export interface LeaveRequest {
  id: number;
  userId: number;
  userName?: string;
  type: "Sick" | "Casual" | "Annual" | "Unpaid";
  fromDate: string;
  toDate: string;
  reason: string;
  status: "Pending" | "Approved" | "Rejected";
  appliedAt: string;
}

export interface UserRecord {
  id: number;
  username: string;
  name: string;
  role: "employee" | "manager";
  leaveBalance?: number;
}

const LEAVES_KEY = "lms_leaves";
const USERS_KEY = "lms_users";

// Seed from JSON on first load
async function seedIfNeeded() {
  if (typeof window === "undefined") return;
  if (!localStorage.getItem(LEAVES_KEY)) {
    const mod = await import("@/data/leaves.json");
    const raw = mod.default ?? mod;
    const leaves = Array.isArray(raw) ? raw : ((raw as any).leaves ?? []);
    localStorage.setItem(LEAVES_KEY, JSON.stringify(leaves));
  }
  if (!localStorage.getItem(USERS_KEY)) {
    const mod = await import("@/data/users.json");
    const raw = mod.default ?? mod;
    const users = Array.isArray(raw) ? raw : ((raw as any).users ?? []);
    localStorage.setItem(USERS_KEY, JSON.stringify(users));
  }
}

export async function getLeaves(): Promise<LeaveRequest[]> {
  await seedIfNeeded();
  const raw = localStorage.getItem(LEAVES_KEY) ?? "[]";
  const leaves: LeaveRequest[] = JSON.parse(raw);
  // Attach userName from users
  const users = getUsers();
  return leaves.map((l) => {
    const u = users.find((u) => u.id === l.userId);
    return { ...l, userName: u?.name ?? "Unknown" };
  });
}

export function getUsers(): UserRecord[] {
  const raw = localStorage.getItem(USERS_KEY) ?? "[]";
  return JSON.parse(raw);
}

export async function getLeavesForUser(userId: number): Promise<LeaveRequest[]> {
  const all = await getLeaves();
  return all.filter((l) => l.userId === userId);
}

export async function applyLeave(
  userId: number,
  data: { type: LeaveRequest["type"]; fromDate: string; toDate: string; reason: string }
): Promise<{ ok: boolean; error?: string }> {
  await seedIfNeeded();

  // Calculate days
  const from = new Date(data.fromDate);
  const to = new Date(data.toDate);
  const days = Math.ceil((to.getTime() - from.getTime()) / 86400000) + 1;

  // Check balance
  const users = getUsers();
  const user = users.find((u) => u.id === userId);
  if (!user) return { ok: false, error: "User not found" };
  if ((user.leaveBalance ?? 0) < days)
    return { ok: false, error: `Insufficient balance. You have ${user.leaveBalance} days left.` };

  const leaves: LeaveRequest[] = JSON.parse(localStorage.getItem(LEAVES_KEY) ?? "[]");
  const newLeave: LeaveRequest = {
    id: Date.now(),
    userId,
    type: data.type,
    fromDate: data.fromDate,
    toDate: data.toDate,
    reason: data.reason,
    status: "Pending",
    appliedAt: new Date().toISOString().split("T")[0],
  };
  leaves.push(newLeave);
  localStorage.setItem(LEAVES_KEY, JSON.stringify(leaves));
  return { ok: true };
}

export async function updateLeaveStatus(
  leaveId: number,
  status: "Approved" | "Rejected"
): Promise<void> {
  await seedIfNeeded();
  const leaves: LeaveRequest[] = JSON.parse(localStorage.getItem(LEAVES_KEY) ?? "[]");
  const idx = leaves.findIndex((l) => l.id === leaveId);
  if (idx === -1) return;

  const leave = leaves[idx];
  const wasApproved = leave.status === "Approved";
  leaves[idx] = { ...leave, status };
  localStorage.setItem(LEAVES_KEY, JSON.stringify(leaves));

  // Adjust balance
  const users = getUsers();
  const user = users.find((u) => u.id === leave.userId);
  if (!user || user.role !== "employee") return;

  const from = new Date(leave.fromDate);
  const to = new Date(leave.toDate);
  const days = Math.ceil((to.getTime() - from.getTime()) / 86400000) + 1;

  if (status === "Approved" && !wasApproved) {
    user.leaveBalance = (user.leaveBalance ?? 0) - days;
  } else if (status === "Rejected" && wasApproved) {
    user.leaveBalance = (user.leaveBalance ?? 0) + days;
  }

  localStorage.setItem(USERS_KEY, JSON.stringify(users));

  // Also update session user if it's the same person
  const sessionUser = localStorage.getItem("lms_user");
  if (sessionUser) {
    const su = JSON.parse(sessionUser);
    if (su.id === user.id) {
      su.leaveBalance = user.leaveBalance;
      localStorage.setItem("lms_user", JSON.stringify(su));
    }
  }
}

export function getUserBalance(userId: number): number {
  const users = getUsers();
  const u = users.find((u) => u.id === userId);
  return u?.leaveBalance ?? 0;
}

export function daysBetween(from: string, to: string): number {
  const f = new Date(from);
  const t = new Date(to);
  return Math.ceil((t.getTime() - f.getTime()) / 86400000) + 1;
}