"use client";

import { motion } from "framer-motion";
import { useAppReducedMotion as useReducedMotion } from "@/lib/motion-pref";
import Link from "next/link";
import { usePathname } from "next/navigation";

import { CompassIcon, FlameIcon, GearIcon, HomeIcon, PlusIcon } from "@/components/icons";
import { haptic } from "@/lib/haptics";
import { useI18n } from "@/lib/i18n";
import { springSnappy } from "@/lib/motion";
import { openSettings } from "@/lib/ui-events";
import { cn } from "@/lib/utils";

/**
 * iOS-style bottom tab bar, phones only: Library · Progress · New deck (the
 * prominent centre button) · Exam mode · Settings. The active item sits on a
 * sliding pill (shared `layoutId`) and its icon gives a small bounce when you
 * land on it; re-tapping the active tab scrolls back to the top.
 *
 * Labels use the short `tab.*` keys so they fit on one line at 360px in both
 * languages — no ellipsis, no wrapping.
 */
export function TabBar() {
  const pathname = usePathname();
  const { t } = useI18n();
  const reduceMotion = useReducedMotion();

  /* The wizards keep their own bottom action bar (Cancel / Next / Freeze) and
     chat keeps its own composer — the flow is deliberately focused, so the tab
     bar steps aside there. */
  const inWizard = pathname === "/create" || pathname === "/homework" || pathname === "/chat";

  const item =
    "relative flex min-h-[52px] min-w-0 flex-1 flex-col items-center justify-center gap-1 py-2 text-[10.5px] font-medium leading-none transition-colors";
  const active = "text-[var(--text)]";
  const idle = "text-[var(--text-subtle)]";

  /** The pill glides between items; hidden under reduced motion. */
  const pill = (isActive: boolean) =>
    isActive && !reduceMotion ? (
      <motion.span
        aria-hidden
        layoutId="tabbar-active"
        transition={springSnappy}
        className="absolute inset-x-2 inset-y-0.5 rounded-2xl bg-[var(--nav-active-bg)] shadow-[inset_0_0_0_1px_var(--nav-active-border)]"
      />
    ) : null;

  /** Small icon bounce on the item you just selected. */
  const icon = (children: React.ReactNode, isActive: boolean, key: string) => (
    <motion.span
      key={`${key}-${isActive ? pathname : "idle"}`}
      animate={isActive && !reduceMotion ? { scale: [1, 1.16, 1] } : { scale: 1 }}
      // A three-keyframe bounce needs a tween: framer-motion's dev build throws
      // on springs with more than two keyframes (which broke client updates in
      // the dev instance).
      transition={isActive && !reduceMotion ? { duration: 0.32, ease: "easeOut" } : springSnappy}
      className="relative z-10 grid place-items-center"
    >
      {children}
    </motion.span>
  );

  const label = (text: string, isActive: boolean) => (
    <span className={cn("relative z-10 whitespace-nowrap", isActive ? active : idle)}>{text}</span>
  );

  const isActive = (key: "library" | "progress" | "create" | "exam") => {
    if (key === "library") return pathname === "/";
    if (key === "progress") return pathname === "/stats";
    // The homework wizard is the other half of the New deck screen.
    if (key === "create") return pathname === "/create" || pathname === "/homework";
    return pathname === "/exam";
  };

  const link = (
    key: "library" | "progress" | "create" | "exam",
    href: string,
    labelText: string,
    iconNode: React.ReactNode,
  ) => {
    const current = isActive(key);
    return (
      <Link
        key={key}
        href={href}
        aria-current={current ? "page" : undefined}
        className={cn(item, current ? active : idle)}
        onClick={(event) => {
          haptic("tap");
          // Re-tapping the active tab scrolls back to the top.
          if (current) {
            event.preventDefault();
            window.scrollTo({ top: 0, behavior: reduceMotion ? "auto" : "smooth" });
          }
        }}
      >
        {pill(current)}
        {icon(iconNode, current, key)}
        {label(labelText, current)}
      </Link>
    );
  };

  if (inWizard) return null;

  return (
    <nav
      aria-label={t("tabbar.main")}
      className="tabbar fixed inset-x-0 bottom-0 z-40 flex items-stretch pb-safe sm:hidden"
    >
      {link("library", "/", t("tab.library"), <HomeIcon className="size-6" />)}
      {link("progress", "/stats", t("tab.progress"), <FlameIcon className="size-6" />)}
      {link(
        "create",
        "/create",
        t("tab.new"),
        <span className="grad-ice grid size-7 place-items-center rounded-full text-[#06111f]">
          <PlusIcon className="size-4" />
        </span>,
      )}
      {link("exam", "/exam", t("tab.exam"), <CompassIcon className="size-6" />)}
      <button
        type="button"
        aria-haspopup="dialog"
        onClick={() => {
          haptic("tap");
          openSettings();
        }}
        className={cn(item, idle)}
      >
        {icon(<GearIcon className="size-6" />, false, "settings")}
        {label(t("tab.settings"), false)}
      </button>
    </nav>
  );
}