import type { Staff } from '@/types/entities';
import React, { useMemo } from 'react';
import { TrendingUp, TrendingDown, Clock, Activity } from 'lucide-react';
import { useTranslation } from 'react-i18next';

const MS_PER_DAY = 1000 * 60 * 60 * 24;

function tenureDays(hireDate, status, now) {
  if (!hireDate) return 0;
  const start = new Date(hireDate).getTime();
  const end = status === 'inactive' && now ? now : Date.now();
  return Math.max(0, Math.floor((end - start) / MS_PER_DAY));
}

interface RetentionMetricsProps {
  staff: Staff[];
}

export default function RetentionMetrics({ staff }: RetentionMetricsProps) {
  const { t } = useTranslation();
  const stats = useMemo(() => {
    const total = staff.length;
    const active = staff.filter((s) => s.status === 'active').length;
    const onboarding = staff.filter((s) => s.status === 'onboarding').length;
    const churned = staff.filter((s) => s.status === 'inactive').length;

    // Retention rate: of hires whose outcome is decided (active + inactive),
    // what share are still active. Onboarding hires are excluded from the denominator
    // since they haven't had time to churn.
    const decided = active + churned;
    const retentionRate = decided > 0 ? Math.round((active / decided) * 100) : null;

    // Cohort retention: % of hires still on board after N days from hire_date.
    // A hire counts as retained past day N if (status !== 'inactive') OR (tenure >= N before churning).
    const now = Date.now();
    const withHireDate = staff.filter((s) => s.hire_date);
    const cohort = (days) => {
      if (withHireDate.length === 0) return null;
      const retained = withHireDate.filter((s) => {
        const tenure = tenureDays(s.hire_date, s.status, now);
        if (s.status === 'inactive') return tenure >= days;
        return true; // still active/onboarding — retained
      }).length;
      return Math.round((retained / withHireDate.length) * 100);
    };

    const avgTenure = withHireDate.length > 0
      ? Math.round(withHireDate.reduce((sum, s) => sum + tenureDays(s.hire_date, s.status, now), 0) / withHireDate.length)
      : 0;

    return { total, active, onboarding, churned, retentionRate, c30: cohort(30), c60: cohort(60), c90: cohort(90), avgTenure };
  }, [staff]);

  return (
    <div className="grid grid-cols-2 lg:grid-cols-4 gap-3">
      <Metric
        icon={<TrendingUp className="w-4 h-4" />}
        label={t('retentionMetrics.retentionRate')}
        value={stats.retentionRate == null ? '—' : `${stats.retentionRate}%`}
        tone={stats.retentionRate == null ? 'neutral' : stats.retentionRate >= 70 ? 'good' : stats.retentionRate >= 40 ? 'warn' : 'bad'}
        sub={`${stats.active} active · ${stats.churned} churned`}
      />
      <Metric
        icon={<Activity className="w-4 h-4" />}
        label={t('retentionMetrics.stillActive')}
        value={stats.active}
        tone="good"
        sub={stats.onboarding > 0 ? `+ ${stats.onboarding} onboarding` : 'On track'}
      />
      <Metric
        icon={<TrendingDown className="w-4 h-4" />}
        label={t('retentionMetrics.churned')}
        value={stats.churned}
        tone={stats.churned === 0 ? 'good' : 'bad'}
        sub={`${stats.total} total hires`}
      />
      <Metric
        icon={<Clock className="w-4 h-4" />}
        label={t('retentionMetrics.avgTenure')}
        value={stats.avgTenure > 0 ? `${stats.avgTenure}d` : '—'}
        tone="neutral"
        sub={`30d: ${stats.c30 ?? '—'} · 90d: ${stats.c90 ?? '—'}`}
      />
    </div>
  );
}

const TONES = {
  good: { bg: 'bg-[#ECFDF5]', text: 'text-[#047857]', icon: 'bg-[#047857]' },
  warn: { bg: 'bg-[#FFF7ED]', text: 'text-[#B45309]', icon: 'bg-[#B45309]' },
  bad: { bg: 'bg-[#FEF2F2]', text: 'text-[#B91C1C]', icon: 'bg-[#B91C1C]' },
  neutral: { bg: 'bg-[#F0F4F8]', text: 'text-[#1E56C1]', icon: 'bg-[#1E56C1]' },
};

/** Props for the local `Metric` helper in this file. Optional throughout:
    the JavaScript validated none of them and callers omit freely. */
interface MetricProps {
  icon?: any;
  label?: any;
  value?: any;
  sub?: any;
  tone?: any;
}

function Metric({ icon, label, value, sub, tone = 'neutral' }: MetricProps) {
  const t = TONES[tone] || TONES.neutral;
  return (
    <div className="bg-white border border-[#E5E7EB] rounded-xl p-4 flex items-start gap-3">
      <div className={`w-9 h-9 rounded-lg flex items-center justify-center shrink-0 ${t.bg}`}>
        <span className={t.text}>{icon}</span>
      </div>
      <div className="min-w-0">
        <p className="text-[11px] font-semibold text-[#6B7280] tracking-wide">{label}</p>
        <p className="text-[20px] font-bold text-[#111827] leading-tight mt-0.5">{value}</p>
        <p className="text-[10px] text-[#9CA3AF] mt-0.5 truncate">{sub}</p>
      </div>
    </div>
  );
}