const { currentDateString, parseDateOnlyString } = require("../utils/date");

function addDays(date, days) {
  const next = new Date(date);
  next.setUTCDate(next.getUTCDate() + days);
  return next;
}

async function buildEmployeeStats(prisma, options = {}) {
  const timeZone = options.timeZone ?? "Asia/Shanghai";
  const todayString = currentDateString(timeZone);
  const today = parseDateOnlyString(todayString);
  const last30DateFrom = addDays(today, -29);
  const next30DateTo = addDays(today, 30);
  const activeEmployeeWhere = { status: "active" };

  const [employmentStatusRows, departmentRows, departments, recentHires, recentDepartures, expiringContracts, validCertificateHolders, expiringCertificates] = await Promise.all([
    prisma.employee.groupBy({
      by: ["employment_status"],
      where: activeEmployeeWhere,
      _count: { _all: true },
    }),
    prisma.employee.groupBy({
      by: ["department_id"],
      where: activeEmployeeWhere,
      _count: { _all: true },
    }),
    prisma.department.findMany({
      where: { archived_at: null },
      select: { id: true, name: true },
    }),
    prisma.employee.count({
      where: {
        hire_date: {
          gte: last30DateFrom,
          lte: new Date(`${todayString}T23:59:59.999Z`),
        },
      },
    }),
    prisma.employee.count({
      where: {
        last_working_date: {
          gte: last30DateFrom,
          lte: new Date(`${todayString}T23:59:59.999Z`),
        },
      },
    }),
    prisma.employeeContract.count({
      where: {
        terminated_date: null,
        end_date: {
          gte: today,
          lte: new Date(`${next30DateTo.toISOString().slice(0, 10)}T23:59:59.999Z`),
        },
        employee: activeEmployeeWhere,
      },
    }),
    prisma.employeeCertificate.groupBy({
      by: ["employee_id"],
      where: {
        employee: activeEmployeeWhere,
        OR: [
          { expiry_date: null },
          {
            expiry_date: {
              gte: today,
            },
          },
        ],
      },
    }),
    prisma.employeeCertificate.count({
      where: {
        employee: activeEmployeeWhere,
        expiry_date: {
          gte: today,
          lte: new Date(`${next30DateTo.toISOString().slice(0, 10)}T23:59:59.999Z`),
        },
      },
    }),
  ]);

  const departmentMap = new Map(departments.map((item) => [item.id, item.name]));

  return {
    asOfDate: todayString,
    employmentStatusSummary: {
      total: employmentStatusRows.reduce((sum, item) => sum + item._count._all, 0),
      items: employmentStatusRows
        .map((item) => ({
          status: item.employment_status,
          count: item._count._all,
        }))
        .sort((left, right) => right.count - left.count || left.status.localeCompare(right.status)),
    },
    departmentHeadcount: departmentRows
      .map((item) => ({
        departmentId: item.department_id,
        departmentName: departmentMap.get(item.department_id) ?? "未知部门",
        count: item._count._all,
      }))
      .sort((left, right) => right.count - left.count || left.departmentName.localeCompare(right.departmentName)),
    recentMovements: {
      dateFrom: last30DateFrom.toISOString().slice(0, 10),
      dateTo: todayString,
      hires: recentHires,
      departures: recentDepartures,
    },
    expiringContracts: {
      dateFrom: todayString,
      dateTo: next30DateTo.toISOString().slice(0, 10),
      count: expiringContracts,
    },
    certificateSummary: {
      dateFrom: todayString,
      dateTo: next30DateTo.toISOString().slice(0, 10),
      validHolderCount: validCertificateHolders.length,
      expiringSoonCount: expiringCertificates,
    },
  };
}

module.exports = {
  buildEmployeeStats,
};