import { useState, useEffect } from 'react';

export default function Calculator() {
  const [current, setCurrent] = useState('0');
  const [previous, setPrevious] = useState(null);
  const [operation, setOperation] = useState(null);
  const [overwrite, setOverwrite] = useState(false);

  // Handle number input
  const appendNumber = (number) => {
    if (overwrite) {
      setCurrent(number.toString());
      setOverwrite(false);
    } else {
      if (number === '0' && current === '0') return;
      if (current === '0' && number !== '.') {
        setCurrent(number.toString());
      } else {
        setCurrent(current + number);
      }
    }
  };

  // Handle decimal point
  const appendDecimal = () => {
    if (overwrite) {
      setCurrent('0.');
      setOverwrite(false);
      return;
    }
    if (current.includes('.')) return;
    setCurrent(current + '.');
  };

  // Clear all
  const clear = () => {
    setCurrent('0');
    setPrevious(null);
    setOperation(null);
    setOverwrite(false);
  };

  // Delete last digit
  const deleteLast = () => {
    if (overwrite) {
      setCurrent('0');
      setOverwrite(false);
      return;
    }
    if (current.length === 1) {
      setCurrent('0');
      return;
    }
    setCurrent(current.slice(0, -1));
  };

  // Choose operation
  const chooseOperation = (op) => {
    if (current === '') return;
    if (previous !== null) {
      compute();
    }
    setOperation(op);
    setPrevious(current);
    setCurrent('');
  };

  // Compute result
  const compute = () => {
    let computation;
    const prev = parseFloat(previous);
    const curr = parseFloat(current);
    if (isNaN(prev) || isNaN(curr)) return;

    switch (operation) {
      case '+':
        computation = prev + curr;
        break;
      case '-':
        computation = prev - curr;
        break;
      case '*':
        computation = prev * curr;
        break;
      case '/':
        computation = prev / curr;
        break;
      default:
        return;
    }

    setCurrent(computation.toString());
    setOperation(null);
    setPrevious(null);
    setOverwrite(true);
  };

  // Button Helper
  const Button = ({ label, onClick, className = '', variant = 'default' }) => {
    let bgClass = 'bg-gray-700 hover:bg-gray-600 text-white';
    if (variant === 'operator') bgClass = 'bg-orange-500 hover:bg-orange-400 text-white';
    if (variant === 'action') bgClass = 'bg-gray-500 hover:bg-gray-400 text-white';
    if (variant === 'danger') bgClass = 'bg-red-500/80 hover:bg-red-400 text-white';

    return (
      <button
        onClick={onClick}
        className={`h-16 w-16 rounded-full font-bold text-xl transition-all duration-200 active:scale-95 flex items-center justify-center shadow-lg ${bgClass} ${className}`}
      >
        {label}
      </button>
    );
  };

  return (
    <div className="flex flex-col items-center justify-center min-h-screen p-4">
      <a
        href="https://huggingface.co/spaces/akhaliq/anycoder"
        target="_blank"
        rel="noopener noreferrer"
        className="mb-8 inline-flex items-center gap-2 px-4 py-2 rounded-full bg-white/10 hover:bg-white/20 text-white/80 transition-colors border border-white/10"
      >
        <span className="text-sm font-medium">Built with anycoder</span>
        <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
          <path strokeLinecap="round" strokeLinejoin="round" strokeWidth="2" d="M14 5l7 7m0 0l-7 7m7-7H3"></path>
        </svg>
      </a>

      <div className="relative bg-gray-900 rounded-3xl p-8 shadow-2xl border border-gray-800 w-full max-w-md">
        {/* Glow Effect */}
        <div className="absolute -inset-1 bg-gradient-to-r from-blue-500/20 to-purple-500/20 rounded-3xl blur opacity-30"></div>

        {/* Display Area */}
        <div className="mb-8 flex flex-col items-end justify-end h-32">
          <div className="text-gray-400 text-sm font-medium h-6 mb-2">
            {previous} {operation}
          </div>
          <div className="text-white text-5xl font-light tracking-tight overflow-hidden text-ellipsis w-full text-right break-all">
            {current}
          </div>
        </div>

        {/* Grid Controls */}
        <div className="grid grid-cols-4 gap-4 justify-items-center">
          <Button label="AC" onClick={clear} variant="danger" />
          <Button label="DEL" onClick={deleteLast} variant="action" />
          <Button label="%" onClick={() => {
             const val = parseFloat(current);
             setCurrent((val / 100).toString());
             setOverwrite(true);
          }} variant="action" />
          <Button label="/" onClick={() => chooseOperation('/')} variant="operator" />

          <Button label="7" onClick={() => appendNumber('7')} />
          <Button label="8" onClick={() => appendNumber('8')} />
          <Button label="9" onClick={() => appendNumber('9')} />
          <Button label="*" onClick={() => chooseOperation('*')} variant="operator" />

          <Button label="4" onClick={() => appendNumber('4')} />
          <Button label="5" onClick={() => appendNumber('5')} />
          <Button label="6" onClick={() => appendNumber('6')} />
          <Button label="-" onClick={() => chooseOperation('-')} variant="operator" />

          <Button label="1" onClick={() => appendNumber('1')} />
          <Button label="2" onClick={() => appendNumber('2')} />
          <Button label="3" onClick={() => appendNumber('3')} />
          <Button label="+" onClick={() => chooseOperation('+')} variant="operator" />

          <Button label="." onClick={appendDecimal} className="text-2xl pb-4" />
          <Button label="0" onClick={() => appendNumber('0')} />
          <Button label="=" onClick={compute} variant="operator" className="bg-blue-600 hover:bg-blue-500" />
        </div>
      </div>

      <div className="mt-12 text-gray-500 text-sm">
        Modern Calculator
      </div>
    </div>
  );
}