import { ChevronLeftIcon, ChevronRightIcon } from "lucide-react";
import Link from "next/link";

import { buttonVariants } from "@/components/ui/button";
import { cn } from "@/lib/utils";

type SearchParams = Record<string, string | string[] | undefined>;

function pageHref(pathname: string, searchParams: SearchParams, page: number) {
  const params = new URLSearchParams();
  for (const [key, value] of Object.entries(searchParams)) {
    if (key === "page" || value === undefined) continue;
    for (const item of Array.isArray(value) ? value : [value]) {
      params.append(key, item);
    }
  }
  if (page > 1) params.set("page", String(page));
  const query = params.toString();
  return query ? `${pathname}?${query}` : pathname;
}

/** Page numbers around the current page, with gaps: 1 … 4 5 6 … 12. */
function pageWindow(current: number, total: number) {
  const pages = new Set([1, total, current - 1, current, current + 1]);
  const sorted = [...pages].filter((p) => p >= 1 && p <= total).sort((a, b) => a - b);
  const result: (number | "gap")[] = [];
  sorted.forEach((page, index) => {
    if (index > 0 && page - sorted[index - 1] > 1) result.push("gap");
    result.push(page);
  });
  return result;
}

export function Pagination({
  pathname,
  searchParams,
  page,
  pageSize,
  total,
  noun = "items",
}: {
  pathname: string;
  searchParams: SearchParams;
  page: number;
  pageSize: number;
  total: number;
  noun?: string;
}) {
  const totalPages = Math.max(1, Math.ceil(total / pageSize));
  const from = total === 0 ? 0 : (page - 1) * pageSize + 1;
  const to = Math.min(total, page * pageSize);

  return (
    <nav
      aria-label="Pagination"
      className="flex flex-wrap items-center justify-between gap-3 text-sm text-muted-foreground"
    >
      <p>
        Showing <span className="font-medium text-foreground">{from}</span>–
        <span className="font-medium text-foreground">{to}</span> of{" "}
        <span className="font-medium text-foreground">{total}</span> {noun}
      </p>
      {totalPages > 1 && (
        <div className="flex items-center gap-1">
          <PageLink
            href={pageHref(pathname, searchParams, page - 1)}
            disabled={page <= 1}
            label="Previous page"
          >
            <ChevronLeftIcon />
          </PageLink>
          {pageWindow(page, totalPages).map((item, index) =>
            item === "gap" ? (
              <span key={`gap-${index}`} className="px-1.5" aria-hidden="true">
                …
              </span>
            ) : (
              <Link
                key={item}
                href={pageHref(pathname, searchParams, item)}
                aria-current={item === page ? "page" : undefined}
                className={cn(
                  buttonVariants({
                    variant: item === page ? "outline" : "ghost",
                    size: "icon-sm",
                  }),
                  "tabular-nums",
                  item === page && "border-primary/30 bg-accent text-accent-foreground",
                )}
              >
                {item}
              </Link>
            ),
          )}
          <PageLink
            href={pageHref(pathname, searchParams, page + 1)}
            disabled={page >= totalPages}
            label="Next page"
          >
            <ChevronRightIcon />
          </PageLink>
        </div>
      )}
    </nav>
  );
}

function PageLink({
  href,
  disabled,
  label,
  children,
}: {
  href: string;
  disabled: boolean;
  label: string;
  children: React.ReactNode;
}) {
  const className = buttonVariants({ variant: "ghost", size: "icon-sm" });
  if (disabled) {
    return (
      <span aria-disabled="true" aria-label={label} className={cn(className, "opacity-40")}>
        {children}
      </span>
    );
  }
  return (
    <Link href={href} aria-label={label} className={className}>
      {children}
    </Link>
  );
}

/** Reads a 1-based page number from search params. */
export function parsePage(value: string | string[] | undefined) {
  const page = Number(Array.isArray(value) ? value[0] : value);
  return Number.isInteger(page) && page > 0 ? page : 1;
}