"use client";

import { useEffect, useState } from "react";
import { formatDistanceToNow } from "date-fns";
import { IconAlertTriangle } from "@tabler/icons-react";
import { Alert, AlertDescription } from "@kandev/ui/alert";
import type { GitHubRateLimitInfo, GitHubRateLimitSnapshot } from "@/lib/types/github";
import { GitHubAccessHelp } from "./github-access-help";

const RESOURCE_LABELS: Record<string, { label: string; unit: string }> = {
  core: { label: "API rate limit", unit: "requests" },
  graphql: { label: "GraphQL query limit", unit: "points" },
  search: { label: "Search limit", unit: "requests" },
};

// useTickNow re-renders every intervalMs and exposes a stable now-value so the
// render pass stays pure (Date.now() in the render body would be impure).
function useTickNow(intervalMs: number): number {
  const [now, setNow] = useState(() => Date.now());
  useEffect(() => {
    const id = setInterval(() => setNow(Date.now()), intervalMs);
    return () => clearInterval(id);
  }, [intervalMs]);
  return now;
}

function isExhausted(snap: GitHubRateLimitSnapshot, now: number): boolean {
  if (snap.remaining > 0) return false;
  const reset = new Date(snap.reset_at).getTime();
  return Number.isFinite(reset) && reset > now;
}

function formatReset(snap: GitHubRateLimitSnapshot): string {
  const reset = new Date(snap.reset_at);
  if (!Number.isFinite(reset.getTime())) return "";
  return formatDistanceToNow(reset, { addSuffix: true });
}

// latestReset returns the snapshot whose reset_at is furthest in the future.
// When multiple buckets are exhausted, background checks remain paused until
// the last one recovers, so the alert must anchor on that bucket — anchoring
// on snapshots[0] would understate the pause window.
function latestReset(snaps: GitHubRateLimitSnapshot[]): GitHubRateLimitSnapshot {
  return snaps.reduce((latest, s) =>
    new Date(s.reset_at).getTime() > new Date(latest.reset_at).getTime() ? s : latest,
  );
}

function snapshotsFromInfo(info: GitHubRateLimitInfo): GitHubRateLimitSnapshot[] {
  const out: GitHubRateLimitSnapshot[] = [];
  if (info.core) out.push(info.core);
  if (info.graphql) out.push(info.graphql);
  if (info.search) out.push(info.search);
  return out;
}

export function GitHubRateLimitDisplay({ info }: { info?: GitHubRateLimitInfo }) {
  const now = useTickNow(30_000);
  if (!info) return null;
  const snapshots = snapshotsFromInfo(info);
  if (snapshots.length === 0) return null;
  const exhausted = snapshots.filter((s) => isExhausted(s, now));

  return (
    <GitHubAccessHelp
      label="Show GitHub API limits"
      title="GitHub API limits"
      description="Current GitHub API rate and query limits for this workspace connection."
      content={<RateLimitDetails snapshots={snapshots} exhausted={exhausted} />}
    />
  );
}

function RateLimitDetails({
  snapshots,
  exhausted,
}: {
  snapshots: GitHubRateLimitSnapshot[];
  exhausted: GitHubRateLimitSnapshot[];
}) {
  return (
    <div className="space-y-2" data-testid="github-rate-limit-display">
      {exhausted.length > 0 && (
        <Alert variant="destructive" data-testid="github-rate-limit-exhausted">
          <IconAlertTriangle className="h-4 w-4" />
          <AlertDescription className="text-xs">
            GitHub API access is exhausted for{" "}
            {exhausted
              .map((snapshot) => RESOURCE_LABELS[snapshot.resource]?.label ?? snapshot.resource)
              .join(", ")}
            . Background PR and issue checks are paused until the last limit resets{" "}
            {formatReset(latestReset(exhausted))}.
          </AlertDescription>
        </Alert>
      )}
      <div className="space-y-1 text-xs text-muted-foreground">
        {snapshots.map((snapshot) => {
          const resource = RESOURCE_LABELS[snapshot.resource] ?? {
            label: snapshot.resource,
            unit: "requests",
          };
          const limit = snapshot.limit > 0 ? snapshot.limit.toLocaleString("en-US") : "unknown";
          const reset = formatReset(snapshot);
          return (
            <p key={snapshot.resource} data-testid={`github-rate-limit-${snapshot.resource}`}>
              <span className="font-medium text-foreground">{resource.label}:</span>{" "}
              {snapshot.remaining.toLocaleString("en-US")} of {limit} {resource.unit} remaining
              {reset ? ` · resets ${reset}` : ""}
            </p>
          );
        })}
      </div>
    </div>
  );
}