'use client';

import { useRef, useEffect } from 'react';

const LetterGlitch = ({
  // Dark base + full-spectrum neon accents (emerald / magenta / blue / periwinkle).
  glitchColors = ['#141225', '#2ee6a6', '#ff5cc8', '#3b9dff', '#d3cbc0'],
  glitchSpeed = 50,
  centerVignette = false,
  outerVignette = true,
  smooth = true,
  characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ!@#$&*()-_+=/[]{};:<>.,0123456789'
}: {
  glitchColors: string[];
  glitchSpeed: number;
  centerVignette: boolean;
  outerVignette: boolean;
  smooth: boolean;
  characters: string;
}) => {
  const canvasRef = useRef<HTMLCanvasElement | null>(null);
  const animationRef = useRef<number | null>(null);
  const letters = useRef<
    {
      char: string;
      color: string;
      targetColor: string;
      colorProgress: number;
    }[]
  >([]);
  const grid = useRef({ columns: 0, rows: 0 });
  const context = useRef<CanvasRenderingContext2D | null>(null);
  const lastGlitchTime = useRef(Date.now());
  // Parsed-color cache: the palette is a handful of hex strings reused across
  // thousands of cells every frame, so parse each one only once.
  const rgbCache = useRef(new Map<string, { r: number; g: number; b: number } | null>());

  const lettersAndSymbols = Array.from(characters);

  const fontSize = 16;
  const charWidth = 10;
  const charHeight = 20;

  const getRandomChar = () => {
    return lettersAndSymbols[Math.floor(Math.random() * lettersAndSymbols.length)];
  };

  const getRandomColor = () => {
    return glitchColors[Math.floor(Math.random() * glitchColors.length)];
  };

  const hexToRgb = (hex: string) => {
    const cached = rgbCache.current.get(hex);
    if (cached !== undefined) return cached;

    const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
    const normalized = hex.replace(shorthandRegex, (_m, r, g, b) => {
      return r + r + g + g + b + b;
    });

    const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(normalized);
    const rgb = result
      ? {
          r: parseInt(result[1], 16),
          g: parseInt(result[2], 16),
          b: parseInt(result[3], 16)
        }
      : null;
    rgbCache.current.set(hex, rgb);
    return rgb;
  };

  const interpolateColor = (
    start: { r: number; g: number; b: number },
    end: { r: number; g: number; b: number },
    factor: number
  ) => {
    const result = {
      r: Math.round(start.r + (end.r - start.r) * factor),
      g: Math.round(start.g + (end.g - start.g) * factor),
      b: Math.round(start.b + (end.b - start.b) * factor)
    };
    return `rgb(${result.r}, ${result.g}, ${result.b})`;
  };

  const calculateGrid = (width: number, height: number) => {
    const columns = Math.ceil(width / charWidth);
    const rows = Math.ceil(height / charHeight);
    return { columns, rows };
  };

  const initializeLetters = (columns: number, rows: number) => {
    grid.current = { columns, rows };
    const totalLetters = columns * rows;
    letters.current = Array.from({ length: totalLetters }, () => ({
      char: getRandomChar(),
      color: getRandomColor(),
      targetColor: getRandomColor(),
      colorProgress: 1
    }));
  };

  const resizeCanvas = () => {
    const canvas = canvasRef.current;
    if (!canvas) return;
    const parent = canvas.parentElement;
    if (!parent) return;

    const dpr = window.devicePixelRatio || 1;
    const rect = parent.getBoundingClientRect();

    canvas.width = rect.width * dpr;
    canvas.height = rect.height * dpr;

    canvas.style.width = `${rect.width}px`;
    canvas.style.height = `${rect.height}px`;

    if (context.current) {
      context.current.setTransform(dpr, 0, 0, dpr, 0, 0);
    }

    const { columns, rows } = calculateGrid(rect.width, rect.height);
    initializeLetters(columns, rows);
    drawLetters();
  };

  const drawLetters = () => {
    if (!context.current || letters.current.length === 0) return;
    const ctx = context.current;
    const { width, height } = canvasRef.current!.getBoundingClientRect();
    ctx.clearRect(0, 0, width, height);
    ctx.font = `${fontSize}px monospace`;
    ctx.textBaseline = 'top';

    letters.current.forEach((letter, index) => {
      const x = (index % grid.current.columns) * charWidth;
      const y = Math.floor(index / grid.current.columns) * charHeight;
      ctx.fillStyle = letter.color;
      ctx.fillText(letter.char, x, y);
    });
  };

  const updateLetters = () => {
    if (!letters.current || letters.current.length === 0) return;

    const updateCount = Math.max(1, Math.floor(letters.current.length * 0.05));

    for (let i = 0; i < updateCount; i++) {
      const index = Math.floor(Math.random() * letters.current.length);
      if (!letters.current[index]) continue;

      letters.current[index].char = getRandomChar();
      letters.current[index].targetColor = getRandomColor();

      if (!smooth) {
        letters.current[index].color = letters.current[index].targetColor;
        letters.current[index].colorProgress = 1;
      } else {
        letters.current[index].colorProgress = 0;
      }
    }
  };

  const handleSmoothTransitions = () => {
    let needsRedraw = false;
    letters.current.forEach(letter => {
      if (letter.colorProgress < 1) {
        letter.colorProgress += 0.05;
        if (letter.colorProgress > 1) letter.colorProgress = 1;

        const startRgb = hexToRgb(letter.color);
        const endRgb = hexToRgb(letter.targetColor);
        if (startRgb && endRgb) {
          letter.color = interpolateColor(startRgb, endRgb, letter.colorProgress);
          needsRedraw = true;
        }
      }
    });

    if (needsRedraw) {
      drawLetters();
    }
  };

  const animate = () => {
    const now = Date.now();
    if (now - lastGlitchTime.current >= glitchSpeed) {
      updateLetters();
      drawLetters();
      lastGlitchTime.current = now;
    }

    if (smooth) {
      handleSmoothTransitions();
    }

    animationRef.current = requestAnimationFrame(animate);
  };

  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;

    context.current = canvas.getContext('2d');
    resizeCanvas();
    animate();

    let resizeTimeout: ReturnType<typeof setTimeout>;

    const handleResize = () => {
      clearTimeout(resizeTimeout);
      resizeTimeout = setTimeout(() => {
        cancelAnimationFrame(animationRef.current as number);
        resizeCanvas();
        animate();
      }, 100);
    };

    window.addEventListener('resize', handleResize);

    // Pause the render loop while the tab is hidden — the animation is purely
    // decorative and would otherwise keep burning CPU in the background.
    const handleVisibility = () => {
      cancelAnimationFrame(animationRef.current as number);
      if (!document.hidden) {
        lastGlitchTime.current = Date.now();
        animate();
      }
    };
    document.addEventListener('visibilitychange', handleVisibility);

    return () => {
      cancelAnimationFrame(animationRef.current!);
      window.removeEventListener('resize', handleResize);
      document.removeEventListener('visibilitychange', handleVisibility);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [glitchSpeed, smooth]);

  return (
    <div className="relative w-full h-full bg-black overflow-hidden">
      <canvas ref={canvasRef} className="block w-full h-full" />
      {outerVignette && (
        <div className="absolute top-0 left-0 w-full h-full pointer-events-none bg-[radial-gradient(circle,_rgba(0,0,0,0)_60%,_rgba(0,0,0,1)_100%)]"></div>
      )}
      {centerVignette && (
        <div className="absolute top-0 left-0 w-full h-full pointer-events-none bg-[radial-gradient(circle,_rgba(0,0,0,0.8)_0%,_rgba(0,0,0,0)_60%)]"></div>
      )}
    </div>
  );
};

export default LetterGlitch;