import { useEffect, useRef, useState } from "react";
import { cn } from "@/lib/utils";
import { AnimatePresence, motion } from "framer-motion";

interface AnimatedQuantityProps {
  value: number;
  format?: (val: number) => string;
  className?: string;
  /** 값 변동 시 배경 깜빡임 */
  useColor?: boolean;
}

/**
 * 실시간 수량 표시 — 값이 변할 때 ±diff를 인라인으로 보여줍니다.
 */
export function AnimatedQuantity({
  value,
  format = (v) => v.toLocaleString(),
  className,
  useColor = false,
}: AnimatedQuantityProps) {
  const prevRef = useRef(value);
  const [diff, setDiff] = useState<number | null>(null);
  const [flash, setFlash] = useState<"up" | "down" | null>(null);

  useEffect(() => {
    if (prevRef.current === value) return;

    const delta = value - prevRef.current;
    prevRef.current = value;

    if (delta === 0) return;

    setDiff(delta);
    setFlash(delta > 0 ? "up" : "down");

    const timer = setTimeout(() => {
      setDiff(null);
      setFlash(null);
    }, 1200);

    return () => clearTimeout(timer);
  }, [value]);

  return (
    <span
      className={cn(
        "relative inline-flex items-center gap-1 tabular-nums",
        className,
      )}
    >
      {/* 배경 깜빡임 */}
      <AnimatePresence>
        {useColor && flash && (
          <motion.span
            initial={{ opacity: 0.5 }}
            animate={{ opacity: 0 }}
            exit={{ opacity: 0 }}
            transition={{ duration: 1 }}
            className={cn(
              "absolute inset-0 z-0 rounded-sm",
              flash === "up" ? "bg-red-200/50" : "bg-brand-200/50",
            )}
          />
        )}
      </AnimatePresence>

      {/* 수량 값 */}
      <span className="relative z-10">{format(value)}</span>

      {/* ±diff (인라인 표시) */}
      <AnimatePresence>
        {diff != null && diff !== 0 && (
          <motion.span
            initial={{ opacity: 1, scale: 1 }}
            animate={{ opacity: 0, scale: 0.85 }}
            exit={{ opacity: 0 }}
            transition={{ duration: 1.2, ease: "easeOut" }}
            className={cn(
              "relative z-20 whitespace-nowrap text-[9px] font-bold leading-none",
              diff > 0 ? "text-red-500" : "text-brand-600",
            )}
          >
            {diff > 0 ? `+${diff.toLocaleString()}` : diff.toLocaleString()}
          </motion.span>
        )}
      </AnimatePresence>
    </span>
  );
}