import { useEffect, useState } from "react";
import { useAuth } from "../context/AuthContext";
import { fetchUsageStats, type UsageStats } from "../api/admin-usage";
import { useDocumentTitle } from "../hooks/useDocumentTitle";
import styles from "./AdminUsage.module.css";

function formatNumber(n: number): string {
  if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(1)}M`;
  if (n >= 1_000) return `${(n / 1_000).toFixed(1)}K`;
  return n.toLocaleString();
}

function shortDay(dateStr: string): string {
  const d = new Date(dateStr + "T00:00:00");
  return d.toLocaleDateString(undefined, { weekday: "short" });
}

export default function AdminUsage() {
  useDocumentTitle("Usage — Admin");
  const { token } = useAuth();
  const [stats, setStats] = useState<UsageStats | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    if (!token) return;
    setLoading(true);
    fetchUsageStats(token)
      .then(setStats)
      .catch((e) => setError(e.message || "Failed to load usage stats"))
      .finally(() => setLoading(false));
  }, [token]);

  if (loading) {
    return (
      <div className={styles.page}>
        <h1 className={styles.title}>Usage</h1>
        <p className={styles.loading}>Loading usage stats…</p>
      </div>
    );
  }

  if (error || !stats) {
    return (
      <div className={styles.page}>
        <h1 className={styles.title}>Usage</h1>
        <p className={styles.error}>{error || "No data available"}</p>
      </div>
    );
  }

  const maxDaily = Math.max(...stats.daily_counts.map((d) => d.request_count), 1);

  return (
    <div className={styles.page}>
      <h1 className={styles.title}>Usage</h1>

      {/* Summary cards */}
      <div className={styles.summaryGrid}>
        {([
          { label: "Today", data: stats.today },
          { label: "This Week", data: stats.week },
          { label: "This Month", data: stats.month },
        ] as const).map(({ label, data }) => (
          <div key={label} className={styles.card}>
            <span className={styles.cardLabel}>{label}</span>
            <span className={styles.cardValue}>
              {formatNumber(data.total_tokens)} tokens
            </span>
            <span className={styles.cardSub}>
              {data.request_count} request{data.request_count !== 1 ? "s" : ""}
              {" · "}
              {formatNumber(data.prompt_tokens)} prompt / {formatNumber(data.completion_tokens)} completion
            </span>
          </div>
        ))}
      </div>

      {/* Daily bar chart */}
      {stats.daily_counts.length > 0 && (
        <div className={styles.section}>
          <h2 className={styles.sectionTitle}>Last 7 Days</h2>
          <div className={styles.chartContainer}>
            {stats.daily_counts.map((d) => (
              <div key={d.date} className={styles.barColumn}>
                <span className={styles.barValue}>{d.request_count}</span>
                <div
                  className={styles.bar}
                  style={{ height: `${(d.request_count / maxDaily) * 80}%` }}
                />
                <span className={styles.barLabel}>{shortDay(d.date)}</span>
              </div>
            ))}
          </div>
        </div>
      )}

      {/* Top creators */}
      <div className={styles.section}>
        <h2 className={styles.sectionTitle}>Top Creators (This Month)</h2>
        {stats.top_creators.length === 0 ? (
          <p className={styles.empty}>No creator usage data yet.</p>
        ) : (
          <table className={styles.table}>
            <thead>
              <tr>
                <th>Creator</th>
                <th className={styles.numCell}>Requests</th>
                <th className={styles.numCell}>Tokens</th>
              </tr>
            </thead>
            <tbody>
              {stats.top_creators.map((c) => (
                <tr key={c.creator_slug}>
                  <td>{c.creator_slug}</td>
                  <td className={styles.numCell}>{c.request_count.toLocaleString()}</td>
                  <td className={styles.numCell}>{formatNumber(c.total_tokens)}</td>
                </tr>
              ))}
            </tbody>
          </table>
        )}
      </div>

      {/* Top users */}
      <div className={styles.section}>
        <h2 className={styles.sectionTitle}>Top Users (This Month)</h2>
        {stats.top_users.length === 0 ? (
          <p className={styles.empty}>No user usage data yet.</p>
        ) : (
          <table className={styles.table}>
            <thead>
              <tr>
                <th>User / IP</th>
                <th className={styles.numCell}>Requests</th>
                <th className={styles.numCell}>Tokens</th>
              </tr>
            </thead>
            <tbody>
              {stats.top_users.map((u, i) => (
                <tr key={`${u.identifier}-${i}`}>
                  <td>{u.identifier}</td>
                  <td className={styles.numCell}>{u.request_count.toLocaleString()}</td>
                  <td className={styles.numCell}>{formatNumber(u.total_tokens)}</td>
                </tr>
              ))}
            </tbody>
          </table>
        )}
      </div>
    </div>
  );
}