import { AlertTriangle, BriefcaseBusiness, Clock3, RotateCcw } from "lucide-react";
import { useCallback, useEffect, useMemo, useState } from "react";
import { Link } from "react-router-dom";
import { toast } from "sonner";

import { api } from "../api";
import { eventTitle } from "../constants";
import { EmptyState } from "../components/EmptyState";
import { StatCard } from "../components/StatCard";
import { StatusIcon } from "../components/StatusIcon";
import type { Health, Job, JobEvent, JobStats, JobStatus } from "../types";

const emptyStats: JobStats = {
  total: 0,
  by_status: { queued: 0, running: 0, succeeded: 0, failed: 0 },
  overdue_running: 0,
  retries_pending: 0,
  oldest_queued_at: null
};

function BarMetric({ label, value, max, tone = "neutral" }: { label: string; value: number; max: number; tone?: string }) {
  const width = max > 0 ? Math.max(4, Math.round((value / max) * 100)) : 0;
  return (
    <div className="metric-bar-row">
      <span>{label}</span>
      <div className="metric-track">
        <i className={tone} style={{ width: `${width}%` }} />
      </div>
      <strong>{value}</strong>
    </div>
  );
}

function MiniHistogram({ data }: { data: Array<{ label: string; value: number; tone: string }> }) {
  const max = Math.max(...data.map((item) => item.value), 1);
  return (
    <div className="histogram" aria-label="histogram">
      {data.map((item) => {
        const height = item.value > 0 ? Math.max(12, Math.round((item.value / max) * 100)) : 4;
        return (
          <div className="histogram-item" key={item.label}>
            <div className="histogram-column">
              <i className={item.tone} style={{ height: `${height}%` }} />
            </div>
            <span>{item.label}</span>
            <strong>{item.value}</strong>
          </div>
        );
      })}
    </div>
  );
}

export function DashboardPage() {
  const [jobs, setJobs] = useState<Job[]>([]);
  const [events, setEvents] = useState<JobEvent[]>([]);
  const [stats, setStats] = useState<JobStats>(emptyStats);
  const [health, setHealth] = useState<Health | null>(null);

  const refresh = useCallback(async () => {
    const [jobsData, statsData, eventsData, healthData] = await Promise.all([
      api.listJobs(),
      api.getStats(),
      api.listEvents({ limit: 50 }),
      api.health()
    ]);
    setJobs(jobsData);
    setStats({ ...emptyStats, ...statsData, by_status: { ...emptyStats.by_status, ...statsData.by_status } });
    setEvents(eventsData.results);
    setHealth(healthData);
  }, []);

  useEffect(() => {
    void refresh().catch((caught) => toast.error(caught instanceof Error ? caught.message : String(caught)));
    const id = window.setInterval(() => void refresh().catch(() => undefined), 2000);
    return () => window.clearInterval(id);
  }, [refresh]);

  const recentJobs = useMemo(() => jobs.slice(0, 20), [jobs]);
  const recentJobStatusData = useMemo(() => {
    const counts: Record<JobStatus, number> = { queued: 0, running: 0, succeeded: 0, failed: 0 };
    recentJobs.forEach((job) => {
      counts[job.status] += 1;
    });
    return [
      { label: "Queued", value: counts.queued, tone: "queued" },
      { label: "Running", value: counts.running, tone: "running" },
      { label: "Succeeded", value: counts.succeeded, tone: "succeeded" },
      { label: "Failed", value: counts.failed, tone: "failed" }
    ];
  }, [recentJobs]);
  const pressureData = useMemo(
    () => [
      { label: "Queued", value: stats.by_status.queued, tone: "queued" },
      { label: "Running", value: stats.by_status.running, tone: "running" },
      { label: "Retry backoff", value: stats.retries_pending, tone: "orange" },
      { label: "Overdue locks", value: stats.overdue_running, tone: "failed" },
      { label: "Failed", value: stats.by_status.failed, tone: "failed" }
    ],
    [stats]
  );
  const eventData = useMemo(() => {
    const counts = events.reduce<Record<string, number>>((accumulator, event) => {
      accumulator[event.type] = (accumulator[event.type] ?? 0) + 1;
      return accumulator;
    }, {});
    return Object.entries(counts)
      .sort((a, b) => b[1] - a[1])
      .slice(0, 6)
      .map(([type, value]) => ({ label: eventTitle(type), value, tone: type.includes("fail") ? "failed" : type.includes("success") ? "succeeded" : "running" }));
  }, [events]);
  const maxPressure = Math.max(...pressureData.map((item) => item.value), 1);

  return (
    <div className="page">
      <header className="page-header">
        <div>
          <span className="eyebrow">Overview</span>
          <h2>Dashboard</h2>
        </div>
        <span className={`connection ${health?.ok ? "open" : "closed"}`}>DB {health?.database ?? "unknown"}</span>
      </header>

      <section className="stats-grid">
        <StatCard label="Total jobs" value={stats.total} icon={<BriefcaseBusiness size={16} />} />
        <StatCard label="Queued" value={stats.by_status.queued} tone="queued" icon={<StatusIcon status="queued" />} />
        <StatCard label="Running" value={stats.by_status.running} tone="running" icon={<StatusIcon status="running" />} />
        <StatCard label="Succeeded" value={stats.by_status.succeeded} tone="succeeded" icon={<StatusIcon status="succeeded" />} />
        <StatCard label="Failed" value={stats.by_status.failed} tone="failed" icon={<StatusIcon status="failed" />} />
        <StatCard label="Overdue locks" value={stats.overdue_running} tone="failed" icon={<AlertTriangle size={16} />} />
      </section>

      <section className="dashboard-grid">
        <section className="panel">
          <div className="section-title">
            <h3>Recent Jobs</h3>
            <Link className="secondary-button" to="/jobs">
              View jobs
            </Link>
          </div>
          {recentJobs.length ? (
            <>
              <MiniHistogram data={recentJobStatusData} />
              <div className="job-tick-chart" aria-label="latest jobs">
                {recentJobs.slice(0, 16).map((job) => (
                  <Link className={`job-tick ${job.status}`} key={job.id} title={`${job.type} ${job.status}`} to={`/jobs/${job.id}`} />
                ))}
              </div>
            </>
          ) : (
            <EmptyState title="No jobs yet" />
          )}
        </section>

        <section className="panel">
          <div className="section-title">
            <h3>Queue Pressure</h3>
            <Clock3 size={16} />
          </div>
          <div className="metric-bars">
            {pressureData.map((item) => (
              <BarMetric key={item.label} label={item.label} max={maxPressure} tone={item.tone} value={item.value} />
            ))}
          </div>
          <div className="dashboard-footnote">
            <span>{stats.oldest_queued_at ? "Oldest queued job is waiting" : "No queued backlog"}</span>
          </div>
        </section>

        <section className="panel">
          <div className="section-title">
            <h3>Recent Events</h3>
            <RotateCcw size={16} />
          </div>
          {eventData.length ? <MiniHistogram data={eventData} /> : <EmptyState title="No events yet" />}
        </section>
      </section>
    </div>
  );
}
