuell noch nicht automatisch zurückgesetzt werden.");
      }
    });

    await createAuditLog(prisma, {
      actorId: viewer.id,
      action: "audit.restore",
      entityType: auditLog.entityType,
      entityId: auditLog.entityId,
      entityLabel: auditLog.entityLabel,
      summary: `Änderung "${auditLog.summary}" wurde zurückgesetzt.`,
      metadata: {
        restoredAuditLogId: auditLog.id,
        restoredAction: auditLog.action
      }
    });

    return NextResponse.json({ ok: true });
  } catch (error) {
    const message = error instanceof Error ? error.message : "Der Zustand konnte nicht zurückgesetzt werden.";
    return NextResponse.json({ error: message }, { status: 400 });
  }
}