muh/frontend/src/pages/AdminDashboardPage.tsx

import { useEffect, useState } from "react";
import {
  Chart as ChartJS,
  CategoryScale,
  LinearScale,
  BarElement,
  Title,
  Tooltip,
  Legend,
} from "chart.js";
import { Bar } from "react-chartjs-2";
import { apiGet } from "../lib/api";

// Chart.js Komponenten registrieren
ChartJS.register(
  CategoryScale,
  LinearScale,
  BarElement,
  Title,
  Tooltip,
  Legend
);

interface VetSampleStats {
  userId: string;
  displayName: string;
  companyName: string | null;
  sampleCount: number;
}

interface AdminStatistics {
  totalVets: number;
  totalSamples: number;
  samplesPerVet: VetSampleStats[];
}

export default function AdminDashboardPage() {
  const [stats, setStats] = useState<AdminStatistics | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    async function loadStats() {
      try {
        const response = await apiGet<AdminStatistics>("/admin/statistics");
        setStats(response);
      } catch (err) {
        setError((err as Error).message);
      } finally {
        setLoading(false);
      }
    }

    void loadStats();
  }, []);

  // Chart Daten vorbereiten
  const chartData = {
    labels: stats?.samplesPerVet.map((vet) => vet.displayName) || [],
    datasets: [
      {
        label: "Anzahl Proben",
        data: stats?.samplesPerVet.map((vet) => vet.sampleCount) || [],
        backgroundColor: "rgba(90, 123, 168, 0.8)",
        borderColor: "rgba(90, 123, 168, 1)",
        borderWidth: 1,
        borderRadius: 8,
        borderSkipped: false,
      },
    ],
  };

  const chartOptions = {
    responsive: true,
    maintainAspectRatio: false,
    plugins: {
      legend: {
        display: false,
      },
      title: {
        display: true,
        text: "Proben pro Tierarzt",
        font: {
          size: 16,
          weight: "bold" as const,
        },
        padding: {
          top: 10,
          bottom: 20,
        },
        color: "#1d2428",
      },
      tooltip: {
        backgroundColor: "rgba(29, 36, 40, 0.9)",
        padding: 12,
        cornerRadius: 8,
        titleFont: {
          size: 14,
        },
        bodyFont: {
          size: 13,
        },
        callbacks: {
          label: (context: { parsed: { y: number } }) => {
            return `${context.parsed.y} Proben`;
          },
        },
      },
    },
    scales: {
      y: {
        beginAtZero: true,
        ticks: {
          stepSize: 1,
          color: "#666",
        },
        grid: {
          color: "rgba(0, 0, 0, 0.05)",
        },
        title: {
          display: true,
          text: "Anzahl Proben",
          color: "#666",
          font: {
            size: 12,
          },
        },
      },
      x: {
        ticks: {
          color: "#666",
          maxRotation: 45,
          minRotation: 45,
        },
        grid: {
          display: false,
        },
        title: {
          display: true,
          text: "Tierarzt",
          color: "#666",
          font: {
            size: 12,
          },
        },
      },
    },
  };

  return (
    <div className="page-stack">
      {/* Header Bereich */}
      <section className="hero-card admin-hero">
        <div>
          <p className="eyebrow">Administration</p>
          <h3>Administrator Dashboard</h3>
          <p className="muted-text">
            Übersicht über Tierärzte und Proben im System.
          </p>
        </div>
      </section>

      {error ? (
        <div className="alert alert--error">{error}</div>
      ) : null}

      {/* Statistik-Karten */}
      <section className="metrics-grid admin-metrics">
        <article className="metric-card metric-card--primary">
          <span className="metric-card__label">Tierärzte</span>
          <strong className="metric-card__value--large">
            {loading ? "..." : stats?.totalVets ?? 0}
          </strong>
        </article>
        <article className="metric-card metric-card--secondary">
          <span className="metric-card__label">Proben insgesamt</span>
          <strong className="metric-card__value--large">
            {loading ? "..." : stats?.totalSamples ?? 0}
          </strong>
        </article>
      </section>

      {/* Chart Bereich */}
      <section className="section-card">
        <div className="chart-container">
          {loading ? (
            <div className="empty-state">Chart wird geladen...</div>
          ) : stats?.samplesPerVet.length === 0 ? (
            <div className="empty-state">Noch keine Proben vorhanden.</div>
          ) : (
            <Bar data={chartData} options={chartOptions} />
          )}
        </div>
      </section>


    </div>
  );
}